Electronics > Projects, Designs, and Technical Stuff
H-bridge DC motor driver with OPAMP as gate driver?
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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