Analysis of several constant current source circuits composed of triode and op amp

Analysis of several constant current source circuits composed of triodes and op amps:


These circuits can obtain constant current output on the load resistor RL.

The first type is rarely used due to RL floating.

The second type of RL is virtual and not too big.

The third type is RL floating, but the RL end is connected to the positive power terminal.

The fourth type is positive feedback balance, which is loved by people because of the grounding of the load RL.

The fifth and fourth principles are the same, but the current output capability is expanded. In the use, the resistor R2 is often taken much larger than the load RL, and the follower op amp is omitted.

The fifth kind is the circuit I want, and it is also the load on the ground.

The latter two are constant current source circuits

Compared with several V/I circuits, any one-way device without a triode can achieve AC constant current. After adding a triode, it can only do one-way DC constant current.

The fourth and fifth are based on the balance of positive and negative feedback. If the balance is lost due to the error of the resistor, the constant current output characteristic will be affected. That is, the output current will vary with the load.

The error of several other resistors only affects the value of the output current without affecting 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.

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