NE555 makes voltage polarity converter

The circuit introduced in this example can convert positive voltage into negative voltage. The output negative voltage is continuously adjustable within 5V~10V, and the current is within 50mA. The 555 integrated circuit and R1, R2, C1, etc. form a square wave multivibrator with a frequency of about 10kHz. VD1 and VD2 are diodes for rectification, and VT1 is used for feedback stabilization. When the output pulse of pin 3 of 555 is a positive half cycle, the charge is charged to C2 through VD2, making the voltage on C2 reach more than 10V. During the negative half cycle of the 555 output, its pins 1 and 3 are turned on, and C2 charges C3 through VDl. After repeated charging and discharging, negative voltage is output on C3. Adjusting RP1 can change the output negative voltage value, and the negative voltage range is -5V ~ -10V.

When the output negative voltage is too large, the VT1 current decreases and the collector voltage increases, so the voltage of pin 5 of the 555 increases accordingly, which causes the oscillation frequency to decrease and the output negative voltage to decrease. On the contrary, when the output negative voltage drops, the oscillation frequency increases to keep the output voltage stable.