CN101122730A - Power factor correction circuit and associated projector - Google Patents

Abstract

A power factor correction circuit, comprising: the boost conversion unit comprises a switching element and an inductance element and is used for converting the rectified voltage into direct current output voltage; the adjusting unit comprises a thermistor with a positive temperature coefficient, and is used for generating an adjusting signal according to the current temperature and the direct current output voltage; and the control unit is used for controlling the working period of the switching element according to the adjusting signal so as to adjust the voltage difference between the direct current output voltage and the rectified voltage.

Description

Power factor correction circuit and associated projector

technical field

The invention relates to a power supply circuit, in particular to a power supply circuit applied to a projector.

Background technique

A common display device, such as a cathode ray tube (CRT) display or a liquid crystal display (LCD), can only display images of 30-40 inches at most, and is difficult to carry due to its huge size. Because the projector can display images of tens or hundreds of inches and is small in size, it is superior to cathode ray tube displays or liquid crystal displays in terms of entertainment purposes and business briefings. .

Traditional projectors include a power factor correction circuit (power factor correction circuit) for supplying a fixed DC voltage independent of temperature to the DC/DC converter and the lamp. Since the power factor control circuit provides most of the power of the entire projector, if the efficiency of the power factor control circuit can be improved and the power loss can be reduced, the thermal design of the projector can be further reduced. effort.

Contents of the invention

The present invention provides a power factor correction circuit, comprising: a step-up conversion unit, including a switch element and an inductance element, for converting the rectified voltage into a DC output voltage; an adjustment unit, including a thermistor with a positive temperature coefficient, The adjustment unit is used to generate an adjustment signal for the current temperature and the DC output voltage; and the control unit is used for controlling the duty cycle of the switch element according to the adjustment signal, so as to adjust the voltage difference between the DC output voltage and the rectified voltage.

The present invention also provides a power factor correction circuit, including: a boost conversion unit, including a switch element and an inductance element, for converting the rectified voltage into a DC output voltage according to the formula, the formula is $V_o=\frac{1}{(1-\mathrm{D.}\left(t\right))}\×V\left(t\right),$ Among them, V(t) represents the rectified voltage, V _O represents the DC output voltage, and D(t) represents the duty cycle of the switching element, where V(t) and D(t) are both functions of time, and V(t) It is the rectified voltage, and D(t) will change accordingly because the control unit detects the V(t) voltage; the voltage divider circuit includes a thermistor with a positive temperature coefficient, and the voltage divider circuit is used according to the current temperature and the DC output voltage to generate an adjustment signal; and the control unit is used to shorten the duty cycle of the switch element to reduce the DC output voltage when the temperature of the switch element or the inductance element rises according to the adjustment signal.

The present invention also provides a projector, including the aforementioned power factor correction circuit, a light bulb, and a ballast, used for coupling the DC output voltage, and used for starting the lighting of the light bulb.

In order to make the above-mentioned and other objects, features, and advantages of the present invention more comprehensible, the preferred embodiments are specifically cited below, and in conjunction with the accompanying drawings, the detailed description is as follows:

Description of drawings

Figure 1 shows an embodiment of the projector of the present invention.

FIG. 2 shows an embodiment of the power factor correction circuit of the present invention.

Detailed ways

Figure 1 shows an embodiment of the projector of the present invention. As shown, the projector 100 includes a rectifier 10 , a power factor correction circuit 20 , a lamp 30 , a direct current/direct current (DC/DC) converter 40 , and a system control unit 50 and a bulb 60 .

The rectifier 10 is used for full-wave rectification of the system AC power so as to output a rectified voltage V(t). The rectifier 10 is a full-bridge rectifier, but it is not intended to limit the present invention. In this embodiment, the voltage V(t) output by the rectifier 10 should be a voltage with ripples, and the magnitude of the ripples is related to the size of the capacitor C0 and may also be related to time.

The power factor correction circuit 20 is used for converting the rectified voltage V(t) output by the rectifier 10 into a DC output voltage V _O , such as 380VDC, and providing it to the lamp 30 and the DC/DC converter 40 . For example, the power factor correction circuit 20 is an active power factor correction circuit. As shown in FIG. 1 , the power factor correction circuit 20 includes a boost conversion unit 21 , a control unit 23 and an adjustment unit 25 .

A step-up conversion unit 21, configured to convert the rectified voltage V(t) from the rectifier 10 into a DC output voltage V _O , for example, the step-up conversion unit 21 includes a switching element Q1 (shown in FIG. 2 ), And it is used to receive the control from the control unit to adjust the output DC output voltage V _O .

