Test circuit for overhauling backlight of display

Abstract

The utility model relates to the technical field of maintenance circuits, and discloses a test circuit for maintaining backlight of a display in order to solve the technical problem of low maintenance effect caused by imperfect maintenance tools in the existing detection process, a constant current circuit comprises an NPN type triode Q6 and a light emitting diode D11, an emitting electrode of the triode Q6 is grounded through a resistor R21, and the emitting electrode of the triode Q6 is grounded through a resistor R21. The base electrode of the triode Q6 is grounded through a diode D9 and a diode D10 in sequence, the anode of the diode D9 is connected with the base electrode of the triode Q6, the cathode of the diode D9 is connected with the anode of the diode D10, the cathode of the diode D10 is grounded, the collector electrode of the triode Q6 is used for being connected with a first meter pen, and the substrate of the triode Q6 is connected with the anode of the output end of the rectifying circuit through a resistor R20. The cathode of the output end of the rectification circuit is grounded, the anode of the output end of the rectification circuit is connected with the anode of the light-emitting diode D11, the cathode of the light-emitting diode D11 is used for being connected with a second meter pen, and constant current is output to improve the maintenance effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of overhauling circuit, in particular to a test circuit for overhauling display backlight. BACKGROUND

[0002] At present, the backlight source of liquid crystal television generally adopts white light LED. However, since the specifications and power supply voltages of backlight lamp beads used by different manufacturers and models of liquid crystal televisions are different, and the protection circuit is usually provided on the backlight driving board, when the backlight does not light failure occurs, it is difficult to quickly and accurately determine whether the fault source is the backlight driving board or the backlight lamp bead, which directly affects the maintenance efficiency and accuracy of the backlight failure, and becomes a big problem that troubles maintenance personnel. CONTENT OF THE UTILITY MODEL

[0003] The utility model aims at providing a test circuit for overhauling display backlight, to solve the technical problem of low overhauling effect caused by imperfect overhauling tools in the existing detection process.

[0004] To achieve the above-mentioned purpose, the specific technical scheme of the test circuit for overhauling display backlight of the utility model is as follows:

[0005] A test circuit for overhauling display backlight, comprising a rectifier circuit for rectifying alternating current, a constant current circuit connected with the output end of the rectifier circuit, comprising an NPN type triode Q6 and a light emitting diode D11, the emitter of the triode Q6 is connected to ground through a resistor R21, the base of the triode Q6 is connected to ground in turn through a diode D9 and a diode D10, the anode of the diode D9 is connected with the base of the triode Q6, the cathode of the diode D9 is connected with the anode of the diode D10, the cathode of the diode D10 is connected to ground, the collector of the triode Q6 is used for connecting a first probe, the base plate of the triode Q6 is connected with the positive pole of the output end of the rectifier circuit through a resistor R20, the negative pole of the output end of the rectifier circuit is connected to ground, the positive pole of the output end of the rectifier circuit is connected with the anode of the light emitting diode D11, and the cathode of the light emitting diode D11 is used for connecting a second probe.

[0006] The rectifier circuit converts alternating current into direct current, providing stable power supply for the whole test circuit; the constant current circuit can output constant current through the combination design of the NPN type triode Q6 and the light emitting diode D11, no matter the voltage specification of the measured backlight lamp bead or lamp strip, the current can be kept stable, thereby effectively preventing the damage of the measured element caused by excessive current, and ensuring the reliability of the test result.

[0007] Further, a protection circuit is further arranged between the constant current circuit and the rectifier circuit, comprising a triode Q2, a triode Q3, a triode Q5 and a triode Q6, all of which are NPN type triodes, the base of the triode Q2 is connected with the emitter of the triode Q3, the collector of the triode Q2 is connected with the collector of the triode Q3, the base and the collector of the triode Q3 are connected with a bias resistor R10, the collector of the triode Q2 is connected with the positive output end of the rectifier circuit, and the base of the triode Q3 is connected with the ground through a capacitor C13;

[0008] A series resistance voltage dividing circuit for providing a bias voltage to the base of the triode Q5 is arranged, the collector of the triode Q5 is connected with the base of the triode Q3, a Zener diode Z1 is arranged, the cathode of the Zener diode Z1 is connected with the emitter of the triode Q5, the cathode of the Zener diode Z1 is connected with the emitter of the triode Q2 through a resistor R17, and the anode of the Zener diode Z1 is connected with the ground.

[0009] The protection circuit works accurately through the cooperation of the triodes Q2, Q3, Q5 and the Zener diode Z1, and can quickly respond when the circuit is abnormal. The combination of Q2 and Q3 realizes automatic current limiting protection when the voltage is too high through the connection relationship of the base and the emitter. The triode Q5 cooperates with the Zener diode Z1 to provide a stable bias voltage by using the voltage dividing circuit, further enhances the anti-interference ability of the circuit, protects the core circuit components from sudden voltage impact, and improves the safety and stability of the circuit.

[0010] Further, an isolation electric transformer is further arranged in the front stage of the rectifier circuit.

