Design principle of ultra-low standby energy consumption with no-load energy consumption less than 16mW

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Overview:
The NCP1246 from ON Semiconductor has a no-load energy consumption of less than 16 mW. The low standby energy solution using the NCP1246 + NCP4354 can easily meet the ENERGY STAR requirements for a 65 W power adapter and can achieve 20 Very low standby power consumption below mW.

1 Introduction AC-DC power adapters are used in a wide variety of applications, such as notebook computers, LCD monitors, and printers. These power adapters are in idle-nosed mode for a long time and are used in large quantities, resulting in huge power losses. The US "Energy Star" standard has clear requirements for the no-load energy consumption of such external power supplies (EPS), that is, the AC-DC EPS no-load energy consumption below 50 W is less than 0.3 W; the power is between 50 W and 250. W's AC-DC EPS no-load energy consumption should not exceed 0.5 W. At present, the best no-load energy consumption performance of the AC-DC adapter with better performance on the market is about 30 mW. The latest adaptation requirement is no-load energy consumption below 30 mW, which requires lowering the output voltage (Vout) to reduce no-load parasitic energy consumption; it also allows the primary-side controller to be turned off to further reduce energy consumption. In this way, during no-load, the adapter output voltage can be automatically reduced, and the output voltage can jump between 19 V and 2.5 V to reduce the regulation power consumption.

2 Low standby energy consumption scheme consisting of two devices
The NCP1246 is a primary side controller that meets the above requirements. The NCP4354 is a secondary-side controller with no-load condition detection and can be turned off by the optocoupler NCP1246. It can replace the TL431 with a current consumption of less than 100 μA. The NCP4354 can detect no-load and add no-load detection circuitry in the device. Compare the "Output Voltage" (Vout) with "No load info". In the high switching frequency or high frequency standby hopping cycle mode, both are equal to the load; in the no-load and very low-frequency hopping cycle modes, the two are different; under small capacitance and constant load conditions, the output voltage remains constant, and "" The no-load information "goes down. This eliminates the need for power detection, has no effect on energy efficiency and safety, and has a small number of external components that are easy to adjust.
Figure 1 is the process of entering the shutdown mode. When the output current is gradually reduced from full load, the primary controller will switch from normal operation to skip cycle operation, and the output voltage and the no-load information are basically close; when the input is very low-cycle or off mode, the output no-load voltage will be Below the output voltage, a very low load or no load is detected and the shutdown mode is activated.

Figure 1: The process of entering the shutdown mode When the output voltage is greater than the "no-load information", the ON/OFF optocoupler turns off the primary-side controller; before the primary-side controller restarts, the output voltage is allowed to decrease to 2.5. V. This allows very low frequency skip cycle modes with frequencies as low as 0.01333 Hz (75 s skip cycle time).

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