The control unit 23 is configured to control the duty cycle of the switch element Q1 in the step-up conversion unit 21 according to the adjustment signal SAD generated by the adjustment unit 25, so as to adjust the voltage difference between the DC output voltage V _O and the rectified voltage V(t) . For example, according to the adjustment signal SAD, the control unit 23 generates the control signal SC for shortening the duty cycle of the switching element Q1 to reduce the DC output voltage V _O when the temperature rises.

The adjustment unit 25 generates an adjustment signal SAD according to the current temperature and the DC output voltage V _O. For example, the adjustment unit 25 is a voltage divider circuit and includes a thermistor (not shown in the figure) with a positive temperature coefficient.

The lighter 30 uses the output voltage V _O generated by the power factor correction circuit 20 to start the lamp 60 to emit light, and maintains the power factor output in a stable state. For example, the lighter 30 is an electronic ballast (Ballast) with an input voltage range of 220VDC-400VDC, but this is not intended to limit the present invention. In other words, as long as the output voltage V _O generated by the power factor correction circuit 20 is within the range of 220VDC-400VDC, the lighter 30 can start the lamp 60 to emit light.

The DC/DC converter 40 is used to convert the output voltage V _O generated by the power factor correction circuit 20 into a DC voltage VDC2 such as 12VDC, 5VDC or 3.3VDC for use by the system control unit 50 . In addition, the system control unit 50 is used to control the operation of the entire projector 100 .

FIG. 2 shows an embodiment of the power factor correction circuit of the present invention. As shown in the figure, the boost conversion unit 21 is composed of a resistor R0 , an inductor L1 , a switching element Q1 and a diode D1 . The adjustment unit 25 is a voltage divider circuit, which is composed of a first resistor R1, a second resistor R2, and a thermistor R3. The first resistor R1 has a first end, which is coupled to the DC output voltage, and a second end; the second resistor R2 has a first terminal coupled to the second terminal of the first resistor, and a second terminal coupled to ground potential; and a thermistor R3 connected in parallel with the second resistor, wherein the second The voltage drop between the first end and the second end of the resistor R2 is used as the adjustment signal, the resistor R3 is a thermistor with a positive temperature coefficient, and the resistor R3 is preferably set at the inductor L1 or the switching element during layout Near the pins of components with large power loss such as Q1.

In addition, the rectifier 10 is used to perform full-wave rectification on the system alternating current VAC so as to output the rectified voltage V(t). In this embodiment, the voltage V(t) output by the rectifier 10 should be a voltage with ripples, The size of the ripple is related to the size of the capacitor C0, and may also be related to time.

According to the circuit structure of the boost conversion unit 21, the relationship between its input voltage V(t) and output voltage V _O can be obtained from the equation $V_o=\frac{1}{(1-\mathrm{D.}\left(t\right))}\×V\left(t\right)$ to represent, where D(t) represents the duty cycle of the switching element Q1. It can be seen that, if the output voltage V _O is higher, the duty cycle D(t) of the switching element Q1 is also larger. However, the greater the duty cycle of the switching element Q1 is, the greater the current _IP flowing through the inductor L1 will be, which will cause greater power loss when the switching element Q1 is switched, and cause the temperature of the element to rise.

Generally speaking, when the input voltage changes from 240VAC to 100VAC, if the boost conversion unit 21 still maintains the output voltage V _O at 380VDC, the duty cycle of the switching element Q1 must be large to achieve this. Since the current I _P flowing through the inductor L1 is proportional to the duty cycle of the switching element Q1 , the switching of the switching element Q1 will cause greater power loss, resulting in a decrease in efficiency and an increase in the temperature of the element.

In order to overcome this problem, the adjustment unit 25 with a thermistor in this embodiment generates an adjustment signal SAD according to the current temperature and the output voltage V _O output by the boost conversion element 21, and provides it to the control unit 23 to control the switching element Q1 duty cycle. In other words, when the boost conversion unit 21 generates power loss due to the switching of the switching element Q1 and the temperature rises, the control unit 23 will generate the control signal SC according to the adjustment signal SAD to shorten the duty cycle of the switching element Q1, so as to reduce the flow through the inductance The current _IP of L1 and the power loss caused by switching.

而r2代表电阻R2的电阻值，r3代表电阻R3的电阻值。The adjustment unit 25 is coupled to the output voltage V _O of the boost conversion unit 21 to generate a divided voltage Vref as an adjustment signal SAD and output it to the control unit 23, and the relationship between the output voltage V _O and the voltage Vref can be expressed as $V_o=\frac{\mathrm{Vref}}{\mathrm{RS}}\×r1+\mathrm{Vref},$ Among them, r1 represents the resistance value of resistor R1, and RS represents the resistance value after resistor R2 and R3 are connected in parallel, namely

And r2 represents the resistance value of the resistor R2, and r3 represents the resistance value of the resistor R3.

