US 6,188,587 B1 · Switching mode power supply having reduced switching losses in standby mode

Abstract

A switching mode power supply reduces switching losses during standby mode by alternately enabling and disabling the switching operation of a main switch during standby mode. When the main switch is enabled, it is forced to operate at a duty cycle which is greater than the minimum duty cycle. Therefore, the average switching frequency is reduced during standby mode, and switching losses are reduced accordingly. The switching mode power supply includes a current supply circuit which provides a first amount of current to a feedback capacitor when the main switch is operating, and a second, lower amount of current when the main switch is not operating. In standby mode, when the main switch is not operating, the reduced current from the current supply circuit causes the voltage across the feedback capacitor to be held at an artificially low level compared to normal mode, thereby causing the main switch to remain off even though the output voltage is below the setpoint level. When the output voltage finally falls low enough to cause the switch to turn on, the current from the current supply circuit returns to the normal level, and the power supply operates as if it was in normal mode. However, because the output voltage is well below the setpoint level, the switch operates at a high duty cycle, and since there is a light load in standby mode, only a few switching cycles are required to bring the output voltage back up to the setpoint level. Therefore, the average number of switching cycles in standby mode is reduced, and switching losses are reduced accordingly.

Claims25

Dependent claims

A method for controlling a switching mode power supply having a main switch for providing power to a load in a normal mode and a standby mode, wherein the switch has a minimum duty cycle, the method comprising:

generating a feedback signal responsive to the output voltage of the power supply;
controlling the output voltage of the power supply by controlling the duty cycle of the main switch responsive to the feedback signal;
alternately enabling and disabling the operation of the main switch during standby mode;
and
operating the main switch at a duty cycle that is greater than the minimum duty cycle when the main switch is enabled during standby mode;
wherein enabling the operation of the main switch during standby mode comprises enabling the operation of the main switch responsive to the output voltage of the power supply.

3 more elements

A switching mode power supply comprising:

a main power section for supplying power to a load during a normal mode and a standby mode;
switch drive means for controlling the main power section responsive to a feedback voltage;
feedback means for generating the feedback voltage responsive to the output voltage of the load;
and
current supply means for supplying a first current to the feedback means during a first period in standby mode and supplying a second current to the feedback means during a second period in standby mode;
wherein the main power section executes a switching operation at a first duty cycle in normal operation mode, stops switching operation during the first period, and executes switching operation at a second duty cycle during the second period;
wherein the feedback means includes:
a capacitor, wherein the feedback voltage is generated across the capacitor;
and
means for diverting current from the capacitor responsive to the output voltage of the load;
wherein the current supply means provides the first current or the second current to the feedback means responsive to a winding voltage applied to a secondary winding coupled to the primary winding;
and
wherein the current supply means includes:
a current source;
a first diode having an anode connected to the current source and a cathode connected to one terminal of the first capacitor in the feedback means;
second and third diodes, each having an anode connected to the current source;
first and second resistors connected in series with a cathode of the second diode, wherein a node voltage between the first and the second resistors is input to the switch drive means;
a third resistor and a third capacitor, each having one terminal connected to a cathode of the third diode;
a zener diode having a cathode connected to the cathode of the third diode;
a fourth resistor having one terminal connected to the cathode of the zener diode;
and
a fourth diode having a cathode connected to the other terminal of the fourth resistor and an anode to which the winding voltage is applied.

19 more elements

A switching mode power supply comprising:

a main power section for supplying power to a load during a normal mode and a standby mode;
switch drive means for controlling the main power section responsive to a feedback voltage;
feedback means for generating the feedback voltage responsive to the output voltage of the load;
and
current supply means for supplying a first current to the feedback means during a first period in standby mode and supplying a second current to the feedback means during a second period in standby mode;
wherein the main power section executes a switching operation at a first duty cycle in normal operation mode, stops switching operation during the first period, and executes switching operation at a second duty cycle during the second period;
wherein the feedback means includes:
a capacitor, wherein the feedback voltage is generated across the capacitor;
and
means for diverting current from the capacitor responsive to the output voltage of the load;
wherein the current supply means provides the first current or the second current to the feedback means responsive to a winding voltage applied to a secondary winding coupled to the primary winding;
and
wherein the current supply means comprises:
a current source;
a first diode having an anode connected to the current source and a cathode connected to one terminal of the first capacitor in the feedback means;
a second diode having an anode connected to the current source;
first and second resistors connected in series with the cathode of the second diode, wherein a node voltage between the first and the second resistors is input to the switch drive means;
a third diode having an anode to which the winding voltage is applied;
a third resistor having a cathode connected to the other terminal of the third resistor;
a zener diode having a cathode connected to the other terminal of the third resistor;
fourth and a fifth resistors each having one terminal connected to the other terminal of the third resistor;
a sixth resistor having one terminal connected to the other terminal of the fourth resistor;
and
a bipolar transistor having a base connected to a node between the fourth resistor and the sixth resistor, a collector connected to the fifth resistor and an emitter connected to one terminal of the capacitor in the feedback means.

21 more elements

Dependencies are inferred from the claim text.

Switching mode power supply having reduced switching losses in standby mode

Life of this patent

Switching mode power supply having reduced switching losses in standby mode

Life of this patent

Abstract

Claims25