Patent Application
20110110121
1. Technical Field
The present disclosure relates to power supply technology, and more particularly, to a switching mode power supply circuit.
2. Description of Related Art
Power supply circuits supply voltage signals to enable operation of electronic devices.
Switching mode power supply circuits provide operating power to liquid crystal displays (LCD).
The first input 11 and the second input 12 are electrically coupled to a live wire and a neutral wire of a commercial power outlet (not shown) respectively, and cooperatively receive a primary alternating-current (AC) voltage signal output by the commercial power outlet.
The full-wave rectifier 13 is electrically coupled to the first and second inputs 11 and 12, and in particular, to the first input 11 via a thermal resistor 16. The full-wave rectifier 13 is adapted to convert the primary AC voltage signal to a direct current (DC) voltage signal. An output of the full-wave rectifier 13 is further electrically coupled to the filter capacitor 17, adapted to filter and stabilize the DC voltage signal and provide the filtered DC voltage signal to the transformer 18. The transformer 18 is adapted to convert the filtered DC voltage signal to a power voltage signal with a desired value in a switching manner, and output the power voltage signal to a load circuit (not shown).
Resistance of the thermal resistor 16 decreases with an increase rise in temperature. When the power supply circuit 10 is powered on and starts to function, temperature of the thermal resistor 16 is low, and resistance of the thermal resistor 16 relatively high, such only limited current flows to the filter capacitor 17. In this configuration, the filter capacitor 17 is prevented from damaged by current surge. That is, the thermal resistor 16 protects the filter capacitor 17 from damaged at power up. Thereafter, the power supply circuit 10 enters a normal working state, and temperature of the thermal resistor 16 increases due to current therethrough, and resistance of the thermal resistor 16 is decreased.
During normal operations, however, the resistance of the thermal resistor 16 maintains a certain positive value, for example, 3Ω (ohms). Such positive resistance means that the thermal resistor 16 needs to consume some power energy, this may further increase power consumption of the power supply circuit 10.
What is needed, therefore, is a power supply circuit that can overcome the described limitations.
The components in the drawings are not necessarily drawn to scale, the emphasis instead placed upon clearly illustrating the principles of at least one embodiment. In the drawings, like reference numerals designate corresponding parts throughout the various views.
Reference will now be made to the drawings to describe certain exemplary embodiments of the present disclosure in detail.
The first input 21 and the second input 22 are electrically coupled to a live wire and a neutral wire of a commercial power outlet (not shown) respectively, and cooperatively receive a primary alternating-current (AC) voltage signal.
The protection circuit 291 and the anti-interference circuit 292 are electrically coupled between the inputs 21, 22 and the rectifying circuit 23. The protection circuit 291 prevents hazards occurring when the power supply circuit 20 is broken. In one embodiment, the protection circuit 29 may include a first safety capacitor C1, a second safety capacitor C2, a third safety capacitor C3, and a fuse wire S1. The first safety capacitor C1 is electrically coupled between the live wire and the ground, and the second safety capacitor C2 is electrically coupled between the neutral wire and the ground, in particular, both of the first safety capacitor C1 and the second safety capacitor C2 can be Y-type safety capacitors. The third safety capacitor C3 can be an X-type safety capacitor, and is electrically coupled between the live wire and the neutral wire. The fuse wire S1 is electrically coupled into the live wire, and between the first safety capacitor C1 and the third safety capacitor C3.
The anti-interference circuit 292 is adapted to inhibit electro-magnetic interference (EMI) in the power supply circuit 20. The anti-interference circuit 292 may be a common mode choke which includes a first coil and a second coil. The first and second coils are electrically coupled into the live wire and the neutral wire respectively.
The rectifying circuit 23 is adapted to convert the primary AC voltage signal into a direct current (DC) voltage signal. In one embodiment, the rectifying circuit 23 may be a full-wave rectifier, for example, a bridge type rectifier. An output of the rectifying circuit 23 is further electrically coupled to the filter member 24.
The at least one filter member 24 is adapted to filter and stabilize the DC voltage signal, and provide the filtered DC voltage signal to the transformer 25. In one embodiment, the at least one filter member 24 may include a filter capacitor, which is grounded via the current-limiting module 26.
