[Guide]How to easily transform a smart switch, it is very important to choose the right single live wire power supply. In this issue, we will explain the principle of the single fire-wire control scheme, the technical difficulties of this scheme and the solutions.

Since the LED and the single live wire power supply are connected in series, it is required that when the LED is not working (hereinafter referred to as the off state), the single live wire power supply has a small working current (the LED is not dimly lit, that is, there is no “wild fire”) and can output Stable voltage to ensure the normal operation of the back-end control system; when the LED is working (hereinafter referred to as: on state), the single live wire power supply cannot affect the normal operation of the LED (that is, no “flicker”), and can output a stable voltage. The end control system works normally.

Key point 1: Single live wire power supply uses a step-down circuit with ultra-low standby power consumption

At present, a step-down circuit with ultra-low standby power consumption is often used to convert the mains power into a set output voltage for the normal operation of the back-end control system, and at the same time, it will not cause the phenomenon of “ghost fire” in the LED.

As shown in the figure, the step-down circuit is connected to the neutral and live wires through the LED. Since the LED is equivalent to a capacitor in parallel with a resistive load, which is equivalent to a resistor in series on the bus, the step-down circuit works normally to supply power to the back-end control system. When in the off state, you need to pay attention to whether there is a “ghost fire” phenomenon in the LED (the LED is dimly bright).

The reason for the “ghost fire” phenomenon is: because the LED and the step-down circuit are connected in series between the zero live wire, when the input current required by the step-down circuit is too large, the current flowing into the LED will also increase, which will cause the LED to work for a short time. There is a dim phenomenon.

In response to this problem, some manufacturers on the market have been able to achieve a few milliwatts of standby power consumption of a single live-wire power supply. Refer to Jinshengyang’s non-isolated LSF01-K5BxxSS series, this product combined with peripheral circuits can meet the global input voltage range (85-264VAC), within this input operating voltage range, it can maintain ultra-low standby power consumption, stable output voltage 5V, 12V, etc., Its standby power consumption is about 5.2mW.

Key point 2: Pay attention to the power consumption of the single live wire power supply application circuit

How to balance the power taking capacity and the inability to flicker, the common solution is to have SCR and relay two solutions. Due to the heating problem of the SCR, the relay scheme is currently more mainstream in the market. The following mainly explains the working principle of the relay scheme. The specific working principle of its open state is shown in Figure 8.

1. The voltage at both ends of the zero live wire is a sine wave. When the alternating current is in the positive half wave, due to the unidirectional conductivity of the diode D2 and the MOS tube Q1 disconnected, the current flows through the diode D1, the energy storage and the control circuit, so that The energy storage and control circuit work to provide a stable output voltage for the back-end control system to work, and at the same time, the MOS transistor Q1 is controlled to be turned on at a certain set voltage. Therefore, when the alternating current is in the positive half-wave, only a small part of the energy is stored to power the back-end control system, and the remaining energy is supplied to the LED through the MOS tube Q1.

2. When the alternating current is in the negative half wave, the current forms a loop through the LED and the diode D2 to supply power to the LED.

It can be seen that two points should be paid attention to in the application of single live wire power supply:

1. The power of the LED light should not be too small. If the power of the LED light is too small, the on-state power-taking circuit will not be able to store energy to supply power to the subsequent circuit. The minimum LED light power that can be used needs to be determined by combining different circuit and device parameters;

2. The operating power consumption of the control circuit should not be too large. If the operating power consumption of the control circuit is too large, it will cause the phenomenon of “ghost fire” in the off state and abnormality of the power-taking circuit in the on-state, because the power-taking circuit of the on-state is in the condition of determining the parameters. , The energy stored in a single cycle is limited, and sufficient energy cannot be provided to the control circuit with excessive working power consumption; if the actual application requires a control circuit with high working power consumption, an additional circuit needs to be built to solve the problem.

The reliability, size and application circuit of the single live wire have become key factors

In view of these two points, the application circuit design and specific parameters of various application environments need to be considered. Customers can design according to the size of the switch box by themselves, but the reliability, volume, and power matching application circuit scheme of the single live wire power supply needs to be taken into consideration.

Based on the differences in the single-fire-wire power supply products of various manufacturers on the market, the peripheral circuits and Electronic components they match are also different. For example, the module-type single-fire-wire power supply has a higher degree of integration, and the IC-type single-fire-wire products are independent of customers. The research and development capabilities are demanding. Take Jinshengyang’s LSF01-K5BxxSS series as an example.

With reference to the needs of different applications on the market, Jinshengyang combined with the LSF-K5BxxSS series to roughly divide the relevant application circuit solutions into two categories.

Reference scheme 1: Use magnetic protection relay as switching device

Its magnetic protection relay application program can support various application requirements with LEDs with power above 3W, and support one LED with power above 3W, two LEDs with power above 3W, and three LEDs with power above 3W.

The characteristics of this application scheme: the off-state LED has no “ghost fire” phenomenon, the on-state power-taking capability is strong, and the output voltage of the single live-wire power supply is stable.

Reference scheme 2: Super capacitor scheme

The back-end control system is an application solution for high-power loads such as NB-loT (hereinafter referred to as the super capacitor solution). Since the back-end control system may be a high-power load such as NB-IoT, when the back-end control system is working, if the single live-wire power supply is in the off state, the LED has no “ghost fire” phenomenon and the power supply voltage is normal; if the single live-wire power supply is in the off state, On state, the power supply voltage is required to be normal, and the LED has no “stroboscopic” phenomenon.

This solution mainly charges and stores energy by supercapacitor/lithium battery, and provides stable output voltage for the back-end control system to work. Since the super capacitor solution is designed with on-state and off-state charging circuits, there is no need to replace the super capacitor/lithium battery due to the lack of voltage of the super capacitor/lithium battery in actual applications. The solution can provide stable output voltage normally for a long time. The working principle diagram of the super capacitor solution is shown in the figure below.

There are two types of relays in the super capacitor solution: ordinary relays or magnetic protection relays. Its main purpose is: if the application requires the back-end control system to be dormant, you can choose the super capacitor solution using magnetic protection relay; if the application requires the back-end control system to not need to sleep, you can choose the super capacitor solution using ordinary relays, the cost of the solution It is cheaper than the super capacitor solution that uses magnetic relays, and the internal control circuit has been designed to detect whether the LED is connected. It has successfully solved the industry where the relay on the branch is turned on when the LED is connected less, and the remaining LEDs are “wildfire”. problem.

In the future, the single live-wire power solution will become the mainstream solution in the market

At present, with the rise of smart homes, the demand for single live wires has also increased. The intelligent market is still an emerging market, and after-sales service is particularly important. If you want to buy intelligent products, you must choose a manufacturer with a good reputation, so that the after-sales service can be guaranteed to the greatest extent, so that it can be practical and practical in the true sense. Worry-free.