CN101750579B - Method for detecting faults of reverse protection circuit on flexible printed circuit - Google Patents

Abstract

The present invention is applicable to the field of liquid crystal display manufacture, and provides a detection method for a reverse protection circuit failure on a flexible circuit board. The method comprises the following steps: causing the Driver IC to exit the sleep mode, and the delay time does not exceed 10 ms; starting the Driver IC The crystal oscillator inside the IC, and the delay time does not exceed 10ms; make the Driver IC perform the first stage boost, and the delay time does not exceed 7ms; make the Driver IC perform the second stage boost, and the delay time does not exceed 7ms; The Driver IC performs the third-level boost, and the delay time does not exceed 5ms; check whether the LCM under test has no display and a large current appears, if so, the reverse protection circuit on the FPC is faulty. The present invention shortens the delay of some related instructions when the Driver IC is initialized, so that the Driver IC enters a locked state when the reverse protection circuit on the FPC fails, and then judges the reverse protection circuit on the FPC by whether there is a large current in the Driver IC Is there a failure.

Description

A detection method for reverse protection circuit faults on flexible circuit boards

technical field

The invention belongs to the field of liquid crystal display manufacture, and in particular relates to a fault detection method for a reverse protection circuit on a flexible circuit board.

Background technique

Liquid crystal display module (Liquid Crystal Module, LCM) is composed of liquid crystal display panel (LCD Panel), driver circuit (Driver IC), flexible circuit board (Flexible Printed Circuit, FPC), backlight, etc., among which FPC is used to carry Driver IC For the general Driver IC, the circuits that need to be carried on the FPC include a voltage doubler circuit, a voltage stabilization circuit, a crystal oscillator circuit, a reverse protection circuit, etc. If there is a problem with these circuits on the FPC (such as components falling off or soldering Poor connection, etc.), will have varying degrees of impact on the work of the LCM. In order to ensure that the LCM works normally on the client side, a display function test will be done before the LCM leaves the factory, that is, simulate the client side such as a communication terminal, MP3 and other test equipment to make the LCM display to check whether the LCM is in good condition, including whether the LCD Panel is in good condition (with or without dots) Bad line, etc.), whether the Driver IC is working normally, whether the circuit on the FPC is normal, etc.

When detecting the circuit on the FPC, the voltage doubler circuit and the voltage stabilization circuit are relatively easy to detect. If there is a problem with these two parts of the circuit, it usually shows that the LCM has no display or abnormal display, that is, we can detect the problematic LCM through a general display test. , the reverse protection circuit is quite special, generally a diode connected in reverse, the lack of this diode or the poor contact of the diode on the FPC (that is, the fault of the reverse protection circuit) may cause the LCM to not display, but it will not As a result, the LCM must not be displayed, but there is a hidden danger of not being displayed. Therefore, our current usual display test basically cannot detect the abnormality of the reverse protection circuit.

Taking diodes as an example, at present, we mainly rely on visual inspection and high-power magnifying glass to check the reverse protection circuit. This method has the following disadvantages:

1. Visual inspection can only check the very serious situation of diode falling off or tin cracking (cracking of diode and FPC solder);

2. In order to detect more tin-cracked products and eliminate hidden dangers, we can only use a high-power magnifying glass to check, and it takes a long time to use a high-power magnifying glass to check a reverse protection circuit, which will seriously affect production efficiency during mass production;

3. The cost of high-power magnifiers is high. To perform microscopic inspection on all FPCs, it is necessary to purchase a large number of high-power magnifiers, which is not conducive to cost control of enterprises.

Contents of the invention

The purpose of the embodiments of the present invention is to provide a detection method for a fault of a reverse protection circuit on a flexible circuit board, so that the fault of the reverse protection circuit on a flexible circuit board can be easily detected, and the detection cost can be reduced, and the detection efficiency can be improved.

The embodiment of the present invention is achieved in this way, a method for detecting a fault in a reverse protection circuit on a flexible circuit board, the method comprising the following steps:

Make the Driver IC exit sleep mode, and the delay time does not exceed 10ms;

Start the crystal oscillator inside the Driver IC, and the delay time does not exceed 10ms;

Make the Driver IC perform the first stage boost, and the delay time does not exceed 7ms;

Make the Driver IC carry out the second stage boost, and the delay time does not exceed 7ms;

Make the Driver IC carry out the third-level boost, and the delay time does not exceed 5ms;

Detect whether the LCM under test has no display and a large current appears, if so, the reverse protection circuit on the FPC is faulty.

In the embodiment of the present invention, by shortening the delay of some related instructions when the Driver IC is initialized, the boost condition of the circuit first connected to the reverse protection circuit in the Driver IC becomes more severe, so as to achieve the reverse protection circuit of the Driver IC on the FPC The purpose of entering the locked state in the event of a fault, and then judging whether the reverse protection circuit on the FPC is faulty by whether there is a large current in the Driver IC, has been verified by multiple tests. When the delay data is reduced to less than 10ms When , the detection rate of reverse protection circuit faults is increasing.