[0011] The isolation electric transformer is designed in the front stage of the rectifier circuit, which not only realizes the electrical isolation of the input and output circuits, prevents the direct interference of the power grid on the circuit or the operator during detection, and improves the safety of the test.

[0012] The test circuit for overhauling the display backlight has the following advantages:

[0013] The rectifier circuit can convert alternating current into stable direct current to provide reliable power support for the test circuit, and ensure that the influence of power fluctuation on the test result is avoided during the test process; the constant current circuit utilizes the combination design of the NPN type triode Q6 and the light emitting diode D11, no matter the voltage specification of the measured backlight lamp bead or light bar, stable current can be outputted, damage to elements caused by excessive current is avoided, and the reliability of the test result is ensured. The whole circuit has strong universality, can adapt to the voltage and current specifications of backlight lamp beads or light bars of different models, thereby significantly improving the efficiency and accuracy of display backlight detection, and effectively solving the problem of low overhauling effect caused by the imperfection of the existing overhauling tool. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The utility model provides a test circuit structure diagram. Specific implementation

[0015] In order to make the utility model purposes, technical scheme and advantages more clearly, following combining with the drawings and example, the utility model is further detailedly explained. It should be understood that the specific example described here is only used to explain the utility model, and is not used to limit the utility model.

[0016] Refer Figure 1 The utility model provides a kind of test circuit for overhauling display backlight, is provided with the isolation transformer T1 for isolation, the rear stage of transformer T1 is provided with the rectifier circuit consisting of diode D1, diode D3, diode D7 and diode D8, the rear stage of rectifier circuit is provided with protection circuit, and protection circuit includes triode Q2, triode Q3, triode Q5 and triode Q6, all are NPN type triode, the base of triode Q2 is connected with the emitter of triode Q3, the collector of triode Q2 is connected with the collector of triode Q3, biasing resistance R10 is connected between the base and collector of triode Q3, the collector of triode Q2 is connected with the output positive pole of rectifier circuit, and the base of triode Q3 is connected with ground through capacitor C13.

[0017] It is provided with series resistance voltage dividing circuit, including two series resistors R18 and resistor R19, one end of resistor R18 is connected with the emitter of triode Q2, the other end of resistor R18 is connected with one end of resistor R19, the other end of resistor R19 is grounded, the base of triode Q5 is connected with one end of resistor R19, the collector of triode Q5 is connected with the base of triode Q3, it is provided with stabilivolt Z1, the cathode of stabilivolt Z1 is connected with the emitter of triode Q5, the cathode of stabilivolt Z1 is connected with the emitter of triode Q2 by resistor R17, and the anode of stabilivolt Z1 is grounded.

[0018] Resistor R10 provides bias voltage for the base of triode Q3, and triode Q3 is turned on by the bias voltage, and then triode Q2 is turned on.Series resistance voltage dividing circuit obtains voltage, when voltage is too high, higher than preset value, triode Q5 is turned on, and the voltage at the base of triode Q3 is pulled down, and triode Q2 is turned off to form protection effect.

[0019] A light-emitting diode D11 is provided for indication, the anode of the diode D11 is connected with the emitter of the triode Q2, the cathode of the diode D11 is used for connecting the first probe, the emitter of the triode Q2 is grounded through the resistor R20, the diode D9 and the diode D10 in turn, the cathode of the diode D9 is connected with the anode of the diode D10, the cathode of the diode D10 is grounded, the base of the triode Q6 is connected with the joint of the resistor R20 and the diode D9 respectively, the emitter of the triode Q6 is grounded through the resistor R21, and the collector of the triode Q6 is used for the second probe.

[0020] The first probe and the second probe are respectively welded at the ends A and B in the figure. The resistor R20, the resistor R21, the diode D9, the diode D10 and the triode Q6 constitute a constant current source circuit, which has excellent stability, and no matter how many LED light beads are connected to the collector of the triode Q1, the collector current is always constant.

[0021] The principle of the constant current circuit is mainly based on the characteristics of the triode and the reasonable design of the circuit elements. In this circuit, the triode Q6 plays a key role, which together with the resistors R20 and R21, and the diodes D9 and D10 forms a feedback mechanism, thereby realizing constant current output. The following is the specific analysis process:

[0022] The diodes D9 and D10 are connected in series and grounded, providing a relatively stable reference voltage. The forward voltage drop of a diode is usually about 0.7V, so the stable voltage drop of D9 and D10 in series under normal working conditions is about 1.4V.

[0023] The base voltage of the triode Q6 is determined by the joint of the resistor R20 and the diode D9. Since the forward voltage drop of the diode D9 is stable, the base voltage will be stabilized at about 0.7V (the forward voltage drop value of the diode D9), ensuring that the base voltage is not significantly affected by load changes, thereby providing the basis for constant current characteristics.

