Negative power generator circuit diagram composed of NAND gate

In electronic equipment, it is sometimes necessary to use a set of negative power supplies with low power . Three NAND gates can be connected as shown in the figure to change the polarity of the power supply. In the circuit shown in the picture, A1 and A2 form a self-excited multivibrator of about 4kHz, and A3 plays a buffering role and also plays a shaping role. When the circuit oscillates A3 and outputs high level, VD1 is turned on, C2 is charged, A is positive and B is negative, and VD2 is turned off at this time. When the output terminal of A3 becomes low level, since the voltage across C2 cannot break through, point B should be a negative voltage at this time, VD1 is cut off, VD2 is turned on, and a negative voltage is output. If this circuit uses +5V as the positive power supply, it can output -3V when no load is used. When the load is 430 ohms, the output is -2V; when the load is 200 ohms, the output is -1.5V; when the load is 100 ohms, the output is -1V. If you want to increase the amplitude of the negative voltage, you can increase the power supply voltage of the A1 ~ A3 integrated circuits.