The current-limiting module 26 is adapted to limit current through the filter capacitor 24 when the power supply circuit 20 is powered on. In one embodiment, the current-limiting module 26 can be a current-limiting resistor having a pre-determined resistance, for example, about 100Ω. In an alternative embodiment, the current-limiting module 26 may include a plurality of current-limiting resistors connected in series between the at least one filter member and the ground, or include other current-limiting elements connected in other manners as needed.
The transformer 25 is adapted to transform the filtered DC voltage signal, in a switching manner, to a main power voltage signal with a desired value, and output the main power voltage signal to a load circuit (not shown). In one embodiment, the transformer 25 may further generate an inner power voltage signal for the control circuit 27 and the switching circuit 28.
In particular, the transformer may include a first winding 251, a second winding 252, and a third winding 253. One end of the first winding 251 receives the filtered DC voltage signal, and the other end of the first winding 251 is electrically coupled to the switching circuit 28. Due to a switching operation performed by the switching circuit 28, a main power voltage signal is induced by the second winding 252, and an inner power voltage signal is induced by the third winding 253. The main power voltage signal is further provided to the load circuit after being rectified and filtered, and the inner power voltage signal is provided to the control circuit 27.
The control circuit 27 is adapted to enable the current-limiting module 26 when the power supply circuit 20 is powered on, and disable the current-limiting module 26 when the power supply circuit 20 is in a normal working state. In one embodiment, the control circuit 27 includes a switch member 271, a voltage-dividing module 277, a diode 276, and a capacitor 275.
A positive end of the diode 276 receives the inner power voltage signal, and a negative end of the diode 276 is grounded via the voltage-dividing module 277. The voltage-dividing module 277 is adapted to convert the inner power voltage signal to a bias voltage by performing a voltage division operation on the inner power voltage signal, and provides the bias voltage to the switch member 271. In this manner, the bias voltage may server as a control signal, and controls a working state of the switch member 271. In the illustrated embodiment, the voltage-dividing module 277 includes a first resistor 273 and a second resistor 272 connected in series. One end of the capacitor 275 is electrically coupled to a node between the first resistor 273 and the second resistor 272, and the other end of the capacitor 275 is grounded.
The switch member 271 includes a control terminal and two connecting terminals. The control terminal is configured to receive the control signal, and is electrically coupled to a node between the first resistor 273 and the second resistor 272. The two connecting terminals are respectively connected to two ends of the current-limiting resistor 26. The switch member 271 may control a connection between the two connecting terminals according to the control signal. The switch member 271 may be a transistor, for example, a metal oxide semiconductor (MOS) transistor, or a bipolar junction transistor (BJT). In the illustrated embodiment, the switch member 271 is an N-channel MOS transistor, which includes a gate electrically coupled to the node between the first resistor 273 and the second resistor 272 via a third resistor 274, a drain electrode electrically coupled to an end of the current-limiting module 26, and a source electrode electrically coupled to the other end of the current-limiting module 26.
In operation, when the power supply circuit 20 is powered on, the inner power voltage signal is induced by the third winding 253, and provided to the control circuit 27. Due to charging of the capacitor 275, a value of the bias voltage generated by the voltage-dividing module 277 is restrained and increases slowly, and before the bias voltage reaches a pre-determined threshold value sufficient to switch the switch member 271 on, the switch member 271 remains off. Thus, the current-limiting module 26 is enabled to limit current through the filter capacitor 242, such that the filter capacitor 24 is prevented from damage by intolerance current. When the charging operation of the capacitor 275 is substantially finished, the bias voltage reaches the pre-determined threshold value, thus, the switch member 271 is switched on and the current-limiting module 26 is shorted and disabled. Accordingly, the power supply circuit 20 enters a normal working state, and stably provides the main power voltage signal to the load circuit. Moreover, when the power supply circuit 20 is shut down, the capacitor 275 can be discharged through the second resistor 272, as such, it can be ensured that the current-limiting module 26 is ready to function the next time the power supply circuit 20 is powered on.
In the configuration disclosed, when the power supply circuit 20 is in normal working state, the current-limiting module 26 is shorted and thereby substantially consumes no energy. Thus, overall power consumption of the power supply circuit 20 is reduced.
It is to be further understood that even though numerous characteristics and advantages of a preferred embodiment have been set out in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only; and that changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200910309445.7 | Nov 2009 | CN | national |
