Re: high-power voltage to current converter

On Sat, 23 Feb 2008 09:27:49 -0600, "Mook Johnson" <mook@xxxxxxxx>
wrote:


"Robert" <renenkel@xxxxxxxxxxx> wrote in message
news:beb39c68-8677-4a73-8d65-728de0fa79e1@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
In case it makes things easier, my signal source is actually a
potentiometer, so if it is more convenient to have resistance rather
than voltage as the input, it is available. However, the
potentiometer cannot handle high currents. I was thinking of simply
attaching the potentiometer to the base of a large transistor, and
have the collector/emitter in series with the motor. But transistors
aren't linear near cutoff, so this won't work.

Robert


Depending on the range where you want to operate this will produce a HUGE
amount of heat. 1HP is ~750Watts. That 7.5A @ 100V If you run at low RPM
or in a stall condition, that would put 750W on the transistor and surely
blow it.

Your best approach is a PWM method.

You're looking for PWM torque control of a DC motor.

Yeah....driving any uncoupled inductive load produces the same loss in
a linear driver as occurs when its driving a short circuit.

RL
.

Relevant Pages

  • Re: Audio amplifier (part 2)
    ... The most common way to produce the approximately 3 diode drop bias voltage between the driver bases is to multiply the base emitter drop of an additional transistor, with the multiplication ratio set by a potentiometer. ... You choose the resistor value to make the total current through the resistor divider to be about 1/10th of the current through the transistor, so that the divider current times the current gain of the transistor dominates the transistor conduction. ...
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  • Re: high-power voltage to current converter
    ... potentiometer cannot handle high currents. ... that would put 750W on the transistor and surely ... You're looking for PWM torque control of a DC motor. ...
    (sci.electronics.design)
  • Re: high-power voltage to current converter
    ... so if it is more convenient to have resistance rather ... than voltage as the input, ... potentiometer cannot handle high currents. ... attaching the potentiometer to the base of a large transistor, ...
    (sci.electronics.design)