Abstract: A multiple-sampling circuit is proposed for measuring a voltage signal and a discharge time of a transformer. Sampling signals are used for generating hold voltages by alternately sampling the reflected voltage from the transformer. A buffer amplifier generates a buffer voltage from the higher voltage of hold voltages. A sampling switch periodically conducts the buffer voltage to produce a voltage-feedback signal. The voltage-feedback signal is proportional to an output voltage of the switching circuit. A threshold signal added to the reflected voltage signal produces a level-shift reflected signal. A discharge-time signal is generated as the switching signal is disabled. The discharge-time signal is disabled once the level-shift signal is lower than the voltage-feedback signal. The pulse width of the discharge-time signal is therefore correlated to the discharge time of the transformer. The sampling signals are enabled to generate hold voltages only when the discharge-time signal is enabled.

Abstract: A switching mode power supply is described. The switching mode power supply includes a power supply unit, a mode setting unit, a feedback circuit, and a switching controller. The switching controller controls a main switch to carry out a switching operation at a predetermined duty according to feedback voltage charged in a first capacitor in the normal operation mode, and controls the main switch to repeat a switching on state and a switching off state in the standby mode. The current inputted to the switching controller varies with the operation mode. Accordingly, the minimum voltage for operating the switching controller can be maintained even if output voltage is decreased in the standby mode, and unnecessary power consumption in the switching controller can be reduced.

Abstract: A power converter delivers electrical power from an electrical power source to a load according to a plurality of operation modes corresponding to different levels of input voltage or output current. The power converter comprises a power stage for delivering the electrical power from the power source to the load, a switch in the power stage that electrically couples or decouples the load to the power source, and a switch controller coupled to the switch for controlling the on-times and off-times of the switch according to the plurality of operation modes. Each of the operation modes correspond to associated ranges of at least one of an input voltage to the power converter and an output current from the power converter, where the associated ranges are different for each of the operation modes.

Abstract: A flyback converter detects an output voltage at the primary coil without using a photo coupler and provides an essentially constant output voltage independent of the load size, thereby minimizing the number of additional coils used in the transformer circuit to realize simple construction and providing accurate power control. In one embodiment, the flyback converter includes: a transformer for changing an input voltage to a predetermined level according to a winding ratio; an output unit for rectifying the voltage signal output from the transformer into a DC signal to drive a load; a switch coupled to the primary coil of the transformer for controlling the on/off state of a power at the primary coil according to a switching control signal; a feedback unit generating a feedback signal and detecting a current of the switch to correct the feedback signal; and a switching controller operating according to the feedback signal.