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I have a mechanical device powered by direct current voltage source. The voltage source is on the order of 100V, and the device consumes about 100W of power when active.

This power input is pulse width modulated with frequency of about 1Hz (I am not allowed to change this), and this results in jerks that degrade the performance of my mechanical device. I want to do something about it. My idea so far is to use some kind of an electrical circuit that can «smoothen» the sharp steps in the input voltage. This is what I have come up with:

the schematic diagram of the proposed circuit

Here, the load on the right is my device and the battery on the left is my voltage source. The resistor should be matched with the resistance of the load — about 100Ω. The capacitor I figure should be about 1mF–10mF.

  • When the voltage source switches to the «on» state, the voltage at the middle junction starts to rise from 0 all the way to 100V, gradually opening the NPN transistor and allowing current to flow through the load.
  • When the voltage source switches to the «off» state, the capacitor starts to discharge through the load, letting it slowly come to a stop.

I modelled this thing with ngsplice and it seems to do what I want. But I have very little experience with electricity, so I am not sure if this result can be trusted.

Will this work in practice? What can I do better?

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  • $\begingroup$ Can you add a flywheel to the motor to smooth out the motion? $\endgroup$ Commented Sep 2 at 13:25

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I think the transistor is not needed.

Capacitors resist change in voltage, inductors resist change in current. Some combination of the two, capacitor in parallel and inductor in series, will do it. A differential equation is the way to solve for both, but my experience with doing such things is decades old.

That said, my opinion is PWM at 1 Hz is probably a poor choice.

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  • $\begingroup$ I wholeheartedly agree about PWM at 1 Hz. $\endgroup$ Commented Sep 3 at 13:10

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