mosfet driver needed for logic-level mosfets?

[default]

On Thu, 18 May 2017 09:36:07 -0500, amdx <nojunk@knology.net> wrote:

On 5/15/2017 10:33 AM, mrdarrett@gmail.com wrote:
Hello,

I've discovered logic-level mosfets, and am using an Arduino to drive a small 12VDC (about an amp or so) pump motor with PWM, using an IRLZ34N as the power mosfet.

Would a mosfet-driver be recommended to switch that mosfet on and off more quickly? Or is a logic-level mosfet already designed to efficiently turn on and off with the weak logic level signal?

Thanks,

Michael

This doesn't sound like a very critical application.
So it might be overkill, have you looked at the TC4420 series of
FET drivers.
http://www.learn-c.com/tc4429.pdf

Mikek

That's what I'm thinking too. He needs to breadboard something, or
simulate it and see what the actual problems are, rather than try to
over-kill it in the ruminating stage of design...

The arduino outputs 5 volts, or 3.3V, and if he only has that to work
with, it may not be enough to fully turn on a so-called logic level
mosfet. But it is so easy to use the Arduino to run a flea power
boost converter so that shouldn't be a problem to just step up voltage
with an inductor and switching transistor.

And then too, the Arduino is over-kill for most projects.

 

On Friday, May 19, 2017 at 4:13:22 AM UTC-7, default wrote:

On Thu, 18 May 2017 09:36:07 -0500, amdx <nojunk@knology.net> wrote:

On 5/15/2017 10:33 AM, mrdarrett@gmail.com wrote:
Hello,

I've discovered logic-level mosfets, and am using an Arduino to drive a small 12VDC (about an amp or so) pump motor with PWM, using an IRLZ34N as the power mosfet.

Would a mosfet-driver be recommended to switch that mosfet on and off more quickly? Or is a logic-level mosfet already designed to efficiently turn on and off with the weak logic level signal?

Thanks,

Michael

This doesn't sound like a very critical application.
So it might be overkill, have you looked at the TC4420 series of
FET drivers.
http://www.learn-c.com/tc4429.pdf

Mikek

That's what I'm thinking too. He needs to breadboard something, or
simulate it and see what the actual problems are, rather than try to
over-kill it in the ruminating stage of design...

The arduino outputs 5 volts, or 3.3V, and if he only has that to work
with, it may not be enough to fully turn on a so-called logic level
mosfet. But it is so easy to use the Arduino to run a flea power
boost converter so that shouldn't be a problem to just step up voltage
with an inductor and switching transistor.

And then too, the Arduino is over-kill for most projects.

I already breadboarded it. I put a 270 ohm resistor (calculated from V=IR, with I set to the max safe current the Arduino could put out... I forget exactly what it was, and V set to 5V) between an output PWM of the Arduino to the gate of an IRLZ34NPbF mosfet, and put one of these pumps between +18V and the drain:

https://www.amazon.com/ZJchao-Dosing-Peristaltic-Aquarium-Analytic/dp/B00F9MXFFQ/ref=sr_1_4?ie=UTF8&qid=1495207608&sr=8-4&keywords=peristaltic+pump

I rather doubt that 80 mA figure; I'll have to measure it one of these days..

My Arduino program displays the current power setting (0-100%) and if I, for example, send a "6" followed by Enter to the serial port, the Arduino sets the PWM at 60% power. The C code is somewhat laughable but I can post it if you really want.

It works fairly well, but I noticed I had to put a heatsink on the MOSFET, which had me wondering why.

Oh! I put an SB140 schottky in parallel with the motor.

Michael

 

[default]

On Fri, 19 May 2017 08:30:22 -0700 (PDT), mrdarrett@gmail.com wrote:

On Friday, May 19, 2017 at 4:13:22 AM UTC-7, default wrote:
On Thu, 18 May 2017 09:36:07 -0500, amdx <nojunk@knology.net> wrote:

On 5/15/2017 10:33 AM, mrdarrett@gmail.com wrote:
Hello,

I've discovered logic-level mosfets, and am using an Arduino to drive a small 12VDC (about an amp or so) pump motor with PWM, using an IRLZ34N as the power mosfet.

Would a mosfet-driver be recommended to switch that mosfet on and off more quickly? Or is a logic-level mosfet already designed to efficiently turn on and off with the weak logic level signal?

Thanks,

Michael

This doesn't sound like a very critical application.
So it might be overkill, have you looked at the TC4420 series of
FET drivers.
http://www.learn-c.com/tc4429.pdf

Mikek

That's what I'm thinking too. He needs to breadboard something, or
simulate it and see what the actual problems are, rather than try to
over-kill it in the ruminating stage of design...

The arduino outputs 5 volts, or 3.3V, and if he only has that to work
with, it may not be enough to fully turn on a so-called logic level
mosfet. But it is so easy to use the Arduino to run a flea power
boost converter so that shouldn't be a problem to just step up voltage
with an inductor and switching transistor.

And then too, the Arduino is over-kill for most projects.


I already breadboarded it. I put a 270 ohm resistor (calculated from V=IR, with I set to the max safe current the Arduino could put out... I forget exactly what it was, and V set to 5V) between an output PWM of the Arduino to the gate of an IRLZ34NPbF mosfet, and put one of these pumps between +18V and the drain:

https://www.amazon.com/ZJchao-Dosing-Peristaltic-Aquarium-Analytic/dp/B00F9MXFFQ/ref=sr_1_4?ie=UTF8&qid=1495207608&sr=8-4&keywords=peristaltic+pump

I rather doubt that 80 mA figure; I'll have to measure it one of these days.

My Arduino program displays the current power setting (0-100%) and if I, for example, send a "6" followed by Enter to the serial port, the Arduino sets the PWM at 60% power. The C code is somewhat laughable but I can post it if you really want.

