TCA0372 troubles

G

George Herold

Guest
I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.
 
On Tuesday, June 4, 2019 at 10:56:08 AM UTC-4, Jan Panteltje wrote:
On a sunny day (Tue, 4 Jun 2019 07:34:25 -0700 (PDT)) it happened George
Herold <gherold@teachspin.com> wrote in
1a529d07-864a-46ed-9dfc-40eda1ee49af@googlegroups.com>:

I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

Transistor (current drive) or a MOSFET (voltage drive) is much better.
Add some opamp for control.
Right I might have to do that... it takes more thinking though.

The opa551 looks nice.
http://www.ti.com/lit/ds/symlink/opa552.pdf

fig 29 shows how to parallel opamps.... I might try that with a different
opamp.

George H.
Or use the transistor or MOSFET itself as heater?
http://panteltje.com/pub/heater_circuit.gif
been working fine for many years.
Drive is filtered PIC PWM output.. PID controller in software.
 
On a sunny day (Tue, 4 Jun 2019 07:34:25 -0700 (PDT)) it happened George
Herold <gherold@teachspin.com> wrote in
<1a529d07-864a-46ed-9dfc-40eda1ee49af@googlegroups.com>:

I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

Transistor (current drive) or a MOSFET (voltage drive) is much better.
Add some opamp for control.

Or use the transistor or MOSFET itself as heater?
http://panteltje.com/pub/heater_circuit.gif
been working fine for many years.
Drive is filtered PIC PWM output.. PID controller in software.
 
On Tuesday, June 4, 2019 at 10:34:31 AM UTC-4, George Herold wrote:
I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.

Say, Can I parallel opamps on the output for more current? How well
will they share current?

GH
 
On 6/4/19 10:49 AM, George Herold wrote:
On Tuesday, June 4, 2019 at 10:34:31 AM UTC-4, George Herold wrote:
I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.

How about a ~10 ohm polyfuse?
<https://www.digikey.com/product-detail/en/littelfuse-inc/600R150-RBZR/F5554TB-ND/1211304>
Say, Can I parallel opamps on the output for more current? How well
will they share current?

Fine, if you use separate feedback networks and a resistor in series
with each one to limit the current consumed by duelling offset voltages.

I often make 50-ohm outputs by parallelling two sections of an LT1260
CFA, each with a 100-ohm resistor in series.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
On Tuesday, June 4, 2019 at 11:44:34 AM UTC-4, Phil Hobbs wrote:
On 6/4/19 10:49 AM, George Herold wrote:
On Tuesday, June 4, 2019 at 10:34:31 AM UTC-4, George Herold wrote:
I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.

How about a ~10 ohm polyfuse?
https://www.digikey.com/product-detail/en/littelfuse-inc/600R150-RBZR/F5554TB-ND/1211304
Huh, I've got some poly fuses... I always thought of them as slow.. but I
could try. (I was thinking I could add some series R on the output, but
inside the feedback loop...)
Say, Can I parallel opamps on the output for more current? How well
will they share current?

Fine, if you use separate feedback networks and a resistor in series
with each one to limit the current consumed by duelling offset voltages.
The OPA552 data sheet showed a master/ slave relationship with two opamps.

George H.
I often make 50-ohm outputs by parallelling two sections of an LT1260
CFA, each with a 100-ohm resistor in series.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
On Tue, 4 Jun 2019 11:44:24 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 6/4/19 10:49 AM, George Herold wrote:
On Tuesday, June 4, 2019 at 10:34:31 AM UTC-4, George Herold wrote:
I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.

How about a ~10 ohm polyfuse?
https://www.digikey.com/product-detail/en/littelfuse-inc/600R150-RBZR/F5554TB-ND/1211304

Say, Can I parallel opamps on the output for more current? How well
will they share current?

Fine, if you use separate feedback networks and a resistor in series
with each one to limit the current consumed by duelling offset voltages.

