A high-precision, high-performance fully automatic AC voltage stabilizing circuit

This fully automatic AC voltage stabilizer circuit can greatly extend the service life of expensive electrical appliances. When the input voltage is 170V ~ 270V, the stable output voltage range is 200V ~ 240V, and the rated power is 2.5kW (as long as the transformer is slightly modified, Rated power can be increased or decreased). Transformers are used to isolate power supply and sampling to ensure safe debugging and maintenance. This voltage regulator has a high-stability base reference voltage source and a two-stage control circuit. The entire circuit is based on a single-chip dual-op-amp integrated circuit, with stable and reliable operation and good anti-interference performance.

The principle circuit is shown in the attached figure.

The secondary side of power transformer T takes out two sets of 12V voltage, and one set is rectified by VD1~VD4 and filtered by Cl to provide 12V DC working voltage for the dual operational amplifier LM358 and relays Kl and K2. At the same time, through the current limiting resistor R2, VD6 is stabilized to 5.6V, which is used as the base reference voltage of the comparators ICA and ICB; the other group is rectified by VD5, C2, and C3 denoising filtered as the power supply error sampling voltage, and is used as the power supply error sampling voltage through the potentiometer RP1, After adjustment, RP2 is used as the comparison signal of ICA and ICB. The primary of the power transformer T also serves as a voltage regulator, with three plugs A (240V), B (220V), and C (200V) for relay Kl and K2 contact selection. C2 is the output power socket and Fu is the fuse. The input or output voltage is indicated by the voltmeter V (or not), and SBI is the selector switch.

When the input voltage VIN=200V~240V, relays Kl and K2 do not operate, and their contacts are in the normally closed position (position shown in the attached figure). Therefore, the input voltage is directly sent to the output socket C2 without any increase or decrease, then the output voltage VOUT=VIV; when the input voltage is lower than 200V, Kl is attracted, and K2 is still in the released state. At this time, the input is connected to T C terminal, thereby increasing the output voltage. According to the measured data, when VIN=170V~200V, the output VOUT=205V~240V; when the input voltage is higher than 240V, K2 pulls in and Kl releases. At this time, the input is connected to the B terminal of T, so that the output voltage is reduced. . When VIN=240V～270V, VOUT=210V～240V (actual measurement value).

LED1 is used as power indicator, and the two-color light-emitting tube LED2 is used as input voltage indicator: when VIN<200V, LED2 green tube (G) lights up; when VIN>240V, LED2 red tube (R) lights up; when VIN=200V~240V, LED2 two tubes None light up.

The circuit can be installed on a printed circuit board, and after checking it can be debugged. Debugging methods and steps are:

(1) Turn RP1 to the uppermost end and RP2 to the lowermost end.

(2) Plug in the power plug CT, use another high-precision voltage regulator to make the CT input voltage 200V (with the help of a voltmeter indication), slowly lower RP1, so that Kl has just closed and LED2 emits green light.

(3) Make the CT input voltage 240V and slowly increase RP2 so that K2 has just closed and LED2 glows red.

(4) When the input voltage ranges from 170V to 270V, the output voltage and LED2 lighting should be divided into three sections as shown in the attached table, otherwise they should be readjusted. If there is still a big difference with the attached table after repeated adjustments, check whether IC, VT1, VT2, Kl, K2 are defective, whether the T core of the transformer is too loose, whether the air gap is too large, etc.