CN2932912Y - Lamp drive circuit - Google Patents

Abstract

The utility model relates to a lamp tube driving circuit, it is including the transformer, and this transformer is the secondary side and couples the optical coupler, and the primary side of this transformer is coupled the output of control circuit. When the optical coupler is not conducted, the driving circuit works normally, and when the optical coupler is not conducted, the open-loop protection circuit is started, so that the output value of the control circuit is reduced, and the function of protecting the lamp tube driving circuit is achieved.

Description

Lamp drive circuit

technical field

The utility model relates to a lamp tube drive circuit, in particular to a lamp tube drive circuit for driving a U-shaped tube.

Background technique

Press, the discharge lamp (Discharge Lamp) is often used in the backlight of the liquid crystal display (Backlight), for example: cold cathode fluorescent lamp (Cold Cathode Fluorescent Lamp, CCFL) is one of them, when the cold cathode fluorescent lamp is turned on Its working voltage will decrease immediately, and its working voltage is about 1/3 of the trigger voltage (about 1000V), but its working current is very wide, it can be driven from 6mA to 500mA, and its working frequency is about 30KHz to 100KHz about.

The above-mentioned discharge lamp has the characteristic of negative impedance, and its equivalent impedance will decrease with the increase of input power. The circuit that supplies power or power to the lamp, that is, the so-called general inverter (Inverter), must provide a controllable AC The power supply and feedback circuit are used to maintain the stability of the circuit. On the other hand, it also needs to have the function of load adjustment.

Please refer to FIG. 1, which is a known circuit structure diagram using the secondary side of the transformer to connect the lamp tube. In the traditional circuit, the parasitic capacitance causes the unbalanced input current at both ends of the lamp tube 12, such as in the lamp tube. 12 The current received by the first contact 13 is 6mA, and the current received by the second contact 14 of the lamp tube 12 is 12mA, and it can be clearly found that the first contact 13 and the second contact 14 have a drop of 6mA, and the contact is unbalanced. It will directly affect the transformer, resulting in excessive temperature difference, and also make the transformer 11 and other components easy to be damaged. Simultaneously, if the current difference between the two ends of the lamp tube 12, especially the U-shaped tube, is too large, it is very easy to cause uneven brightness of the lamp tube 12 (which is more obvious when applied to a panel) and is easy to burn out (that is, the service life of the lamp tube is also shortened). Thereupon shorten) all kinds of problems, so those who are engaged in this industry are to be overcome.

Contents of the invention

Based on solving the deficiencies of the prior art described above, the utility model is a lamp driving circuit, the main purpose of which is to use a photo-coupler (Photo-coupler) to couple to the low-voltage terminals of the two secondary sides of the transformer, so that The two low-voltage terminals on the secondary side form a virtual short circuit, and the optocoupler is coupled to the open loop protection circuit (Open Loop Protection, OLP). The feedback value of the circuit (controller) is reduced, so that the output value of the control circuit is reduced, so as to achieve the function of protecting the lamp driving circuit.

In order to achieve the above purpose, the structure of the first embodiment of the lamp driving circuit of the present invention includes:

A transformer having a primary side, a first secondary side and a second secondary side;

an optical coupler, coupled to the first secondary side and the second secondary side;

Open loop protection circuit, coupled with optocoupler;

The lamp tube is coupled to the high voltage end of the first primary side and the second secondary side;

The control circuit has an output terminal and a feedback terminal, the output terminal is coupled to the primary side of the transformer, and the feedback terminal is coupled to the open-loop protection circuit;

When the optocoupler is not conducting, the potential of the open-loop protection circuit is pulled up, so that the output value of the output terminal of the control circuit is reduced, so as to achieve the function of protecting the lamp tube driving circuit.

