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They appear to be operating in tandem to bias the gate of the MOSFET, but it's not clear to me why that particular configuration was chosen.
I understand that. But why couldn't it be biased with a simple resistor? (unless the input voltage varies significantly).It's a constant current source for feeding the shunt regulator - ignore the FET!.
I understand that. But why couldn't it be biased with a simple resistor? (unless the input voltage varies significantly).
Here is a sim when the input voltage is fixed at 50V showing the output current as a function of the output voltage and temperature. This normally the way a current source is characterized (to show the output impedance of the current source). In the voltage regulator, the output voltage is very close to 10V, so that is why I showed that case first.
Note that the current source works very well, but its current is a strong function of temperature...
The emitter resistor is 2.2k, not 22k, so the current will be about 10 time the amount shown in the simulations.