The working principle of a high-precision DC stabilized power supply with constant voltage and current
The whole machine is divided into four parts: a series type DC stabilized power supply, including adjustment amplification and constant voltage circuit; Constant current regulation and constant voltage constant current conversion display section; Reference stabilized power supply; Automatic adjustment circuit for secondary AC voltage of transformer.
1. Series type DC stabilized power supply and constant voltage circuit. It mainly consists of adjustment tubes T1, T2, T10, and T11. The operational amplifier IC1, p1, p2 voltage adjustment potentiometers, and reference voltage form a constant voltage circuit to control the T2 base voltage, change the conductivity of the adjustment tube, and ensure the normal operation of the voltage stabilizing circuit. Here, p1 and p2 are used as coarse and fine potentiometers to adjust the voltage. The reference voltage and adjustment voltage are connected to the same phase end of IC1, and compared with the sampling voltage at the opposite phase end to change the current of the adjustment tube.
2. Constant current circuit - also known as current limiting circuit. When adjusting to the predetermined current limit, the output current remains unchanged, and the output voltage decreases proportionally with further increase in load. The constant current circuit consists of an operational amplifier IC2 and a sampling resistor of 0.15 Ω, as well as a constant voltage and constant current conversion display circuit. The reference voltage is obtained from the P3 current adjustment potentiometer and the reference power supply adjustment W1 at the same phase end of IC2, and the reverse phase end is connected to the front end of the sampling resistor 0.15 Ω through a resistor 1k Ω. When the sampling voltage is greater than the reference voltage, the output voltage of IC2 decreases, causing a decrease in Vb of T2 and a decrease in output voltage. However, the output current remains unchanged, achieving the goal of current limiting. At constant voltage, T8 conducts and T9 cuts off, so the green light for constant voltage (CV) is on and the red light for constant current (CC) is off. Because the IC2 output is at a high level at constant voltage, T8 conducts and the green light is on through the voltage regulator DZ (6V). When the current limiting protection plays a protective role, the output of IC2 is 0. At this time, the Vb of T2 drops to 0 through the diode voltage, causing the adjustment tube to cut off.
3. Reference stabilized power supply. Composed of TL431 and 78L12, T3. TL431 not only serves as a standard voltage, but also plays a role in amplifying error voltage and controlling T3 transistors. The internal reference voltage of TL431 is 2.5V. The actual sampling voltage is compared with the 2.5V reference voltage of TL431, and the cathode voltage of TL431 is changed to adjust the conductivity of T3. In addition, the base voltage of T3 is stabilized by 78L12 and then passed through a resistor 1k Ω to the base, keeping the output+15V stable. The output+15V is mainly used as the reference voltage for IC1 and IC2 integrated operational amplifier power supplies, constant voltage and constant current circuits, and the reference voltage for AC voltage switching circuits 6V is connected to the output positive pole of the main voltage regulator.
4. The output automatically switches between+10V and+20V. The base of T6 is connected to the reference voltage through a 45k Ω resistor, which is provided by the reference voltage. The other side of the base is connected to the output negative pole of the main power supply through an 18k Ω resistor and a series connected diode for sampling. When the output voltage is below 10V, T6 conducts, T7 shuts off, relay J2 releases, and the normally closed contact is connected to the input voltage at the AC 14V low gear. When the output DC voltage reaches 10V, the T6 base voltage appears negative and cuts off, so T7 conducts, relay J2 closes, and the normally closed contact is connected at the 24 V high gear. When the total output power of the voltage regulator reaches+20V, T5 is cut off, T4 is conductive, J1 is closed, and the normally open contact of J1 is connected. Adjust the input voltage of the regulator to AC switch to the third high gear 32. The TpR adjustable voltage regulator always ensures a certain voltage difference when adjusting the voltage, mainly relying on automatic adjustment of AC voltage.