Since the resistor R3 (thermistor) has a positive temperature coefficient and is disposed near the inductor L1 or the pin of the switching element Q1 (not shown in the figure). For example, the resistor R3 (thermistor) can be adjacent to the first terminal or the second terminal of the inductor L1, or adjacent to the first terminal or the second terminal of the switching element Q1. Therefore, when the temperature of the inductor L1 and the switching element Q1 rises, the resistance r3 of the resistor R3 will increase, and the resistance RS will increase, so that the output voltage V _O will decrease. Therefore, the control unit 23 will reduce the duty cycle of the switching element Q1 according to the adjustment signal SAD generated by the adjustment unit 25, so as to reduce the power loss caused by switching, and finally the output voltage V _O of the boost conversion element 21 will maintain a balance with the temperature .

Since the lighting device 30 in this embodiment is an electronic ballast (ballast) with an input voltage range of 220VDC to 400VDC, even if the output voltage V _O generated by the power step-up conversion unit 21 decreases, as long as it is within the range of 220VDC to 400VDC Within the range, the lighter 30 can start the lamp tube 60 to emit light.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention, any skilled in the art can make some changes and changes without departing from the spirit and scope of the present invention, so the protection scope of the present invention Subject to what is defined in the appended claims.

Description of main component symbols

10: Rectifier 20: Power factor correction circuit

21: Boost conversion unit 23: Control unit

25: Adjustment unit 30: Lighter

40: DC/DC converter 50: System control unit

60: Lamp 100: Projector

VAC: system alternating current V(t): rectified voltage

V _O : DC output voltage SAD: Adjustment signal

SC: Control signal C0～C1: Capacitance

R0～R3: Resistor Q1: Switching element

L1: inductance element D1: diode

Vref: divided voltage I _P : charging current

Claims (23)

1. A power factor correction circuit, comprising:

the boost conversion unit comprises a switching element and an inductance element and is used for converting the rectified voltage into direct-current output voltage;

the adjusting unit comprises a thermistor with a positive temperature coefficient, and generates an adjusting signal according to the temperature and the direct current output voltage; and

and the control unit is used for controlling the working period of the switching element according to the adjusting signal so as to adjust the voltage difference between the direct current output voltage and the rectified voltage.

2. The power factor correction circuit according to claim 1, wherein the control unit shortens a duty cycle of the switching element to lower the dc output voltage when a temperature of the switching element or the inductance element rises according to the adjustment signal.

3. The power factor correction circuit of claim 1, wherein the adjustment unit comprises:

a first resistor having a first end coupled to the DC output voltage and a second end;

a second resistor having a first end coupled to the second end of the first resistor and a second end coupled to ground potential; and

the thermistor is connected with the second resistor in parallel, wherein the voltage drop between the first end and the second end of the second resistor is used as the adjusting signal.

4. The power factor correction circuit of claim 2, wherein the boost conversion unit comprises:

the inductance element is provided with a first end which is coupled with the rectified voltage and a second end;

the switch element has a first terminal coupled to the second terminal of the inductor element, a second terminal coupled to a ground voltage, and a control terminal coupled to the control unit;

a diode element having an anode terminal coupled to the first terminals of the inductor element and the switching element, and a cathode terminal; and

the first capacitor is coupled between the cathode terminal of the diode element and the ground voltage.

5. The power factor correction circuit of claim 4, wherein the thermistor is adjacent to a first end or a second end of the inductive element.

6. The power factor correction circuit of claim 4, wherein the thermistor is adjacent to a first end or a second end of the switching element.

7. A power factor correction circuit comprising;

a boost conversion unit including a switching element and an inductance element for converting the rectified voltage into a DC output voltage according to a formula

Wherein V (t) represents rectified voltage, V _O Represents the dc output voltage and D (t) represents the duty cycle of the switching element;

the voltage division circuit comprises a thermistor with a positive temperature coefficient, and generates an adjusting signal according to the temperature and the direct current output voltage; and

and the control unit is used for shortening the working period of the switching element according to the adjusting signal when the temperature of the switching element or the inductance element rises so as to reduce the direct-current output voltage.

8. The power factor correction circuit of claim 7, wherein the voltage divider circuit comprises:

a first resistor having a first end coupled to the DC output voltage and a second end;

a second resistor having a first end coupled to the second end of the first resistor and a second end coupled to ground potential; and

the thermistor is connected with the second resistor in parallel, and the voltage drop between the first end and the second end of the second resistor is used as the adjusting signal.

