Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
1999-05-17
2001-02-13
Han, Jessica (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S049000
Reexamination Certificate
active
06188587
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to switching mode power supplies, and more particularly, to a method and apparatus for reducing switching losses during standby mode in a switching mode power supply.
2. Description of the Related Art
Conventional electronic devices such as televisions, computer monitors, VCRs, etc., operate in a normal mode in which considerable power is consumed, and in a standby mode in which little power is consumed while waiting for the normal mode to resume.
Although most electronic devices consume less power in standby mode than in normal mode, most electronic devices remain in standby mode much longer than normal mode. Consequently, most countries have recently started placing restrictions on the amount of power consumed by devices in standby mode.
Conventional electronic devices attempt to reduce power consumption in standby mode by utilizing auxiliary power supplies, reducing input power, etc. However, the implementation of these methods increases the manufacturing cost considerably.
When a switching mode power supply (“SMPS”) operates in standby mode, most of the input power is consumed by the switching losses of a main switch, which is coupled to the primary winding of a transformer, and by an integrated circuit (IC) which controls the operation of the main switch. Therefore, to reduce power consumption in standby mode, it would be desirable to reduce switching losses from the main switch in standby mode.
SUMMARY OF THE INVENTION
It is therefore, an object of the present invention to reduce the power consumption of an SMPS in standby mode.
A further object of the present invention is to provide an inexpensive technique for reducing the power consumption of an SMPS in standby mode.
Another object of the present invention is to reduce the switching losses of an SMPS in standby mode.
To accomplish these and other objects, an SMPS in accordance with the present invention 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, only a few switching cycles are required to maintain the output voltage, so the average switching frequency is reduced during standby mode, and switching losses are reduced accordingly.
One aspect of the present invention is an SMPS which includes a current supply circuit that supplies a first amount of current when the main switch is enabled (i.e., is switching), and a second, lower amount of current when the main switch is disabled (i.e., has stopped switching). The current from the current supply circuit is used to charge a feedback capacitor, thereby generating a feedback voltage across the capacitor. A switch driver controls the operation of the main switch in response to the feedback voltage. A higher feedback voltage causes the switch to operate at a higher duty cycle. When the feedback voltage drops below a level that corresponds to the minimum duty cycle, the main switch stops switching.
Feedback control of the power supply output voltage is provided by a dependent current source which is coupled in parallel with the feedback capacitor so as to divert current from the current supply circuit away from the feedback capacitor. As the output voltage increases, the current flow through the dependent current source increases, and more current is diverted from the feedback capacitor. This causes the feedback voltage to decrease, and consequently, the duty cycle of the main switch decreases.
During normal mode, the power supply operates in a condition of equilibrium in which the current flowing through the dependent current source balances the first, higher amount of current from the current supply circuit, thereby maintaining the feedback voltage at a level required to maintain the output voltage at a predetermined level.
Standby mode begins when the load decreases rapidly. This causes the output voltage to momentarily rise higher than the predetermined output level because the main power section tends to provide constant power. As the output voltage rises, the current through the dependent current source increases rapidly, thereby diverting additional current from the feedback capacitor and causing the feedback voltage to fall below the level corresponding to the minimum duty cycle. This causes the main switch to stop switching, which in turn, causes the current supply circuit to begin supplying the second, lower amount of current, and also causes the output voltage to begin decreasing.
With the current supply circuit operating at the second, lower current level, the dependent current source diverts enough current from the feedback capacitor to maintain the feedback voltage below the level corresponding to the minimum duty cycle, even though the output voltage is below the predetermined level. Therefore, the main switch remains off.
As the output voltage continues to fall, the current through the dependent current source decreases until it falls below the second, lower current level from the current supply circuit, and the feedback capacitor then begins charging. This causes the feedback voltage to increase, and when it reaches the level corresponding to the minimum duty cycle, the main switch begins operating again. The switching operation of the main switch causes the current supply circuit to begin sourcing current at the first, higher level again, which consequently causes the feedback voltage across the feedback capacitor to rise rapidly, so the main switch operates at a duty cycle that is greater than the minimum duty cycle. The output voltage rises rapidly because there is only a small load on the power supply during standby mode even though the switch is operating at a relatively high duty cycle.
The increasing output voltage causes the current flowing through the dependent current source to increase, so more current from the current supply circuit is diverted from the charging capacitor. The feedback voltage is pulled below the level corresponding to the minimum duty cycle, so the main switch stops switching. The power supply continues to alternately start and stop the switching operation of a main switch as long as it remains in standby mode.
Another aspect of the present invention is a switching a switching mode power supply comprising: a main power section having a main switch for providing output power to a load in a normal mode and a standby mode; a switch driver coupled to the main switch for controlling the main switch responsive to a feedback signal, wherein the switch driver disables the main switch when the feedback signal reaches a level corresponding to a minimum duty cycle; a feedback circuit coupled to the switch driver for generating the feedback signal responsive to the output power; and a feedback manipulation circuit coupled to the feedback circuit for manipulating the feedback signal during standby mode to disable the main switch during a first period in standby mode and to force the main switch to operate at a duty cycle which is greater than the minimum duty cycle during a second period of standby mode.
REFERENCES:
patent: 4937728 (1990-06-01), Leonardi
patent: 5689407 (1997-11-01), Marinus et al.
patent: 5812383 (1998-09-01), Majid et al.
Choi Hyung-Mook
Yun Jeong-Yul
Han Jessica
Marger & Johnson & McCollom, P.C.
Samsung Electronics Co,. Ltd.
LandOfFree
Switching mode power supply having reduced switching losses... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Switching mode power supply having reduced switching losses..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Switching mode power supply having reduced switching losses... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2584459