Power supply circuit diagram of single wire electronic switch

After the author introduced a "Single-wire Electronic Switch Power Supply Circuit" in the 50th issue of "Electronic News" in 2005, it was used for reference and imitation by many electronic manufacturers and electronic enthusiasts. The feedback from their telephone consultation was: the circuit used in the circuit Small transformers are difficult to find and difficult to make, especially because they are large and difficult to install. To this end, the author designed and produced a power supply circuit for a single-wire electronic switch. It was found through experiments that the power supply circuit has a strong load capacity, the output voltage is stable and easy to adjust, and the circuit is simple and easy to make. We now provide colleagues with reference and discussion to work together to perfectly solve the problem of single-line electronic switch power supply.

1. Performance introduction:

The ingenuity of this circuit is that the circuit adopts the thyristor chopping principle and only uses the initial section after the alternating current crosses zero to power the circuit itself; after the voltage rises to the set value, the one-way thyristor conductor , the circuit is bypassed. In this way, on the one hand, it ensures the stability of the output voltage and solves the problem of the circuit's own power supply being affected by changes in load current; on the other hand, because the thyristor works in a switching state, it also has its own small voltage drop and low power consumption. Etc. If the user wants to change the level of the output power supply voltage, he can easily achieve this by changing the voltage stabilization value of the Zener diode.

2. Circuit principle: (see attached picture for circuit)

Transfer files for PCB proofing

As shown in the figure: The power circuit is shown in the dotted box. The AB terminal on the left side of the circuit is the single-wire input and output terminal, which is connected in series with the load L and then connected to the 220V mains; the CD terminal on the right side is the low-voltage power supply terminal of the electronic switch, and G is the switch control terminal. The bidirectional thyristor VT is used as a switch to control the on and off of the negative load. The conduction of the thyristor is equivalent to the closure of the switch.

The core problem of single-wire electronic switch power supply is the power supply before the electrical appliance is turned on and the power maintenance after it is turned on. The difficulty is that after the switch is closed, the voltage across the switch is almost zero. How to solve the problem of self-power supply of the electronic switch? The following is an analysis of the working principle of the circuit in two situations.

Power supply before the electronic switch is turned on: At this time, the triac VT is cut off, and the 220V mains power is divided by the capacitor R1, rectified by the full bridge Q, passed through D1 and filtered by the capacitor C1, providing low-voltage DC standby power to the electronic switch itself. In this process, the Zener diode DW and the unidirectional thyristor SCR only play a voltage limiting role and will only turn on when the output voltage is too high.

Power supply after the electronic switch is turned on: After the electronic switch is turned on, the triac VT is triggered to conduct, which is equivalent to the switch closing; the mains power becomes pulsating DC after being rectified by the full bridge Q. Due to the isolation effect of D1, the unidirectional thyristor SCR turns off every time the voltage crosses zero. The following is a detailed analysis of the circuit principle in two stages: in the initial section after the voltage crosses zero and before the output voltage reaches a stable value, the unidirectional thyristor does not conduct, and the current flows through D1 and is filtered by capacitor C1. Power the circuit; when the output voltage rises to a stable voltage, the Zener diode is broken down, and the unidirectional thyristor is triggered to conduct and act as a bypass. At this time, the circuit is powered by capacitor C1, regardless of the load. This is repeated every half cycle to ensure the power supply after the electronic switch is turned on.

It can be seen that whether the electronic switch is on or off, it can solve the problem of self-power supply of the electronic switch circuit.

3. Equipment selection and debugging:

1 In the figure, the thyristor, diode and bridge stack should be selected according to the load current. Generally, 1A is enough, and the breakdown voltage should be above 400V.

2 In the figure, the triac is used as a switch. It can also be directly replaced by electronic control devices such as relays, solid-state relays, and MOC3060 according to specific circumstances.

3 If the circuit within the dotted line is packaged into a module, there will only be 5 terminals. Among them, AB is the incoming line terminal, CD is the low-voltage DC output terminal, and G is the switch control terminal.

In this way, as long as it is used to power the corresponding circuit, it can be made into a single-wire inlet and outlet: "pyroelectric human body infrared switch", "sub-ultrasonic remote control switch", "human body induction electronic switch", "infrared remote control electronic switch", etc. There are many kinds of electronic switches, and their application prospects can be imagined.