WO2008040251A1

WO2008040251A1 - Current control method and driving circuit for multi-lamps

Info

Publication number: WO2008040251A1
Application number: PCT/CN2007/070788
Authority: WO
Inventors: Dongping Yang
Original assignee: Proview Technology (Shenzhen) Co., Ltd.
Priority date: 2006-09-30
Filing date: 2007-09-26
Publication date: 2008-04-10
Also published as: CN101155454A

Abstract

This invention discloses a multi-lamps electric current control method which includes: When any of the said multi-lamps is open or the resonance circuit parameter is changed, the output voltage of the transformer is adjusted to ensure the output voltage of the transformer conforms to the range determined by the relation between the output voltage and the frequency of the said transformer required to stabilize the current of a single lamp, and the relation between the said lamp and the voltage and the frequency of the capacitance series circuit, so as to stabilize the current value of each of the lamps. The multi-lamps driving circuit disclosed in this invention has the operating mode controlling unit which includes the storage module to store the data of the relationship curve of the voltage and the frequency of the said lamp and the capacitance series circuit, and the controlling module used to control the voltage output from the transformer falling into the range determined by the relation between the voltage and the frequency of the said transformer to keep the current of a single lamp stable, and the relationship curve between the said voltage and the frequency. This invention can precisely control the current of a lamp to ensure a stable illumination and normal operating condition of the current even under interference.

Description

Multi-lamp current control method and multi-lamp driving circuit This application claims to be submitted to the Chinese Patent Office on September 30, 2006, the application number is 200610141779.4, and the invention name is "multi-lamp current control method and its driving circuit" Priority of Chinese Patent Application, the entire contents of which is incorporated herein by reference. Technical field

The invention relates to the technical field of power supply and power distribution, in particular to a method for controlling multi-lamp current and a multi-lamp driving circuit. Background technique

The planar light source can be composed of a plurality of fluorescent lamps side by side, and can be applied to devices such as LCD TVs or LCD monitors as backlights for these devices. One of the fluorescent lamps is called a Cold Cathode Fluorescent Lamp (CCFL), which is commonly used in the industry as a planar light source.

In order for the CCFL to illuminate, the planar light source includes the drive circuit, and the CCFL and other electronic components are the load of the drive circuit. Prior art lamp drive circuits include transformers and inverters. The driving circuit including the transformer and the inverter needs to meet the following conditions: 1. It can provide a sufficiently high voltage for each CCFL to break down and discharge; 2. Ensure that the current of each CCFL is stable and substantially equal, thereby ensuring the brightness Hook; 3, to ensure that the current waveform in each CCFL is basically sinusoidal, to ensure luminous efficiency and CCFL life; 4, CCFL open circuit and transformer output short circuit provides protection. At present, the backlight is designed to refer to the above requirements.

The existing lamp driving circuit is generally a circuit in which series resonance is output in parallel. 1 is a prior art planar light source including a drive circuit of the type described above. The planar light source comprises a plurality of CCFL lamps, each of which is provided with one transformer and one inverter, or a plurality of CCFL lamps with a plurality of transformers T1~Tn connected to one inverter. In addition, a control circuit is provided to measure the lamp current, thereby controlling the output of the inverter. The input end of the inverter is connected to a low-voltage DC signal isolated from the power grid, and the AC signal is output to the transformer Τ1~ Τη, the transformer Τ1~ Τη boost, and each transformer output terminal is connected to the parallel CCFL and the two voltage detecting capacitors CI, C11 or Cn, Cnl. The transformers T1~Τη are high leakage magnetic transformers, and respectively constitute an oscillating circuit with capacitors CI, C11 or Cn, Cnl. Its resonant waveform is shown in Figure 2. The operating frequency f _{w is to} the left of the resonant frequency f _Q , that is, the inverter is working. Sexual modality. Thus, the leakage inductance of the transformer and the voltage sensing capacitor and the lamp form a circuit that is connected in series with the parallel output.

