Voltage Limiter...

[Ricketty C]

I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated.

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[Lasse Langwadt Christensen]

lørdag den 29. august 2020 kl. 20.28.33 UTC+2 skrev Ricketty C:

I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out.. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated..

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.

why does the motor need a voltage limit?

 

[Ricketty C]

On Saturday, August 29, 2020 at 3:01:39 PM UTC-4, Lasse Langwadt Christensen wrote:

lørdag den 29. august 2020 kl. 20.28.33 UTC+2 skrev Ricketty C:
I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated.

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.


why does the motor need a voltage limit?

It is specifically rated for 12 volts and not higher. We were using a motor from Pololu and it worked at 12ish voltage, but they also self destructed when jammed. The new motors will also self destruct, but we have rating limits to prevent that and the voltage is part of it. I guess the maker had a spite of failures they traced to the users over voltaging the units. I don\'t know, I just design to the spec sheet. This circuit produces 12.45 volts because we will lose a bit in the H-bridge.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

 

[Lasse Langwadt Christensen]

lørdag den 29. august 2020 kl. 21.26.12 UTC+2 skrev Ricketty C:

On Saturday, August 29, 2020 at 3:01:39 PM UTC-4, Lasse Langwadt Christensen wrote:
lørdag den 29. august 2020 kl. 20.28.33 UTC+2 skrev Ricketty C:
I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated.

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.


why does the motor need a voltage limit?

It is specifically rated for 12 volts and not higher. We were using a motor from Pololu and it worked at 12ish voltage, but they also self destructed when jammed. The new motors will also self destruct, but we have rating limits to prevent that and the voltage is part of it. I guess the maker had a spite of failures they traced to the users over voltaging the units. I don\'t know, I just design to the spec sheet. This circuit produces 12.45 volts because we will lose a bit in the H-bridge.

as long as you limit the current so it doesn\'t burn out, the voltage just relates to the max speed and I assume you are already controlling the speed
and the mechanics limits how long you can run at speed

 

[Ricketty C]

On Saturday, August 29, 2020 at 3:54:02 PM UTC-4, Lasse Langwadt Christensen wrote:

lørdag den 29. august 2020 kl. 21.26.12 UTC+2 skrev Ricketty C:
On Saturday, August 29, 2020 at 3:01:39 PM UTC-4, Lasse Langwadt Christensen wrote:
lørdag den 29. august 2020 kl. 20.28.33 UTC+2 skrev Ricketty C:
I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated.

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.


why does the motor need a voltage limit?

It is specifically rated for 12 volts and not higher. We were using a motor from Pololu and it worked at 12ish voltage, but they also self destructed when jammed. The new motors will also self destruct, but we have rating limits to prevent that and the voltage is part of it. I guess the maker had a spite of failures they traced to the users over voltaging the units. I don\'t know, I just design to the spec sheet. This circuit produces 12.45 volts because we will lose a bit in the H-bridge.


as long as you limit the current so it doesn\'t burn out, the voltage just relates to the max speed and I assume you are already controlling the speed
and the mechanics limits how long you can run at speed

Yes, I know. But the spec is the spec. The circuit I came up with adds two 2N7002 FETs and a few resistors. I\'m happy using it. The voltage drop is down to 150 mV once the battery is used and starts dropping below the set point.

If we have problems with the motor, it won\'t be because the voltage was high.

I think we are not limiting the max speed directly. The loop control variable is pressure or could be flow rate. If the arm is raised off the bag the forward stroke is going to try to move air when the arm is not yet touching the bag so the speed will ramp up pretty quick. I don\'t know what they are doing to control the return stroke. They may use a fixed PWM cycle, i.e. a fixed setting without control until it hits the limit switch.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

 

[Robert Baer]

Ricketty C wrote:

I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated.

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.

That would be VERY interesting..input down to 10V and output staying
near 12.4V...you did imply linear...

 

[Robert Baer]

Lasse Langwadt Christensen wrote:

lørdag den 29. august 2020 kl. 20.28.33 UTC+2 skrev Ricketty C:
I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated.

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.


why does the motor need a voltage limit?

Just try 24V on a 6V motor some day...
Better yet, 120VAC...

 

[Lasse Langwadt Christensen]

mandag den 31. august 2020 kl. 23.55.43 UTC+2 skrev Robert Baer:

Lasse Langwadt Christensen wrote:
lørdag den 29. august 2020 kl. 20.28.33 UTC+2 skrev Ricketty C:
I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated.

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.


why does the motor need a voltage limit?

