MOSFET driver: popular, cheap, all-in-one for analog PWM?

Thread Starter

Hamlet

Joined Jun 10, 2015
517
I've created many projects using MOSFETS, but never with a driver, I don't have any drivers in my junk box.
Currently, I'm working with analog PWM modulators, driving motors.

I'm looking for an easy to use driver, that will work with analog inputs, 555 PWM designs, or comparitor-PWM, etc.

Can anybody share their recommendations for a popular, east to use, easy to find, and hopefully inexpensive MOSFET driver?

???


I'd like to order a handful to have at my workbench. I want to avoid building drivers from discrete parts
like this one:




Thanks!
 

dannyf

Joined Sep 13, 2015
2,197
the choice depends on your specific needs.

generally, it can be just a SE driver, emitter followers are pretty common. for cases where voltage drops are critical, collector output may be desired. quite often, totem poles are used as well.

then you have the question of topology: are you driving low-side, high-side or a half bridge?

from there, you want to ask yourself if you wish to program dead time? do you want to use an integrated oscillator? ....

IRF is a big player in that space, as is ONSemi. ON's website is a lot easier to search.

The typical inexpensive choice is TC44xx - tons of them out there. Personally, I have used a lot of irf self-oscillating gate drivers - I got a lot of them during my class D builds.

With that said, the (bjt) 555 itself is a good mosfet driver, and can be used as such.

again, it is hard to give you a choice that suits all possible applications, as each design choice is made to a specific design. That's why there are so many gate drivers out there.
 

Thread Starter

Hamlet

Joined Jun 10, 2015
517
No H-bridges. It's not a robot. One direction only. Drive N-MOSFETS to 20KHz. Analog. From my limited understanding,
bootstrap is not involved with one direction motors (pumps, fans).

High side, low-side, are terms I don't understand. Do I need inverting, non-inverting or something that does both?

I haven't found a tutorial that doesn't jump immediately into undefined terms, so I'm lost. I am not using a raspberry,
micro, pic, or adumo. If it has logic level capabilities, fine, but I'm still poking around with analog for now. C+ comes later.
 

Thread Starter

Hamlet

Joined Jun 10, 2015
517
You might take a look at the MCP1406/MCP1407 (inverting and non-inverting, respectively). I've used them with good results.
From what I am able to understand, this will accept LOGIC LEVEL inputs, an ANALOG inputs with their attendant higher voltages?
Looks good, simple, does only one thing. Only problem is that I can't find MCP1406 on ebay, and for the MCP1407 the only offering is
10pcs for $20.
 

crutschow

Joined Mar 14, 2008
31,555
One direction only. Drive N-MOSFETS to 20KHz.
Then OBW0549's suggestion should work for you.
High side, low-side, are terms I don't understand. Do I need inverting, non-inverting or something that does both?
High-side is when the switch is between the power supply and a grounded load.
Low-side is when the load goes to the power and the switch is between the low side of the load and ground.

Whether you need inverting or non-inverting depends upon your application.
The only difference is that the inverting has the output high when the input is low and vice versa, and the non-inverting has the output high when the input is high and vice versa.
 

dannyf

Joined Sep 13, 2015
2,197
Drive N-MOSFETS to 20KHz. Analog.
the general design process starts with topology - you need a low-side driver (a half bridge driver can work as a low side driver or a high side driver); and then current capabilities - that's a function of gate capacitance, switching frequency and drive voltage, mostly. You have to a little bit of math here. but typical applications will put you north of 1amp, with some gate drivers capable of delivering near or over 10amp.

Generally, you want the input signal to be referenced to ground -> easier to interact with a mcu / logic device. TC4420 for example is quite inexpensive and often multi-sourced. It also has a lot of sisters / brothers under slight different names.
 

OBW0549

Joined Mar 2, 2015
3,566
From what I am able to understand, this will accept LOGIC LEVEL inputs, an ANALOG inputs with their attendant higher voltages?
No, logic inputs only.

I'm not sure what you have in mind when you say "analog inputs with their attendant higher voltages." Do you mean driving the MOSFET in a linear fashion (i.e., as a voltage-controlled current source or current sink), in contrast to using it as an ON/OFF switch? I don't think any MOSFET driver is needed for that (nor any available for that), as just about any ordinary op amp will do the job.

We could probably be more help if you could clarify that; better yet, tell us what you're trying to do.
 

Thread Starter

Hamlet

Joined Jun 10, 2015
517
the choice depends on your specific needs.


The typical inexpensive choice is TC44xx - tons of them out there. Personally, I have used a lot of irf self-oscillating gate drivers - I got a lot of them during my class D builds.