During operation, the transformer Tl~ Τη output voltage does not cause CCFL breakdown, that is, the output voltage of the transformer Tl~Tn is low relative to the breakdown voltage of the CCFL. The breakdown and illumination of the CCFL is realized by amplifying the output voltage of the transformer after the oscillation circuit composed of the transformer T1 or Tn and the capacitor CI, C11 or Cn, Cnl is oscillated. Thus, the current flowing through the CCFL is sinusoidal, the output voltage of the transformer Tl ~ Tn is the steady state operating voltage of the CCFL, corresponding to the operating frequency f _w.

Among them, the current of the CCFL is controlled by controlling the pulse width or frequency of the inverter. Specifically, the detected current of the CCFL lamp is used as an input of the control circuit and compared with a reference value set in the control circuit. When the lamp current deviates from the reference value, the output pulse width or frequency of the inverter is changed to return the lamp current to the reference value. However, the lamp current cannot be stabilized well when the lamp current is not available or difficult to detect.

In addition, the above planar light source also has the following technical defects: 1) When a CCFL is open, the output voltage of the transformer will rise, the inverter circuit must stop working, other CCFLs are forced to stop working, and the entire backlight fails; 2) The CCFL is connected to a transformer, and the components of the transformer and CCFL are not exactly the same, and the balance of the lamp current is not good. 3) Each CCFL is equipped with a transformer and an inverter circuit. When there are more CCFLs, the cost High; The inverter requires a low-voltage DC that provides a safe isolation between the power supply and the grid. The cost of the power supply increases, so the system cost is still high. Summary of the invention

The present invention provides a multi-lamp drive circuit that provides for stabilizing lamp current. Each of the plurality of lamps in the embodiment of the present invention has a capacitor connected in series, and the plurality of lamps connected in series are connected in parallel, and are connected to the output winding of the driving transformer.

The invention provides a multi-lamp current control method, comprising:

Adjusting a transformer output voltage such that a transformer output voltage conforms to a predetermined output voltage and frequency relationship of the transformer that stabilizes a single lamp current when the lamp tube is open or the resonant circuit parameters are changed in the plurality of lamps The relationship between the voltage and frequency of the lamp and capacitor series circuit is determined to stabilize the current value of each lamp.

The invention provides a multi-lamp driving circuit, the driving circuit has a working state control list The working state control unit includes:

a storage module storing data of a voltage and frequency relationship between the lamp and the capacitor series circuit in a case where the required single lamp current value is constant;

And a control module for controlling the output voltage of the transformer to fall within a predetermined range of the transformer output voltage and frequency relationship for which the single lamp current is stable and the relationship between the voltage and frequency.

It can be seen from the technical solution provided by the present invention that the multi-lamp current control method provided by the present invention drives the lamp tube based on the transformer and the oscillating circuit of the capacitor connected to the transformer load of the tandem lamp, such an oscillating circuit The oscillation curve satisfies the voltage and frequency relationship of the predetermined required single lamp current value, and controls the output voltage of the transformer so that it falls on or near the voltage and frequency relationship, thereby ensuring the flow The current of the lamp is stable, ensuring that the lamp is stable and normal, and the lamp will not be unstable or unable to work due to the abnormality of the circuit; at the same time, by judging the position of the circuit working point at the curve, it can be known that the normal operation The number of lamps provides the basis for troubleshooting.

