The compliance range for operating voltage extends from a minimum of 4 V (both circuits) to a maximum that is slightly lower for the Figure 1a circuit (90 V), because of its different output device.

Figure 1 A series of LM317 circuits investigated in simulation and on the test bench for suitability as a current source. The circuit’s broadband PSRR was simulated, measured in ohms, and defined as ...

However, those current limiting resistors are really a poor excuse for a current source or sink. In many applications, you need a real current source and luckily, they aren’t hard to create.

Over on his YouTube channel [Aaron Danner] explains biasing transistors with current sources in the 29th video of his Transistors Series. In this video, he shows how to replace a bias resistor (and… ...

1. In the circuit for the 1 mA two-terminal current source, the leftmost PNP transistor (Q4) is a "bolt-on" to harvest the approximately 0 temperature-coefficient current in the left leg (a).