Just try 24V on a 6V motor some day...
Better yet, 120VAC...

the speed,current are regulated with pwm, 24V on 6V motor is not a problem,

stepper motors are commonly rated for a few volts and run with 24-48V or more

 

[Ricketty C]

On Monday, August 31, 2020 at 5:53:52 PM UTC-4, Robert Baer wrote:

Ricketty C wrote:
I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated.

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.

That would be VERY interesting..input down to 10V and output staying
near 12.4V...you did imply linear...

I assume there is a joke in there somewhere. You do realize I\'m talking about an output dropping once the input drops below the output plus some drop out. That\'s my point, regulators are spec\'d for a minimum drop out where they meet full specs. I\'m interested in the drop out once they are out of regulation and the pass transistor is turned on fully.

Actually, using a regulator may not be an option anymore. We are combining the input DC @ 15V with the battery voltage through diodes to feed the main power rail. The motor is the only heavy draw. I\'m wondering if it makes sense to use two FETs back to back to prevent reverse current flow between the two circuits. One pair for the main power source and a second pair for the battery resulting in a lower voltage drop so the battery can be used more effectively.

Using a regulator will still require a diode to prevent back current flow to the main power input. So two diodes and a regulator or four FETs?

I actually saw this circuit on a schematic for a Trenz FPGA board, but much lower power levels. Not sure which way I want to go.

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

 

[Lasse Langwadt Christensen]

tirsdag den 1. september 2020 kl. 01.02.06 UTC+2 skrev Ricketty C:

On Monday, August 31, 2020 at 5:53:52 PM UTC-4, Robert Baer wrote:
Ricketty C wrote:
I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated.

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.

That would be VERY interesting..input down to 10V and output staying
near 12.4V...you did imply linear...

I assume there is a joke in there somewhere. You do realize I\'m talking about an output dropping once the input drops below the output plus some drop out. That\'s my point, regulators are spec\'d for a minimum drop out where they meet full specs. I\'m interested in the drop out once they are out of regulation and the pass transistor is turned on fully.

Actually, using a regulator may not be an option anymore. We are combining the input DC @ 15V with the battery voltage through diodes to feed the main power rail. The motor is the only heavy draw. I\'m wondering if it makes sense to use two FETs back to back to prevent reverse current flow between the two circuits. One pair for the main power source and a second pair for the battery resulting in a lower voltage drop so the battery can be used more effectively.

Using a regulator will still require a diode to prevent back current flow to the main power input. So two diodes and a regulator or four FETs?

I actually saw this circuit on a schematic for a Trenz FPGA board, but much lower power levels. Not sure which way I want to go.

you just need a \"diode\" from each, something like this has been used on the raspberry pi to enable using a psu or USB power and not backfeed the USB

https://robotics.ong.id.au/wp-content/uploads/2014/07/rpi_protection.png

 

[John Larkin]

On Mon, 31 Aug 2020 14:55:35 -0700, Robert Baer
<robertbaer@localnet.com> wrote:

Lasse Langwadt Christensen wrote:
lørdag den 29. august 2020 kl. 20.28.33 UTC+2 skrev Ricketty C:
I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated.

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.


why does the motor need a voltage limit?

Just try 24V on a 6V motor some day...
Better yet, 120VAC...

Does a shorted mosfet protect a motor?

 

[Ricketty C]

On Monday, August 31, 2020 at 7:07:22 PM UTC-4, Lasse Langwadt Christensen wrote:

tirsdag den 1. september 2020 kl. 01.02.06 UTC+2 skrev Ricketty C:
On Monday, August 31, 2020 at 5:53:52 PM UTC-4, Robert Baer wrote:
Ricketty C wrote:
I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated.

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.

That would be VERY interesting..input down to 10V and output staying
near 12.4V...you did imply linear...

I assume there is a joke in there somewhere. You do realize I\'m talking about an output dropping once the input drops below the output plus some drop out. That\'s my point, regulators are spec\'d for a minimum drop out where they meet full specs. I\'m interested in the drop out once they are out of regulation and the pass transistor is turned on fully.

Actually, using a regulator may not be an option anymore. We are combining the input DC @ 15V with the battery voltage through diodes to feed the main power rail. The motor is the only heavy draw. I\'m wondering if it makes sense to use two FETs back to back to prevent reverse current flow between the two circuits. One pair for the main power source and a second pair for the battery resulting in a lower voltage drop so the battery can be used more effectively.

Using a regulator will still require a diode to prevent back current flow to the main power input. So two diodes and a regulator or four FETs?