The multi-lamp driving circuit provided by the invention comprises a transformer, a working state control unit and an oscillating circuit of a capacitor connected to the transformer-connected lamp to drive the lamp tube, and the oscillation curve of the oscillating circuit satisfies a predetermined single required The voltage and frequency relationship curves when the lamp current value is constant, the working state control unit stores the data of the curve, and stores control software for controlling the output voltage of the transformer to fall on or near the voltage and frequency. On the relationship curve, the current flowing through the lamp tube can be stabilized, and the lamp tube can be stably and normally illuminated without causing the lamp to be unstable or inoperable due to the abnormality of the circuit. At the same time, by judging the working point of the circuit in the curve The position can be used to know the number of lamps that work normally, and provide a basis for troubleshooting. DRAWINGS

1 is a circuit diagram of a prior art CCFL backlight;

Figure 2 is a frequency-voltage graph of the transformer output of Figure 1;

3 is a schematic diagram of a lamp driving circuit provided by the present invention;

Figure 4 is a voltage-frequency graph of the output of the transformer required to maintain the required single lamp current without changing in the lamp driving circuit provided by the present invention;

Figure 5 is a voltage-frequency graph of the transformer output inherent to the circuit of Figure 3; Figure 6 is a composite view of Figures 4 and 5;

Figure 7 is a circuit diagram of a lamp driving circuit of the present invention made in accordance with Figure 3;

Figure 8 is a schematic block diagram of the working state control unit of Figure 7;

Figure 9 is a voltage-frequency graph of the transformer output inherent in the number of different lamps driven by the circuit of Figure 7;

Figure 10 is a composite view of Figures 4 and 9. detailed description

The basic principle of the invention is: for the lamp driving circuit for driving the lamp tube by using the resonance of the transformer leakage inductance and the capacitance of the series connected lamp, the output voltage of the transformer is the series voltage of the capacitor and the lamp, in order to maintain the lamp current No change, the output voltage and frequency of the transformer must conform to a certain relationship curve, that is, each frequency corresponds to a specific transformer output voltage to keep the lamp current unchanged. In addition, in the case where the characteristics of the lamp are determined and the parameters of the respective electrical components are fixed, the output voltage and frequency of the transformer of the drive circuit have an inherent resonance curve. The above two curves have intersection points, and the working state of the lamp is controlled so as to be located at the intersection of the two curves, that is, the lamp current can be controlled to the set value.

When the output of the transformer drives multiple lamps, such as an open circuit of a lamp or a change in the parameters of the resonant circuit, the natural resonance curve of the output voltage and frequency of the transformer will change accordingly. At this time, it is necessary to control the operating point of the lamp to return it to the above. Keep the lamp output voltage and frequency curve under the condition that the lamp current is constant, so that other lamp currents can be returned to the set value. Since the number of lamps is different, the operating point of the driving circuit is different. Therefore, it is judged at which frequency point the circuit operates, which is helpful for judging the number of lamps that actually work normally, and as a troubleshooting basis, the principle of the present invention will be described in detail below.

Referring to Fig. 3, the present invention will be described in detail by taking a circuit configuration in which a lamp is connected in series and as a transformer load as an example. Further, the transformer is a high leakage magnetic transformer whose leakage inductance is used as an inductance of the oscillation circuit, and together with the capacitance constitutes an oscillation circuit. The input of the transformer is connected to the output of the inverter. The output of the inverter is connected to the input end of the transformer. The steady-state output voltage of the transformer is higher than the breakdown voltage of the lamp, so that the lamp can be broken down and the operating frequency f _w of the lamp is above the resonance frequency f ₀ . As shown in Figure 5.

The output voltage of the transformer in Figure 3 is the series voltage of the capacitor and the lamp. According to the circuit knowledge: Ilamp= IC=0)C VC =(DC ( V _tr ² - V _lamp ² ) Equation 1

Wherein, Ilamp is the lamp current, C is the capacitance value or equivalent capacitance value of a series capacitor connected to the lamp, VC is the voltage value of the capacitor, V _tr is the voltage output value of the secondary side of the transformer, and V _lamp is the lamp The steady state operating voltage value of the tube.

