Re: [CAD_CAM_EDM_DRO] Re: H bridge progress

Lee Studley wrote:

> Jon,
> Good ideas! I have a Class D Audio bass amp that
> has a 'reconstuction'filter on the output with a
> similar role as the filter you describe, before
> the speaker.

No surprise, as my servo amp was derived from a Harris demo design
for a class D amp based on the HIP4080 chip.

> Does your high-side sensing give a linear feedback, or an opto
> or translated feedback to the drive circuitry? I like your idea of
> incorperating it into the drive as high-side current sense.

No, although it could. All you would need to do is use one of those
linear optocouplers with one emitter and two matched detectors.
But, this does NOT measure MOTOR current, it measures SUPPLY
current, which are two different things. In a servo amp with a torque
loop, you need to measure motor armature current for torque feedback.
That's the inner loop in my amp. (The outer loop is velocity.)

The circuit I use has some amount of rate-of-rise sensitivity, ie.
it trips earlier for a rapidly rising current due to sense resistor inductance.
I use a micropower op-amp that is powered by the same charge pump that
drives the high side fet drivers. As my amp can go to 100% duty cycle, I
don't use the standard bootstrap capacitor/diode circuit.

Jon