Current-level Decision Device for a Power Supply Device and Related Power Supply Device
An current-level decision device for a power supply device includes a reception end for receiving a current sense signal, a reference voltage generator for generating a first reference voltage, a reference voltage correction unit coupled to the reference voltage generator and the reception end for adjusting the reference voltage according to variation of the current sense signal, so as to generate a second reference voltage, a comparator coupled to the reception end and the reference voltage correction unit for comparing the current sense signal and the second reference voltage to generate a comparison result, and a control unit coupled to the comparator for controlling a switch transistor of the power supply according to the comparison result.
This application claims the benefit of U.S. Provisional Application No. 61/044,908, filed on Apr. 15, 2008 and entitled “Over Current Protection Circuit with Adaptive Reference in a Power Supply Device”, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention is related to a current-level decision device for a power supply and related power supply, and more particularly, to a current-level decision device and related power supply capable of regulating a reference voltage based upon variation of a current sense signal, to make an actual voltage for activating over-current protection equal to an expected voltage for activating the over-current protection, to greatly improve the problem of time delay and voltage draft of the protection point.
2. Description of the Prior Art
Power supply is used to provide an electrical power for operating an electronic device. According to the circuit architecture, power supplies can be classified into two types, Linear and Switching. A switching power supply has benefits of small volume, light weight and high power efficiency, so it can be widely used in various kinds of electronic devices, such as mobile phone, PDA, computer and peripherals, server and network appliances.
For sustaining the normal operation of the power supply, the protection mechanism of a control circuit for protecting the power supply is a very critical part (for example, protection functions of over-voltage, over-current, and over-power), and once the overload or the short condition happens, a power supply with complete protection functions can prevent the internal components or related appliances from being damaged.
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Simply speaking, the protection mechanism mentioned above is to compare the current sense signal VCS and the reference voltage VREF, such that the primary winding current can be controlled within a proper range for the purpose of protection. However, when the current sense signal VCS is higher than the reference voltage VREF, the switch transistor Q1 cannot be turned off immediately owing to some non-ideal factors, and it will take an interval of time for the control unit 102 to turn off the switch transistor Q1. That is to say, there exists a time delay T_D, starting from the moment for the over-current condition being detected to the time for the switch transistor Q1 being turned off, and the current level right before being turned off will surpass the pre-defined level by a specific amount. In other words, the voltage level right before the over-current protection starts (abbreviated as “protection point voltage” hereafter) will be larger than the voltage level when the over-current condition is taking place. For different voltage level of the input voltage VIN, the voltage level of the protection point voltage varies accordingly.
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It is therefore a primary objective of the claimed invention to provide a current-level decision device for a power supply and the related power supply.
The present invention discloses a current-level decision device for a power supply, which comprises a reception end for receiving a current sense signal, a reference voltage generator for generating a first reference voltage, a reference voltage correction unit, coupled to the reference voltage generator and the reception end, for adjusting the first reference voltage according to variation of the current sense signal, so as to generate a second reference voltage, a first comparator, coupled to the reception end and the reference voltage correction unit, for comparing the current sense signal and the second reference voltage, to generate a first comparison result, and a control unit, coupled to the first comparator, for controlling a power switch of the power supply according to the first comparison result.
The present invention also discloses a power supply capable of preventing an over-current damage, which comprises a transformer, comprising a primary winding circuit and a secondary winding circuit, a switch transistor, coupled to the secondary winding circuit, a current sensing unit, coupled to the switch transistor, for generating a current sense signal according to current flowing through the switch transistor in the primary winding circuit, and a current-level decision device, coupled to the current sensing unit and the switch transistor, which further comprises a reception end for receiving a current sense signal, a reference voltage generator for generating a first reference voltage, an reference voltage correction unit, coupled to the reference voltage generator and the reception end, for adjusting the first reference voltage according to variation of the current sense signal, so as to generate a second reference voltage, a first comparator, coupled to the reception end and the reference voltage correction unit, for comparing the current sense signal and the second reference voltage, to generate a first comparison result, and a control unit coupled to the first comparator for controlling a power switch of the power supply according to the first comparison result.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
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Therefore, the power supply 30 can adjust the first reference voltage VREF1 via the reference voltage correction unit 404, to solve the problem of time delay, and prevent the voltage drifting problem associated with the protection points. Note that,
To sum up, the present invention regulates the reference voltage based upon variation of the current sense signal, such that the actual voltage for activating the over-current protection is identical to the expected voltage for activating the over-current protection, meanwhile, the problems of time delay and the drift of the protection point voltage can be greatly improved.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
Claims
1. A current-level decision device for a power supply comprising:
- a reception end for receiving a current sense signal;
- a reference voltage generator for generating a reference voltage;
- a reference voltage correction unit, coupled to the reference voltage generator and the reception end, for adjusting the first reference voltage according to variation of the current sense signal, so as to generate a second reference voltage;
- a first comparator, coupled to the reception end and the reference voltage correction unit, for comparing the current sense signal and the second reference voltage, to generate a first comparison result; and
- a control unit, coupled to the first comparator, for controlling a power switch of the power supply according to the first comparison result.
