High frequency power source control circuit and protective circuit apparatus

• US 20060220595A1
• Filed: 04/04/2005
• Published: 10/05/2006
• Est. Priority Date: 04/04/2005
• Status: Active Grant

• Current Assignee: Chao-Cheng Lu
• Original Assignee: Chao-Cheng Lu
• Inventors: Lu, Chao-Cheng
• Granted Patent: US 7,332,871 B2
• Time in Patent Office: Days
• US Class Current: 315/291
• CPC Class Codes: H05B 41/2813 Arrangements for protecting lamps or circuits against abnormal operating conditions
• CPC Class Codes: H05B 41/285 Arrangements for protecting lamps or circuits against abnormal operating conditions
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

Abstract

A precision voltage control circuit applicable to a PWM (Pulse Width Modulation) circuit can offer CCFL (Cold Cathode Fluorescent Lamp) or EEFL (External Electrode Fluorescent Lamp) tubes a stable high frequency voltage or current, so that each CCFL or EEFL tube can get an appropriate compensation current and an optimal emitting efficiency and enhance its emitting quality. The circuit also has an overload current, low current, and overload voltage and low voltage protective circuit to protect the CCFL or EEFL tubes from being injured. The circuit can also be applied to the TFT LCD TV or other large LCD panels, and develops the best display effect of each LCD tube.

Claims

1. A high frequency power source control circuit, comprising:

an active power factor corrector, which has input terminals for receiving an AC power and has functions of power factor correcting and voltage boosting;

a PWM (Pulse Width Modulation) and high frequency power output circuit, which is coupled to the active power factor corrector and is a PWM integrated circuit as a main circuit;

a DC power supply circuit coupled to the active power factor corrector;

a DC load system, wherein the DC power supply circuit supplies a DC power to the load system; and

a starting circuit, wherein the DC load system feeds a signal back to the starting circuit, and when the load system receives the DC power, the load system generates a voltage and outputs the voltage to the PWM and high frequency power output circuit in order to start CCFL tubes or EEFL tubes and offer each of the CCFL tubes or EEFL tubes a stable high frequency voltage or a stable high frequency current, such that each of the CCFL tubes or EEFL tubes gets an appropriate compensation current to obtain an optimal emitting efficiency and enhance an emitting quality.

2. The circuit according to claim 1, wherein the input terminals of the active power factor corrector are AC power input terminals for receiving an input voltage ranging from 90V to 265V and a power frequency of 50 Hz or 60 Hz.

3. The circuit according to claim 1, wherein the DC power supply circuit is a single-piece of switch power integrated circuit for receiving an input voltage substantially ranging from DC 120V to 700V with a power efficiency of 80% or more than 80%, and a programmable precision shunt regulator integrated circuit capable of outputting an output voltage ranging from 2.5V to 36V.

4. The circuit according to claim 3, wherein the DC power supply circuit is an overload current protective circuit composed of comparison integrated circuits, and a photocoupler disables the single-piece of switch power integrated circuit and no DC power is outputted when a load is too large.

5. The circuit according to claim 4, wherein the photocoupler is a structure of a photo thyristor.

6. The circuit according to claim 3, wherein the DC power supply circuit is a multiple independent DC outputs.

7. The circuit according to claim 1, wherein a tuner of a TFT LCD TV serves as one example of the load system, and when the DC power supply system is supplying the DC power to the DC power load system, a voltage is outputted from an output side of the DC power load system as a starting power, and transferred to input terminals of the starting circuit to achieve a starting function.

8. The circuit according to claim 1, wherein the PWM circuit comprises photocouplers serving as components for controlling a pulse width of the PWM integrated circuit, and an operational amplifier integrated circuit is used to control and amplify a sawtooth wave so as to get an optimal control effect.

9. The circuit according to claim 1, wherein output terminals of the integrated circuit of the PWM and high frequency power output circuit respectively transfer pulse signals to gates of two power MOSFETs through photocouplers, and input terminals of the two power MOSFETs have no noise to interfere a half-bridge type oscillation circuit so as to replace the conventional transformer coupling method.

