# pwm variable power supply

#### Victor Cubias

Joined Apr 19, 2017
3
Hi

I am trying to create a circuit that will generate a variable DC voltage from a 300VDC power supply, the output needs to vary from about 5V to 300VDC at 2A. The load is a 2.2H inductor with a ESR of 165 Ohms. So far, I have tried many things, including a PWM signal that gets filtered out, a buck converter with variable PWM input to control the output voltage, etc. Any ideas or suggestions would be greatly appreciated.

#### LowQCab

Joined Nov 6, 2012
2,498
as well as the overall-purpose and operational-end-result.
Were does the 300-Volts come from ?
Also, how, and why, is the Voltage adjusted ?
A Schematic and/or Pictures would replace a lot of words.
.
.
.
.
.
.

#### Victor Cubias

Joined Apr 19, 2017
3
Thank you @LowQCab , the 300V come from a High Voltage DC Power Supply, the reason why I need a variable DC is because the voltage will be used to power an electromagnet to be able to control the torque a clutch. Using low side PWM switching generates too much noise, and this affects the entire circuit.

I will work on making a drawing or block diagram with what I need. So far, I have not been able to successfully being able to control the voltage using a PNP high side switch controlling it with a PM generator. The output is not linear vs. PWM duty cycle. I have tried just a plain RC filter feeding the output to the coil.

Thank you again

Victor

#### Victor Cubias

Joined Apr 19, 2017
3
I forgot to mention, the output voltage needs to respond to any duty cycle changes within 5msec max, from any DC to any DC value.

#### ronsimpson

Joined Oct 7, 2019
2,381
the output voltage needs to respond to any duty cycle changes within 5msec max, from any DC to any DC value.
If we start out with 0 current. Apply 300V for 5mS the current will ramp from 0 to .57A. In 10mS the current goes to .96A. In 20mS the current goes to 1.6A. This is Physics. That is the response time.
It may be hard to see the blue line. I applied 300V for 60mS and then 0V.

#### LowQCab

Joined Nov 6, 2012
2,498
Inductors don't have an "Equivalent-Series-Resistance",
they have a "DC-Resistance", and "Reactance".

So your "Clutch-Coil" is going to have to be capable of
dissipating ~600-Watts of Heat without failure.
That's a serious amount of Heat, can Your Clutch-Coil withstand it ?
( and that doesn't include the Heat generated by Friction when it's slipping )

~5ms for a Voltage change is not terribly difficult,
but the ~2.2-Henries of Inductance is another matter entirely.
The Electromagnetic-Force generated will not change in ~5ms.
To achieve this, You would probably need close to ~1200-Volts available,
possibly more, ( I haven't done the Math, just guessing ).

This is why I asked for details, Pictures, etc.,
it sounds like what You want is not very practical at all.

Did this Electromagnetic-Clutch have an original Power controlling Circuit ?
What does it do, and why do You need less than ~5ms variable control ?

Any device that can withstand ~600-Watts of Heat is going to be BIG and HEAVY,
so accelerating, or decelerating, it in ~5ms will create some very serious forces.
.
.
.