Upgrade your Switch to build a Smart home with MORNSUN Single live wire Power Supply
Abstract: With the emergence of Smart Home, the demand for single live wire power supply also increases and there are many kinds of single live wire power supplies happening on the market.
* How to find a practical and high-quality one of all kinds?
* For the design difficulties of a single live wire power supply, what are the solutions?
It is of great importance to select the proper single live wire when upgrading the smart switch. In this article, we will explain in detail the principle, technical difficulties, and solutions of a single live wire switch scheme.
The Challenges & Potential of Smart Home
As the concept of environmental protection and energy-saving permeates our life, we gradually enjoy a convenient and energy-saving lifestyle --- Smart Home.
In Smart Home, household appliances not only can be controlled remotely but also collected and analyzed the energy consumption data in its monitored system, such as refrigerators, LED lights, bath heaters, exhaust fans, etc.
A smart switch, as known as BANG-BANG Control, is smart on/off controller by programming and a combination of PCBA and components. As a practical control mode, it is widely applied in household appliances and lights.
● In the past, the installation of smart switches required rewiring
Besides the monotonous function, the main way of switch wiring is the single live wire access mode embedded in the wall is an important reason why smart switch can not completely replace the conventional mechanical switch. There is only the live line without a neutral line in the switch because the null line directly connected to the load, which is not a loop and can not be a normal power supply.
● At present, there are a variety of ways to install or upgrade smart switches based on the existing wiring
Technological innovation has helped the power switch connected from a single live wire in the wall to achieve a major breakthrough. In this way, the microcomputer chips can be embedded in the power switch and realize different functions.
For example, the exhaust fan needs to be turned off after people leave the restroom to eliminate peculiar smell; ceiling fan installed in the living room not only needs a remote control switch, but also needs free control of wind speed. For LED lamps, the switch function is required, and more importantly, the dimming or toning function is required... For different household appliances, more smart switches are required to match them. At present, there are power line carrier control, wireless RF control, bus control and single live line control in technology.
● In the future, single live wire power supply will become the main tool of transformation into smart homes
To upgrade the switches to the smart one in the old housed with single live wire, there is a great advantage over the other control methods that is the single live wire control can use the existing wiring. Single live wire control is a kind of wireless communication similar to GSM technology, with built-in transmitting and receiving modules.
Smart switches are divided into single live wire switches and neutral wire & live wire switches. The design of the neutral wire & live wire switches is relatively simple. It is powered by the neutral wire and the live wire directly through an AC/DC converter and power to the communication module in the back-end.
Although this design method is simple, the switch wiring is relatively complex, because one more live wire needs to be pulled into the switch box. Therefore, only some houses with an extra neutral wire can use the neutral wire & live wire switch.
In the process of upgrading to smart switches from the conventional mechanical switches, it must pull an extra neutral wire and the whole house must be rewired. Therefore, the single live wire smart switches will be the best choice in the smart switch upgrade project.
A complete set of smart power supply systems is to be built in combination with the single live wire power supply module to realize a smart switch transform from the mechanical switch, as shown in the figure above.
The smart switch function is required that whether the LED lamps work or not, the single live wire power supply can provide a stable output voltage to ensure the normal operation of the control system in the back-end.
At present, with the emergence of smart home, the demand for single live wire also increases. There are many single live wire power supplies on the market. How to find a worry-free, practical and high-quality single live wire power supply on the market? For the design difficulties of single live wire power supply, what are the solutions?
The principle, technical difficulties, and solutions of a Single Live Wire Switch Scheme
It is of great importance to select the proper single live wire when upgrading the smart switch. We will explain in detail the principle, technical difficulties, and solutions of a single live wire switch scheme.
Since the LED and the single live wire power supply are in series, it is required that when the LED does not work (hereinafter referred to as “off”), the working current of the single live wire power supply is small (the LED is not slightly bright, that is, there is no “ghost fire”), and it can output a stable voltage to ensure the normal operation of the back-end control system; when the LED is working (hereinafter referred to as “on”), the single live wire power supply will not influence the normal operation of the LED (i.e. no “strobo flash”), and can output a stable voltage to ensure the normal operation of the back-end control system.
To solve the two above technical difficulties, we can take the following two countermeasures:
● Measure 1: The single live wire power supply adopts a step-down circuit with ultra-low standby power consumption
At present, the step-down circuit with ultra-low standby power consumption is mostly used to convert its main power into the fixed output voltage for the normal operation of the back-end control system. At the same time, it will not lead to LED “ghost fire”.
As shown in the above figure, the step-down circuit is connected to the neutral wire and live wire through the LED. Since the LED is equivalent to a capacitor connected in parallel with a resistor, it is equivalent to a resistor connected in series on the bus. The step-down circuit works normally to supply power to the back-end control system. When it is off, it is necessary to focus on whether the LED has “ghost fire” (the LED is slightly bright).
The reason for the “ghost fire” is that the LED and the step-down circuit are connected in series between the neutral wire and 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 lead to the LED working briefly and slightly bright.