10. The circuit according to claim 9, wherein DC powers for the PWM and high frequency power output circuit and photocouplers are independent powers, output terminals of the half-bridge type electronic ballast are coupled to terminals of a primary coil of a high frequency transformer, and a secondary coil terminal thereof has a dedicated set of tap H terminal for the CCFL or EEFL as a dedicated set of coil terminals of a voltage detection and protective circuit.

11. The circuit according to claim 10, wherein the half-bridge type electronic ballast or a full-bridge type oscillation circuit.

12. The circuit according to claim 1, wherein:

the PWM and high frequency power output circuit further comprises a programmable precision voltage regulator, which is composed of a voltage comparator, a transistor for executing ON and OFF operations, a current-limiting resistor, a photocoupler, a current-limiting resistor and a voltage stabilizing diode;

the programmable precision voltage regulator can supply a power to a voltage source of a comparator IC₆, and to a negative terminal and a positive terminal of the comparator IC₆;

a resistance value and a watt value of the measurement resistor are determined according to a magnitude of a load current.

13. The circuit according to claim 11, wherein the precision voltage regulator can be replaced with a programmable precision shunt regulator integrated circuit.

14. The circuit according to claim 1, wherein:

the starting circuit generates a voltage for responding when the load system is supplied with the DC power, and the voltage is 5V or other values;

When an input terminal of the starting circuit receives the voltage, a secondary side of a photo coupler (Ph₆) is in an ON state, and a N-terminal DC power is serially coupled to a LED of a photo coupler (Ph₇) from the secondary side of a the photo coupler (Ph₇) to a time constant resistor and then serially coupled to a time constant condenser to form a short time control circuit, such that the LED emits light only for a moment;

When the LED emits light, the secondary side of the photocoupler (Ph₇) is a control voltage terminal of the integrated circuit of the PWM circuit being short-circuited, such that a pulse width between two output voltages of the integrated circuit reaches a maximum so as to start the CCFL tubes or EEFL tubes.

15. The circuit according to claim 1 to 14, comprising a protective circuit for protecting the load, wherein a primary coil of a high frequency transformer is coupled to a half-bridge type oscillation circuit of the PWM and high frequency power output circuit, and a secondary coil of the high frequency transformer is coupled to a CCFL circuit.

16. The circuit according to claim 15, wherein the high frequency transformer has multiple secondary coils for independently supplying power to the CCFL or EEFL circuit.

17. The circuit according to claim 15, wherein the primary coil of the high frequency transformer is coupled to a full-bridge type electronic ballast of the PWM.

18. The circuit according to claim 15, 16 or 17, wherein the protective circuit is characterized in that the secondary coil of the high frequency transformer is coupled to one or multiple high-voltage condensers, a CCFL or EEFL, one or multiple bridge rectifiers, one or multiple measurement resistors, which are serially connected to form a basic unit of a CCFL or EEFL set.

19. The circuit according to claim 18, wherein multiple CCFL or EEFL sets of the protective circuits can be connected in parallel.

20. The circuit according to claim 15, 16, 17, or 19, wherein the protective circuit has an overload current, low current protective circuit, and when the voltage across the two terminal of the measurement resistor of a CCFL or EEFL tube unit is too large, it means that the CCFL or EEFL tube unit is short-circuited or has a leakage current, so that an object of overload current protection is achieved.

21. The circuit according to claim 18, wherein the protective circuit is an overload current, low current protective circuit, and when the voltage across the two terminal of the measurement resistor of a CCFL or EEFL tube unit is too large, it means that the CCFL or EEFL tube unit is short-circuited or has a leakage current, so that an object of overload current protection is achieved.

22. The circuit according to claim 15, 16, 17, or 19, wherein the protective circuit has an overload current, low current protective circuit, and when the voltage across the two terminals of the measurement resistor is too low or zero, it means that the CCFL or EEFL tubes are open-circuited or the voltage across the two terminals of the secondary coil of the high frequency transformer is too low, so that an object of low current protection is achieved.

23. The circuit according to claim 18, wherein the protective circuit has an overload current, low current protective circuit, and when the voltage across the two terminals of the measurement resistor is too low or zero, it means that the CCFL tubes or EEFL tubes are open-circuited or the voltage across the two terminals of the secondary coil of the high frequency transformer is too low, so that an object of low current protection is achieved.

