Op amps are used as voltage comparators for constant current control of power supplies

1.The OPA2277 is a monolithic dual op amp, IC9A and IC9B are the code names of these two op amps, and the power supply has been connected to the IC9A.

2.IC9A and IC9B are both negative feedback linear amplification working states, not comparison states! Therefore, the output voltage varies with the deviation value, and it will not be "either the maximum or the minimum". Should there be a pull-up resistor on the gate of VT3?

Take IC9B as an example:

When the load current is relatively small, the output voltage of IC10 is very small, IC9B output positive voltage, VD8 cut-off, will not control VT3, only IC9A through VD7 in the VT3 adjustment effect, to ensure that the output voltage is unchanged: when the output voltage is low, IC9A's 2 pin voltage is low, IC9A's output increases, VT3's gate voltage increases, VT3's conductivity increases, its tube voltage drop decreases, and the output voltage increases...

When the current exceeds the limit value, the output of IC10 increases, which decreases the output of IC9B, and the voltage drop of VT3 increases by pulling down the gate potential of VT3, and the output current is limited by decreasing the output voltage.

The IC9B is used for current-limiting feedback control. The IC9A is used for constant voltage output feedback, right?!

This power supply must be connected to the working voltage, did not find that there is a reference voltage, the circuit is incomplete, it may be sampled at -5V, or it cannot be with this - constant current when the voltage cannot be reached, and constant voltage when the current cannot be reached!

1. The two are in different working states: the op amps in the voltage comparator are working in the saturated state; Op amps in arithmetic circuits are all working in amplified state.

2. The resistors required for the two are different: the output of the voltage comparator generally needs to be connected to a load resistor to work; The op amp used in the operation circuit has no special requirements for resistance.

3. The performance of the op amp in the operation circuit is different: the op amp in the voltage comparator generally does not have high requirements for the performance of the op amp; In the operation circuit of the op amp sometimes need to use some special requirements of the op amp, such as the instrument generally use high-precision op amp, high-end audio must use high-speed op amp, etc.

The op amps working in the voltage comparator are all working in the saturated state, and the output generally needs to be connected to a load resistor to work, and the performance of the op amp is generally not high.

The op amp working in the operation circuit is working in the amplified state, generally with depth negative feedback, according to different circuit requirements, sometimes need to use some special requirements of the op amp, such as the instrument generally has to use high-precision op amp, high-end audio has to use high-speed op amp, etc.