[SOLVED] Step Up DC-DC 12V to 400v converter

[NikoTico]

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Hi
I was needing a variable power supply between about 50V and 400V, with a current of only a couple of milliamps, to reform electrolytic capacitors in valve equipment. To do this, I came up with the idea of designing a boost converter using a 555, with a small feedback towards pin 5. However, the problem is that I don't have mosfets that handle those voltages (I only have a couple of IRF630s), but it does have transistors like the 13007, 2SC5353 and RC3866, as well as other small bjts. As diodes, I have FR307. I also have unwound transformers from ATX sources, in a flyback type power supply I find myself more lost.

I would appreciate it if someone could advise me on calculations and design to get the best configuration. [Google translated from Spanish]

 

[BradtheRad]

Many recommend using a variac to gradually turn on old equipment from house voltage. I've used one rated for 1.75A, 120VAC.

Did you rule out building a simple voltage doubler? Even a half-wave supply (one diode) should give 330VDC.

I built a bridge-style doubler to step up 170V peak, to a high enough voltage that I could run a xenon flash tube as an automobile ignition tester.
However if you really need a supply referenced to ground, then a Villard doubler is suitable.

 

[prairiedog]

Also search for "nixie tube power supply" there are many circuits out there using boost converters with a 555 or MC34063 etc.
I have seen old CCFL transformers or even a backwards connected mains transformer like 6V-220V used to make HVDC.
You can use a DC-DC converter salvaged from a disposable camera (xenon flash), or buy the DC-DC converters from Aliexpress.
It depends on what you want. Easy, low cost or to learn and have fun.

 

[cupoftea]

12v to 400v is easy with a cascaded boost converter. Just use simple UCC28C43 based thing. If you want i send LTspice sim of it to you?
Search google "Cascaded Boost edaboard" because we have discussed it on here many many times.

 

[NikoTico]

Hello, thanks for your response. The truth is that I don't know much about cascade converters. I tried to make a boost converter, but the problem I encountered was with the Vpk and Ipk. Also, since I didn’t have MOSFETs, I had to use NPN transistors, which, due to their response time, overheated too much, to the point where the voltage started to decrease over time and the transistor kept getting hotter. Because of that, and because I have few components available, I decided to try making a flyback converter with the same integrated circuit. The biggest problem in the boost converter is the Iout, which is about 10 mA.