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P and N Channel H-Bridge with PWM

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drwarm

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Hey stumbled on this great forum after searching for this topic, but can't find an exact answer for my question (with schematic if possible!).

I have been looking at the circuit shown here:
A better MOSFET H Bridge Schematic - The Using MOSFETS Website

I will be driving two motors from a typical R/C car supplied with 9.6V NiCad (I assume they'll draw about 1 amp).

But currently have the following items which differ slightly from those ones (sorry my part numbers might be different as I'm from Australia :) ) :
  • NPN = 2N3904
  • PNP = BC558 (general purpose PNP)
  • N-Channel MOSFET = MPT3055
  • P-Channel MOSFET = IRF9540N

From my reading on the theory of H-Bridges these should be fine, as the Rds(ON) is about the same for both MOSFETS (approx .1 Ω), and they're both logic level driven (I hope i read the datasheets correctly).

My question is do I need the transistors at all because I have logic level MOSFETS?

And can I drive this with two PWM signals as the MCU I'm using (from an autopilot) doesn't have plain digital I/O!! Otherwise I have 8 PWM signals (max) and I can just have them fully on and act like digital outputs, but I'm a little uncertain because I don't think I can fully turn them off (as they're meant to drive servo motors the only settings I have are: min="1000" neutral="1000" max="2000" which are in ms).

Hopefully that all made sense, as I'm quite an amateur!!!
Thanks for your time.
 

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Nigel Goodwin

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Most Helpful Member
I will be driving two motors from a typical R/C car supplied with 9.6V NiCad (I assume they'll draw about 1 amp).
At 9.6V presumably these are motors from 'real' R/C cars, like Tamiya ones?.

They take massively more than 1A, 90A upwards ECS's are commonly used for controlling them.
 

drwarm

New Member
Sorry I should have worded that better, the 9.6V is the supply to the whole RC (it is just a toy one bought from a toy store), that includes other electronics transmitter/receiver etc. I have driven it off a 1.5Amp micro controller that I used for another project some time ago with no issues.
 

sPuDd

New Member
drwarm (&fuzzy),
that diagram is dated 2001. There are much better single chip solutions around today to do the job. Driving P-channel MOSFETS is expensive.
You could probably salvage a H bridge IC from an old VCR load/mode select motor drive, if you wanted to experiment. They come as a monolithic solution, where the chip drives the motor directly, no transistors or MOSFETs to add.

The attached pdf is an older example IC. Full H bridge driving 4x N-channel MOSFETS. Very easy.

sPuDd..
 

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drwarm

New Member
Still had a lot of trouble getting the H-Bridge going, but managed to find some L6203 DMOS H-bridge driver ICs.

Just a couple question before I try out the circuit, I'm using pg 11 of this pdf as reference (I won't use the L6506 and just connect micro straight to L6203):
http://www.otocoup.com/DocTech/Stepper_cont_driver_bip_2.8A_L6208_ApN_microstep.pdf

Do you think a 0.5Ω resistor is ok going from Sense to Ground?

Also is there any way to control it with just 2 PWMs per L6203, for instance if I have the two signals also go into an XOR that goes to enable?


Thanks for all your help!

PS I also know that this circuit doesn't have any dead time, I will try an accomplish this with code.
 
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