High voltage power supply for low current control circuit

Does the low power control circuit require isolation from the supply?

Find out how your solenoid responds to PWM from a 1000V supply

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  Jasen.

ly low power control circuit. The input voltage is from mains 110VAC up to

690VAC, which is about~980VDC fully rectified. The control circuit needs 3. 3V/10 mA, and I also need to provide a pulse of about 48V/170mA = 8W to a solenoid for ~50ms.

eries pass regulator with HV FETs.

It does not require isolation. Even though for this wide dynamic range I've seen flybacks are preferred. Maybe I can build the power supply to output

48V and from the 48V I step down to 3.3V. So the PWM would not be directly from 1000V supply.

Here's a little 1400v flyback supply that uses all standard parts.

And a very low power HV supply:

Later on I can post an ingenious circuit to take your 110-690VAC input and make a non isolated 3.3v 10ma output.

As has been said the solenoid can be effectively driven by PWM the rectified unsmoothed input, the PWM duty cycle has to track the input , low duty at 690v , higher at 110v. This should be straightforward if you have a microcontroller in the system.

piglet (Using google groups on a phone while travelling in Africa)

pply low power control circuit. The input voltage is from mains 110VAC up t o 690VAC, which is about~980VDC fully rectified. The control circuit needs

3.3V/10 mA, and I also need to provide a pulse of about 48V/170mA = 8W to a solenoid for ~50ms.

series pass regulator with HV FETs.

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Then a handful of Ds & Cs would get you the volts.

NT

So you want to use it with 120/208, 230/400, 277/480 and (400)/690 V mains ?

Since isolation is not required, how about a capacitive voltage divider, series capacitors to both phases and a shunt capacitor between them. A rectifier across the shunt capacitor followed by a zener (or other shunt regulator).

Is this is a fixed installation or are test leads used. If fixed installation and wye connection is available (neutral available), make a connection from neutral to the cold end of the shunt capacitor. Thus, you would have to support only 208/400/480/690 V delta connected and 120/230/277/400 V Wye with a neutral connection. This would limit the voltage range to about 1:3, reducing power dissipation in the shunt regulator at high voltages.

How often do those 48 V pulses occur ? Would it be possible to slowly charge a big capacitor to 48 V ?

In an ordinary relay circuit with long hold time, just make sure the capacitive voltage divider can provide the relay hold current and voltage. Between activations charge the DC capacitor back to 48 V to provide the kick the next time the relay is activated.

Hi again,

So as promised a few days back I have recreated a schematic I have seen use d to create a low power 3.3v logic supply from 84-264vac and using a PWM dr ive for 24v relay coil. I think it can be extended to encompass your higher voltage range.

Although it looks at first glance that it works on DC it will not since it switches the unfiltered rectified input to charge the storage cap C1 only d uring the leading and trailing portion of the input waveform.

The design works most efficiently when C1 is small enough for the ripple vo ltage V3 to be large, of course it must not droop so low that it causes the linear regulator U1 to dropout. I saw it used with D1 at 39V R1-330k, R2-2

2k, R3-68k, R4-2.2k, C1-22u, Q1-3904, Q2-STN0214, D2-1n4148. All of which m eant the C1 voltage swung between 35v and 6v. Dissipation is mostly in R4 b ut I think a half watt device was sufficient since the action is more switc hing than linear.

It could be that Q2 was actually two in a Darlington configuration but when I return from travelling next week I can investigate further.

The application I saw drove the 24 v relay coil with pulses of the unfilter ed rectified input as I show in the sketch and the microcontroller drove at a duty cycle that varied with input voltage. Although I drew a mosfet I th ink they actually used a high voltage npn bjt, maybe same device as Q2.

I suppose you might also want to consider increasing the C1 voltage to enco mpass the solenoid 48v and drive the solenoid more conventionally from dc. The drawbacks then are that the C1 value will have to very large (eg 820uF) to support the solenoid current for 50ms and that it will take some time t o recharge enough to support another activation, also dissipation in U1 wil l be higher.

This should be very easy to simulate on lt-spice.

piglet

sed to create a low power 3.3v logic supply from 84-264vac and using a PWM drive for 24v relay coil. I think it can be extended to encompass your high er voltage range.

t switches the unfiltered rectified input to charge the storage cap C1 only during the leading and trailing portion of the input waveform.

voltage V3 to be large, of course it must not droop so low that it causes t he linear regulator U1 to dropout. I saw it used with D1 at 39V R1-330k, R2

-22k, R3-68k, R4-2.2k, C1-22u, Q1-3904, Q2-STN0214, D2-1n4148. All of which meant the C1 voltage swung between 35v and 6v. Dissipation is mostly in R4 but I think a half watt device was sufficient since the action is more swi tching than linear.

en I return from travelling next week I can investigate further.

ered rectified input as I show in the sketch and the microcontroller drove at a duty cycle that varied with input voltage. Although I drew a mosfet I think they actually used a high voltage npn bjt, maybe same device as Q2.

compass the solenoid 48v and drive the solenoid more conventionally from dc . The drawbacks then are that the C1 value will have to very large (eg 820u F) to support the solenoid current for 50ms and that it will take some time to recharge enough to support another activation, also dissipation in U1 w ill be higher.

Nice, thank you. GH