Simple zero-crossing power regulator circuit

Although the zero-crossing power adjustment circuit introduced in this article is simple, it can work reliably. It is suitable for power adjustment of various types of electric heating appliances, power adjustment of series-excited motors, etc. It can be used as a reference for electrical staff. 　　The circuit working principle of this device is shown in Figure 1. It is composed of a power supply circuit, an AC zero-crossing detection circuit, a decimal counter/pulse distributor and a two-way thyristor. After the 220V mains power is stepped down by the power transformer T, it is rectified by a full-wave rectifier circuit composed of diodes VD1 and VD2, and then filtered by C to supply the complete circuit operation. After full-wave rectification by diodes VD3 and VD4, the resulting pulsating DC voltage is added to the inverting input end of operational amplifier IC1 through R1. When the pulsating voltage crosses zero (that is, the AC voltage crosses zero), a zero-crossing pulse occurs in IC1. IC2 is used to count and distribute the zero-crossing pulses to generate a thyristor trigger signal. S is the power adjustment switch. S changes the counting method of IC2 to adjust the power of the AC load. For example, when S is in the "3" position, IC2 performs quaternary counting and only generates 2 trigger pulses for every 4 zero-crossing pulses input to trigger the bidirectional thyristor to conduct, so this gear is a half-power gear. The figure shows 4 levels. Since IC2 has 10 output terminals, different power levels can be obtained by appropriately combining these output terminals. The VT is connected into a large current switch, which can trigger high current on the thyristor VS with different flow rates, thereby making it work reliably. Among them, IC1 uses a general-purpose operational amplifier integrated circuit (such as LM324N, TL082, etc.). IC2 uses CD4O17. VT can use 3DK4 or other medium power switching transistors, β≥1OO. VS should be selected according to the current of the load. Its withstand voltage is not less than 600V. The withstand voltage of inductive loads can be increased. T uses a 2~3W power transformer with a secondary voltage of 9V. S is the power adjustment selection switch, and porcelain band switch can be used. There are no special requirements for other components and can be selected according to the values ​​shown in the figure.