Electronics > Projects, Designs, and Technical Stuff

H-bridge DC motor driver with OPAMP as gate driver?

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lordvader88:

--- Quote from: David Hess on June 24, 2019, 06:50:50 pm ---Operational amplifiers make slow comparators and they become even slower when driving the relatively high input capacitance of power MOSFETs.


--- End quote ---
So if u had a common LM393 comparator vs  a common LM358 op-amp as a comp., how much difference is there ?

I think I only have a few comparators, I should get a few better ones for special projects.

jmelson:

--- Quote from: lordvader88 on June 26, 2019, 06:19:09 pm ---
So if u had a common LM393 comparator vs  a common LM358 op-amp as a comp., how much difference is there ?

--- End quote ---
The LM393 has no pull-up transistor, it is not designed to sink more than a few mA ouptut with a pull-up resistor.  The FET gate drivers I use from International Rectifier can source close to an amp and sink over 1 amp.  You need this to keep the transistors out of the linear region, where they do not perform well.

lordvader88:
I have a few salvaged motors and controller/driver chips. Now I wish I save more boards. I want to make a few simple things like a remote IR curtain opener and light switch flicker. But not like Doc Brown cooking my breakfast.

ahbushnell:
There is a problem with the way the MOSFET's are installed.  Better check that.

Also as other people said opamps are not a good idea. 

andy

David Hess:

--- Quote from: lordvader88 on June 26, 2019, 06:19:09 pm ---
--- Quote from: David Hess on June 24, 2019, 06:50:50 pm ---Operational amplifiers make slow comparators and they become even slower when driving the relatively high input capacitance of power MOSFETs.
--- End quote ---

So if u had a common LM393 comparator vs  a common LM358 op-amp as a comp., how much difference is there ?
--- End quote ---

The LM339/LM393 comparator is like 200 nanoseconds while the LM358/LM324 will take 12 microseconds just to slew its output *after* recovering from saturation.  So 100 times faster is not out of the question.

But an LM339/LM393 will require some kind of output driver which might be as simple as the example I gave or more likely an NPN/PNP emitter follower pair with a pull-up resistor.

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