Industry news

2016August

How to reduce the standby power consumption of LED lighting switching power supp

From: www.szbako.com Data:08/08/2016

now, LED lights switch power consumption has become the focus of widespread concern in the LED industry. In the application of LED lighting, special to the standby power supply auxiliary power level does not apply, because lighting applications in the course of work there is no standby condition, but the lighting power supply switching power supply even still in power consumption under the condition without lamp or lamp is damaged. Therefore, this paper discusses how to introduce a simple auxiliary circuit to reduce the standby power consumption. Compared with ordinary light source, LED has the characteristics of high efficiency, environmental protection and long service life, so they are becoming the main solution to reduce the energy consumption of indoor and external lighting. Design for lighting power supply switching power supply should also have high efficiency, in order to adapt to the LED lamp energy saving characteristics. In addition to the normal working process with high power conversion efficiency, the standby power consumption of the switching power supply has become the focus of the LED industry. In the near future, the standby power consumption is expected to be adjusted to 300mW or even below 1W. However, in the application of LED lighting, the auxiliary power level of the standby power supply is not applicable, mainly because there is no standby condition during the working period of the lighting application. However, switching power supply for the light bulb is connected with the power grid even in the condition of no lamp or lamp damaged. This is the main reason for the level of standby power in lighting applications.

in the empty office building, the standby power consumption of the poor performance of the lighting system is not environmentally friendly, this paper discusses how to introduce a simple auxiliary circuit to reduce the standby power consumption. The proposed circuit can achieve a power factor correction (PFC) level of the intermittent operation, the PFC level is required to reduce the power consumption of the lighting switch power. In order to evaluate the proposed circuit, we designed a rated power of two 120W switching power supply, in the broad input voltage range can be obtained below the 1W standby power consumption.

two class configuration

due to the rated power and improve the power factor of demand, led streetlights switching power supply usually use two class configuration, it by the first level of PFC module and the second level downstream DC-DC converter. The critical conduction mode (CRM) is a suitable control scheme for the PFC level in the medium power range of about 100W. In the rated power range, a quasi resonant flyback topology is usually used in the downstream DC-DC converter. Highly integrated FAN6300 pulse width modulation (PWM) controller with an internal trough voltage detector, can guarantee the power supply system in broad line voltage range in the quasi resonant state, and reduce the switching losses and the power MOSFET drain pole of the switch voltage minimized.

in order to maximize reduce standby power consumption and improve the light load efficiency, proprietary green mode function provides off time modulation (off time), in order to reduce the switching frequency, and the implementation of the extension of the trough voltage switching, guarantee on MOSFET switch leakage source voltage is maintained at the lowest level. Using this characteristic, the second DC-DC level can be used in batch mode without load, and it can obtain the ideal standby power consumption characteristics. Most of the existing PFC controller and departed to intermittent work function, mainly because the PFC stage initially for consumer applications and display applications, and in those with PFC and DC provides auxiliary power supply voltage source is separated. In LED lighting applications, usually does not use the auxiliary power level, therefore, should turn off the PFC level, otherwise the standby power consumption can not be less than 1W.

PFC level intermittent operation mode

in the two switch power supply, should turn off the PFC level, in order to meet the requirements of standby power consumption regulation. The main reason for the shutdown of the PFC level is that most PFC controllers have no intermittent work (operation Burst-). If the PFC controller does not support the intermittent operation mode, the PFC level will work continuously even in the absence of load conditions. Therefore, for the design of the two stage switching power supply with the existing PFC controller, it is the only feasible method to turn off the PFC level. However, there will be a large impact current when restarting the PFC level, and lead to the increase of the voltage or current stress on the power switch, such as MOSFET. In addition, it will lead to LED lights flashing in the constant current work. The industry needs to find a new way to meet the regulatory requirements of standby power consumption, while avoiding the above problems. A possible way to solve the side effects of PFC level is PFC class using intermittent operation mode.

suggested using a simple auxiliary circuit, PFC and quasi resonant reverse forward DC-DC converter synchronization, because when the DC-DC converter is started to work intermittently, the PFC stage can also enter the intermittent mode. Once the second stage flyback converter to end the intermittent mode of operation, PFC will immediately quit the intermittent operation mode. Figure 1. Working principle of the auxiliary circuit. The bias power supply of PFC is controlled by the feedback of quasi resonant flyback DC-DC converter.

Figure 1: to achieve the PFC level intermittent operation of the circuit
in no load condition, when the feedback voltage of the flyback converter is decreased, the power supply voltage of the PFC level is cut off, the PFC controller stops working. Figure 2 shows the load from full load to no load, and then to the full load process of working waveform. Once the second stage flyback converter is in batch operation, the PFC stage enters the intermittent operation mode, and the intermittent operation mode is synchronized with the flyback converter. Through the implementation of intermittent work on the PFC level, you can eliminate the potential problems caused by a large surge current, and a significant reduction in standby power consumption.

to the intermittent working of the evaluation of the PFC stage, using FAN7930 critical pass mode PFC controller, with intermittent working function of quasi resonant flyback controller FAN6300A and the proposed PFC control circuit, design of the A for LED streetlights 120W 48V/2.5A LEB-016 demo line board. As shown in Figure 2, the proposed circuit works well. Table 1 shows the measured value of standby power consumption at various input line voltages. Can prove that: in a wide range of input, the standby power consumption can be reduced by more than 80%. The standby power consumption of less than 0.3W can be obtained at the high line input voltage.

shown in Figure 2: in the intermittent working (left) and return to full load (pictured right)




this is a simple but very effective to improve lighting switch power source standby power consumption method. The proposed circuit can make the PFC stage and the second stage DC-DC converter synchronized to the intermittent operation. This method eliminates the current problems associated with the shutdown and restart of the PFC class. The proposed circuit can effectively reduce the standby power consumption. Through the evaluation of circuit boards, in a wide range of input voltage, the standby power consumption is less than 1W. The proposed method is very attractive for lighting applications without standby power conditioning modules.

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