To solve this problem, some manufacturers on the market can lower the standby power consumption of single live wire power supply to few mW. For example, MORNSUN’s non-isolated DC/DC Converter LSF01-K5BxxSS series can meet the global input voltage range (85-264VAC) with specific peripheral circuits. In this input working voltage range, it can maintain ultra-low standby power consumption, stabilize output voltages of 5V and 12V, and standby power consumption is about 5.2mW.
● Measure 2: pay attention to the power consumption of a single live wire power supply application circuit
How to balance the capacity of power extraction and the avoidance of stroboscopic, the conventional solutions are thyristor and relay. Due to the heating issue of thyristor, the relay scheme is more popular in the market. The following mainly explains the working principle of the relay scheme. The specific working principle of its “on” station is shown in the Figure below.
1. The voltage at both ends of the neutral wire and live wire is a sine wave. When the AC is at the positive half-wave, due to the unidirectional conductivity of diode D2 and the disconnection of MOS transistor Q1, the current flows through diode D1, energy storage, and control circuit to make the energy storage and control circuit work, provide a stable output voltage to the back-end control system, and control MOS transistor Q1 to turn on at a set voltage. Therefore, when the AC is at the positive half-wave, only a small part of the energy is stored to supply power to the back-end control system, and the remaining energy supplies power to the LED through MOS tube Q1.
2. When the alternating current is in the negative half-wave, the current forms a loop through the LED and diode D2 to supply power to the LED.
● Two points should be paid attention to in the application of single live wire power supply:
1. The power of the LED should not be too small. If the power of the LED is too small, the open power extraction circuit will not be able to store energy to supply power to the subsequent circuit. The minimum amount of LED power that should be used depends on different circuits and device parameters;
2. The working power consumption of the control circuit should not be too large. If the working power consumption of the control circuit is too large, there is “ghost fire” in the off-state and an abnormal power extraction circuit in the on-state. Due to the limited energy stored in a single cycle when the parameters of the on-state power extraction circuit are determined, it is unable to provide sufficient energy to the control circuit with excessive working power consumption, while if the actual application requires a control circuit with high power consumption, another circuit needs to be built to solve this problem.
MORNSUN's Power Supply Solutions
Based on these two measures, we should take the circuit designs and specific parameters of various applications into consideration. The design of a single live wire power supply, not only should according to the dimension of the switch box, but also the reliability, size, and application circuit, which all should match the power.
Various single live wire power supplies of different manufacturers in the market, the matched peripheral circuits and electronic components are also diversified. For example, the single live wire module power supply has higher integration, and the single live wire IC products have higher requirements for customers’ independent R&D ability. Take the MORNSUN LSF01-K5BxxSS series as an example.
Referring to the requirements of different applications in the market, MORNSUN divides the relevant application circuits into two categories with LSF-K5BxxSS series.
● Scheme 1: The magnetic protection relay is used as the switching device
The scheme of magnetic protection relay can be connected to LEDs with more than 3W power, and meets the requirements of multi-channel in parallel LED applications.
Advantages: No “ghost fire” in off-state of LED, strong power extraction capacity in on-state, and stable output voltage of single live wire power supply.
● Scheme 2: Super capacitor
The scheme of which the back-end control system is NB-loT and other high-power loads (hereinafter referred to as the super capacitor scheme). When the back-end control system is NB-IoT and other high-power loads and it works, no “ghost fire” of LED happens and the power supply voltage is normal if the single live wire power supply is off; while the power supply voltage is required to be normal to avoid the LED “stroboflash” if the single live wire power supply is on.
By charging and storing supercapacitors/lithium batteries, the scheme shows a stable output voltage is provided for the back-end control system to work. Since the internal design of on-state and off-state charging circuits in the super capacitor scheme, there is no need to replace the super capacitor / lithium battery with no voltage in practical application. A stable output voltage can be provided for a long time when in this scheme. The operating principle of super capacitor scheme is shown below.
The relays of super capacitor scheme are divided into two types: ordinary relays and magnetic protection relays. The selection criteria can be referred to as follows:
1. If the back-end control system is required to be dormant, you can choose the schemes with magnetic protection relay.
2. If the back-end control system is not required to be dormant, you can choose the schemes with ordinary relay.
It is worth mentioning that the cost of the scheme with an ordinary relay is lower than the one with magnetic protection relay.
In addition, the internal control circuit has been designed to detect whether the LED is connected. It has successfully solved the industrial problem that when the relay on the branch is turned on because of the lack of LED, the remaining LEDs have a "ghost fire" problem.
A manufacturer with a good reputation is to a great extent ensures the reliability of the product and good after-sales service, to achieve practical and worry-saving in the real sense.
MORNSUN has over 23 years of experience in delivering reliable and safe power supply solutions for a wide range of applications, including for smart home and smart city. Besides, the MORNSUN power supply solutions space from AC/DC converters to DC/DC converters and other electrical components.