hi thank you very much for this very interesting information
At the beginning i was wondering why they are not more popular
Now i wonder why they are not banned from audio 🙄
Seriously at least in cap multipliers they can be very convenient i guess For their very high hfe i mean Just one should be enough
At the beginning i was wondering why they are not more popular
Now i wonder why they are not banned from audio 🙄
Seriously at least in cap multipliers they can be very convenient i guess For their very high hfe i mean Just one should be enough
Last edited:
I would like to add that with integrated darlingtons turnoff characteristics are set by a fixed, inernal BE-resistor of the power bjt.The only issues with Darlingtons are that the integrated versions (both transistors
in the same package) have greater thermal drift (because the driver transistors shares
the heat) and the inability to independently set the bias current of the driver.
Using a discrete Darlington you can speed up turn-off using a common B(npn)B(pnp)-resistor with a parallel cap.
Agree.The only issues with Darlingtons are that the integrated versions (both transistors
in the same package) have greater thermal drift (because the driver transistors shares
the heat) and the inability to independently set the bias current of the driver.
Many, perhaps older amps cannot be safely driven to full power at 10KHz+ because the output transistor turn-off time leaves them floating in the on state causing shoot through current that destroys the OPs. This is why feedback instability causes catastrophic failure. The use of 100 Ohm BE resistors to discharge the output transistor is marginal and some amps used 220 Ohms. Modern amps use cross-coupling, AKA "speed-up capacitors" so that the opposing driver drives the opposite OP off as well as its OP on. But Darlingtons integrate the OP BE resistor, so you have to live with whatever turn-off speed that gives you.
Darlingtons also often integrate another resistor ~load on the base of the driver. This is a handicap if driven from a high impedance VAS stage.
So Darlingtons are just fine for driving slow things like relays, but not so great for a wide-band amplifier. You can make a fair amplifier with them, but you are sacrificing performance and reliability to make a simple low parts count circuit.
Also, you have to live with the combined saturation voltage, compared to a CFP. These are also why IGBTs are not used often for amplifiers.
Darlingtons also often integrate another resistor ~load on the base of the driver. This is a handicap if driven from a high impedance VAS stage.
So Darlingtons are just fine for driving slow things like relays, but not so great for a wide-band amplifier. You can make a fair amplifier with them, but you are sacrificing performance and reliability to make a simple low parts count circuit.
Also, you have to live with the combined saturation voltage, compared to a CFP. These are also why IGBTs are not used often for amplifiers.
I should add that a slow output requires an even slower VAS in order for it to be the "dominant pole", ie stable feedback. This means that there is very little feedback left at 20KHz when you have to start cutting the loop gain at a very low frequency. A slow VAS aggravates problems like slew distortion, as well.