How to Reduce Standby Power Consumption of Power Supply
What is an X-Capacitor
X capacitor is connected between two power lines, i.e. "L-N". X capacitor can suppress differential mode interference. Usually, metallized film capacitor is adopted, and the capacitance is UF. Most x capacitors are square, that is, similar to the shape of a box. Its surface is generally marked with safety certification mark, withstand voltage words (generally ac300v or ac275v), relying on standards and other information.
The application of X safety regulation capacitor includes the following three aspects
1〠Suppression of electromagnetic interference
Anti electromagnetic interference is the most common function of X capacitor. Generally, two pins are connected between zero line and live line. It is suitable for high-frequency, DC, AC, coupling and jumper pulse circuits. It can withstand overvoltage impact. It is generally used in parallel with resistance to discharge charge;
2〠Resistance capacitance Depressurization
Resistance capacitance step-down is also often used by X capacitors. Especially for low-cost finished products, the working principle of capacitor step-down is to limit the maximum working current by using the capacitive reactance generated by the capacitor at a certain AC signal frequency. At the same time, if a resistive element is connected in series on the capacitor, the voltage obtained at both ends of the resistive element and the power consumption generated by it completely depend on the characteristics of the resistive element. Therefore, the capacitor step-down actually uses the capacitive reactance to limit the current, and the capacitor actually plays a role in limiting the current and dynamically distributing the voltage at both ends of the capacitor and the load. As shown below
3〠Filtering
X2 safety capacitor can be used as DC filter and can be used in parallel.
X capacitor is a safety regulation capacitor, that is, the capacitor must not cause harm to human body. Therefore, the safety standard stipulates that when the power cord of the working machine is unplugged, the energy storage of X capacitor shall be reduced to below 34V DC within one second.
Now, with the continuous improvement of equipment power, X capacitors with larger capacity are required for both EMI requirements and filtering requirements, ranging from 100 NF for small household appliances to 6 µ f for washing machines. However, in order to meet the requirements of rapid energy discharge, the discharge resistance required for the discharge of X capacitor needs to decrease with the increase of X capacitor. The smaller the resistance will increase the no-load power consumption, which brings great difficulties to improve the standby power consumption.
Meet new challenges and upgrade CAPZero
Recently, in order to reduce the discharge power consumption of X capacitor, PI specially developed capzero3 series products. CAPZero, as its name implies, is a technology that "reduces the influence of capacitance to zero". Jason Yan, senior technical training manager of PI, said that CAPZero can be regarded as an intelligent switch. Only when the AC voltage is disconnected will it provide a discharge circuit for the filter capacitor, so as to achieve the minimum standby power consumption. CAPZero adopts self powered working mode, and the power consumption is less than 4MW, which is far lower than the standby power consumption of discharge resistance. Yan Jinguang said that for some large-scale x capacitors, the corresponding resistance standby power consumption may even exceed 1W.
How CAPZero works
X capacitor and the corresponding standby power consumption. It can be seen that the larger the capacity of X capacitor, the higher the standby power consumption. The relationship between them is linear.
Yan Jinguang pointed out that it is the third generation of CAPZero products. Compared with the previous generation products, it supports lower total series resistance, that is, it supports larger x capacitance.
In addition, capzero-3 IC can be placed either before or after the system input fuse. The new device has high common mode anti surge capability, so there is no need for external grounding connection, and 1000 V MOSFET is integrated internally. It also has high differential mode anti surge capability. The creepage distance between package and PCB shall be kept below 4 mm.
According to Yan Jinguang, CAPZero products are fully pin compatible. Therefore, if there are specifications that capzero-2 cannot meet, it can be directly replaced with capzero-3. At the same time, the product meets IEC60335, iec62368 and other safety standards. Capzero-3 devices are certified to meet the safety requirements of CB and Nemko, so developers do not need to conduct separate safety tests on the X-Capacitor discharge circuit of the power supply.
Review the senzero product
Senzero is not a new device of PI, but the product is also developed to reduce standby power consumption. Senzero can disconnect the detection resistance connected to the high-voltage bus during the existence of AC power supply, so as to eliminate the power consumption generated by the detection resistance, thus helping to reduce the total power consumption of the system and help meet the strict requirements of energy-saving product manufacturers and energy efficiency standard regulators.
On the power factor correction (PFC) circuit of the power supply and / or in the power conversion stage, senzero device can disconnect the high-voltage detection resistance or resistance voltage divider from the DC high-voltage bus in no-load or standby mode, so as to reduce power consumption. In this way, the function blocks in the power supply can be turned off or disabled, so that the power supply saves unnecessary power consumption in incomplete operation mode.
Whether CAPZero or senzero, the principle is to realize the switching control of key devices through IC, so as to realize more stringent standby power consumption, which is also the development direction of PI. While reducing power consumption, it greatly simplifies the circuit design.
