Looking in another thread whith an unusual current limiter an idea struck me.
Here is a simple current limiter working on the base current of the output transistors.
Of course there is some potential problems. We must have output transistors with a known current gain jus as well as the drivers and the limiters.
And when the base current is limited the fast switching will also be limited. But it is simple and nearly fits a SOA with max current at low voltage for the output tranistor and 0 current with max voltage. If the current gain is 100 for all transistors max current is about 15 ohm from full voltage. Max current 5,3 A in this case and the half with the output short to ground.
The IS 1 and 2 is just for DC simulation.
Here is a simple current limiter working on the base current of the output transistors.
Of course there is some potential problems. We must have output transistors with a known current gain jus as well as the drivers and the limiters.
And when the base current is limited the fast switching will also be limited. But it is simple and nearly fits a SOA with max current at low voltage for the output tranistor and 0 current with max voltage. If the current gain is 100 for all transistors max current is about 15 ohm from full voltage. Max current 5,3 A in this case and the half with the output short to ground.
The IS 1 and 2 is just for DC simulation.
Hfe varies widely, both among transistors of the same type and with temperature. Current sensing can be accurate only at the output.
Ed
Ed
I don't remember last time I blew a power transistor.
I just let the fuses do the limiting. I did blow fuses in my Quad 405 one time. The transistors survived.
PS: It might not suggest anything, as Quad 405 has current limit circuitry besides the fuses.
I just let the fuses do the limiting. I did blow fuses in my Quad 405 one time. The transistors survived.
PS: It might not suggest anything, as Quad 405 has current limit circuitry besides the fuses.
Yes it varies widely but modern transistors seem a little more stable. With 100 degrees C on the output and 50 on the drivers total Hfe will be about the double.
But i still find it interesting for small amplifiers even if you ought to trim in R3 and R4.
But i still find it interesting for small amplifiers even if you ought to trim in R3 and R4.