First, the circuit principle
In the circuit, IC(TL084) constitutes four comparators, respectively driving the field effect tube T1 ~ T4. PR1, R1 ~ R4, PR2 are AC input partial voltage sampling circuits. R5 ~ R8 is the DC output partial voltage sampling circuit. When the AC positive half-cycle input voltage amplitude is higher than the output voltage of the rectifier power supply, the inverting terminal voltage of IC1a and IC1b is higher than the in-phase terminal voltage, so the two comparators flip over and drive T3 and T4 respectively, and the current returns from the A end of the power supply through T3, load RL and T4 to the B end, completing the AC positive half-cycle rectification process. When the AC input is negative half cycle, IC1a and IC1b flip over, and T3 and T4 stop. At the same time, IC1c and IC1b flip over to drive T1 and T2 on respectively and enter AC negative half cycle rectification. Because the FET has the transient diode unidirectional conduction characteristic, when the rectifier power supply is turned on, a pair of FET heads are piloted to provide the starting voltage to the IC.
Second, component selection:
R2, R3, R6, and R7 partial voltage resistors: When the rectifier supply voltage is 6V, 9V, or 12V, the value can be 8.2kΩ, 15 kω, or 22 kω, respectively. In order to avoid the difference in the working state of the FET due to the error of the resistance value. To cause additional power consumption, the precision of the selection of resistance components should be between 1% and 0.1%. The working parameters of the selected P-channel FET IRF4905 are: Umax=55V, Imax=75A, and on-resistance is 22mΩ. The working parameters of the n-channel FET IRFZ48N are: Umax=55V, Imax=64A, and on-resistance is 35mΩ.