Principle of single live wire power taking circuit

The power supply of the single live wire switch applies the single live wire power supply technology, which is generally divided into two parts to realize the power supply to the control circuit: off-state power supply (off-state power supply) and open-state power supply (on-state power supply), which are discussed below. illustrate:

1. Off-state power supply (lights off, standby power supply):

When the lights are turned off, the micro-power power supply module PI-3V3-B4 takes power when the silicon controlled silicon is cut off and does not conduct (refer to the circuit schematic diagram below). The single live wire power supply module PI-3V3 -B4 is responsible for converting the 220V grid voltage into a stable low-voltage DC output of 3.3V. From the path in Figure 1, we can see that the mains power grid goes from the neutral line (N) through the lamp load (LAMP) through the rectifier diode D5, and then the current limiting resistor R1 is added in series to the high-voltage input of the power module PI-3V3-B4 Pin (IN), a current loop is formed from the common ground terminal (GND) of the power module back to the live wire terminal (L) of the power grid through a diode (D1) in the bridge rectifier (D1-D4). The power module has a high-voltage power input, and the low-voltage output terminal (OUT) has a stable DC voltage output of 3.3V for use by the control circuit (such as control chip, wireless module, etc.).

Some friends will ask: Since it is called a single live wire switch, does it work without a neutral wire? In fact, the "single live wire" is relative to the electronic switch box (it only needs to connect the live wire to the switch box, and does not need to connect the neutral wire). wire to the switch box), the entire circuit actually works through the neutral live wire, but the lamp is borrowed as a path to connect the neutral wire, which creates a problem, because energy-saving lamps or LED lamps only need Through a very small current, the phenomenon of flickering will occur when the light is turned off, especially when the LED light flashes very brightly, this current should generally not be greater than 30μA. Of course, some lamps with larger sizes (such as 100μA) will not flicker, but in order to The completed switch can adapt to more lamps and lanterns. The smaller the current, the better. Since the conversion efficiency of micropower power modules is generally relatively low, most of which do not exceed 50% (can reach 65% after optimization), so when the input current is 30μA, the low-voltage output terminal (OUT) can be provided to the control circuit. The current will not exceed 1mA (even if the instantaneous current can be tens of mA, the average current must be controlled below 1mA).

In addition to controlling the current of the downstream control circuit as small as possible, the no-load current of the power module itself is also a key factor. If the no-load input current of the power module itself is greater than 30μA, even if the current used by the subsequent control circuit is zero, the overall standby current of the electronic switch cannot be reduced to less than 30μA, so we have improved and developed this power module. Its no-load current is very small (nearly "zero" power consumption). In this way, if the current of the control circuit can be made very small, the standby current of the entire switch can be made very small, and it can adapt to more applications. Energy-saving lamps or LED lamps.

2. Power on (light on):

When the light is turned on, the controlled silicon is turned on. In order to maintain the power supply of the circuit, we use two voltage regulator tubes (Z1, Z2) and a bridge rectifier (D1-D4) to form an open-state power supply. circuit.