I often make 50-ohm outputs by parallelling two sections of an LT1260
CFA, each with a 100-ohm resistor in series.

Cheers

Phil Hobbs

I'm designing a laser controller that has to power five external
energy sensors, 12v at up to 100 mA each. I've considered polyfuses in
the 12v outputs, but if the customer shorts things, they can pull a
lot of current before they heat up and open, which could reset my box.

I might use some LDOs as non-regulators, just to get their current
limiters.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On Tue, 4 Jun 2019 07:34:25 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.

The data sheet is sketchy, if not evasive. It claims that the chip has
thermal protections but warns against exceeding 1 amp out. There is
nothing that specs actual current capability or current limit.

Is your heater a resistor? That should limit the opamp output current.

What's your supply voltage?

One alternative to using a big opamp is to use a little one and boost
its output using a 3t voltage regulator, LM317 or LM1117, as a power
booster, essentially a smart, protected emitter follower.

I've used the TCAs without problems, but I'm usually driving a fast
output switch that has a final 50 ohm resistor, which takes a lot of
stress off the opamp.

Probably too much voltage drop x current can blow out a transistor
before the thermal limit kicks in.

Don't short the output!


--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On Tuesday, June 4, 2019 at 11:46:49 AM UTC-4, John Larkin wrote:
On Tue, 4 Jun 2019 07:34:25 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.

The data sheet is sketchy, if not evasive. It claims that the chip has
thermal protections but warns against exceeding 1 amp out. There is
nothing that specs actual current capability or current limit.

Is your heater a resistor? That should limit the opamp output current.
Right, but kids have access to the output and can short it.

What's your supply voltage?
24V.
(Here's a pic of the output.)
https://www.dropbox.com/s/v8teqh5a0jep8qt/tca0372.JPG?dl=0


One alternative to using a big opamp is to use a little one and boost
its output using a 3t voltage regulator, LM317 or LM1117, as a power
booster, essentially a smart, protected emitter follower.
Huh.. 317 as power booster? I've used LM395 for that.. but they are
spendy... How do I do that with an LM317? (and what's the dropout?)

I've used the TCAs without problems, but I'm usually driving a fast
output switch that has a final 50 ohm resistor, which takes a lot of
stress off the opamp.

Probably too much voltage drop x current can blow out a transistor
before the thermal limit kicks in.

Don't short the output!
Then I can't sell it. :^)

George H.
--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On Tuesday, June 4, 2019 at 1:06:36 PM UTC-4, Phil Hobbs wrote:
On 6/4/19 12:20 PM, George Herold wrote:
On Tuesday, June 4, 2019 at 11:46:49 AM UTC-4, John Larkin wrote:
On Tue, 4 Jun 2019 07:34:25 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.

The data sheet is sketchy, if not evasive. It claims that the chip has
thermal protections but warns against exceeding 1 amp out. There is
nothing that specs actual current capability or current limit.

Is your heater a resistor? That should limit the opamp output current.
Right, but kids have access to the output and can short it.

What's your supply voltage?
24V.
(Here's a pic of the output.)
https://www.dropbox.com/s/v8teqh5a0jep8qt/tca0372.JPG?dl=0



One alternative to using a big opamp is to use a little one and boost
its output using a 3t voltage regulator, LM317 or LM1117, as a power
booster, essentially a smart, protected emitter follower.

Huh.. 317 as power booster? I've used LM395 for that.. but they are
spendy... How do I do that with an LM317? (and what's the dropout?)

Just like the LM395. IIRC JT said that it's the same silicon with
different metal. If you have more than one supply voltage involved, you
might need some protection diodes.

OK thanks, I found this,
https://electronics.stackexchange.com/questions/17852/how-does-this-power-supply-circuit-work-mcu-lm317

The LM395 looks like a Darlington... there is the 1.25 V drop in the LM317..
but I guess with feedback it all comes out in the wash.


