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Topic: MOSFETs after h-bridge chip? (Read 987 times) previous topic - next topic

freakdaddy

Is it generally acceptable to place MOSFETs after an h bridge to control a motor requiring high current using PWM?  In this case around 6A @ 12VDC.  If not is there a better way to do it?

kf2qd

No = you need a bigger H-Bridge. Do a little research into how an H-Bridge works and you will understand.

freakdaddy

I understand how they work I just wondered if it was acceptable to add mosfets to the output of something like an L293D so it would handle higher current.  It sounds like you are saying to build my own h bridge out of mosfets and skip the L293D?

CrossRoads

So you're talking something like this, where the L293D is used to drive the Gates of standard MOSFETs from 0 to +12V say (need more than 10V for full on).
I don't see why it couldn't be used as a MOSFET driver.
L239D has diodes built in, you'd want to add those here with the external MOSFETs if controlling a motor.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

freakdaddy

Yes that's what I was talking about. If that is outside the norm I can make the h bridge if that is what most would do.

CrossRoads

A lot depends on the voltage you use.  You are talking high power, which usually means higher voltage, so you need some kind of buffer in front of the PNPs anyway to let them swing up to 12V (in this example), can use single transistor with pullup resistor, or use the L293 for that.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

MarkT


So you're talking something like this, where the L293D is used to drive the Gates of standard MOSFETs from 0 to +12V say (need more than 10V for full on).
I don't see why it couldn't be used as a MOSFET driver.
L239D has diodes built in, you'd want to add those here with the external MOSFETs if controlling a motor.


You would get better performance from a purpose-designed MOSFET driver of course (much faster switching speed
for instance), and the L293D probably won't fully turn-off most MOSFETs due to the 1V or so drop across the darlington
output stage (but it'll probably turn off enough to be workable).  A H-bridge made from MOSFETs doesn't need diodes
BTW, power MOSFETs have built-in body diodes.
[ I won't respond to messages, use the forum please ]

zoomkat

Quote
Yes that's what I was talking about. If that is outside the norm I can make the h bridge if that is what most would do.


You probably need to buy an h-bridge off of ebay instead of DIY.
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