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Switched-mode power supply

  • US 5,689,407 A
  • Filed: 04/02/1996
  • Issued: 11/18/1997
  • Est. Priority Date: 04/05/1995
  • Status: Expired due to Fees
First Claim
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1. A switched-mode power supply circuit adapted to operate in a normal operating mode and a standby mode, said switched-mode power supply circuit comprising:

  • a switch;

    a control circuit for controlling the switch, said control circuit comprising a voltage-detection means coupled to receive a power supply voltage for bringing the control circuit to an off-state if the power supply voltage has decreased to an off-level, and for bringing the control circuit to an on-state if the power supply voltage has increased to a starting level;

    a transformer having a primary winding and being incorporated in a series arrangement with the switch, said series arrangement being coupled to a DC input voltage source, the transformer further having a power supply winding coupled to the voltage-detection means, the power supply winding supplying a take-over voltage in the normal operating mode at a value at which the control circuit is in the on-state; and

    power supply means coupled to the DC input voltage source for receiving an input current for applying a power supply current to the control circuit;

    characterized in thatthe switched-mode power supply circuit further comprises means for decreasing the take-over voltage in the standby mode and, in response to a standby mode indication signal, to a value at which the control circuit may be alternately in the on-state and in the off-state.

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