GH
Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
On 6/4/19 12:20 PM, George Herold wrote:
On Tuesday, June 4, 2019 at 11:46:49 AM UTC-4, John Larkin wrote:
On Tue, 4 Jun 2019 07:34:25 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.

The data sheet is sketchy, if not evasive. It claims that the chip has
thermal protections but warns against exceeding 1 amp out. There is
nothing that specs actual current capability or current limit.

Is your heater a resistor? That should limit the opamp output current.
Right, but kids have access to the output and can short it.

What's your supply voltage?
24V.
(Here's a pic of the output.)
https://www.dropbox.com/s/v8teqh5a0jep8qt/tca0372.JPG?dl=0



One alternative to using a big opamp is to use a little one and boost
its output using a 3t voltage regulator, LM317 or LM1117, as a power
booster, essentially a smart, protected emitter follower.

Huh.. 317 as power booster? I've used LM395 for that.. but they are
spendy... How do I do that with an LM317? (and what's the dropout?)

Just like the LM395. IIRC JT said that it's the same silicon with
different metal. If you have more than one supply voltage involved, you
might need some protection diodes.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
On Tue, 4 Jun 2019 09:20:04 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Tuesday, June 4, 2019 at 11:46:49 AM UTC-4, John Larkin wrote:
On Tue, 4 Jun 2019 07:34:25 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.

The data sheet is sketchy, if not evasive. It claims that the chip has
thermal protections but warns against exceeding 1 amp out. There is
nothing that specs actual current capability or current limit.

Is your heater a resistor? That should limit the opamp output current.
Right, but kids have access to the output and can short it.

What's your supply voltage?
24V.
(Here's a pic of the output.)
https://www.dropbox.com/s/v8teqh5a0jep8qt/tca0372.JPG?dl=0



One alternative to using a big opamp is to use a little one and boost
its output using a 3t voltage regulator, LM317 or LM1117, as a power
booster, essentially a smart, protected emitter follower.

Huh.. 317 as power booster? I've used LM395 for that.. but they are
spendy... How do I do that with an LM317? (and what's the dropout?)

Drive the ADJ pin with your signal from a small opamp. A series
resistor and a zener or something can do your square root.

You'll get the +1.25 volt offset, and the dropout on the data sheet.
You'd have to drive ADJ to -1.25 to get zero out.

I tried abusing the ADJ pin of an 1117 all the ways I could, and
couldn't break it.

The 1117 has lower dropout than the 317, but it's only rated for 12
volts. The ones that I tried failed at around 60.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On Tuesday, June 4, 2019 at 1:36:07 PM UTC-4, John Larkin wrote:
On Tue, 4 Jun 2019 09:20:04 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Tuesday, June 4, 2019 at 11:46:49 AM UTC-4, John Larkin wrote:
On Tue, 4 Jun 2019 07:34:25 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.

The data sheet is sketchy, if not evasive. It claims that the chip has
thermal protections but warns against exceeding 1 amp out. There is
nothing that specs actual current capability or current limit.

Is your heater a resistor? That should limit the opamp output current.
Right, but kids have access to the output and can short it.

What's your supply voltage?
24V.
(Here's a pic of the output.)
https://www.dropbox.com/s/v8teqh5a0jep8qt/tca0372.JPG?dl=0



One alternative to using a big opamp is to use a little one and boost
its output using a 3t voltage regulator, LM317 or LM1117, as a power
booster, essentially a smart, protected emitter follower.

Huh.. 317 as power booster? I've used LM395 for that.. but they are
spendy... How do I do that with an LM317? (and what's the dropout?)


Drive the ADJ pin with your signal from a small opamp. A series
resistor and a zener or something can do your square root.