I actually saw this circuit on a schematic for a Trenz FPGA board, but much lower power levels. Not sure which way I want to go.


you just need a \"diode\" from each, something like this has been used on the raspberry pi to enable using a psu or USB power and not backfeed the USB

https://robotics.ong.id.au/wp-content/uploads/2014/07/rpi_protection.png

I can\'t seem to make that work for me. It is set up to equalize the voltage when passing current in one direction. But it can\'t be used to limit the output voltage so well because the lowest drop you can get is 0.7 volts or so through the parasitic diode. I need to scrub about 2.5 volt from the main power input or a varying amount from the battery, down to as close to zero as possible.

I could just use a FET for the limiter and then use two of these to combine the two supplies. Or maybe only one is needed on the battery. When the power source is unplugged, I\'m not sure it would hurt anything to reverse power the input. I only feeds the battery charger. I guess it would create some additional power drain. There is an OFF state where only the minimal circuitry is powered with the intent to use less power than the battery self drain current of ~100 uA. Heck, the FET diode circuit as drawn would draw <300 uA! I\'d need to knock the resistors up to 1Meg to get the current low enough at 14V. But that sounds like a winner. Thanks.

So the final circuit can be a diode from the DC input (no worry with the drop and it\'s used elsewhere so it\'s on the BoM regardless), this circuit for the battery connection to the common power rail. Then my previous voltage limiter circuit to supply the motor and provide a means of cutting power in case the software runs amuck resulting in an over current.

I\'m not a fan of adding unique parts to the BOM, but I think this one is worth it! Thanks again.

--

Rick C.

+- Get 1,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209

 

[Robert Baer]

Ricketty C wrote:

On Monday, August 31, 2020 at 7:07:22 PM UTC-4, Lasse Langwadt Christensen wrote:
tirsdag den 1. september 2020 kl. 01.02.06 UTC+2 skrev Ricketty C:
On Monday, August 31, 2020 at 5:53:52 PM UTC-4, Robert Baer wrote:
Ricketty C wrote:
I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated.

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.

That would be VERY interesting..input down to 10V and output staying
near 12.4V...you did imply linear...

I assume there is a joke in there somewhere. You do realize I\'m talking about an output dropping once the input drops below the output plus some drop out. That\'s my point, regulators are spec\'d for a minimum drop out where they meet full specs. I\'m interested in the drop out once they are out of regulation and the pass transistor is turned on fully.

Actually, using a regulator may not be an option anymore. We are combining the input DC @ 15V with the battery voltage through diodes to feed the main power rail. The motor is the only heavy draw. I\'m wondering if it makes sense to use two FETs back to back to prevent reverse current flow between the two circuits. One pair for the main power source and a second pair for the battery resulting in a lower voltage drop so the battery can be used more effectively.

Using a regulator will still require a diode to prevent back current flow to the main power input. So two diodes and a regulator or four FETs?

I actually saw this circuit on a schematic for a Trenz FPGA board, but much lower power levels. Not sure which way I want to go.


you just need a \"diode\" from each, something like this has been used on the raspberry pi to enable using a psu or USB power and not backfeed the USB

https://robotics.ong.id.au/wp-content/uploads/2014/07/rpi_protection.png

I can\'t seem to make that work for me. It is set up to equalize the voltage when passing current in one direction. But it can\'t be used to limit the output voltage so well because the lowest drop you can get is 0.7 volts or so through the parasitic diode. I need to scrub about 2.5 volt from the main power input or a varying amount from the battery, down to as close to zero as possible.

* I am just a dumb Baer, just neglecting specs for a while and looking
at ONLY the circuitry in the box, i see something like a fancy zero-drop
voltage follower: Vo=Vin.
Apx limits: Vo(min) 0.6V, Vo(max) 150V.

So what is the beef?
Well, if the load (at ANY Vin 0.6-15V) is sufficient to cause a drop
in that \"voltage follower\" more than say) 0.6v, that parasitic diode
starts to conduct.

Try variants..different FET, 12K instead of 47K; both; no FET as no
power source at load.

I could just use a FET for the limiter and then use two of these to combine the two supplies. Or maybe only one is needed on the battery. When the power source is unplugged, I\'m not sure it would hurt anything to reverse power the input. I only feeds the battery charger. I guess it would create some additional power drain. There is an OFF state where only the minimal circuitry is powered with the intent to use less power than the battery self drain current of ~100 uA. Heck, the FET diode circuit as drawn would draw <300 uA! I\'d need to knock the resistors up to 1Meg to get the current low enough at 14V. But that sounds like a winner. Thanks.

So the final circuit can be a diode from the DC input (no worry with the drop and it\'s used elsewhere so it\'s on the BoM regardless), this circuit for the battery connection to the common power rail. Then my previous voltage limiter circuit to supply the motor and provide a means of cutting power in case the software runs amuck resulting in an over current.