24. The circuit according to claim 15, 16, 17, or 19, wherein:

The protective circuit has an overload voltage, low voltage protective circuit, a tap H terminal between the terminals of the secondary coil of the high frequency transformer serves as a voltage measurement point so that the voltage of the secondary coil is judged;

A current flowing through the tap H terminal is rectified by a diode and then filtered by a condenser to form a DC voltage;

the measurement voltage of the high frequency transformer is proportional to the voltage of the secondary coil in a predetermined proportion; and

the voltage of the secondary coil terminal can be read according to the voltage at a voltage measurement terminal and the proportion.

25. The circuit according to claim 18, wherein:

the protective circuit has an overload voltage, low voltage protective circuit, a tap H terminal between the terminals of the secondary coil of the high frequency transformer serves as a voltage measurement point so that the voltage of the secondary coil is judged;

a current flowing through the Tap H terminal is rectified by a diode and then filtered by a condenser to form a DC voltage;

the measurement voltage of the high frequency transformer is proportional to the voltage of the secondary coil in a predetermined proportion; and

the voltage of the secondary coil terminal can be read according to the voltage at a voltage measurement terminal and the proportion.

26. The circuit according to claim 25, wherein:

the protective circuit has an overload voltage, low voltage protective circuit;

when the voltage across two terminals of the secondary coil of the high frequency transformer rises, the voltage at the measurement voltage terminal also rises, such that the voltage across two terminals of the filter condenser also rises; and

if the voltage of the filter condenser is higher than a set voltage of the negative terminal of a comparator A₅, the comparator A₅ outputs a positive voltage to disable the integrated circuit ICs, and the voltage across the two terminals of the secondary coil of the high frequency transformer disappears so that the object of overload voltage protection is achieved.

27. The circuit according to claim 25, wherein the protective circuit is an overload voltage, low voltage protective circuit, and when a voltage across two terminals of the secondary coil of the high frequency transformer is too low, the voltage across two terminals of the filter condenser decreases, and a comparator A₆ generates and outputs a positive voltage while the two terminals of the secondary coil of the high frequency transformer has no voltage output, so that the object of the low voltage protection is achieved.

28. The circuit according to claim 15, 16, 17, or 19, wherein the protective circuit has an overload current, low current, overload voltage, low voltage protective circuit.

29. The circuit according to claim 18, wherein the protective circuit has an overload current, low current, overload voltage, low voltage protective circuit.

30. The circuit according to claim 18, wherein a DC positive terminal of the bridge rectifier is coupled to a collector of the photocoupler, a negative terminal of the bridge rectifier is coupled to an emitter of the photocoupler, a N-terminal of a LED of the photocoupler is grounded, a P-terminal of the LED of the photocoupler is coupled to an output terminal of a comparator to control a CCFL or EEFL tube current.

31. The circuit according to claim 19, wherein a DC positive terminal of the bridge rectifier is coupled to a collector of the photo coupler, a negative terminal of the bridge rectifier is coupled to an emitter of the photo coupler, a N-junction of a LED of the photo coupler is grounded, a P-junction of the LED of the photo coupler is coupled to an output terminal of a comparator to control a CCFL or EEFL tube current.

32. The circuit according to claim 30 or 31, wherein an output side of the photocoupler is used or multiple output sides of the photocouplers is connected in serially.

33. A CCFL or EEFL protective circuit, where in a secondary coil of a high frequency transformer is serially coupled to one or multiple high-voltage condensers, a CCFL (Cold Cathode Fluorescent Lamp) or EEFL, one or multiple bridge rectifiers and one or more measurement resistors to form a basic combination of a CCFL or EEFL set.

34. The circuit according to claim 33, wherein multiple CCFL or EEFL sets can be connected in parallel.

35. The circuit according to claim 33 or 34, further comprising a delay circuit having a delay time determined by a time constant resistor, a time constant capacitor and a voltage stabilizing diode.

36. The circuit according to claim 33 or 34 is an overload current, low current protective circuit, wherein when a voltage across two terminals of a measurement resistor of the CCFL tubes or EEFL tubes is too high, it represents that the CCFL tubes or EEFL tubes is short-circuited or has a leakage current, so that an object of overload current protection is achieved.

