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I'm working with a GaN FET for a half bridge application. During reverse conduction of the GaN FET, to minimize losses, I have to use a Schottky diode in parallel to the low side of the GaN FET.

The reverse current is around 70 A. I didn't find any Schottky diode with an If larger than 5 A.

How do I select a Schottky diode to carry the reverse current properly?

ocrdu
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Nh K
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  • Mouser (the first distributor I went to) has schottky diodes up to 600A. This isn't hard to find, is there some other reason you're having difficulty? (check your spelling if that helps) SE.EE doesn't take questions for component recommendations, so if you're asking for someone to find you a suitable diode that won't be answered. – LordTeddy May 08 '23 at 22:01
  • With GaN's fast switching speed and minimized deadtime you may not get much of a benefit from an external Schottky. It's very difficult to get the parasitics low enough in the layout so that the Schottky will actually conduct during the deadtime. (Unless of course for some reason you choose to have a long deadtime, but it's not clear why you would do that with GaN. – John D May 08 '23 at 22:34
  • Which GaN are you using? Last ones I saw at least, the "body diode" effect is simply ordinary enhancement (Vgd > Vgs(th)) so has zero recovery associated with it (as a schottky), a higher voltage drop (~Vgs(th)), but no capacitance from an added diode. A synchronous (half bridge) circuit with sufficiently low dead time minimizes conduction loss in this (passive "rectifying") mode. Is this not the case in your situation? Are one of these assumptions incorrect? – Tim Williams May 08 '23 at 22:45
  • I would like to use schottkey diode for proper bootstrap voltage management due to ground bounce. GaN are from EPC . They are smaller but the diode that I got is rediculously large in size for pcb. – Nh K May 09 '23 at 05:46
  • Using a schottky in parallel to the GaN device a major purpose of using GaNFeTs (ultra low Rds-on). Though you may use a schottky diode in parallel to the LS FET, (as you mentione) high current rated diodes will be huge in comparison with the FET. either way, the question is better answerable if you provide other specifications of your converter such as voltage ranges (input & output) Topology etc., – Stoic_beast May 22 '23 at 12:14
  • Input voltage 20V and phase output current supposed to be 140 A. I could not find any diode in SOD package greater than 7 A for each parallel GaN FET. does that mean my current is limited to 14 A for each leg ? Or I can overcome the limitation by adjusting the deadtime properly? – Nh K May 24 '23 at 13:25

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