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I'm trying to design a capacitor discharge circuit for a hobby rocket launching system. In some cases we have long wire runs with multiple rockets so a CD circuit seemed the way to go. I'm trying to use an IGBT and the Avago ACPL-312U driver. What I didn't realize is that an IGBT can't be used as a high side switch. Is this correct? Can I get some suggestions on how I can configure the circuit to use the IGBT for switching 100 volts? capacitor discharge firing circuit

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  • \$\begingroup\$ IGBT's can be used as a high-side switch, you just need to ensure the gatedrive is suitable: ie the gate can be raised to +15V with respect to the local emitter. do you have a floating psu for the ACPL-312U. NOTE. I am switching an IGBT inverter using ACPL-312U right now \$\endgroup\$ – JonRB Apr 13 '15 at 12:50
  • \$\begingroup\$ The circuit is powered from a 12v SLA and uses a dc-dc converter for the 100v output. I then use an 18v Zener Diode as a regulator to power the ACPL-312U. Comments? \$\endgroup\$ – Johnny Holguin Apr 13 '15 at 16:15
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You can use a IGBT for the high side switch.

But you need a supply with a voltage higher than 100V to drive your IGBT. I usually do it with a separated and isolated supply just for the gate driver (a small switched supply), there are some on chip solutions for that (Power Convertibles HPR 105 for example). The supply's GND is tied to the IGBT emitter. Then you have a voltage to drive your IGBT.

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  • \$\begingroup\$ See above comment. For power I'm taking the 100v and using a zener as a regulator to get 18v for the gate driver. My concern is that I was told IGBT's are NPN transistors and cannot be used as a high side switch unless you incorporate a boot-strap circuit? I was also told I would need more than 100v to get the IGBT into full saturation. Comments? \$\endgroup\$ – Johnny Holguin Apr 13 '15 at 18:12
  • \$\begingroup\$ Yes, you will need more than 100V to drive the IGBT. You can use a bootstrap capacitor or change the way you supply your gate drivers. I'm afraid you can't just use a zener for the high side. \$\endgroup\$ – Alexandre Bueno Apr 13 '15 at 20:34

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