Comparison of several VI conversion and constant current source circuit diagrams

These types of circuits can obtain constant current output on the load resistor RL.
The first type is rarely used because RL is floating.
The second type RL is a virtual ground and is rarely used.
The third type is although RL is floating, but one end of RL is Connect to the positive power supply terminal. The fourth commonly used
type is the positive feedback balanced type, which is popular because the load RL is grounded.
The fifth and fourth methods have the same principle, but only expand the current output capability. People often use the resistor R2 is much larger than the load RL, and the follower op amp is omitted.
The fifth circuit is the circuit I want, which is also for the ground load.
The latter two are constant current source circuits.
Comparing several V/I circuits, usually there is no triode. All unidirectional devices of this type can achieve AC constant current. After adding a transistor, it can only achieve unidirectional DC constant current.
The fourth and fifth are based on the balance of positive and negative feedback. If the error occurs due to the resistance of the resistor, Loss of balance will affect the constant current output characteristics, that is to say, the output current will change with the load,
and the errors of other resistors will only affect the value of the output current, but will not affect the output characteristics.
If the output current is large, or the transistor is not enough The collector current and emitter current are not equal, you can replace the transistor with a MOSFET