I\'m not a fan of adding unique parts to the BOM, but I think this one is worth it! Thanks again.

 

[piglet]

On 01/09/2020 6:45 am, Robert Baer wrote:

* I am just a dumb Baer, just neglecting specs for a while and looking
at ONLY the circuitry in the box, i see something like a fancy zero-drop
voltage follower: Vo=Vin.
  Apx limits: Vo(min) 0.6V, Vo(max) 150V.

  So what is the beef?
  Well, if the load (at ANY Vin 0.6-15V) is sufficient to cause a drop
in that \"voltage follower\" more than say) 0.6v, that parasitic diode
starts to conduct.

  Try variants..different FET, 12K instead of 47K; both; no FET as no
power source at load.

Dear dumb Baer, I am an equally dumb piglet but I don\'t see it as a
voltage follower - to me it looks like a \"perfect\" diode for a 5V
system. Any load current flowing left to right will turn on the pfet so
very low voltage drop across the \"diode\". When the power input goes down
the comparator diff amp turns the pfet off and no current can flow right
to left? (The load side may still be receiving power from some other
input not shown or simply have a large supply capacitance).

piglet

 

[Ricketty C]

On Tuesday, September 1, 2020 at 1:45:46 AM UTC-4, Robert Baer wrote:

Ricketty C wrote:
On Monday, August 31, 2020 at 7:07:22 PM UTC-4, Lasse Langwadt Christensen wrote:
tirsdag den 1. september 2020 kl. 01.02.06 UTC+2 skrev Ricketty C:
On Monday, August 31, 2020 at 5:53:52 PM UTC-4, Robert Baer wrote:
Ricketty C wrote:
I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated.

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.

That would be VERY interesting..input down to 10V and output staying
near 12.4V...you did imply linear...

I assume there is a joke in there somewhere. You do realize I\'m talking about an output dropping once the input drops below the output plus some drop out. That\'s my point, regulators are spec\'d for a minimum drop out where they meet full specs. I\'m interested in the drop out once they are out of regulation and the pass transistor is turned on fully.

Actually, using a regulator may not be an option anymore. We are combining the input DC @ 15V with the battery voltage through diodes to feed the main power rail. The motor is the only heavy draw. I\'m wondering if it makes sense to use two FETs back to back to prevent reverse current flow between the two circuits. One pair for the main power source and a second pair for the battery resulting in a lower voltage drop so the battery can be used more effectively.

Using a regulator will still require a diode to prevent back current flow to the main power input. So two diodes and a regulator or four FETs?

I actually saw this circuit on a schematic for a Trenz FPGA board, but much lower power levels. Not sure which way I want to go.


you just need a \"diode\" from each, something like this has been used on the raspberry pi to enable using a psu or USB power and not backfeed the USB

https://robotics.ong.id.au/wp-content/uploads/2014/07/rpi_protection.png

I can\'t seem to make that work for me. It is set up to equalize the voltage when passing current in one direction. But it can\'t be used to limit the output voltage so well because the lowest drop you can get is 0.7 volts or so through the parasitic diode. I need to scrub about 2.5 volt from the main power input or a varying amount from the battery, down to as close to zero as possible.
* I am just a dumb Baer, just neglecting specs for a while and looking
at ONLY the circuitry in the box, i see something like a fancy zero-drop
voltage follower: Vo=Vin.
Apx limits: Vo(min) 0.6V, Vo(max) 150V.

So what is the beef?
Well, if the load (at ANY Vin 0.6-15V) is sufficient to cause a drop
in that \"voltage follower\" more than say) 0.6v, that parasitic diode
starts to conduct.

Try variants..different FET, 12K instead of 47K; both; no FET as no
power source at load.

What is wrong with the parasitic diode conducting other than the fact that the power losses have increased? That\'s happening whether or not the diode is there or conducts. In fact, the diode starts conducting limiting the voltage drop if the current gets that high.

I don\'t get your point?

Actually, I needed to bump up the resistor to 1 Meg to reduce the leakage current when the circuit is powered down. It\'s a bit slow if the power supply quits suddenly, but only for less than 1 ms, then it drive the FET into conduction. This is powering a motor. It\'s not like it cares about small transients. I just want to keep it happy with the proper voltage as best as possible.

--

Rick C.

++ Get 1,000 miles of free Supercharging
++ Tesla referral code - https://ts.la/richard11209

 

[Robert Baer]

piglet wrote:

On 01/09/2020 6:45 am, Robert Baer wrote:
* I am just a dumb Baer, just neglecting specs for a while and looking
at ONLY the circuitry in the box, i see something like a fancy
zero-drop voltage follower: Vo=Vin.
   Apx limits: Vo(min) 0.6V, Vo(max) 150V.

