Patent ID: 7495875
Filing Date: 2009-02-24
Classification: H02M,Y02B

Abstract:
1. A power abnormal protection circuit to control OFF time series of a power supply when an abnormal voltage occurs, the power supply receiving an input power which passes through a rectification unit, a power factor correction unit and a transformer and is sent to a main power output unit and a standby power output unit, the power factor correction unit having an output capacitor to maintain an output voltage for the power factor correction unit, the power supply further including a power factor correction control unit, a pulse width modulation (PWM) unit, a standby power control unit and a power abnormal protection circuit, the power factor correction control unit controlling operation of the power factor correction unit, the PWM unit and the standby power control unit controlling respectively the main power output unit and the standby power output unit, the power abnormal protection circuit comprising: a power detection unit to receive the input power and get an input power average value and output a voltage drop signal when the input power average value decreases; a voltage drop correction unit which outputs an average voltage normal signal to the power factor correction control unit when the input power average value is normal, and is connected to the power detection unit and receives the voltage drop signal when the input voltage average value decreases to generate a reference power signal which is sent to the power factor correction control unit, and continuously receives the voltage drop signal until a first delay time has elapsed then stops sending the average voltage normal signal to set off the power factor correction control unit; a drop out detection unit which receives the voltage of the output capacitor and sets a stop voltage value, and determines whether the voltage of the output capacitor is smaller than the stop voltage value; when the voltage of the output capacitor is greater than the stop voltage value an input voltage normal signal is sent to a delay unit, a delay masking unit and the PWM unit to make the PWM unit in normal operation, the delay unit and the masking delay unit sending the input voltage normal signal to the standby power control unit and the power factor correction control unit so that they are set in normal operation; when the voltage of the output capacitor is smaller than the stop voltage value the drop out detection unit stops sending the input voltage normal signal to make the PWM unit to stop operation, the delay unit setting off the standby power control unit after a second delay time has elapsed, the delay masking unit immediately setting off the power factor correction control unit which does not start within a third delay time period so that OFF protection time series of the power supply is formed in brown out and drop out conditions.