It works fairly well, but I noticed I had to put a heatsink on the MOSFET, which had me wondering why.

Oh! I put an SB140 schottky in parallel with the motor.

Michael

I'd doubt the 80 mils too. They don't give the conditions, like speed
and back-pressure. Peristaltic pumps aren't known for their
free-spinning characteristics, they are better suited for intermittent
use (especially when directly driven). If the tubing isn't silicon
tubing I'd recommend a change because the energy used to pinch the
tubing is waste. (and I don't ever remember seeing any peristaltic
with a direct drive, they always used gearboxes, even the ones driven
with stepper motors)

Motor current would be worth checking.

I worked in a pharmaceutical chemistry lab doing electronic and
electromechanical design.

I take it the Arduino is basically just chopping the power to the pump
motor? No inductors or filter caps involved? What frequency are you
chopping power at? Have you looked at the waveforms with a scope?

As for current limiting to the gate drive, that may not be necessary
or desirable. The gate is essentially a capacitor. (of 880 pico
farads in this case) The current is just necessary for a brief time
to charge and discharge the gate. Do you have any idea what the peak
current the Arduino chip can sink and source? If you have 18 Volts to
play with it may be better to just drive the gate with a higher
voltage (but absolute max for that part is 16 volts...)

A scope might tell you what is going on to cause it to heat...

I designed a variable speed (large) fan for my last tower computer.
The specs on the brushless fan said it was 500 MA at 12 V and the
mosfet was toggling at 15 KHZ and ran cool, with no heat sink. But
then I wasn't using straight pwm and driving a brushed motor either, I
was using it as a switching mode power supply and sending pure DC to
the fan motor, except on the highest setting, then it was just turning
on the mosfet with no chopping.

My drive circuit was a single ended npn transistor, but only because I
started out using pwm and a BJT transistor. (it turned out that the
fan didn't like that; pulses from the drive would alias with the
pulses to the fan coils) When I changed the programming for smooth DC
(added an inductor diode and filter cap) and switched to a mosfet I
just left the transistor in the circuit. (too lazy to rewire the
perf-board I was using, and 12V meant there was no need for a logic
level device)

 

On Friday, May 19, 2017 at 10:48:44 AM UTC-7, default wrote:

....

I already breadboarded it. I put a 270 ohm resistor (calculated from V=IR, with I set to the max safe current the Arduino could put out... I forget exactly what it was, and V set to 5V) between an output PWM of the Arduino to the gate of an IRLZ34NPbF mosfet, and put one of these pumps between +18V and the drain:

https://www.amazon.com/ZJchao-Dosing-Peristaltic-Aquarium-Analytic/dp/B00F9MXFFQ/ref=sr_1_4?ie=UTF8&qid=1495207608&sr=8-4&keywords=peristaltic+pump

I rather doubt that 80 mA figure; I'll have to measure it one of these days.

My Arduino program displays the current power setting (0-100%) and if I, for example, send a "6" followed by Enter to the serial port, the Arduino sets the PWM at 60% power. The C code is somewhat laughable but I can post it if you really want.

It works fairly well, but I noticed I had to put a heatsink on the MOSFET, which had me wondering why.

Oh! I put an SB140 schottky in parallel with the motor.

Michael

I'd doubt the 80 mils too. They don't give the conditions, like speed
and back-pressure. Peristaltic pumps aren't known for their
free-spinning characteristics, they are better suited for intermittent
use (especially when directly driven). If the tubing isn't silicon
tubing I'd recommend a change because the energy used to pinch the
tubing is waste. (and I don't ever remember seeing any peristaltic
with a direct drive, they always used gearboxes, even the ones driven
with stepper motors)

Motor current would be worth checking.

I worked in a pharmaceutical chemistry lab doing electronic and
electromechanical design.

I take it the Arduino is basically just chopping the power to the pump
motor? No inductors or filter caps involved? What frequency are you
chopping power at? Have you looked at the waveforms with a scope?

I think it's either around 400 or 900 Hz, and nope I have no scope.

As for current limiting to the gate drive, that may not be necessary
or desirable. The gate is essentially a capacitor. (of 880 pico
farads in this case) The current is just necessary for a brief time
to charge and discharge the gate. Do you have any idea what the peak
current the Arduino chip can sink and source? If you have 18 Volts to
play with it may be better to just drive the gate with a higher
voltage (but absolute max for that part is 16 volts...)

A scope might tell you what is going on to cause it to heat...

Here's the schematic for it. I was practicing my CAD drawing skills too...

https://978f7929-a-62cb3a1a-s-sites.googlegroups.com/site/michaeldarrett/autocad/pwm.png

I designed a variable speed (large) fan for my last tower computer.
The specs on the brushless fan said it was 500 MA at 12 V and the
mosfet was toggling at 15 KHZ and ran cool, with no heat sink. But
then I wasn't using straight pwm and driving a brushed motor either, I
was using it as a switching mode power supply and sending pure DC to
the fan motor, except on the highest setting, then it was just turning
on the mosfet with no chopping.

My drive circuit was a single ended npn transistor, but only because I
started out using pwm and a BJT transistor. (it turned out that the
fan didn't like that; pulses from the drive would alias with the
pulses to the fan coils) When I changed the programming for smooth DC
(added an inductor diode and filter cap) and switched to a mosfet I
just left the transistor in the circuit. (too lazy to rewire the
perf-board I was using, and 12V meant there was no need for a logic
level device)

Brushless fan... there's a controller board in there too. Seems kind of strange when you think about it, PWMing the power to a brushless fan which will also have its controller board, Hall sensors, etc. buried under the fan blade hub. Ceramic iron magnets too... and how do I know this? I somehow managed to corrode one, and decided to take it apart

Michael