You'll get the +1.25 volt offset, and the dropout on the data sheet.
You'd have to drive ADJ to -1.25 to get zero out.
Right thanks. Say speaking of the 1.25 V drop, if I added a small R
to the output of the '317 and feed that back to the adj pin I could
have it current limit when shorted... I guess I'd need a diode between
the adj pin and low voltage side of current sense R.

I'll try just the '317 first.

George H.
I tried abusing the ADJ pin of an 1117 all the ways I could, and
couldn't break it.

The 1117 has lower dropout than the 317, but it's only rated for 12
volts. The ones that I tried failed at around 60.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On 6/4/19 11:52 AM, John Larkin wrote:
On Tue, 4 Jun 2019 11:44:24 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 6/4/19 10:49 AM, George Herold wrote:
On Tuesday, June 4, 2019 at 10:34:31 AM UTC-4, George Herold wrote:
I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.

How about a ~10 ohm polyfuse?
https://www.digikey.com/product-detail/en/littelfuse-inc/600R150-RBZR/F5554TB-ND/1211304

Say, Can I parallel opamps on the output for more current? How well
will they share current?

Fine, if you use separate feedback networks and a resistor in series
with each one to limit the current consumed by duelling offset voltages.

I often make 50-ohm outputs by parallelling two sections of an LT1260
CFA, each with a 100-ohm resistor in series.


I'm designing a laser controller that has to power five external
energy sensors, 12v at up to 100 mA each. I've considered polyfuses in
the 12v outputs, but if the customer shorts things, they can pull a
lot of current before they heat up and open, which could reset my box.

I might use some LDOs as non-regulators, just to get their current
limiters.

Sounds sensible as long as they don't short it to someplace nastier than
ground, e.g. 240VAC. But if the circuit board is charred, it's a bit
harder to blame the manufacturer. ;)

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
https://hobbs-eo.com
 
On Tue, 4 Jun 2019 13:56:06 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 6/4/19 11:52 AM, John Larkin wrote:
On Tue, 4 Jun 2019 11:44:24 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 6/4/19 10:49 AM, George Herold wrote:
On Tuesday, June 4, 2019 at 10:34:31 AM UTC-4, George Herold wrote:
I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.

How about a ~10 ohm polyfuse?
https://www.digikey.com/product-detail/en/littelfuse-inc/600R150-RBZR/F5554TB-ND/1211304

Say, Can I parallel opamps on the output for more current? How well
will they share current?

Fine, if you use separate feedback networks and a resistor in series
with each one to limit the current consumed by duelling offset voltages.

I often make 50-ohm outputs by parallelling two sections of an LT1260
CFA, each with a 100-ohm resistor in series.


I'm designing a laser controller that has to power five external
energy sensors, 12v at up to 100 mA each. I've considered polyfuses in
the 12v outputs, but if the customer shorts things, they can pull a
lot of current before they heat up and open, which could reset my box.

I might use some LDOs as non-regulators, just to get their current
limiters.

Sounds sensible as long as they don't short it to someplace nastier than
ground, e.g. 240VAC. But if the circuit board is charred, it's a bit
harder to blame the manufacturer. ;)

Cheers

Phil Hobbs

This customer had a giant ground loop somehow between two of our boxes
connected by an RS485 link. After the first box smoked, they tried
several more.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
tirsdag den 4. juni 2019 kl. 17.52.15 UTC+2 skrev John Larkin:
On Tue, 4 Jun 2019 11:44:24 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 6/4/19 10:49 AM, George Herold wrote:
On Tuesday, June 4, 2019 at 10:34:31 AM UTC-4, George Herold wrote:
I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.

How about a ~10 ohm polyfuse?
https://www.digikey.com/product-detail/en/littelfuse-inc/600R150-RBZR/F5554TB-ND/1211304

Say, Can I parallel opamps on the output for more current? How well
will they share current?

Fine, if you use separate feedback networks and a resistor in series
with each one to limit the current consumed by duelling offset voltages.

I often make 50-ohm outputs by parallelling two sections of an LT1260
CFA, each with a 100-ohm resistor in series.

