Application of NE555 in power conversion

1. Single power supply to dual power supply circuit

As shown in Figure 1. The time base circuit NE555 is connected to an astable circuit, and the output frequency of the 3rd pin is 20kHz and the duty cycle is 1:1 square wave. When the 3rd pin is high, C4 is charged; when the 3rd pin is low, C3 is charged. Due to the existence of VD1 and VD2, C3 and C4 are only charged but not discharged in the circuit. The maximum charging value is the power supply voltage G. When the B terminal is grounded, the dual power supply of +/-G is obtained at the A and C terminals. The output current of this circuit exceeds 50mA.

2. DC voltage doubler power supply

As shown in Figure 2(a). The NE555 integrated circuit and peripheral components form a self-excited multivibrator, which outputs a square wave with a frequency of about 3kHz at its output terminal ③. The oscillation frequency depends on the values ​​of R1, R2 and capacitor C2. The output pulse passes through the double voltage rectifier circuit composed of C4, VD1 and C5, VD2 to generate a DC voltage of twice the power supply voltage at its output terminal. For example, if the power supply voltage of the integrated circuit is 5~15V, the output DC voltage is 10~30V. To obtain a higher voltage, just add more voltage doubler circuits at the output end. Figure 2(b) is a triple voltage circuit.

3. Negative voltage doubler power supply

The NE555 integrated circuit can be used to convert not only positive voltage doubler output, but also negative voltage doubler output. Figure 3 is an example of negative voltage output. The negative voltage is approximately equal to the power supply voltage, but the polarity has changed. It is a polarity conversion circuit.

4. Inverter power supply circuit

The NE555 integrated circuit can also be used to convert DC voltage into AC voltage. Figure 4 is a DC-AC conversion circuit. The NE555 has an oscillation frequency of 4kHz. The square wave output passes through resistor R and transformer T1, and can form an AC voltage of several hundred volts on the secondary side of T1. For example, if the turns ratio between the primary and secondary sides of the transformer is 1:20, and the voltage on the primary side of the transformer is 10V, then the secondary side voltage output of T1 is 200V. If the resistor R4 and neon lamp in Figure 4 (a) are replaced by C3 and diode VD1 in Figure 4 (b), a DC voltage of 5 to 15V can be converted into a low current, high voltage DC voltage (which can be several hundred times higher than the DC output voltage).

5. Sinusoidal power supply circuit

Figure 5 uses the NE555 integrated circuit to convert the DC voltage into a 50-60Hz sinusoidal AC voltage. The NE555 circuit is a low-frequency oscillator, and the potentiometer R4 is used to tune the oscillation frequency within the range of 50-60Hz. The output pulse of NE555 is amplified by transistors VT1 and VT2, and added to the primary side of transformer T1 through capacitor C4 and inductor L1, and a sine wave of about 50Hz is output on its secondary side. The

square wave output by NE555, its positive pulse turns on VT1, and the negative pulse turns on VT2. The emitter of VT1 and VT2 is a pulse wave with amplified power (current). Inductor L1 presents a large impedance to high-order harmonics, so the primary side of transformer T1 is approximately a sine wave.

Circuit working process: In Figure 2-42 (a), after the power supply is turned on, the power supply first charges C4 through VD1, so that the voltage across C4 is close to the power supply voltage. When the NE555's pin ③ outputs the rising edge of the pulse, it charges C4 again. According to the principle that rising water lifts all boats, the voltage between the positive electrode of C4 and the ground reaches: power supply voltage + pulse peak voltage. Then this voltage charges C5 through VD2, so that the voltage between the positive electrode of C5 and the ground reaches the voltage of C4, which is equal to 2 times the power supply voltage. When the falling edge of the pulse arrives, the power supply charges C4 again through VD1, and the above process is repeated.

Figure 2-42 (b) shows a 3-fold voltage boost circuit. As can be seen from the figure, the boost circuit of this circuit is composed of 3 groups of diode-capacitor circuits. If you compare its connection method with Figure 2-42 (a), you will find that the components added to this circuit are VD1 and C4 according to their positions. In this circuit, each stage of the 3 groups of diode-capacitor circuits can increase the output voltage of the previous stage by a power supply voltage value. 3 groups of such circuits can increase the output voltage to 3 times the power supply voltage. Figure 2-42 (c) shows a 4-fold voltage boost circuit composed of a 555 circuit. This circuit is composed of 4 groups of diode-capacitor circuits, which can ultimately increase the output voltage to 4 times the power supply voltage.