[0024] The emitter voltage of the triode is different from the base voltage by a forward bias voltage (about 0.7V). Since the base voltage is stable, the emitter voltage also remains stable. At the same time, the emitter current is grounded through the resistor R21, and according to Ohm's law, the emitter current Ie can be calculated by Ie = Ve / R21, where Ve is the emitter voltage and R21 is the resistance value. Because Ve is fixed, the emitter current Ie is also constant.

[0025] According to the current relationship of the triode, the collector current Ic = Ie, because the base current Ib is very small and can be ignored. Therefore, the collector current Ic of the triode is determined by the emitter resistance R21 and the emitter voltage Ve, and is completely unaffected by changes in load (number of LED light beads and voltage specifications).

[0026] No matter how the number of LED connected to the collector and the voltage specification change, as long as the total load voltage is within the range allowed by the power supply and the transistor, the transistor Q6 will automatically adjust the voltage Vce between its collector and emitter to ensure that the current remains constant.

[0027] The stable reference voltage provided by the diode, combined with the amplification characteristics of the transistor and the voltage distribution of the resistor, strictly controls the emitter current at a fixed value, and the collector current is approximately equal to the emitter current, thereby achieving constant current output.

[0028] In an embodiment, the current is constant at 14mA, and the constant current of the constant current source can be changed by changing the resistance value of R21, and the output voltage can reach 180V.

[0029] The LEDs on the backlight panel are connected in series, and when in use, the first and second probes are respectively overlapped on the detection position of the LED, and the plurality of LEDs on the backlight panel form a series circuit with the light emitting diode D11, and when the tested LED is fault-free, the light emitting diode D11 emits light.

[0030] Therefore, the test circuit is not only suitable for detecting the working state of most backlight strips, but also can measure single or multiple LED lamp beads with different voltage characteristics.

[0031] The test circuit for overhauling the backlight of the display has the following advantages:

[0032] The rectifier circuit can convert alternating current into stable direct current to provide reliable power support for the test circuit, ensuring that the influence of power fluctuations on the test results is avoided during the test process; the constant current circuit uses the combination design of NPN transistor Q6 and light emitting diode D11, regardless of the voltage specification of the measured backlight lamp bead or lamp strip, and can output stable current, avoiding damage to components caused by excessive current, while ensuring the reliability of the test results; the protection circuit realizes rapid response and protection of abnormal states of the circuit through the cooperative work of transistors Q2, Q3, Q5 and voltage stabilizing tube Z1, especially the automatic current limiting function of Q2 and Q3 and the anti-interference design of transistor Q5 and voltage stabilizing tube Z1, which effectively improves the stability and safety of the circuit; the isolation electric transformer added in front of the rectifier circuit further realizes the electrical isolation of the input and output circuits, which not only prevents the influence of power grid interference on the test results, but also ensures the safety of operation.

[0033] The above only describes the preferred embodiments of the utility model, and does not limit the utility model, and any modification, equivalent replacement and improvement made within the spirit and principle of the utility model shall be included in the protection scope of the utility model.

Claims

1. A test circuit for servicing a display backlight comprising a rectifier circuit for rectifying an alternating current, characterized in that, The constant current circuit connected with the output end of the rectifier circuit comprises a NPN type triode Q6 and a light emitting diode D11. The emitter of the triode Q6 is grounded through a resistor R21. The base of the triode Q6 is grounded through a diode D9 and a diode D10 in sequence. The anode of the diode D9 is connected with the base of the triode Q6. The cathode of the diode D9 is connected with the anode of the diode D10. The cathode of the diode D10 is grounded. The collector of the triode Q6 is used for connecting a first probe. The base of the triode Q6 is connected with the positive pole of the output end of the rectifier circuit through a resistor R20. The negative pole of the output end of the rectifier circuit is grounded. The positive pole of the output end of the rectifier circuit is connected with the anode of the light emitting diode D11. The cathode of the light emitting diode D11 is used for connecting a second probe.

2. The test circuit for servicing a display backlight according to claim 1, characterized in that The protection circuit is arranged between the constant current circuit and the rectifier circuit and comprises triodes Q2, Q3, Q5 and Q6, which are all NPN type triodes. The base of the triode Q2 is connected with the emitter of the triode Q3. The collector of the triode Q2 is connected with the collector of the triode Q3. The base and the collector of the triode Q3 are connected with a bias resistor R10. The collector of the triode Q2 is connected with the positive pole of the output end of the rectifier circuit. The base of the triode Q3 is grounded through a capacitor C13. The series resistor voltage dividing circuit is arranged for providing a bias voltage to the base of the triode Q5. The collector of the triode Q5 is connected with the base of the triode Q3. The voltage stabilizing tube Z1 is arranged. The cathode of the voltage stabilizing tube Z1 is connected with the emitter of the triode Q5. The cathode of the voltage stabilizing tube Z1 is connected with the emitter of the triode Q2 through a resistor R17. The anode of the voltage stabilizing tube Z1 is grounded.

3. The test circuit for servicing a display backlight according to claim 2, characterized in that, The front stage of the rectifier circuit is further provided with an isolation electric transformer.

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