Hi guys,

I was just wondering how do I decide what type of transistor to use if intend to build a H-Bridge driver? What are the specification i should look out for in the datasheet?
A PWM pulse would be used as the input.

Thx in advance for any recommendation

 

For a start you need to decide on the specification of the H bridge, what sort of voltage and current are you looking at!. Bear in mind the stall current of your motor, it will probably be something like ten times it's normal load current!.

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go for FET based.

then as nigel states look at the operating voltage and current. Then find suitable ones around that.

 

I intend to use a 24VDC motor.
By stalling the motor, the curent seem to shoot up to 4 Ampere which could burn up any transistor in use. Furthermore, in my design i also intend to use the dynamic braking. of course this would burn up all the transistor in use.
Therefore, should i consider using relays as my switch instead?

 

Relays are rather crude, and prevent you using PWM for speed control.

How big is your motor (and what is the application), 4 amps sounds EXTREMELY low for stall current - also, what is the power feed, a lead acid battery?.

__________________
PIC programmer software, and PIC Tutorials at:
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yer 4A is nothing

I am working with a IGBT switch that cat take 800A so you can definitly find some 4A switches.

As to breaking you will need to do work out the operating duty on this to size the resistor (power-wise) as well as the value (based on how fast you want to brake the machine)

Check out IR FET's they do some good quality ones. IRFR024N is a 55V D-S and a maximum pulse or current of 68A (at 25C) or contiuous of 16A.

just remember you will be PWM the FET's so they will not see a continous current.

 

Thx for giving me an idea on what to use. My knowledge on transistors are only limited to BJT.
Anyway, a surge of 5A current probably wont damage the low ampere BJT transistors would it? Since dynamic braking is done only in a moment. But then again i better be on the safe side and learn up on FET transistors.

 

You can use either, but FET's are generally higher power - but you need to evaluate your requirements. I asked above about your supply and motor size, you haven't mentioned them?.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

Yes look at MOSFETs..you can find suitable units for your application. How fast wil you be switching? If you go with bipolar solution, keep in mind that your base drive circuit will have to provide quite a bit of current under surge/stall conditions if you are to keep the switch on and the forward gain for power types is pretty low (especially at high freq)
Mosfets are easier to drive in this respect, only having to deal with charging parasitics in a transient sense.

 

Sorry for not stating what im using. First of all, i will be using a 12V feld lead acid to drive a 12VDC motor.
What im trying to do a build a R/C car using the 12V battery as my source. Problem is the battery weight is pretty heaevy and i am not even sure that two 12V motor can support it. The motor size is rather small.
Anyway the 4 Ampere value i stated actually came from a 12V motor. Sorry bout that!.
Coming back to the subject, if i intend to use PWM pulse, what is the proper frequency to use? I heard the high frequency causes high power dissipation and of course im trying to prevent that!
Therefore, would 500 Hz suffice?

Looks like FETs are the best way of solving this. But how do i see the maximum transistor switching frequency? Isit the transition frequency stated in the datasheets? I have no idea what is that