Homemade high stability and large current DC adjustable voltage stabilized power supply

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

For sampling of high-stability DC power supply, the output voltage is generally divided by a voltage dividing resistor (about 1/2) and supplied to the comparison circuit. However, it is unrealistic to use an adjustable DC stabilized power supply as a very precise reference source. If necessary, it is necessary to add an additional winding to the transformer to supply power separately, which is very troublesome.

The author chooses to change the sampling voltage to change the output voltage. An adjustable voltage was produced.

The input voltage adopts divided power supply to reduce the voltage drop on the adjustment tube within the stable current range, reduce the tube temperature, further increase the thermal stability, and also improve the efficiency. Of course, when the input voltage is adjusted in steps, the problem that arises is that the power supply of the reference source will also change from low to high. In order to further improve the stability of the reference, a three-terminal voltage stabilizing block is inserted in the front end of the reference to initially stabilize it and then supply the reference. Circuit, after such processing, LM317 is used as the reference source, and its stability is higher.

The attached picture is a high-stability, high-current DC voltage stabilizing circuit with a voltage comparator that the author has made through practice. It is mainly composed of power transformer, rectifier and filter, reference source circuit, voltage comparison, composite power adjustment, overcurrent protection circuit and other parts. The power supply transformation, rectification and filtering are relatively simple and will not be discussed here. IC1 (7805) and IC2 (EM317) constitute a precision reference source; IC3 is connected here as an inverting comparator as a voltage comparison circuit, and the non-inverting terminal is connected to the reference source, and the inverting terminal inputs the sampling voltage, which is passed through the non-inverting terminal reference in IC3 After comparison, the output terminal outputs the comparison result to control the conduction degree of the composite adjustment tube to adjust the rise and fall of 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 to improve the driving capability. Among them, V1 does not need to increase the bias current resistance between the c and b poles like the ordinary "series stabilized" power supply. V3, R6, and R5 form a load overcurrent protection circuit. The overcurrent sampling resistor R6 is connected in series to the negative terminal of the power supply and is not included in the voltage stabilization control, so that it has almost no impact on the voltage stabilization output (for the sampling resistor R6 is connected in series to the adjustment tube) output circuit).

working principle

After the power supply is transformed, the rectified, filtered and smoothed DC voltage is supplied to the voltage stabilizing circuit. One channel is initially stabilized to 5V by IC1 and then supplied to the regulated output of IC2 as the reference voltage 1.25V. This reference voltage is directly supplied to the non-inverting end of the voltage comparator IC3 (LM358); while the other channel is used as the power supply of IC3. When power is on, IC3 is cut off and has no output because V1 and V2 are not started, and its inverting terminal has no voltage (OV). The inverting comparator IC3 will immediately output a high voltage, causing V1 and V2 to quickly conduct, and the regulated output starts from 0V. rises, the turtle voltage sent to the inverting terminal of IC3 after being divided and sampled by R3, RP, and R4 also rises. After voltage comparison with the 1.25V reference of the non-inverting terminal of IC3, the voltage at the output terminal of IC3 drops back to the set voltage regulation value. superior.

When the regulated output voltage has a downward trend due to the connection of the load, the stabilization process is: regulated output ↓→IC3 inverting terminal voltage ↓→qC3 inverting comparison output terminal ↑→V1 and V2 conduct ↑→The 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 is turned on, and the b pole of V1 is grounded to reduce the output voltage to achieve the purpose of overcurrent protection.

Circuit characteristics

The output stability is high. Under the rated load current and the normal voltage drop of the adjustment tube V2, the output voltage does not move at all on the digital meter (see attached table).