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555 HV FB


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Hi Guys

I need a circuit that can charge (1 or 2) - 2.2uF cap(s) to 550v in ±4.7m sec. I do need the pri and sec grounds to be isolated.

This circuit does a good job ( according to LT Spice) please see attached, but I need to replace Q2 with an OPTO to get the isolation as needed and would appreciate any feedback !

I have stick and paste this circuit from various diagrams on the web to get it working thus far.

Any suggestions and advice I desperately need at this stage.



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I have looked at LT3751 chip designed to do this fly-back circuit, the data sheet circuit is running nice in LT spice, but I could not get a bread-board or a fully built pcb version to work, (lease see attached)

So KISS is the next step using a 555 timer.

Thanks Virus


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I have got it this far, please see attached,

Any suggestions on this,

Can the OPTO be turned on more gradually (or is it only on/of like shown), it will allow for a faster charge to get to 550v in 4.7 msec needed, but then it needs to flatten out faster and not still rise on the out put.

Can currant regulation be done with a 555 on the primary side?



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