Description of drawings

Figure 1 is a schematic diagram of the circuit part related to the reverse protection circuit on the FPC inside the Driver IC;

Figure 2 is a schematic diagram of the connection between the reverse protection circuit on the FPC and the internal circuit of the Driver IC;

Fig. 3 is a flow chart of the implementation of the method for detecting the fault of the reverse protection circuit on the flexible circuit board provided by the embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

In the embodiment of the present invention, the delay of some related instructions is shortened when the Driver IC is initialized, so that the Driver IC

The boost condition of the circuit first connected to the reverse protection circuit in the IC becomes more stringent, so that the Driver IC enters the locked state when the reverse protection circuit on the FPC fails, and then depends on whether the Driver IC has a large current To judge whether the reverse protection circuit on the FPC is faulty.

Figure 1 shows the circuit part inside the Driver IC related to the reverse protection circuit on the FPC. When the Driver IC is working normally, several voltages in Figure 1 satisfy the following relationship: VGH (LCD drive positive voltage) > VCI1 (one-stage boost voltage) reference voltage) > VGL (the negative voltage driven by the LCD). However, when initializing the Driver IC, their relationship may be: VCI1>VGH>VGL. In the circuit in Figure 1, because VCI1>VGH, transistor Q1 is turned on, causing VGL to be pulled high, and transistor Q2 is turned on at the same time, VGH voltage Pulled down, the circuit is in a locked state so that the Driver IC has a large current. In order to avoid this state, we need to set up a reverse protection circuit on the FPC, as shown in Figure 2, the reverse protection circuit is a diode D, when the situation of VCI1>VGH>VGL also occurs, the transistor Q1 is turned on, After VGL is pulled high instantly, it will directly turn on the diode D, unload the current through the diode D, the voltage of VGL will not exceed VSS, and the transistor Q2 will not be turned on, which prevents the locking of this part of the circuit, and waits until it returns to VGH In the state of >VCI1>VGL, the Driver IC works normally.

From the above principle, we can see that there is no reverse protection diode D on the FPC or the reverse protection diode D does not work, the Driver IC circuit may be locked, and the Driver IC cannot work normally (LCM does not display) , and there will be a large current. Using this principle, we can detect this part of the circuit failure problem through a general display test. As mentioned earlier, this situation is only possible during the initialization phase of the Driver IC. The key to solving the problem is how to make the Driver IC easily enter the situation of VCI1 > VGH > VGL during the initialization phase.

Driver IC adjusts a series of parameters and characteristics such as voltage, phase, frequency, peak value, effective value, timing, and duty cycle applied to the pixel through the instruction system (initialization instruction and delay after executing the instruction) to establish a certain drive. conditions, so as to realize the display of LCM. In general, for the reliability of the Driver IC, Driver IC manufacturers will suggest that the delay in the command system be as long as possible, so that the Driver IC can perform initial settings more reliably. We have proved through many experiments that in this Under normal circumstances, it is very difficult for the Driver IC to have a voltage of VCI1 > VGH > VGL, so the current display test used by LCM manufacturers basically cannot detect the problem of the reverse protection diode.

From the point of view of the voltage boosting principles of VCI1, VGH, and VGL, if we properly shorten the delay after the completion of each command in the command system and make the boosting conditions more stringent, it is very likely that the DriverIC will When the reverse protection circuit on the FPC fails, it enters into a locked state.

Fig. 3 shows the implementation process of the detection method for the fault of the reverse protection circuit on the flexible circuit board provided by the embodiment of the present invention, which is described in detail as follows:

In step S301, make the Driver IC exit the sleep mode, and the delay time is not more than 10ms.

The effect of shortening the delay after exiting the sleep mode command is to allow the Driver IC to enter the wake-up state at the fastest speed.

In step S302, the crystal oscillator inside the Driver IC is started, and the delay time does not exceed 10ms.

When the Driver IC wakes up from the sleep mode, the crystal oscillator must be turned on for the subsequent boosting work, and the delay after turning on the crystal oscillator is shortened, so that the Driver IC starts to work immediately after exiting the sleep mode.

In step S303, the Driver IC is made to perform the first-stage voltage boost, and the delay time does not exceed 7ms.

In step S304, the Driver IC is made to perform a second-stage voltage boost, and the delay time does not exceed 7ms.

In step S305, the Driver IC is made to perform a third-stage voltage boost, and the delay time does not exceed 5 ms.

In step S306, it is detected whether the LCM to be tested has no display and a large current occurs, if yes, the reverse protection circuit on the FPC is faulty.