With that said, the (bjt) 555 itself is a good mosfet driver, and can be used as such.

again, it is hard to give you a choice that suits all possible applications, as each design choice is made to a specific design. That's why there are so many gate drivers out there.
These are available on ebay, and price isn't too bad. In reading over the datasheet, it looks like ONLY LOGIC LEVEL inputs?
If I use these for analog, will the voltage from pin 3 of a 555 be too high?
 

dannyf

Joined Sep 13, 2015
2,197
the input pins on those devices are typically clamped to their Vcc, or in this case to a 5v zener. So just put a serial resistor on the line and call it a day.
 

Thread Starter

Hamlet

Joined Jun 10, 2015
517
What I want to be able to do is drive a wide selection of mosfets, maybe the input capacitance is very high,
and my PWM design might be as high as 20KHz...

Analog like this, not analog like linear region...



And so it goes...
 

Thread Starter

Hamlet

Joined Jun 10, 2015
517
Then OBW0549's suggestion should work for you.
High-side is when the switch is between the power supply and a grounded load.
Low-side is when the load goes to the power and the switch is between the low side of the load and ground.

Whether you need inverting or non-inverting depends upon your application.
The only difference is that the inverting has the output high when the input is low and vice versa, and the non-inverting has the output high when the input is high and vice versa.
Yes! Thumbs up! Could I say, with reference to MOSFET drivers, that a High-side driver is for P-Channel, & low-side is for N-Channel?
 

OBW0549

Joined Mar 2, 2015
3,566
What I want to be able to do is drive a wide selection of mosfets, maybe the input capacitance is very high, and my PWM design might be as high as 20KHz... Analog like this, not analog like linear region...
Ah. Now I understand. PWM is digital, even if it is used to achieve the effect of an analog signal such as controlling a heater, a light bulb or an LED. So any of the MOSFET drivers that have been recommended here should do the job just fine at 20 kHz, provided you observe their voltage ratings and the voltage ratings of the MOSFET.
 

dannyf

Joined Sep 13, 2015
2,197
maybe the input capacitance is very high,
again, you cannot design one circuit and hope it can drive something that's non-specific (aka "very high").

Analog like this
not sure what that circuit does. the 2nd comparator is more like a 555, and probably provides some latching back and forth for the 1st comparator.

the input signal is likely low, given R7/R8. you can probably get by without having it and feed the input signal to a mosfet driver directly.
 

OBW0549

Joined Mar 2, 2015
3,566
not sure what that circuit does. the 2nd comparator is more like a 555, and probably provides some latching back and forth for the 1st comparator.

the input signal is likely low, given R7/R8. you can probably get by without having it and feed the input signal to a mosfet driver directly.
That circuit is a classic voltage-to-PWM converter circuit. CP1 is a free-running oscillator, with its triangle wave output AC coupled to one input of CP2 which is biased to some positive voltage somewhere in the input voltage range. As the input voltage changes, the PWM duty cycle out of CP2 changes accordingly.
 

Thread Starter

Hamlet

Joined Jun 10, 2015
517
That circuit is a classic voltage-to-PWM converter circuit. CP1 is a free-running oscillator, with its triangle wave output AC coupled to one input of CP2 which is biased to some positive voltage somewhere in the input voltage range. As the input voltage changes, the PWM duty cycle out of CP2 changes accordingly.
Right. Here is the control:





Can I put a mosfet driver on the output signal of the first schematic that I posted and drive a two IRFP350, three IRF740, etc., or not?
Do I even need a mosfet driver?

At this point, I think I need to make a guess, buy some parts, and make smoke. Maybe I can get 20KHz, or maybe only 500Hz, or whatever.

My first attempt, that works well and runs cool was this:



The finer points were discussed in another thread that I started. In reading, reading, reading other posts about PWM,
there were many suggestions that one kind of MOSFET driver or another should be used, to drive the MOSFET hard,
and thus keep them out of the linear region. Lots of folks burning up their MOSFET stage, so I want to avoid that, implement
good design practice, and learn something.

I want to pump water, drive grinders, fans, and all manner of fun stuff like that. However, I don't want to do it with a pic, or adrino, or
do any programming just yet. Before I get back into programming, I will need to completely refocus, scrub my shop, clean off
my workbenches, and sweep the floors. That ain't happening anytime soon.
 

OBW0549

Joined Mar 2, 2015
3,566
Can I put a mosfet driver on the output signal of the first schematic that I posted and drive a two IRFP350, three IRF740, etc., or not?
Looking at the input capacitance specs for those MOSFETs, I would say yes; 20 kHz shouldn't be any problem.

Do I even need a mosfet driver?
I'd say yes; I seriously doubt the comparator could provide sufficient drive on its own.
 

Thread Starter

Hamlet

Joined Jun 10, 2015
517
Looking at the input capacitance specs for those MOSFETs, I would say yes; 20 kHz shouldn't be any problem.


I'd say yes; I seriously doubt the comparator could provide sufficient drive on its own.
Great. What kind of MOSFET drivers should I be looking for that I can use with that comparator PWM design,
or even for a 555 PWM design?
 
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