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I have in hand a 220V:600V isolated transformer and a HV bridge rectifier and I'd like to charge a 250uF capacitor with adjustable voltage from 200V to 500V. My idea is to use a switch between the supply and the capacitor and open it when the capacitor reaches the desired voltage (that will be monitored using a microcontroller), like this:

enter image description here

My questions are:

  1. Is IGBT suitable for this? Would it require a snubber if I open it during the charging period? The secondary inductance of the transformer would result in transient voltage when I open the switch?

  2. To control the IGBT I would need to provide a voltage in the gate that is referenced to the HV of the capacitor? Using an optocoupler for example, it would require a power supply that the GND is connected to the emitter of the IGBT, is that correct?

  3. GTO or SCR would be better choices in this case? I also could charge it to the maximum peak voltage of the transformer (850V) and then discharge the capacitor using another switch. Any thoughts?

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  • \$\begingroup\$ Why not use a low side switch that doesn't require an isolated drive voltage? \$\endgroup\$
    – Andy aka
    May 14 '20 at 14:06
  • \$\begingroup\$ Like a solid state relay? They are often slow to turn off (about 10ms). The capacitor would be charged a lot more than required. \$\endgroup\$
    – Rohde
    May 14 '20 at 17:21
  • \$\begingroup\$ No, I didn't imply that. \$\endgroup\$
    – Andy aka
    May 14 '20 at 17:28
  • \$\begingroup\$ What kind of switch you say? \$\endgroup\$
    – Rohde
    May 14 '20 at 17:30
  • \$\begingroup\$ That is immaterial to the point I make and you haven't answered my question... \$\endgroup\$
    – Andy aka
    May 14 '20 at 17:31
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  1. Yes

  2. Yes. An ISOLATED supply.

  3. Not SCRs because they latch on and cannot turn themselves off once you turn them on. Unless you are fine with only ever turning off at current zero cross, then yes. If you do this then minimum snubbing is required.

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