What topology should I use if I'm wanting to obtain CC/CV -- 300ma / 180Vdc from a 120Vac input, where mains isolation isn't a concern? My application will tolerate slight overcurrent (maybe to 600ma) at lower voltages (90vdc), and will tolerate slight overvoltage (to 200v) if the current tapers below 300ma once exceeding 180V.

I'm hoping it can be as simple as a ballasted voltage doubler or something along those lines. The BOM for a single piece would ideally be below $20. I do not care at all about efficiency, only low BOM cost and "relative" robustness.

  • \$\begingroup\$ More to the point, will it tolerate slight undervoltage, like 1.4 * 110V - 2 diode drops, whatever that is exactly? And how much ripple on the DC? If so, there's a possible simplification. ... OK, apparently not. \$\endgroup\$
    – user16324
    Jan 6, 2017 at 19:57
  • \$\begingroup\$ I see where you're going, Brian, but I need the CV phase to be at least 180v :) I'm chargin' batteries. \$\endgroup\$ Jan 6, 2017 at 19:58
  • \$\begingroup\$ If the required voltage was 170VDC then simple 1:1 100W transformer and a rectifier would be enough. Sigh! \$\endgroup\$ Jan 6, 2017 at 21:26

2 Answers 2


The simplest way is to use an inexpensive power transformer with a 120 volt primary and a low voltage (about 12v) secondary.

Connect the two windings in series as follows to boost the transformer output voltage up to the sum of the primary and secondary voltages (in this case 132 volts).

  1. Connect one leg of the secondary to one leg of the primary.*

  2. Apply 120 volts across the primary. Between one leg of the primary and the other leg of the LV secondary, you'll have 132 volts!

132*1.414=186 volts P-P. Feed your 132 volts to a full-wave bridge rectifier, and filter the DC from it with a capacitor, and you'll have 186 VDC no-load.

A 12 volt secondary may or may not be high enough to get 180 VDC @ 300 mA. However, Mouser has them in various secondary voltages, with and without a center tap. (While you're at it, buy a suitable fuse and holder!)

*The secondary has to be connected in the correct phase, so that the voltages add.

  • \$\begingroup\$ What kind of witchcraft is this. This might be perfect! \$\endgroup\$ Jan 6, 2017 at 21:24

Sounds like you need a flyback switcher. Can't you live with ~150V? Then you could use just a diode and a capacitor.

Also you can try building boost converter. Diode and capacitor to rectify, then boost.

I think both boost and flyback may be implemented around st viper controller. But you will have to study the datasheet carefully.

By the way. If you could take two phases instead phase and normal, it would be 180VAC. One of my clients in Taiwan does that.


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