Generating -3700v from 375-0-375v transformer how to

[neazoi]

Hello I need to drive a small electrostatic CRT that requires -3700V at the cathode.

How can I generate this the easy way with a transformer that has a 375-0-375v output?

 

[pradeep.g.belchada]

use a ferrite core transformer at the o/p side use a reverse conected diode

 

[betwixt]

Not sure what that last post is talking about. If the transformer isn't being used for anything else, ignore the 0V tap completely, connect one of the 375V connections to ground and the other will then be 750V AC. From there you can use a standard diode capacitor voltage multiplier to get 3.7KV.

Brian.

 

[mtwieg]

Take your pick:
https://en.wikipedia.org/wiki/Voltage_multiplier

 

[neazoi]

Not sure what that last post is talking about. If the transformer isn't being used for anything else, ignore the 0V tap completely, connect one of the 375V connections to ground and the other will then be 750V AC. From there you can use a standard diode capacitor voltage multiplier to get 3.7KV.
Brian.

Yes, it is only used for HV of the tube so I can do that. What short of ciodes should I use for the multiplier?
Also what should be the voltage rating of the capacitors?

 

[betwixt]

The current will be very small, maybe only 1 - 2 mA so there is no need to use power rectifiers. What really matters is their PIV rating. If you use a multiplier like the first one in Mtwieg's post the total voltage is shared along the chain of diodes but you should still allow for twice the peak AC input voltage so ones rated at more than 1.5KV should be used. Also be very careful when assembling the multiplier, try not to leave wire ends sticking out or solder spikes on any joints as the concentrated charge on them will make them prone to arcing. I would suggest a suitable and readily available type would be the BY203-20.

Brian.

 

[mtwieg]

Yes, it is only used for HV of the tube so I can do that. What short of ciodes should I use for the multiplier?
Also what should be the voltage rating of the capacitors?

Depends on what kind of multiplier topology you use. Find what blocking voltage you need, and then find a part that meets that spec with minimum reverse leakage. Nothing terribly specific, something like this would probably work fine.
https://www.digikey.com/product-detail/en/GP02-30-E3/73/GP02-30-E3/73GICT-ND/3025889

Simulating it with SPICE is a good way to experiment with different topologies, and to estimate what kind of capacitances you need.

 

[BradtheRad]

Just because simulating voltage multipliers is a hobby of mine...

Here is an example that will do what you want. A Villard style multiplier containing 4 stages.



750 VAC has peaks of 1,060 V. The load is chosen to draw about 1 mA.

Each capacitor and diode is exposed to 2 x 1,060 V. (The exception is cap #1 which is exposed to 1,060 V.)