   So what is the beef?
   Well, if the load (at ANY Vin 0.6-15V) is sufficient to cause a
drop in that \"voltage follower\" more than say) 0.6v, that parasitic
diode starts to conduct.

   Try variants..different FET, 12K instead of 47K; both; no FET as no
power source at load.


Dear dumb Baer, I am an equally dumb piglet but I don\'t see it as a
voltage follower - to me it looks like a \"perfect\" diode for a 5V
system. Any load current flowing left to right will turn on the pfet so
very low voltage drop across the \"diode\". When the power input goes down
the comparator diff amp turns the pfet off and no current can flow right
to left?  (The load side may still be receiving power from some other
input not shown or simply have a large supply capacitance).

piglet

MMMmmm...
Redraw the circuit with NO FET.
Do you now see a current mirror?
Input drives the mirror,and the load is driven by the current output.

Maybe the mirror configuration is confusing, almost all of the time,
(NPN style now) the emitters go to ground, drive via resistor from
supply and load at collector of 2nd transistor.

Step one, turn that upside-down using PNP transistors; common E-B,
load still on collector.

Step two, shift/trade emitter and collector roles.
Looks a little different but still a current mirror.

With a large output/input current ratio, the beta of the pair needs
to be high and the Rbb\' of the output transistor needs to be low for
minimal Vin-Vout differential.

In fact one could be tempted to use a small-signal transistor at the
input current reference, and a power transistor for the load driver side.
Matching for decent operation becomes messy,to say the least; stick
with the Zetek specialty lines (hi beta, low Vsat, etc) when trying
parts..especially high beta, high current, low sat for power part.

The ZTX694B may be an NPN,but the Vce(sat) is less than 400mV at 400mA.
You did not indicate the motor current requirements, but if that is
OK. turning all up-side down NPNs may give a better Vin-Vout solution.

Back to PNP transistors, do not know your requirements, but try the
ZXTP25012EFH, or ZXTP07012EFF or the ZXTP25012EZ all 12V 4A beta 500,
<300mV Vce(sat) parts.
Or for higher voltages, the DXTP22040DFG or the DXTP22040CFG at 40V
2A beta 200 or better, <400mV Vce(sat) parts.

Use Diodes Inc selector for these neat Zetek parts at:
https://www.diodes.com/products/discrete/bipolar-transistors/transistor-bjt-master-table/transistors-29v/#Category:%22Low%20Saturation%20Transistor%22;Polarity:[%22PNP%22];VCE%28sat%29%20Max%20%28mV%29:{%22min%22%3A10%2C%22max%22%3A%22500%22}


Thanks

 

[Robert Baer]

Ricketty C wrote:

On Monday, August 31, 2020 at 7:07:22 PM UTC-4, Lasse Langwadt Christensen wrote:
tirsdag den 1. september 2020 kl. 01.02.06 UTC+2 skrev Ricketty C:
On Monday, August 31, 2020 at 5:53:52 PM UTC-4, Robert Baer wrote:
Ricketty C wrote:
I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated.

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.

That would be VERY interesting..input down to 10V and output staying
near 12.4V...you did imply linear...

I assume there is a joke in there somewhere. You do realize I\'m talking about an output dropping once the input drops below the output plus some drop out. That\'s my point, regulators are spec\'d for a minimum drop out where they meet full specs. I\'m interested in the drop out once they are out of regulation and the pass transistor is turned on fully.

Actually, using a regulator may not be an option anymore. We are combining the input DC @ 15V with the battery voltage through diodes to feed the main power rail. The motor is the only heavy draw. I\'m wondering if it makes sense to use two FETs back to back to prevent reverse current flow between the two circuits. One pair for the main power source and a second pair for the battery resulting in a lower voltage drop so the battery can be used more effectively.

Using a regulator will still require a diode to prevent back current flow to the main power input. So two diodes and a regulator or four FETs?

I actually saw this circuit on a schematic for a Trenz FPGA board, but much lower power levels. Not sure which way I want to go.


you just need a \"diode\" from each, something like this has been used on the raspberry pi to enable using a psu or USB power and not backfeed the USB

https://robotics.ong.id.au/wp-content/uploads/2014/07/rpi_protection.png

I can\'t seem to make that work for me. It is set up to equalize the voltage when passing current in one direction. But it can\'t be used to limit the output voltage so well because the lowest drop you can get is 0.7 volts or so through the parasitic diode. I need to scrub about 2.5 volt from the main power input or a varying amount from the battery, down to as close to zero as possible.

