High Voltage DC-DC Boost Converter 5V-12V Step up to 300V-1200V Power Module

[Calambres]

Hi there!

The topic title is quite self explanatory:

https://www.aliexpress.com/item/32804054222.html

Its is a simple 555 square wave generator (forty-something KHz... can't remember) driving a small transformer and a classic Cockcroft–Walton diode-capacitor voltage multiplier. It works quite well and goes up to nearly the promised voltage: 3200Vpp (about 1130VRMS) with an input of 12V.  Utterly dangerous toy by all means! It also has three additional taps for lower voltage output taken from the various steps in the voltage multiplier.

I'm trying to understand the circuit as it is not very stable and responds wildly to the regulation trimmer and, as usual with these chinesium products, there's no documentation besides some chinglish in the description. My main problem is that there's a component I cannot recognize. It is marked in the PCB as ENSW and has a single "3" label on top of it. Anyone knows what is this component and what is the meaning of ENSW?



Thanks a lot in advance.

[T3sl4co1l]

"Enable Switch"?

Looks like a PolyFuse.  "3" could be amperes?

You can trace the circuit if you want. Guessing from the 555, it's embarrassingly bad, which seems supported by your observations (lack of output regulation, sensitive control).  If I had to guess, I'd bet the trimmer is duty cycle, so, roughly it controls energy into the winding (roughly a flyback topology, but the CW multiplier complicates that), and output will be load sensitive because no one ever uses a 555 in a feedback loop, let alone in any kind of proper (e.g. peak current mode) SMPS control scheme.  For which you'd reach for a UC3843 or better, but, who knows.

The "complication" is, CW mult. draws current on both phases of the waveform, whereas flyback proper only delivers current during the off phase.  When the transistor turns on, it's hard* switching into the capacitive load of the whole mult. chain, so, a large peak current is drawn, particularly during startup.  Which makes it awkward to use a multiplier with current-mode SMPS controllers/regulators.  (The solution for those, is to use several secondaries in series, each individually rectified, to reduce the effect of winding capacitance.  Not use a multiplier at all.  Else, an LLC resonant topology is best, quite suitable to drive a multiplier.)

*But still not completely, as dI/dt is limited by transformer leakage, and peak current by that and total output capacitance.  Which given they're using ceramic caps, the capacitance is probably pretty small, also meaning the output isn't capable of, heck maybe not even fractional mA, but surely not more than a few mA near whatever counts as "full voltage" output.  (Which again, is complicated by the flyback phase being able to reach fairly high voltages, just at ever tinier currents; I'd consider "full output" to be something near a symmetrical switching waveform, i.e. peak flyback voltage maybe one or a few times the supply voltage.)

Tim

[Calambres]

"Enable Switch"?

Looks like a PolyFuse.  "3" could be amperes?

Most likely...

...Which given they're using ceramic caps, the capacitance is probably pretty small, also meaning the output isn't capable of, heck maybe not even fractional mA, but surely not more than a few mA near whatever counts as "full voltage" output.

Anticipating the more than previsible use of this converter to test HV capacitors, the Ali Express description states, in perfect chinglish (sic):

The capacitor can he charged, but charging speed is somewhat slow, please note.

Yes, the output current should be minute. The ripple is also abysmal, in the range of 120Vpp at max output. As I already said this is a dangerous toy but still a toy nonetheless.

Thanks for your answer, Tim.

By the way, the CW diodes are RS1M, suitable for 1000Vpp / 700V RMS 

[Calambres]

This recent youtube video explains clearly the charge pump part of this very converter: