Personal computer power supply with low-power standby mode activated by secondary side protection circuit

A power supply for a computer having at least one energy demanding component requiring a first DC voltage for operation thereof, said power supply comprising:

• an input line for coupling said power supply with an AC main;
• an output line for coupling said power supply with said at least one energy demanding component;
• a transformer having a primary side coupled to said input line and a secondary side coupled to said output line;
• a charging circuit coupled between said secondary side of said transformer and said output line, said charging circuit charging whenever said primary side of said transformer is connected to said input line;
• an optical switch having an optical transmitter and an optical receiver, said optical transmitter requiring a second DC voltage, lower than said first DC voltage, for operation thereof and coupled to said charging circuit to receive said second DC voltage;
• a short circuit protection circuit coupled to said charging circuit, said output line and said optical receiver, said short circuit protection circuit detecting short circuits on said output line;
• a pulse width modulator having a first input coupled to an output of said optical receiver and an output;
• and
• a transformer switch having an input coupled to said output of said pulse width modulator;
• said optical transmitter transmitting a signal to said optical receiver in response to said short circuit protection circuit detecting a short circuit on said output line;
• said pulse width modulator receiving said signal at said first input and selectively issuing, at its output, a pulse sequence which alternates between first and second states at said first frequency if said short circuit protection circuit has not detected said short circuit or at said second frequency if said short circuit protection circuit has detected said short circuit;
• said transformer switch selectively connecting or disconnecting said primary side of said transformer with said input line at each change between said first and second states;
• whereby said secondary side of said transformer provides sufficient DC voltage to operate said at least one energy demanding component when said short circuit protection circuit has not detected said short circuit and provides sufficient DC voltage to operate said optical transmitter but insufficient DC voltage to operate said at least one energy demanding component when said short circuit protection circuit has detected said short circuit.

A power supply for a computer having at least one energy demanding component, said power supply comprising:

• a rectifier connected to receive an AC voltage and provide rectified power and ground voltages therefrom;
• a transformer having a primary winding and a secondary winding which is inductively coupled to said primary winding;
• a switching transistor operatively connected to said primary winding and to one of said rectified voltages, to switchably drive said primary winding;
• a control circuit connected to drive said switching transistor selectably in first and second selectable modes of operation;
• a switch which is operatively connected, through a first optical isolation element, to select said first or second mode of operation of said control circuit;
• said first optical isolation element having a transmitter side which is powered from said secondary winding of said transformer, and not from said primary winding of said transformer;
• said switch not being powered from said primary winding of said transformer;
• wherein in said first mode, but not in said second mode, said switching transistor is driven so that said transformer transfers sufficient power to operate said energy demanding component;
• and wherein, in said second mode, said switching transistor is driven so that said transformer transfers sufficient power to operate said first optical isolation element, but not to power said energy demanding component;
• a feedback circuit connected, through a second optical isolation element, to provide an error signal to said control circuit;
• wherein said control circuit, in said first mode, varies the operation of said switching transistor in accordance with said error signal;
• and
• a short circuit protection circuit, connected to drive said first optical isolation element to therethrough place said control circuit into said second mode when said short circuit protection circuit detects a short circuit on said output line.

A personal computer, comprising:

• a computer subsystem having at least one energy demanding component;
• and a power supply having an input line for coupling to an AC main and an output line coupled to said at least one energy demanding component, said power supply receiving, at said input line, a high voltage AC power from said AC main and providing, at said output line, a first DC voltage to said energy demanding component;
• said power supply further comprising:
• a transformer having a primary winding and a secondary winding which is inductively coupled to said primary winding;
• a switching transistor operatively connected to said primary winding and to one of said rectified voltages, to switchably drive said primary winding;
• a control circuit connected to drive said switching transistor selectably in first and second selectable modes of operation;
• a switch which is operatively connected, through a first optical isolation element, to select said first or second mode of operation of said control circuit;
• said first optical isolation element having a transmitter side which is powered from said secondary winding of said transformer, and not from said primary winding of said transformer;
• said switch not being powered from said primary winding of said transformer;
• wherein in said first mode, but not in said second mode, said switching transistor is driven so that said transformer transfers sufficient power to operate said energy demanding component;
• and wherein, in said second mode, said switching transistor is driven so that said transformer transfers sufficient power to operate said first optical isolation element, but not to power said energy demanding component;
• a feedback circuit connected, through a second optical isolation element, to provide an error signal to said control circuit;
• wherein said control circuit, in said first mode, varies the operation of said switching transistor in accordance with said error signal;
• and
• a fan protection circuit, connected to detect cooling fan failure, and to drive said first optical isolation element to therethrough place said control circuit into said second mode when said fan protection circuit detects a failure of a cooling fan.

A personal computer, comprising:

• a computer subsystem having at least one energy demanding component;
• and a power supply having an input line for coupling to an AC main and an output line coupled to said at least one energy demanding component, said power supply receiving, at said input line, a high voltage AC power from said AC main and providing, at said output line, a first DC voltage to said energy demanding component;
• said power supply further comprising:
• a transformer having a primary winding and a secondary winding which is inductively coupled to said primary winding;
• a switching transistor operatively connected to said primary winding and to one of said rectified voltages, to switchably drive said primary winding;
• a control circuit connected to drive said switching transistor selectably in first and second selectable modes of operation;
• a switch which is operatively connected, through a first optical isolation element, to select said first or second mode of operation of said control circuit;
• said first optical isolation element having a transmitter side which is powered from said secondary winding of said transformer, and not from said primary winding of said transformer;
• said switch not being powered from said primary winding of said transformer;
• wherein in said first mode, but not in said second mode, said switching transistor is driven so that said transformer transfers sufficient power to operate said energy demanding component;
• and wherein, in said second mode, said switching transistor is driven so that said transformer transfers sufficient power to operate said first optical isolation element, but not to power said energy demanding component;
• a feedback circuit connected, through a second optical isolation element, to provide an error signal to said control circuit;
• wherein said control circuit, in said first mode, varies the operation of said switching transistor in accordance with said error signal;
• and
• a short circuit protection circuit, connected to drive said first optical isolation element to therethrough place said control circuit into said second mode when said short circuit protection circuit detects a short circuit on said output line.