Since the lamp voltage is basically unchanged in the lighting state, and the capacitance in series is also unchanged, in order to keep the lamp current constant, that is, to keep the lamp light stable, the output voltage and frequency of the transformer must satisfy the above relationship. Figure 4 shows the relationship between the input voltage of the oscillating circuit, that is, the output voltage of the transformer and the frequency, when the required single lamp current is constant. It can be seen that the input voltage of the oscillating circuit, that is, the output voltage and frequency of the transformer, is monotonically decreasing, and the output voltage of the transformer is controlled to fall on or near the preset voltage and frequency curve. The required single lamp current does not change. The output voltage of the control transformer is realized by controlling the switching frequency of the inverter. If there are multiple single lamp currents required, then multiple curves are also required.

In the circuit of Figure 3, the leakage inductance of the secondary winding of the transformer and the parallel capacitor Cp and the series capacitor C of the lamp are resonated. The output voltage of the transformer is the input voltage V _m and the frequency f, the sub-leakage inductance, and the series connection of the lamps. The function of capacitor C and parallel capacitor Cp and the equivalent impedance R of the lamp is as follows: V=F(V _m , f, L, C+Cp, R) Equation 2 where f is the oscillation frequency and L is the transformer The leakage inductance, C+Cp is the total capacitance of all series capacitors and bypass capacitors, R is the internal resistance of the lamp, and V _m is the primary voltage of the transformer.

Equation 2 shows the circuit characteristics inherent to the drive circuit, and FIG. 5 is a curve obtained according to Equation 2. When V _{m is} constant and the lamp is operating in steady state, V _tr varies monotonically with f _w . The present invention is set above the resonance frequency of the circuit, V _tr f _w with a negative exponential function, f _w V _tr is the rise fall.

The above formula can be expressed by the transformer output voltage vs. frequency curve of Figure 5. Put the curves in Figure 4 and Figure 5 into the same coordinate system to get Figure 6. Referring to Figure 6, the intersection of the curve of Figure 5 and the curve of Figure 4 is the steady-state operating point of the lamp. At this point, the lamp works to ensure that the lamp current is set and remains unchanged.

By embodying the circuit of Fig. 3, a circuit as shown in Fig. 7 can be obtained.

The circuit is a multi-lamp driving circuit comprising a plurality of parallel cold cathode fluorescent tubes and a driving circuit thereof. The driving circuit includes a rectifying circuit and a power factor correction (PFC, Power Factor) Correction) Circuit, inverter, high leakage transformer Tl, T2, capacitor C _n , control circuit and detection circuit of tandem cold cathode fluorescent tube.

The input of the inverter is directly connected to the high-voltage DC of the power grid, specifically the direct rectification output of the AC grid or the high-voltage DC of 380 ~ 400V boosted by the power factor correction PFC circuit, and the output is connected to two high leakage transformers. The primary side of the parallel connection of T1, T2. Two transformers Τ1, Τ2 The opposite end of each side constitutes an output terminal, which directly drives a cold cathode fluorescent tube in which a capacitor is connected in series. In addition, the transformer Τ1, Τ2 output is connected with four series connected capacitors C01, C11, C21, C02, and the midpoint of the four capacitor connections is connected to the control ground. The other pair of different names at the output of the transformer Tl, T2 are connected in series, and two identical resistors R1, R2 are connected in series. The two resistors R1 and R2 are connected to the control ground. The primary sides of the two transformers T1, T2 belong to the hot ground, and the secondary side belongs to the cold ground, so the two transformers Tl, T2 need to meet the requirements of the safety regulations.

The plurality of parallel cold cathode fluorescent lamps are connected in series with two capacitors Cn having the same capacitance value, and the two capacitors Cn are respectively connected in series on both sides of the cold cathode fluorescent lamp. The impedance of the series capacitor Cn is greater than the impedance of the lamp. Since the transformers T1 and T2 are high leakage magnetic transformers, the leakage inductance of the transformers ,1, Τ2 and the capacitance Cn of the cold cathode fluorescent lamps connected in series constitute a resonance circuit, which is a series resonance series output circuit.

