Self-made high-stability, high-current, DC adjustable voltage-stabilized power supply using operational amplifier

A high-current DC regulated power supply with high stability should have a precise and stable reference source.

The sampling of high-stability DC power supply is generally done by dividing the output voltage through a voltage-dividing resistor (about 1/2) and supplying it to the comparison circuit. However, it is unrealistic for an adjustable DC regulated power supply to be a very high-precision reference source. If necessary, it is necessary to add another winding to the transformer for separate power supply, which is very troublesome.

The author chose to change the output voltage by changing the sampling voltage and made an adjustable voltage.

The input voltage is powered by a step-by-step method, which reduces the voltage drop on the adjustment tube within the stable current range, reduces the tube temperature, further increases thermal stability, and also improves efficiency. Of course, the step-by-step adjustment of the input voltage will cause the reference source power supply to change from low to high. To further improve the reference stability, a three-terminal voltage regulator is connected in series to the front end of the reference to stabilize it first and then supply it to the reference circuit. After this treatment, the LM317 is used as the reference source, and its stability is relatively high.

The attached picture is a high-stability, high-current DC voltage regulator circuit with a voltage comparator that I made in practice. It is mainly composed of power supply transformation, rectification and filtering, reference source circuit, voltage comparison, compound power adjustment, overcurrent protection circuit, etc. Power supply transformation and rectification and filtering are relatively simple, so they are not described here. IC1 (7805) and IC2 (EM317) form a precision reference source; IC3 is connected here as an inverting comparator as a voltage comparison circuit, and the in-phase end is connected to the reference source, and the inverting end inputs the sampling voltage. After comparison with the in-phase end reference in IC3, the comparison result is output from the output end to control the conduction degree of the compound adjustment tube to adjust the output voltage.

V1 and V2 form a composite power adjustment circuit, which amplifies the control current of the comparator circuit to a load current of several amperes, thus improving the driving capability. V1 does not need to add a bias resistor between the c and b poles like an ordinary "series stabilized" power supply. V3, R6, and R5 form a load overcurrent protection circuit. The overcurrent sampling resistor R6 is connected in series with the negative end of the power supply and is not set within the voltage regulation control, so that it has almost no effect on the voltage regulation output (for the circuit in which the sampling resistor R6 is connected in series with the output end of the adjustment tube).

Working Principle
After the power supply is transformed, the DC voltage that is smoothed by rectification and filtering is supplied to the voltage stabilizing circuit. One path is initially stabilized to 5V by IC1 and then supplied to IC2 for regulated output as a reference voltage of 1.25V. This reference voltage is directly supplied to the non-inverting end of the voltage comparator IC3 (LM358); and the other path is used as the power supply for IC3. When the power is turned on, IC3 is cut off and has no output because V1 and V2 are not started, and there is no voltage (OV) at its inverting end. The inverting comparator IC3 will immediately output a high voltage, causing V1 and V2 to turn on quickly, and the regulated output starts to rise from 0V. The tortoise voltage sent to the inverting end of IC3 after being sampled by R3, RP, and R4 also rises. After voltage comparison with the 1.25V reference at the inverting end of IC3, the voltage at the output end of IC3 drops back to the set regulated value.

When the voltage of the regulated output voltage decreases due to the connection of the load, the stabilization process is: regulated output ↓→IC3 inverting terminal voltage ↓→qC3 inverting comparison output ↑→V1, V2 conduction ↑→stable output is normal. Working process of overcurrent protection tube V3: When the voltage on the overcurrent sampling resistor R6 exceeds 0.7V due to excessive load, V3 conducts, grounding the b pole of V1 to reduce the output voltage, achieving the purpose of overcurrent protection.

Circuit Features
: High output stability. Under the conditions of rated load current and ensuring the normal voltage drop of the adjustment tube V2, the output voltage does not change at all on the digital meter (see the attached table).

Component selection and production First of all, to achieve high current regulated output, at least the power of the power transformer should be increased accordingly. The author's experiment uses a 120VA transformer, which can be selected according to actual needs. The rectifier tube can be 6A/200V, the C1 main filter electrolytic requires ≥8200μF/50V, V2 is a silicon NPN high-power tube with BVceo>100V, Icm>10A, PCM≥100W, such as C5198, C3263, etc. V1 and V3 should be selected from silicon NPN medium-power small-volume tubes with BVceo≥50V, Icm≥1A, Pcm≥0.6W, β≥180, recommended model: C8050 (both domestic and imported).

IC1 is a common three-terminal 7805, and IC2 is a LM317.

IC3 requires a single power supply op amp. And the common mode voltage is small GV temperature drift. It is required that the negative end of IC3 power supply, C3 ground, R4 sampling ground, C4 ground, and output ground (the width of the circuit board ground line is 2em) must be connected together, and it is not advisable to use crossover wires, otherwise high stable output cannot be guaranteed.

The attached table is the actual reference data measured by disconnecting the overcurrent protection circuit (disconnecting the R5- terminal). As long as the soldering is correct according to the attached figure, it can be put into use after simple debugging. If you choose military op amps and metal resistors, the stability will be even higher.