I could just use a FET for the limiter and then use two of these to combine the two supplies. Or maybe only one is needed on the battery. When the power source is unplugged, I\'m not sure it would hurt anything to reverse power the input. I only feeds the battery charger. I guess it would create some additional power drain. There is an OFF state where only the minimal circuitry is powered with the intent to use less power than the battery self drain current of ~100 uA. Heck, the FET diode circuit as drawn would draw <300 uA! I\'d need to knock the resistors up to 1Meg to get the current low enough at 14V. But that sounds like a winner. Thanks.

So the final circuit can be a diode from the DC input (no worry with the drop and it\'s used elsewhere so it\'s on the BoM regardless), this circuit for the battery connection to the common power rail. Then my previous voltage limiter circuit to supply the motor and provide a means of cutting power in case the software runs amuck resulting in an over current.

I\'m not a fan of adding unique parts to the BOM, but I think this one is worth it! Thanks again.

Color me confused; you talk about 12V motor max and yet have a 5V
\"transient protector\" at the output???
And it takes only 250K for those resistors to get a \"leakage\" of 48uA
at 12V in.
Looked at the DMMT5401, a good choice, beta may be a little low at a
measly 100 but seems adequate,giving Vce(sat) <200mV up to 100mA.
Again NO HINT as to motor current.
More info??

Thanks.

 

[Lasse Langwadt Christensen]

tirsdag den 1. september 2020 kl. 22.18.09 UTC+2 skrev Robert Baer:

Ricketty C wrote:
On Monday, August 31, 2020 at 7:07:22 PM UTC-4, Lasse Langwadt Christensen wrote:
tirsdag den 1. september 2020 kl. 01.02.06 UTC+2 skrev Ricketty C:
On Monday, August 31, 2020 at 5:53:52 PM UTC-4, Robert Baer wrote:
Ricketty C wrote:
I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated.

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.

That would be VERY interesting..input down to 10V and output staying
near 12.4V...you did imply linear...

I assume there is a joke in there somewhere. You do realize I\'m talking about an output dropping once the input drops below the output plus some drop out. That\'s my point, regulators are spec\'d for a minimum drop out where they meet full specs. I\'m interested in the drop out once they are out of regulation and the pass transistor is turned on fully.

Actually, using a regulator may not be an option anymore. We are combining the input DC @ 15V with the battery voltage through diodes to feed the main power rail. The motor is the only heavy draw. I\'m wondering if it makes sense to use two FETs back to back to prevent reverse current flow between the two circuits. One pair for the main power source and a second pair for the battery resulting in a lower voltage drop so the battery can be used more effectively.

Using a regulator will still require a diode to prevent back current flow to the main power input. So two diodes and a regulator or four FETs?

I actually saw this circuit on a schematic for a Trenz FPGA board, but much lower power levels. Not sure which way I want to go.


you just need a \"diode\" from each, something like this has been used on the raspberry pi to enable using a psu or USB power and not backfeed the USB

https://robotics.ong.id.au/wp-content/uploads/2014/07/rpi_protection.png

I can\'t seem to make that work for me. It is set up to equalize the voltage when passing current in one direction. But it can\'t be used to limit the output voltage so well because the lowest drop you can get is 0.7 volts or so through the parasitic diode. I need to scrub about 2.5 volt from the main power input or a varying amount from the battery, down to as close to zero as possible.

I could just use a FET for the limiter and then use two of these to combine the two supplies. Or maybe only one is needed on the battery. When the power source is unplugged, I\'m not sure it would hurt anything to reverse power the input. I only feeds the battery charger. I guess it would create some additional power drain. There is an OFF state where only the minimal circuitry is powered with the intent to use less power than the battery self drain current of ~100 uA. Heck, the FET diode circuit as drawn would draw <300 uA! I\'d need to knock the resistors up to 1Meg to get the current low enough at 14V. But that sounds like a winner. Thanks.

So the final circuit can be a diode from the DC input (no worry with the drop and it\'s used elsewhere so it\'s on the BoM regardless), this circuit for the battery connection to the common power rail. Then my previous voltage limiter circuit to supply the motor and provide a means of cutting power in case the software runs amuck resulting in an over current.

I\'m not a fan of adding unique parts to the BOM, but I think this one is worth it! Thanks again.

