Analysis of LM7812 input voltage range

The digital controlled 100-current stabilized power supply circuit is composed of +l2V stabilized circuit, voltage control/display circuit and stabilized output circuit. +l2V stabilized circuit, power transformer T, rectifier bridge uR, filter capacitors Cl, c2, c6, It is composed of c7 and three-terminal voltage regulator integrated circuit ICl. The voltage control/display circuit consists of the control button Sl, the reset button S2, the resistor RO-R11, the potentiometer RP, the capacitor C3-C5, the Schmitt trigger integrated circuit IC2, the ten-bucket counting/pulse distributor integrated circuit IC3, Electronic switch integrated circuit IC4, 1C5 and light-emitting diodes VLl-VL8 composition. The voltage stabilization output circuit is composed of three-terminal adjustable voltage stabilization integrated circuit IC6, resistor Rl2 and capacitors C6-C9. After switching on SO, the AC 220V voltage is reduced by T, UR rectified and filtered by C6 and C7, and one is used as the input voltage of lC6; the other is stabilized by ICl to +l2V, as the working power supply of IC2-IC5. After lC3 is powered on and reset, its YO terminal outputs a high level (YI-Y8 terminals output a low level), the electronic switch SOl inside IC4 is turned on, and R4 is connected to the voltage regulator circuit. The output voltage at this time is +3V. At the same time VLl lights up.

After pressing S1, the pulse signal generated by the oscillator composed of IC2 and peripheral resistance-capacitance components is added to the 14 pin (CP end) of IC3 via S1, as the counting pulse of IC3, and the Yl end of IC3 outputs a high level ( The YO end becomes low level), S02 is turned on, R5 is connected to the voltage regulator circuit, the output voltage at this time is +4·5V, and VL1 is lit at the same time. When 51 is pressed continuously, the YO-Y8 terminal of IC3 will output high level in turn, so that S01-S08 will be turned on in turn, resistor M-Rll will be connected to the voltage regulator circuit in turn, and IC6 will output from low to high in turn. (+3V, +4·5V, +5V, +6V, +7·5V, +9V, +l2V, +l5V) 8 voltages. VLl-VL8 turns on in turn. In any gear other than +3V, just press S2, IC2 will be reset to zero and return to the lowest voltage gear of +3V.