In order to achieve the above purpose, the structure of the second embodiment of the lamp driving circuit of the present invention includes:

a transformer having a primary side, a first secondary side and a second secondary side;

a protection transformer coupled to the first secondary side and the second secondary side;

Open loop protection circuit, coupled with protection transformer;

The lamp tube is coupled to the high voltage end of the first primary side and the second secondary side;

The control circuit has an output terminal and a feedback terminal, the output terminal is coupled to the primary side of the transformer, and provides an input signal to the transformer, and the feedback terminal is coupled to the open-loop protection circuit;

When the voltage value of the secondary side of the protection transformer decreases, the potential of the open-loop protection circuit is pulled up, so that the output value of the control circuit decreases, so as to achieve the function of protecting the lamp tube driving circuit.

In order to provide a more in-depth explanation of the utility model, the following illustrations, drawing number descriptions and detailed descriptions of the invention are used, hoping to be helpful to your review committee in the review work.

Description of drawings

FIG. 1 is a circuit structure diagram of a known circuit that utilizes a secondary side of a transformer to connect to a lamp.

Fig. 2 is the first embodiment of the lamp driving circuit of the present invention.

FIG. 3 is a second embodiment of the lamp driving circuit of the present invention.

[Description of main components]

11～transformer

12～lamp tube

L～lamp tube

13～first contact

14～Second contact

20～Lamp drive circuit

30～Lamp drive circuit

21～transformer

22～Optocoupler

23～resistor

24～diode

25 ~ control circuit

26～Open circuit protection circuit

31～transformer

32～protection transformer

33～Filter circuit

35～Open circuit protection circuit

36 ~ control circuit

P～primary side

S1～secondary side

S2～secondary side

Detailed ways

The detailed structure of the present utility model and connection relationship thereof are described in conjunction with the following diagrams, so as to facilitate your review committee to understand.

Please refer to FIG. 2, which is the first embodiment of the lamp driving circuit of the present invention. The lamp driving circuit 20 includes:

A transformer 21, the transformer 21 has a primary side P, a first secondary side S1 and a second secondary side S2;

an optical coupler 22, coupled to the low-voltage ends of the first secondary side S1 and the second secondary side S2;

An open-loop protection circuit 25, coupled to the optocoupler 22;

The lamp tube L is coupled to the high voltage end of the first primary side S1 and the second secondary side S2;

The control circuit 25 has an output terminal (output) and a feedback terminal FB, the output terminal is coupled to the primary side P of the transformer 21, and the feedback terminal FB is coupled to the open-loop protection circuit 26;

When the optocoupler 22 is not turned on, the potential of the open-loop protection circuit 25 is pulled up to reduce the output value of the control circuit, so as to protect the lamp driving circuit.

The action flow of the lamp driving circuit of the first embodiment is as follows:

The input voltage on the primary side of the transformer 21 is induced by two secondary sides (S1, S2), and converted into a high voltage (about 1000V), and the photocoupler (Photocoupler) 22 is coupled to the first secondary side of the transformer 21 S1 and the low-voltage end of the second secondary side S2, the resistor R1 can be used as a shunt and current limiting function to protect the two light-emitting diodes D1, so the optocoupler 22 can be turned on in the positive half cycle and the negative half cycle of the voltage. , to generate low-voltage alternating current, and through the light-emitting diode D1 of the optocoupler 22 and the receiving transistor to form a non-contact switch, and has an isolation function. After the optocoupler 22 is turned on, the voltage of node A in the open loop protection circuit 26 can be close to the voltage value of 5V. The output value of the control circuit 25 decreases, thereby protecting the driving circuit and avoiding burning or other damages.