9. The power factor correction circuit of claim 7, wherein the boost conversion unit comprises:

the inductance element is provided with a first end which is coupled with the rectified voltage and a second end;

the switch element is provided with a first end, a second end and a control end, wherein the first end is coupled with the second end of the inductance element and the ground voltage, and the control end is coupled with the control unit;

a diode element having an anode terminal coupled to the inductance element and the first terminal of the switching element, and a cathode terminal; and

the first capacitor is coupled between the cathode terminal of the diode element and the ground voltage.

10. The power factor correction circuit of claim 9, wherein the thermistor is adjacent to a first end or a second end of the inductive element.

11. The power factor correction circuit of claim 9, wherein the thermistor is adjacent to a first end or a second end of the switching element.

12. A projector, comprising:

a rectifier coupled to the ac voltage and outputting a rectified voltage;

a power factor correction circuit comprising:

a boost conversion unit including a switching element and an inductance element for converting the rectified voltage into a direct current output voltage;

the adjusting unit comprises a thermistor with a positive temperature coefficient, and generates an adjusting signal according to the temperature and the direct current output voltage; and

the control unit is used for controlling the working period of the switching element according to the adjusting signal so as to adjust the voltage difference between the direct-current output voltage and the rectified voltage;

a bulb; and

and the lamp igniter is coupled with the direct current output voltage and used for starting the illumination of the lamp tube.

13. The projector according to claim 12, further comprising a dc/dc converter for converting the dc output voltage to a second dc voltage for supplying power to a system control unit, wherein the dc output voltage is higher than a peak value of the rectified voltage, and the second dc voltage is lower than the dc output voltage.

14. The projector of claim 12 wherein the light igniter is an electronic ballast.

15. The projector of claim 12, wherein

The adjusting unit includes:

a first resistor having a first terminal coupled to the DC output voltage and a second terminal;

a second resistor having a first end coupled to the second end of the first resistor and a second end coupled to ground potential; and

the thermistor is connected with the second resistor in parallel, wherein the voltage drop between the first end and the second end of the second resistor is used as the adjusting signal.

16. The projector according to claim 12, wherein the boost conversion unit includes:

the inductance element is provided with a first end which is coupled with the rectified voltage and a second end;

the switch element has a first terminal coupled to the second terminal of the inductor element, a second terminal coupled to a ground voltage, and a control terminal coupled to the control unit;

a diode element having an anode terminal coupled to the first terminals of the inductor element and the switching element, and a cathode terminal; and

a first capacitor coupled between the cathode terminal of the diode element and the ground voltage.

17. The projector of claim 16, wherein the thermistor is adjacent to the first end or the second end of the inductive element.

18. The projector according to claim 16, wherein the thermistor is adjacent to a first end or a second end of the switching element.

19. A projector includes;

a rectifier coupled to the ac voltage and outputting a rectified voltage;

a power factor correction circuit comprising:

a boost conversion unit including a switching element and an inductance element for converting the rectified voltage into a DC output voltage according to a formula

Wherein V (t) represents the rectified voltage, V _O Represents the DC output voltage, and D (t) represents the working period of the switching element;

the voltage division circuit comprises a thermistor with a positive temperature coefficient, and generates an adjusting signal according to the temperature and the direct current output voltage; and

the control unit is used for shortening the working period of the switching element according to the adjusting signal when the temperature of the switching element or the inductance element rises so as to reduce the direct-current output voltage;

a bulb; and

and the stabilizer is used for being coupled with the direct current output voltage and starting the illumination of the lamp tube.

20. The projector according to claim 19, wherein the boost conversion unit comprises:

the inductance element is provided with a first end which is coupled with the rectified voltage and a second end;

the switch element has a first terminal coupled to the second terminal of the inductor element, a second terminal coupled to a ground voltage, and a control terminal coupled to the control unit;

a diode element having an anode terminal coupled to the first terminals of the inductor element and the switching element, and a cathode terminal; and

the first capacitor is coupled between the cathode terminal of the diode element and the ground voltage.

21. The projector of claim 20, wherein the thermistor is adjacent to the first end or the second end of the inductive element.

22. The projector according to claim 20, wherein the thermistor is adjacent to a first end or a second end of the switching element.

23. The projector of claim 19, wherein the voltage divider circuit comprises:

a first resistor having a first terminal coupled to the DC output voltage and a second terminal;

a second resistor having a first terminal coupled to the second terminal of the first resistor and a second terminal coupled to a ground potential; and

the thermistor is connected with the second resistor in parallel, wherein the voltage drop between the first end and the second end of the second resistor is used as the adjusting signal.

Images