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If I want to control a motor by simply giving it a variable specific voltage or current, to control the RPM, not by flipping the power on and off as in pulse width modulation, what is that called?

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    \$\begingroup\$ .....DC? ...... \$\endgroup\$ – Oldfart Nov 17 '19 at 15:16
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    \$\begingroup\$ variable DC voltage? \$\endgroup\$ – Brian Drummond Nov 17 '19 at 15:19
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    \$\begingroup\$ Linear? Analog? \$\endgroup\$ – sstobbe Nov 17 '19 at 15:31
  • \$\begingroup\$ Lowpass filtered PWM? \$\endgroup\$ – Harry Svensson Nov 17 '19 at 16:28
  • \$\begingroup\$ The IRIG Inter Range Instrumentation Group standardized many forms of modulation, about 1950. PAM pulse-amplitude-modulation might be your answer. I worked for a company that handed the Ground Data recording and de-commutation (sorting out of the multiplexed data) and driving the myriad Chart Recorders, for the Gemini and Apollo projects. Learned a lot. \$\endgroup\$ – analogsystemsrf Nov 17 '19 at 16:53
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Controlling a DC motor by simply controlling the voltage is called armature voltage control or adjustable voltage control. That is not really the opposite of pulse width modulation. It is a different way of doing the same thing. You might say it is an analog method rather than a digital method.

Controlling the current is a method of controlling torque. That can be used for speed control by adjusting the current in response to a speed error signal.

Controlling a DC motor using a controlled rectifier (thyristor) is sometimes called pulse amplitude control. More often, it is called SCR (silicon controlled rectifier) control.

For AC motors, voltage control is quite limited. Frequency control is preferred.

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  • \$\begingroup\$ How did you know that the question was related to motor and motor-controller? \$\endgroup\$ – Harry Svensson Nov 17 '19 at 16:29
  • \$\begingroup\$ PWM isn't really digital in itself, really, since it isn't necessarily discrete-time. You can have analog PWM, and that is actually what some simple (and old-fashioned) DC-DC converters use (hysteresis control with a few op amps). \$\endgroup\$ – Hearth Nov 17 '19 at 16:38
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    \$\begingroup\$ @Harry Svensson Are you serious? The body of the question seems pretty clear to me. \$\endgroup\$ – Charles Cowie Nov 17 '19 at 16:48
  • \$\begingroup\$ @Hearth I agree. It isn't digital in itself, but in a liberal use of the term, you might say that. \$\endgroup\$ – Charles Cowie Nov 17 '19 at 16:50
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    \$\begingroup\$ @CharlesCowie Oh, it appears that I was very blind, I missed the word "motor" that OP wrote. Whoopsie. \$\endgroup\$ – Harry Svensson Nov 17 '19 at 17:15

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