Marger Johnson & McCollom, P.C.
Switching mode power supply having reduced switching losses in standby mode
 A switching mode power supply reduces switching losses during standby mode by alternately enabling and disabling the switching operation of a main switch during standby mode. When the main switch is enabled, it is forced to operate at a duty cycle which is greater than the minimum duty cycle. Therefore, the average switching frequency is reduced during standby mode, and switching losses are reduced accordingly. The switching mode power supply includes a current supply circuit which provides a first amount of current to a feedback capacitor when the main switch is operating, and a second, lower amount of current when the main switch is not operating. In standby mode, when the main switch is not operating, the reduced current from the current supply circuit causes the voltage across the feedback capacitor to be held at an artificially low level compared to normal mode, thereby causing the main switch to remain off even though the output voltage is below the setpoint level. When the output voltage finally falls low enough to cause the switch to turn on, the current from the current supply circuit returns to the normal level, and the power supply operates as if it was in normal mode. However, because the output voltage is well below the setpoint level, the switch operates at a high duty cycle, and since there is a light load in standby mode, only a few switching cycles are required to bring the output voltage back up to the setpoint level. Therefore, the average number of switching cycles in standby mode is reduced, and switching losses are reduced accordingly. 
Samsung Electronics Co., Ltd.
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inventional additional additional additional
Hyung-Mook Jeong-Yul
Choi Yun