Switch-mode power supply with control of output supply voltage and overcurrent

A switch-mode power supply having a switch-mode supply voltage conversion means for converting an input AC supply voltage into a DC supply voltage, the power supply comprising:

• a first supply voltage conversion means for controlling applying of said input AC supply voltage to said switch-mode supply voltage conversion means;
• a second supply voltage conversion means for providing a converted supply voltage corresponding to a signal applied by said first supply voltage conversion means;
• a supply voltage generating means, coupled to said second supply voltage conversion means, for providing a stabilized driving supply voltage to said control means by rectifying and smoothing said converted supply voltage provided from said second supply voltage conversion means;
• and
• a control means operated by said driving supply voltage provided from said supply voltage generating means, and having a sensing means, coupled to said second supply voltage conversion means, for simultaneously sensing a converted output supply voltage level from said second supply voltage conversion means and an output supply current according to said converted output supply voltage level, said control means sensing said converted output supply voltage and said output supply current simultaneously or separately and providing a control signal corresponding to said converted output supply voltage and said output supply current, said control means being coupled to said first supply voltage conversion means and controlling said first supply voltage conversion means according to said control signal.

A switch-mode power supply for converting an input AC supply voltage into a DC supply voltage, the power supply comprising:

• a first voltage conversion circuit including a pulse width modulation (PWM) section coupled to a first phototransistor for varying the output duty cycle of the PWM section and a switching transistor coupled to the output of the PWM section;
• a second voltage conversion circuit including a transformer coupled to an output of said switching transistor which applies an AC current to a primary winding of said transformer, said transformer having a secondary winding coupled to a first diode, said first diode having its output coupled to a second diode and a coil, said coil coupled to a capacitor and to a load;
• and
• a control circuit having an output supply voltage applied thereto from an internal power supply, a first and a second resistor for dividing the output supply voltage, a third diode having an input to which the divided voltage from the first and second resistors is applied and an output, a third and a fourth resistor for dividing the output supply voltage according to the output supply voltage supplied from the internal power supply, a fourth diode having an input to which the divided voltage from the third and fourth resistors is applied and an output, a shunt regulator connected to the outputs of the third and fourth diodes, an output of said shunt regulator coupled to a second phototransistor for sending a control signal to the first phototransistor according to an output supply voltage from the shunt regulator.