prolly - might work for that

well this has convinced me to write a HOWTO on power electeronics for this forum - will take a bit of time but will be done

 

It is not fabbie's own design, mentioned he got it off the net

http://www.armory.com/~rstevew/Publi...d/h-bridge.htm

 

well i dont like the whole design..
even the two upper gate inputs are tied to Vcc throuh a resistor , which will also receive massive spikes when turning on and off..

 

I think the reason it works, is that the motor size may be small so none of the harmful effects are amplified enough to be a real problem.

The original "designer" mention and warns about the "not allowed" state but made no attempt to employ a (easy) lock-out circuit to prevent this :?:

 

. can anyone suggest a better h-bridge using mosfet ? im not good enough to design one by myself yet :cry: . i feel demoralised. thx for informing me though of the poor design

 

There is a load of information (good reading) of application notes on IRF's site. www.irf.com

fabbie, don't feel sad. See what the link below mention..

"Designing safe and reliable automotive motor drive circuits up to 80W can rapidly become a complex task involving a multitude of components and requiring experience in power electronics, controls and thermal design...." which just confirm you must learn to walk before running

http://www.irf.com/product-info/auto/autohbridge.html

This said, maybe you should try your circuit as you already bought the components. It will be a good learning experience.

 

Basic question, just what do you want to do? What voltage? Would you use PWM with this circuit? Is it microcontroller-controlled?

 

awwww fafbbie now i feel bad.. ops:

 

i'm wondering what that would look like..?

 

this is a start..
any sugestions for the control circuit..

Attached Thumbnails

 

 

i was just wondering .. why couldent you use all n channel Fets..?

 

You can but the turn-on voltage for the FETs connected to the 5v rail would have to be above 5v+vth.

With only a 5v source, it may be possible to hook the N and P gate together, but I'd recommend against it due to the obvious possibility of them both being on at the same time and shorting out the power supply. The exact behaviour depends on the device, the mfg lot, age, and temperature. It's a good idea to have a short delay between turning off one transistor and turning on another.

Are you planning to use PWM? If so, best thing is to leave on one of the P-channels all the time and PWM modulate only the N-channel's gate signal.

 

i designed IC1A to be a 74LS76 dual JK Flip Flop W/Preset and Clear..
I would Like the 74126 to be a CMOS equivalent of the 126 .. thus giving better rail to rail switching with Tristate output ,hence the enable input..
oh the 126 is a just a tristate buffer..

Attached Thumbnails

   

 

i just tested the hbridge i posted previously and it works fine. the main reason it works ok might be due to the low voltage applied(12V) and also without any pwm signal.

Forgot to mention this earlier, i will be using PWM from the PIC.

Lastly, i dont get it why the turn on voltage for NPNs connected to the +5v rail has to be 5v + vth. This sounds like a BJT to me.I thought that as long as the gate voltage overcomes the threshold voltage, it would turn on immediately and have all the voltage drop across the g-s.

thx willib for the cool design. but it seems it is operated by switch.

 

that would be a really good idea 8)