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I'm presently considering building a half-bridge converter, which means I have a transistor that's not tied to circuit common. To drive it, I'll need some voltage supply referenced to its source. This is a common problem with many switching topologies.

I'm aware of two general ways to power such a driver: a magnetically isolated DC/DC converter, or a bootstrap. But magnetic isolators still see some capacitive coupling across the isolation barrier, which can cause problems in the control circuit. And bootstrap converters can have EMI issues and only work if you switch a lower transistor often enough to recharge them.

All this is very vague in my head. Are there other ways of powering a high-side transistor drive? Are there other design considerations between the means I've mentioned?

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    \$\begingroup\$ All you need is the higher voltage, so every means to get there (e.g. charge pumps) is a possibility. \$\endgroup\$ – PlasmaHH Oct 29 '15 at 14:42
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    \$\begingroup\$ Why not use a simple/standard NMOS/PMOS stage and avoid having to generate "difficult" voltages ? \$\endgroup\$ – Bimpelrekkie Oct 29 '15 at 14:58
  • \$\begingroup\$ @FakeMoustache I need 1500V devices, and I haven't seen any PMOS capable of that. \$\endgroup\$ – Stephen Collings Oct 29 '15 at 20:41
  • \$\begingroup\$ NOW you tell us it is 1500V. You couldn't have mentioned that in the question? ;-) \$\endgroup\$ – mkeith Oct 29 '15 at 21:47
  • \$\begingroup\$ I didn't know it was a design consideration! \$\endgroup\$ – Stephen Collings Oct 29 '15 at 22:03
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Yes. Any form of isolated or boost supply can provide the high-side gate voltage referenced to its source. Some ideas:

  • Floating Charge pump (I was considering the LTC1754 for a very similar application)
  • Small flyback with output referenced to source
  • Floating boost
  • Photovoltaic cells powered by on-board LEDs (Photovoltaic Isolator)

The main concern is level-shifting the control signal without killing your deadtime, introducing too much latency, or slowing down turn-on.

Obviously you need to be cautious of exceeding the Vgs during turn on/off of the floating supply also.

Some references:

http://www.vishay.com/docs/91421/appnote9.pdf

Is it safe to "top up" bootstrap capacitors using a charge pump?

http://www.ti.com/lit/an/slva444/slva444.pdf

https://www.fairchildsemi.com/application-notes/AN/AN-6076.pdf

http://www.irf.com/technical-info/appnotes/an-937.pdf

http://www.vishay.com/docs/91421/appnote9.pdf

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