Six common constant current source circuit diagrams and analysis

Comparing several V/I circuits, any unidirectional device without a triode can achieve AC constant current. After adding a triode, it can only achieve unidirectional DC constant current. Of course, the output current can be expanded with a power amplifier.

The fourth and fifth types are based on the balance of positive and negative feedback. The loss of balance due to resistance errors will affect the constant current output characteristics, that is, the output current will change with the load.

The error in the resistors in other circuits will only affect the value of the output current, but will not affect the output characteristics.

If the output current is large, or if the collector current and emitter current of the triode are not equal, you can replace the triode with a MOSFET.

I need to use a constant current source circuit at work. In an emergency, I found a circuit diagram and built one myself. The following is an analysis of six common constant current source circuits:

These types of circuits can obtain constant current output on the load resistor RL;

The first type is rarely used because the RL is floating;

The second type of RL is virtual land and is rarely used;

In the third type, although RL is floating, one end of RL is connected to the positive power supply terminal, which is more commonly used;

The fourth type is the positive feedback balanced type, which is popular because the load RL is grounded;

The fifth principle is the same as the fourth one, except that the current output capability is expanded. In use, people often make the resistor R2 much larger than the load RL, and omit the follower op amp;

The sixth type is the V/I conversion circuit for the ground load designed by myself;

The latter two are constant current source circuits.