Color me confused; you talk about 12V motor max and yet have a 5V
\"transient protector\" at the output???

you do seem to need to have every spelled out

12V regulator limits the voltage to the motor, regulator can be feed by 15V supply or a ~12V battery, to avoid back feeding the battery diodes are needed.

the circuit is an ideal diode designed for 5V USB, with changes the same can be used for the ~12V battery avoiding the waste of a diode voltage

 

[Ricketty C]

On Tuesday, September 1, 2020 at 4:18:09 PM UTC-4, Robert Baer wrote:

Ricketty C wrote:
On Monday, August 31, 2020 at 7:07:22 PM UTC-4, Lasse Langwadt Christensen wrote:
tirsdag den 1. september 2020 kl. 01.02.06 UTC+2 skrev Ricketty C:
On Monday, August 31, 2020 at 5:53:52 PM UTC-4, Robert Baer wrote:
Ricketty C wrote:
I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated.

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.

That would be VERY interesting..input down to 10V and output staying
near 12.4V...you did imply linear...

I assume there is a joke in there somewhere. You do realize I\'m talking about an output dropping once the input drops below the output plus some drop out. That\'s my point, regulators are spec\'d for a minimum drop out where they meet full specs. I\'m interested in the drop out once they are out of regulation and the pass transistor is turned on fully.

Actually, using a regulator may not be an option anymore. We are combining the input DC @ 15V with the battery voltage through diodes to feed the main power rail. The motor is the only heavy draw. I\'m wondering if it makes sense to use two FETs back to back to prevent reverse current flow between the two circuits. One pair for the main power source and a second pair for the battery resulting in a lower voltage drop so the battery can be used more effectively.

Using a regulator will still require a diode to prevent back current flow to the main power input. So two diodes and a regulator or four FETs?

I actually saw this circuit on a schematic for a Trenz FPGA board, but much lower power levels. Not sure which way I want to go.


you just need a \"diode\" from each, something like this has been used on the raspberry pi to enable using a psu or USB power and not backfeed the USB

https://robotics.ong.id.au/wp-content/uploads/2014/07/rpi_protection.png

I can\'t seem to make that work for me. It is set up to equalize the voltage when passing current in one direction. But it can\'t be used to limit the output voltage so well because the lowest drop you can get is 0.7 volts or so through the parasitic diode. I need to scrub about 2.5 volt from the main power input or a varying amount from the battery, down to as close to zero as possible.

I could just use a FET for the limiter and then use two of these to combine the two supplies. Or maybe only one is needed on the battery. When the power source is unplugged, I\'m not sure it would hurt anything to reverse power the input. I only feeds the battery charger. I guess it would create some additional power drain. There is an OFF state where only the minimal circuitry is powered with the intent to use less power than the battery self drain current of ~100 uA. Heck, the FET diode circuit as drawn would draw <300 uA! I\'d need to knock the resistors up to 1Meg to get the current low enough at 14V. But that sounds like a winner. Thanks.

So the final circuit can be a diode from the DC input (no worry with the drop and it\'s used elsewhere so it\'s on the BoM regardless), this circuit for the battery connection to the common power rail. Then my previous voltage limiter circuit to supply the motor and provide a means of cutting power in case the software runs amuck resulting in an over current.

I\'m not a fan of adding unique parts to the BOM, but I think this one is worth it! Thanks again.

Color me confused; you talk about 12V motor max and yet have a 5V
\"transient protector\" at the output???
And it takes only 250K for those resistors to get a \"leakage\" of 48uA
at 12V in.
Looked at the DMMT5401, a good choice, beta may be a little low at a
measly 100 but seems adequate,giving Vce(sat) <200mV up to 100mA.
Again NO HINT as to motor current.
More info??

Thanks.

Sorry, I\'m confused. Where do you see a 5 volt transient protector??? The diagram you are likely looking at was posted by someone else to illustrate the properties of the circuit, not a suggestion for what I should use. I don\'t think the beta is a critical parameter. The circuit seem to produce a voltage drop of 80 mV used with an AOD4185 in my circuit.

To minimize leakage from the battery I used 1 Meg resistors which slow the response to the line power dropping resulting in a half volt drop in voltage for half a millisecond in the simulation. I consider that acceptable. The requirements on this circuit are not severe. It\'s powering a motor, not digital logic. There are also some whopping big caps on this rail to deal with the flyback current from the PWM turning off. Cutting power at this FET is a different matter, so I added a flyback diode and small resistor.

The motor current trips a cut off over 4 amps. Motor rating is 3.5 amps continuous. Don\'t know what current it will actually be operated or if any of these numbers need to be limited instantaneous or average. Not sure how long it takes to snap the motor shaft when the mechanism binds. They\'ve broken several Pololu units so far. They are using a better motor now.

The rev 2 board will have the building blocks to manage this no matter what.. The current limit will actually be done in the FPGA, so no worry about the software crashing and breaking the hardware.

--

Rick C.

