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Connecting a small-signal N-channel MOSFET and a power NPN BJT like this darlington-ish configuration, what does it produce? Is it equivalent to what people call IGBT? What about its P-channel counterpart?

schematic

simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ Look like a triac to me \$\endgroup\$ – MathieuL Sep 15 '15 at 0:37
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The circuit is interesting .I did the same basic thing with a MPF102 Jfet in a plastic to92 package and a BD139 BJT in a to126 package.My idea of doing this was to preserve the Analog input characteristics like low capacitance of the FET and get the power dissipation of the to126 package.The aggregate handles more current and hence power but not voltage.YOUR circuit is valid because you wouldnt be able to get a big mosfet with such low gate source capacitance.Switching performance would be terrible at turnoff in fact it would be worse than an IGBT because you have no base emitter resistor and in effect the IGBT does .Compared to an IGBT your circuit will have less input capacitance .Also you have more control over switching performance because the base and emmiter of the BJT are both accesable.Finaly your circuit wont ever latch up! like some IGBTs are rumoured to do.

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    \$\begingroup\$ What would happen if I add a 4.7k resistor between the base and emitter of the BJT, and insert a 220 ohm resistor between the drain of the FET and the collector of the BJT? \$\endgroup\$ – Maxthon Chan Sep 18 '15 at 6:43
  • \$\begingroup\$ The 220 ohm wont help and it will hinder on state voltage ,but your 4k7 is useful in fact I would go much lower like say 100 ohm between B E of 2n3055. \$\endgroup\$ – Autistic Sep 19 '15 at 9:24

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