37. The circuit according to claim 35 is an overload current, low current protective circuit, wherein when a voltage across two terminals of a measurement resistor of the CCFL tubes or EEFL tubes is too high, it represents that the CCFL tubes or EEFL tubes is short-circuited or has a leakage current, so that an object of overload current protection is achieved.

38. The circuit according to claim 33 or 34 is an overload current, low current protective circuit, and when the voltage across the two terminals of the measurement resistor is too low or zero, it means that the CCFL tubes or EEFL tubes are open-circuited or the voltage across the two terminals of the secondary coil of the high frequency transformer is too low, so that an object of low current protection is achieved.

39. The circuit according to claim 35 is an overload current, low current protective circuit, and when the voltage across the two terminals of the measurement resistor is too low or zero, it means that the CCFL tubes or EEFL tubes are open-circuited or the voltage across the two terminals of the secondary coil of the high frequency transformer is too low, so that an object of low current protection is achieved.

40. The circuit according to claim 33 or 34 is an overload voltage, low voltage protective circuit, wherein:

a tap H terminal between the terminals of the secondary coil of the high frequency transformer serves as a voltage measurement point so that the voltage of the secondary coil is judged;

a current flowing through the Tap H terminal is rectified by a diode and then filtered by a condenser to form a DC voltage;

the measurement voltage of the high frequency transformer is proportional to the voltage of the secondary coil in a predetermined proportion; and

the voltage of the secondary coil terminal can be read according to the voltage at a voltage measurement terminal and the proportion.

41. The circuit according to claim 35 is an overload voltage, low voltage protective circuit, wherein:

a tap H terminal between the terminals of the secondary coil of the high frequency transformer serves as a voltage measurement point so that the voltage of the secondary coil is judged;

a current flowing through the Tap H terminal is rectified by a diode and then filtered by a condenser to form a DC voltage;

the measurement voltage of the high frequency transformer is proportional to the voltage of the secondary coil in a predetermined proportion; and

the voltage of the secondary coil terminal can be read according to the voltage at a voltage measurement terminal and the proportion.

42. The circuit according to claim 33 or 34 is an overload voltage, low voltage protective circuit, wherein:

when the voltage across two terminals of the secondary coil of the high frequency transformer rises, the voltage at the measurement voltage terminal also rises, such that the voltage across two terminals of the filter condenser also rises; and

if the voltage of the filter condenser is higher than a set voltage of the negative terminal of a comparator A₅, the comparator A₅ outputs a positive voltage to disable the integrated circuit IC₅, and the voltage across the two terminals of the secondary coil of the high frequency transformer disappears so that the object of overload voltage protection is achieved.

43. The circuit according to claim 35 is an overload voltage, low voltage protective circuit, wherein when a voltage across two terminals of the secondary coil of the high frequency transformer is too low, the voltage across two terminals of the filter condenser decreases, and a comparator A₆ generates and outputs a positive voltage while the two terminals of the secondary coil of the high frequency transformer has no voltage output, so that the object of the low voltage protection is achieved.

44. The circuit according to claim 33 or 34 is an overload current, low current, overload voltage, low voltage protective circuit.

45. The circuit according to claim 35 is an overload current, low current, overload voltage, low voltage protective circuit.

46. The circuit according to claim 33 or 34, wherein a DC positive terminal of the bridge rectifier is coupled to a collector of the photocoupler, a negative terminal of the bridge rectifier is coupled to an emitter of the photo coupler, a voltage drop resistor connected to the collector and emitter of photo coupler, a N-junction of a LED of the photo coupler is grounded, a P-junction of the LED of the photo coupler is coupled to an output terminal of a comparator to control a CCFL or EEFL tube current.

47. The circuit according to claim 35, wherein a DC positive terminal of the bridge rectifier is coupled to a collector of the photo coupler, a negative terminal of the bridge rectifier is coupled to an emitter of the photo coupler, a voltage drop resistor connected to the collector and emitter of photo coupler, a N-junction of a LED of the photo coupler is grounded, a P-junction of the LED of the photo coupler is coupled to an output terminal of a comparator to control a CCFL or EEFL tube current.

48. The circuit according to claim 46, wherein an output side of the photo coupler is used or multiple output sides of the photo couplers is connected in serially.

49. The circuit according to claim 47, wherein an output side of the photo coupler is used or multiple output sides of the photo couplers is connected in serially.