2. The current-level decision device of claim 1, wherein the reference voltage correction unit comprises:
- a switch unit, comprising a first end, a second end and a third end, for conducting a signal connection between the first end and the third end according to signals received by the second end;
- a first current source, coupled to the first end of the switch unit, for generating a first current;
- a second comparator, coupled to the reference voltage generator, the reception end and the second end of the switch unit, for comparing the first reference voltage and the current sense signal, to generate a second comparison result to the second end of the switch unit;
- a filtering unit, coupled to the third end of the switch unit, for performing filtering on signals of the third end of the switch unit;
- a division unit, coupled to the filtering unit, for generating a current signal according to a filtering result of the filtering unit; and
- a current to voltage conversion unit, coupled to the division unit and the first comparator, for generating the second reference voltage to the first comparator according to the current signal generated by the separation unit.
3. The current-level decision device of claim 2, wherein the switch unit is a p-type metal oxide semiconductor field effect transistor, the first end is a source, the second end is a gate, and the third end is a drain.
4. The current-level decision device of claim 2, wherein the filtering unit comprises:
- a first capacitor, having one end coupled to the third end of the switch unit, and the other end coupled to a ground;
- a resistor, coupled to the third end of the switch unit; and
- a second capacitor, having one end coupled to the resistor, and the other end coupled to a ground.
5. The current-level decision device of claim 2, wherein the division unit comprises:
- a current output end, coupled to the current to voltage conversion unit, for outputting the current signal;
- a second current source, coupled to the current output end, for generating a second current to the current output end; and
- a third current source, coupled to the current output end, the filtering unit and a ground, for generating a third current from the current output end to the ground, and adjusting the third current according to the filtering result of the filtering unit.
6. The current-level decision device of claim 2, wherein the current to voltage conversion unit is a resistor.
7. The current-level decision device of claim 2 further comprising a reset unit, having a first end coupled to the third end of the switch unit, a second end coupled to a reset signal generator, and a third end coupled to a ground, for conducting a signal connection between the first end and the third end according to signals received by the second end.
8. The current-level decision device of claim 7, wherein the reset unit is an n-type metal oxide semiconductor field effect transistor, the first end is a drain, the second end is a gate, and the third end is a source.
9. A power supply capable of preventing an over-current damage comprising:
- a transformer, comprising a primary winding circuit and a secondary winding circuit;
- a switch transistor, coupled to the primary winding circuit;
- a current sensing unit, coupled to the switch transistor, for generating a current sense signal according to current flowing through the switch transistor in the primary winding circuit; and
- a current-level decision device, coupled to the current sensing unit and the switch transistor, comprising: a reception end for receiving a current sense signal; a reference voltage generator for generating a first reference voltage; a reference voltage correction unit, coupled to the reference voltage generator and the reception end, for adjusting the first reference voltage according to variation of the current sense signal, so as to generate a second reference voltage; a first comparator, coupled to the reception end and the reference voltage correction unit, for comparing the current sense signal and the second reference voltage, to generate a first comparison result; and a control unit, coupled to the first comparator, for controlling a power switch of the power supply according to the first comparison result.
10. The power supply of claim 9, wherein the reference voltage correction unit comprises:
- a switch unit, comprising a first end, a second end and a third end, for conducting a signal connection between the first end and the third according to signals received by the second end;
- a first current source, coupled to the first end of the switch unit, for generating a first current;
- a second comparator, coupled to the reference voltage generator, the reception end and the second end of the switch unit, for comparing the first reference voltage and the current sense signal, to generate a second comparison result to the second end of the switch unit;
- a filtering unit, coupled to the third end of the switch unit, for performing filtering on signals of the third end of the switch unit;
- a division unit, coupled to the filtering unit, for generating a current signal according to a filtering result of the filtering unit; and
- a current to voltage conversion unit, coupled to the division unit and the first comparator, for generating the second reference voltage to the first comparator according to the current signal generated by the separation unit.
11. The power supply of claim 10, wherein the switch unit is a p-type metal oxide semiconductor field effect transistor, the first end is a source, the second end is a gate, and the third end is a drain.
12. The power supply of claim 10, wherein the filtering unit comprises:
- a first capacitor, having one end coupled to the third end of the switch unit, and the other end coupled to a ground;
- a resistor, coupled to the third end of the switch unit; and
- a second capacitor, having one end coupled to the resistor, and the other end coupled to a ground.
13. The power supply of claim 10, wherein the division unit comprises:
- a current output end, coupled to the current to voltage conversion unit, for outputting the current signal;
- a second current source, coupled to the current output end, for generating a second current to the current output end; and
- a third current source, coupled to the current output end, the filtering unit and a ground, for generating a third current from the current output end to the ground, and adjusting the third current according to the filtering result of the filtering unit.
14. The power supply of claim 10, wherein the current to voltage conversion unit is a resistor.
15. The power supply of claim 10 further comprising a reset unit, having a first end coupled to the third end of the switch unit, a second end coupled to a reset signal generator, and a third end coupled to a ground, for conducting a signal connection between the first end and the third end according to signals received by the second end.
16. The power supply of claim 15, wherein the reset unit is an n-type metal oxide semiconductor field effect transistor, the first end is a drain, the second end is a gate, and the third end is a source.
Type: Application
Filed: Dec 18, 2008
Publication Date: Oct 15, 2009
Inventors: Chi-Hao Wu (Taipei City), Chia-Chieh Hung (Taoyuan County)
Application Number: 12/338,907
International Classification: G05F 1/613 (20060101);