Please refer to FIG. 3 , which is the second embodiment of the lamp driving circuit of the present invention. The lamp driving circuit 30 includes:

A transformer 21, the transformer 21 has a primary side P, a first secondary side S1 and a second secondary side S2;

a protection transformer 32, coupled to the first secondary side S1 and the second secondary side S2;

An open-loop protection circuit 35, coupled to the protection transformer 32;

The lamp tube L is coupled to the high voltage end of the first primary side S1 and the second secondary side S2;

The control circuit 36 has an output terminal (output) and a feedback terminal FB, the output terminal is coupled to the primary side P of the transformer 21, and the feedback terminal FB is coupled to the open-loop protection circuit 26;

When no voltage is sensed on the secondary side of the protection transformer 32, the potential of the open-loop protection circuit 25 is pulled up to reduce the output value of the control circuit 36 to protect the lamp driving circuit.

The operation flow of the lamp driving circuit of the second embodiment is as follows: the structure disclosed in FIG. 3 is approximately the same as that in FIG _. , C ₁ ) constitute the filter circuit 33, when the voltage on the secondary side of the protection transformer 32 decreases, the potential of the open-loop protection circuit 35 is pulled up, and then the output value of the control circuit 36 is reduced, so as to protect the lamp tube drive circuit, resulting in burnout or other damage.

Through the disclosure of the above-mentioned Figures 2 and 3, it can be understood that the utility model can indeed use an optical coupler or a transformer to cooperate with an open-loop protection circuit to achieve the purpose of protecting the lamp drive circuit and avoid burning or other damages. It is different from the traditional protection structure and has better protection.

In summary, the structural features and various embodiments of the present utility model have been disclosed in detail, and it can be fully demonstrated that the utility model is highly progressive in terms of purpose and efficacy, and has great industrial utilization value, and For the unprecedented application on the market, according to the spirit of the patent law, the utility model fully complies with the requirements of the invention patent.

Only those described above are only preferred embodiments of the present utility model, and should not be used to limit the scope of implementation of the present utility model, that is, all equivalent changes and modifications made according to the scope of the claims of the present utility model should still be It falls within the scope covered by the utility model patent, and I would like to ask your review committee to learn from it and pray for your approval.

Claims (9)

1. A lamp drive circuit, characterized in that it comprises: a transformer having a primary side, a first secondary side and a second secondary side; an optical coupler, coupled to the first secondary side and the low voltage end of the second secondary side; a lamp tube, coupled to the high voltage end of the first secondary side and the second secondary side; an open loop protection circuit coupled to the optocoupler; and The control circuit has an output terminal and a feedback terminal, the output terminal is coupled to the primary side of the transformer, and the feedback terminal is coupled to the open-loop protection circuit; When the optocoupler is not conducting, the potential of the open-loop protection circuit is pulled up, and the output value of the control circuit is reduced, so as to protect the lamp tube driving circuit. 2. The lamp driving circuit according to claim 1, wherein the lamp is a cold cathode lamp. 3. The lamp driving circuit according to claim 2, wherein the lamp is a U-shaped tube. 4. The lamp driving circuit according to claim 1, further comprising a diode and a resistor, the resistor and the diode are connected in parallel, and are coupled between the transformer and the optocoupler. 5. A lamp driving circuit, characterized in that it comprises: a transformer having a primary side, a first secondary side and a second secondary side; a protection transformer coupled to the low-voltage end of the first secondary side and the second secondary side; a lamp tube, coupled to the high voltage end of the first secondary side and the second secondary side; an open-loop protection circuit coupled to the protection transformer; and The control circuit has an output terminal and a feedback terminal, the output terminal is coupled to the primary side of the transformer, and the feedback terminal is coupled to the open-loop protection circuit; When the voltage of the secondary side of the protection transformer drops, the potential of the open-loop protection circuit is pulled up, so that the output value of the control circuit is reduced, so as to protect the lamp driving circuit. 6. The lamp driving circuit according to claim 5, wherein the lamp is a cold cathode lamp. 7. The lamp driving circuit according to claim 6, wherein the lamp is a U-shaped tube. 8. The lamp driving circuit according to claim 5, further comprising a filter circuit coupled between the protection transformer and the open-loop protection circuit. 9. The lamp driving circuit according to claim 5, wherein the protection transformer is a 1:1 transformer.

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