Cheers

Phil Hobbs

I'm designing a laser controller that has to power five external
energy sensors, 12v at up to 100 mA each. I've considered polyfuses in
the 12v outputs, but if the customer shorts things, they can pull a
lot of current before they heat up and open, which could reset my box.

I might use some LDOs as non-regulators, just to get their current
limiters.

https://www.onsemi.com/pub/Collateral/NCV47722-D.PDF
 
On Tuesday, June 4, 2019 at 2:38:46 PM UTC-4, George Herold wrote:
On Tuesday, June 4, 2019 at 1:36:07 PM UTC-4, John Larkin wrote:
On Tue, 4 Jun 2019 09:20:04 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Tuesday, June 4, 2019 at 11:46:49 AM UTC-4, John Larkin wrote:
On Tue, 4 Jun 2019 07:34:25 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.

The data sheet is sketchy, if not evasive. It claims that the chip has
thermal protections but warns against exceeding 1 amp out. There is
nothing that specs actual current capability or current limit.

Is your heater a resistor? That should limit the opamp output current.
Right, but kids have access to the output and can short it.

What's your supply voltage?
24V.
(Here's a pic of the output.)
https://www.dropbox.com/s/v8teqh5a0jep8qt/tca0372.JPG?dl=0



One alternative to using a big opamp is to use a little one and boost
its output using a 3t voltage regulator, LM317 or LM1117, as a power
booster, essentially a smart, protected emitter follower.

Huh.. 317 as power booster? I've used LM395 for that.. but they are
spendy... How do I do that with an LM317? (and what's the dropout?)


Drive the ADJ pin with your signal from a small opamp. A series
resistor and a zener or something can do your square root.

You'll get the +1.25 volt offset, and the dropout on the data sheet.
You'd have to drive ADJ to -1.25 to get zero out.
Right thanks. Say speaking of the 1.25 V drop, if I added a small R
to the output of the '317 and feed that back to the adj pin I could
have it current limit when shorted... I guess I'd need a diode between
the adj pin and low voltage side of current sense R.

I'll try just the '317 first.

George H.
Well the LM317 was a fail as a power transistor. The output never went
below 1.2 volts even with -5V on the 'base' adjust pin.
I plugged in the LM395 and it worked fine. I'm going to try the
dual opamp (master/ slave) thing.

George H.
I tried abusing the ADJ pin of an 1117 all the ways I could, and
couldn't break it.

The 1117 has lower dropout than the 317, but it's only rated for 12
volts. The ones that I tried failed at around 60.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On Wed, 5 Jun 2019 07:22:15 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Tuesday, June 4, 2019 at 2:38:46 PM UTC-4, George Herold wrote:
On Tuesday, June 4, 2019 at 1:36:07 PM UTC-4, John Larkin wrote:
On Tue, 4 Jun 2019 09:20:04 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Tuesday, June 4, 2019 at 11:46:49 AM UTC-4, John Larkin wrote:
On Tue, 4 Jun 2019 07:34:25 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.

The data sheet is sketchy, if not evasive. It claims that the chip has
thermal protections but warns against exceeding 1 amp out. There is
nothing that specs actual current capability or current limit.

Is your heater a resistor? That should limit the opamp output current.
Right, but kids have access to the output and can short it.

What's your supply voltage?
24V.
(Here's a pic of the output.)
https://www.dropbox.com/s/v8teqh5a0jep8qt/tca0372.JPG?dl=0



One alternative to using a big opamp is to use a little one and boost
its output using a 3t voltage regulator, LM317 or LM1117, as a power
booster, essentially a smart, protected emitter follower.

Huh.. 317 as power booster? I've used LM395 for that.. but they are
spendy... How do I do that with an LM317? (and what's the dropout?)


Drive the ADJ pin with your signal from a small opamp. A series
resistor and a zener or something can do your square root.

