[OpenTRV-dev] H-bridge transistor selection

[Damon Hart-Davis]

Hi,

I *should* be confident with this, but I am not.

Is it possible to run a bipolar H-bridge from 2 tri-state outputs properly 'class C' ie avoiding ever having shoot-through by being able to let all four transistors be off at once?

It's trivially possible with 4 tri-state outputs, or even 4 non-tri-state outputs.

Rgds

Damon


On 16 May 2013, at 11:38, Stuart Poulton wrote:

> On 16/05/13 11:32, Mike Stirling wrote:
>> Interesting. The poor performing transistors do so because he is running them far too hard, although he does acknowledge this. He is also running out of gain at the lower voltages, and would get an improvement there by reducing the value of the 1k base resistor. This is evidenced by the reduction in voltage drop with increasing supply voltage. The important figures in the datasheet are Ic from the absolute max ratings, which needs to be well above the expected stall current of the motor, Vce-sat, which should be small, and the worst case hFE (large signal current gain), which should be high enough to allow for an acceptably low base current during motor stall conditions. Mike 
> 
> Mike,
> 
> Coming up with a nice H-Bridge for battery operation would be great, esp if it could be driven with a low pin count from a uP.
> 
> I did measure the stall current of my dissected TRV head,
> 
> 2 - Motor run current (no load)  13-15mA
> 3 - Motor Stall current - 95-100mA
> 
> Cheers
> 
> Stuart
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