In the embodiment of the present invention, after the initialization command of the LCM to be tested has been modified and verified multiple times, it is found that the delay after the Driver IC exits the sleep mode command, the delay of starting the internal crystal oscillator of the Driver IC, and the first stage of the Driver IC When the boost delay, the delay for the Driver IC to perform the second-stage boost, and the delay for the Driver IC to perform the second-stage boost are modified to less than 10ms, the detection rate of the reverse protection circuit fault on the FPC is found. Improvements have been made, as shown in the table below:

Delay for exiting sleep mode Delay to start the internal crystal oscillator The delay of the first stage boost The delay of the second stage boost The delay of the third stage boost Increase boost frequency The detection rate original settings 20mS 20mS 25mS 25mS 25mS 1/16 0% After modifying the settings for the first time 10mS 10mS 10mS 10mS 10mS 1/16 0% After modifying the settings for the second time 10mS 10mS 7mS 7mS 5mS 1/16 8% After modifying the settings for the third time 5mS 5mS 5mS 5mS 5mS 1/16 20% After modifying the settings for the fourth time 1mS 1mS 1mS 1mS 1mS 1/16 80% After modifying the settings for the fifth time 1mS 1mS 1mS 1mS 1mS 1/8 More than 90

It can be seen from the above table that when the delay data is reduced to less than 10ms, the detection rate of FPC reverse protection circuit faults increases gradually.

The specific way to verify whether the modified initialization instruction is valid is as follows:

1. Prepare several pieces of good-quality LCM, take some good-quality LCMs and remove the reverse protection circuit, and apply the initialization instructions after each modification and delay in the above table to the good-quality LCMs that have removed the reverse protection circuit. From the above table, you can It can be seen that when the various delay data are reduced to less than 10ms, the detection rate of reverse protection circuit faults increases gradually: the delay of exiting sleep mode is changed to 10ms, and the delay of starting the crystal oscillator is changed to 10ms , the delays of the first, second, and third stages of boosting are 7ms, 7ms, and 5ms respectively, and the detection rate is 8%; when the delay data is further modified to 5ms, the detection rate is increased to 20%; further When the delay data is modified to 1ms, the detection rate increases to 80%; and when the boost frequency is further increased from the original crystal oscillator frequency 1/16 to 1/8, the detection rate exceeds 90%.

2. Connect one end of the reverse protection circuit of 10 good LCMs in series with resistors of different resistances to simulate the degree of open circuit of the reverse protection circuit, so as to measure the degree of falling off of the reverse protection circuit on the FPC. Detection, the test results prove that it can effectively detect different degrees of shedding. For example, the fifth revised data in the above table can detect the situation that the disconnection resistance is 330OHM.

3. Apply the modified and delayed initialization command in the above table to other good LCMs, and it can be tested that all work normally.

In the embodiment of the present invention, by shortening the delay of some related instructions when the Driver IC is initialized, the boost condition of the circuit first connected to the reverse protection circuit in the Driver IC becomes more severe, so as to achieve the reverse protection circuit of the Driver IC on the FPC The purpose of entering the locked state in the event of a fault, and then judging whether the reverse protection circuit on the FPC is faulty by whether there is a large current in the Driver IC, has been verified by multiple tests. When the delay data is reduced to less than 10ms , the detection rate of reverse protection circuit faults is increasing; when the delay data is modified to 5ms, the detection rate increases to 20%, and when the delay data is further modified to 1ms, the detection rate increases to 80%, and when the step-up frequency is further increased from 1/16 of the principle crystal oscillator frequency to 1/8, the detection rate is above 90%.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (4)

1. the detection method of a faults of reverse protection circuit on flexible printed circuit is characterized in that, said method comprising the steps of:

Make driving circuit withdraw from sleep pattern, and delay time is no more than 10ms;

Start the inner crystal oscillator of driving circuit, and delay time is no more than 10ms;

Make driving circuit carry out the first order and boost, and delay time is no more than 7ms;

Make driving circuit carry out the second level and boost, and delay time is no more than 7ms;

Make driving circuit carry out the third level and boost, and delay time is no more than 5ms;

Whether do not have demonstration and have big electric current occur, if then the reverse protection circuit on the FPC breaks down if detecting liquid crystal display module to be measured.

2. detection method as claimed in claim 1; It is characterized in that, the delay time that driving circuit withdraws from the delay time of sleep pattern, the delay time that starts the inner crystal oscillator of driving circuit, the delay time that makes driving circuit carry out the first order to boost, make driving circuit carry out the second level boosts, make driving circuit carry out the delay time that the third level boosts all to be no more than 5ms.

3. according to claim 1 or claim 2 detection method; It is characterized in that, the delay time that driving circuit withdraws from the delay time of sleep pattern, the delay time that starts the inner crystal oscillator of driving circuit, the delay time that makes driving circuit carry out the first order to boost, make driving circuit carry out the second level boosts, make driving circuit carry out the delay time that the third level boosts all to be no more than 1ms.

4. detection method as claimed in claim 3 is characterized in that, said method further may further comprise the steps:

The frequency of boosting is increased to 1/8 of said crystal oscillator frequency.

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