--- Get 1,000 miles of free Supercharging
--- Tesla referral code - https://ts.la/richard11209

 

[Robert Baer]

Lasse Langwadt Christensen wrote:

tirsdag den 1. september 2020 kl. 22.18.09 UTC+2 skrev Robert Baer:
Ricketty C wrote:
On Monday, August 31, 2020 at 7:07:22 PM UTC-4, Lasse Langwadt Christensen wrote:
tirsdag den 1. september 2020 kl. 01.02.06 UTC+2 skrev Ricketty C:
On Monday, August 31, 2020 at 5:53:52 PM UTC-4, Robert Baer wrote:
Ricketty C wrote:
I suppose this works like a voltage regulator but it is hard to search those to find which ones will work down to what voltage with minimum drop out. This circuit limits the output voltage to about 12.4 volts and has a minimum drop out of 0.15 volts down to a Vin of around 6 volts. This is powering a motor, so the current probably won\'t change as fast as I\'ve simulated.

This seems to work pretty well without instabilities. The parts cost is minimal even if the parts count is higher than with a regulator.

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.asc

http://arius.com/temp/MotorOverCurrent_Vlimit_FET.plt

I\'m pretty sure there aren\'t any missing models. At least not in LTspice XVII. I wonder why it went from IV to XVII...?

Does anyone know of a regulator that will provide 12.4 volts from 17 volts max with minimum drop out voltage as the input drops to 10 volts? It needs to have a shutdown input as well and draw very low idle current, <100 uA, better to be <50 uA.

That would be VERY interesting..input down to 10V and output staying
near 12.4V...you did imply linear...

I assume there is a joke in there somewhere. You do realize I\'m talking about an output dropping once the input drops below the output plus some drop out. That\'s my point, regulators are spec\'d for a minimum drop out where they meet full specs. I\'m interested in the drop out once they are out of regulation and the pass transistor is turned on fully.

Actually, using a regulator may not be an option anymore. We are combining the input DC @ 15V with the battery voltage through diodes to feed the main power rail. The motor is the only heavy draw. I\'m wondering if it makes sense to use two FETs back to back to prevent reverse current flow between the two circuits. One pair for the main power source and a second pair for the battery resulting in a lower voltage drop so the battery can be used more effectively.

Using a regulator will still require a diode to prevent back current flow to the main power input. So two diodes and a regulator or four FETs?

I actually saw this circuit on a schematic for a Trenz FPGA board, but much lower power levels. Not sure which way I want to go.


you just need a \"diode\" from each, something like this has been used on the raspberry pi to enable using a psu or USB power and not backfeed the USB

https://robotics.ong.id.au/wp-content/uploads/2014/07/rpi_protection.png

I can\'t seem to make that work for me. It is set up to equalize the voltage when passing current in one direction. But it can\'t be used to limit the output voltage so well because the lowest drop you can get is 0.7 volts or so through the parasitic diode. I need to scrub about 2.5 volt from the main power input or a varying amount from the battery, down to as close to zero as possible.

I could just use a FET for the limiter and then use two of these to combine the two supplies. Or maybe only one is needed on the battery. When the power source is unplugged, I\'m not sure it would hurt anything to reverse power the input. I only feeds the battery charger. I guess it would create some additional power drain. There is an OFF state where only the minimal circuitry is powered with the intent to use less power than the battery self drain current of ~100 uA. Heck, the FET diode circuit as drawn would draw <300 uA! I\'d need to knock the resistors up to 1Meg to get the current low enough at 14V. But that sounds like a winner. Thanks.

So the final circuit can be a diode from the DC input (no worry with the drop and it\'s used elsewhere so it\'s on the BoM regardless), this circuit for the battery connection to the common power rail. Then my previous voltage limiter circuit to supply the motor and provide a means of cutting power in case the software runs amuck resulting in an over current.

I\'m not a fan of adding unique parts to the BOM, but I think this one is worth it! Thanks again.

Color me confused; you talk about 12V motor max and yet have a 5V
\"transient protector\" at the output???

you do seem to need to have every spelled out

12V regulator limits the voltage to the motor, regulator can be feed by 15V supply or a ~12V battery, to avoid back feeding the battery diodes are needed.

the circuit is an ideal diode designed for 5V USB, with changes the same can be used for the ~12V battery avoiding the waste of a diode voltage

Make up your mind; a 12V regulator (for the motor), or a 5V regulator
for USB?
A 5V USB regulator to be up-zapped for motor use, or a 12V regulator
to be downgraded for USB?

Note that fancy zero-drop voltage follower: Vo=Vin, limits: Vo(min)
0.6V, Vo(max) 150V.
Drop with up to 400mA load less than 400mV.