The circuit of series regulated power supply and adjustable constant current source composed by Op-amp

The circuit of series regulated power supply and adjustable constant current source composed by Op-amp

The integrated op amp has the advantages of high open-loop gain and low output impedance, and it is ideal for comparison amplifiers in regulated power supplies.

As shown in Figure 1-34, the 12V reference voltage provided by the regulator VDW is added by the potentiometer RP to the co-phase input of the OP amp A1,

The output voltage of the regulated power supply VSC also feeds back to the A1 inverting input,

When the VSC changes, the difference between it and the voltage at the co-phase input is amplified,

To control the base current of the transistor VT, the voltage drop between the emitter and the collector is changed to keep the output voltage stable.

This circuit is simple, but customer service has the effect of the sampling resistor voltage ratio on the stability, the same feedback depth in different VSC,

The amplifier has a closed-loop gain of 1, the deepest feedback and the stability of the VSC.

Because VSC is equal to the voltage at the same phase input, adjusting the potentiometer RP can make VSC change arbitrarily in the 0~12v range.

Fig. 1-35 is an adjustable constant current source circuit composed of op amp.

The R2 in the circuit is much larger than RF, because the inverting input is virtual, and the amplifier input current is very small,

It can be thought that the current flowing through the R1 all flow to R2, so there is es/r1=il[rf/(RF+R2)],

Therefore, the IL and the amplifier parameters independent of the constant current source, adjust the R2 can adjust the constant current size.

When RL changes, IL can stabilize itself, because this is a current shunt negative feedback circuit.

The circuit of series regulated power supply and adjustable constant current source composed by Op-amp