You'll get the +1.25 volt offset, and the dropout on the data sheet.
You'd have to drive ADJ to -1.25 to get zero out.
Right thanks. Say speaking of the 1.25 V drop, if I added a small R
to the output of the '317 and feed that back to the adj pin I could
have it current limit when shorted... I guess I'd need a diode between
the adj pin and low voltage side of current sense R.

I'll try just the '317 first.

George H.
Well the LM317 was a fail as a power transistor. The output never went
below 1.2 volts even with -5V on the 'base' adjust pin.

Makes no sense. How would it know where ground was, to stay 1.2 above
that?

Was your load heater resistor connected, with ground on its other end?


--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On 04/06/2019 15:49, George Herold wrote:
On Tuesday, June 4, 2019 at 10:34:31 AM UTC-4, George Herold wrote:
I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.

Say, Can I parallel opamps on the output for more current? How well
will they share current?

GH

Paralleling op-amps works fine, see:

<http://www.ti.com/lit/an/snoa862/snoa862.pdf>

Back in 1980s I used that very successfully with the oft-mocked LM324.

piglet
 
On Wednesday, June 5, 2019 at 11:19:41 AM UTC-4, John Larkin wrote:
On Wed, 5 Jun 2019 07:22:15 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Tuesday, June 4, 2019 at 2:38:46 PM UTC-4, George Herold wrote:
On Tuesday, June 4, 2019 at 1:36:07 PM UTC-4, John Larkin wrote:
On Tue, 4 Jun 2019 09:20:04 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Tuesday, June 4, 2019 at 11:46:49 AM UTC-4, John Larkin wrote:
On Tue, 4 Jun 2019 07:34:25 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

I'm using my first TCA0372 as a ~1-2 Watt heater drive. Unfortunately
I've blown it up three times... twice by accident and this morning on purpose.
Apparently the TCA can't have it's output shorted to ground.
I_out max is 1.0 A (DC),
https://www.onsemi.com/pub/Collateral/TCA0372-D.PDF

So I need either some output protection.. current limit. Or another
opamp that does ~100 mA, or I'll have to do some transistor pass element..
it's dead slow so speed is not important.

thoughts?
George H.

The data sheet is sketchy, if not evasive. It claims that the chip has
thermal protections but warns against exceeding 1 amp out. There is
nothing that specs actual current capability or current limit.

Is your heater a resistor? That should limit the opamp output current.
Right, but kids have access to the output and can short it.

What's your supply voltage?
24V.
(Here's a pic of the output.)
https://www.dropbox.com/s/v8teqh5a0jep8qt/tca0372.JPG?dl=0



One alternative to using a big opamp is to use a little one and boost
its output using a 3t voltage regulator, LM317 or LM1117, as a power
booster, essentially a smart, protected emitter follower.

Huh.. 317 as power booster? I've used LM395 for that.. but they are
spendy... How do I do that with an LM317? (and what's the dropout?)


Drive the ADJ pin with your signal from a small opamp. A series
resistor and a zener or something can do your square root.

You'll get the +1.25 volt offset, and the dropout on the data sheet.
You'd have to drive ADJ to -1.25 to get zero out.
Right thanks. Say speaking of the 1.25 V drop, if I added a small R
to the output of the '317 and feed that back to the adj pin I could
have it current limit when shorted... I guess I'd need a diode between
the adj pin and low voltage side of current sense R.

I'll try just the '317 first.

George H.
Well the LM317 was a fail as a power transistor. The output never went
below 1.2 volts even with -5V on the 'base' adjust pin.


Makes no sense. How would it know where ground was, to stay 1.2 above
that?

Was your load heater resistor connected, with ground on its other end?
Yeah, I've already ripped up the test circuit.... but the LM395 worked
perfectly in it's place. I could try again... it would be nice to have a
cheap, thermally protected output drive.

George H.
--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 

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