The control circuit is a single-chip computer and its peripheral circuits, the input of which is the output voltage of the transformer T1, T2, and the output is connected to the control end of the inverter. The control circuit includes an operating state control unit that stores data of a voltage and frequency relationship between the lamp and the capacitor series circuit in a case where the required single lamp current value is constant, and the control software is solidified. It is used to issue a frequency control signal, and control the transformer output voltage by controlling the inverter switching frequency so that it falls on or near the voltage and frequency relationship curve.

The detection circuit includes a current detection circuit and a voltage detection circuit. Specifically, a voltage is connected between the voltage-dividing detection capacitors CO 1 and C 11 at the output end of the transformer, and a voltage is detected between the voltage-dividing detection capacitors C21 and C02 to the input end of the voltage detecting circuit. These voltage-dividing detecting capacitors C01 and C11 After the voltage of C21 and C02 is processed by the voltage detection circuit, it is used as the output voltage of the transformers T1 and T2, and is output to the working state control unit in the control circuit as a judgment as to whether the output voltage of the transformer is the current inverter. The basis of the voltage corresponding to the relationship curve at the switching frequency. Each of the resistors R1, R2 leads a wire to the input end of the current detecting circuit, and is converted into a voltage value and input to the control circuit after processing.

Referring to FIG. 8, the control circuit includes an operating state control unit including a storage unit 810 and a voltage comparison unit 820. The storage unit 810 stores voltage versus frequency curve data 811, which is the required single lamp data. The storage unit 810 also stores firmware control software 812 for controlling the transformer output voltage to fall on or near the voltage and frequency relationship.

The voltage comparison unit 820 compares the input voltage detection value with the voltage value corresponding to the relationship curve at the current inverter switching frequency, and outputs a frequency control signal to the inverter to control the switching frequency according to the comparison result, The comparison result indicates that if the voltage difference between the voltage value and the voltage measurement value corresponding to the relationship curve is too large, if the voltage measurement value is greater than the voltage value corresponding to the relationship curve, the control software is used to issue an improved inverter. The frequency control signal of the switching frequency, otherwise the frequency control signal that reduces the switching frequency of the inverter is issued.

The storage unit 810 further stores data of different operating points on the relationship curve corresponding to different lamps participating in the resonant circuit and working normally, and the current working point is equal to or close to the number of corresponding different lamps. At the point of operation, control software 812 obtains data on the number of lamps.

In the vicinity of the cold cathode fluorescent tube, a temperature sensor (not shown) is disposed, and the input end of the control circuit receives the temperature signal of the cold cathode fluorescent tube transmitted from the temperature sensor, and outputs a temperature compensated signal to the inverter. Control terminal.

During operation, the current from the grid is converted to a DC high voltage of 380 - 400V after passing through the rectifier circuit and the power factor correction circuit. The inverter converts the DC high voltage into a high frequency AC voltage output to the two transformers T1, T2. The output voltage of the two transformers T1 and 副2 in series is higher than the breakdown voltage of the cold cathode fluorescent lamp, and is stabilized at a set high voltage by the single-chip microcomputer control circuit. [Tau] 1 two transformers, leakage inductance Τ2 connected in series and each of the cold cathode fluorescent lamp in the resonance capacitance C _n, so that each of the cold cathode fluorescent lamp current through the sine wave. The operating frequency of the inverter is higher than this resonant frequency, so the switching transistor in the inverter can easily realize zero voltage switching and reduce switching loss. Based on the above circuit structure and principle description, the lamp driving method of the present invention mainly controls the working state of the lamp tube to be located on the relationship between the output voltage and the frequency of the transformer under the condition that the required single lamp current value is constant. Specifically, the following steps are included:

1. Obtaining a transformer output voltage measurement value by measuring the voltage division detection capacitor voltage; 2. Comparing the voltage measurement value with the voltage of the preset voltage and frequency corresponding to the current inverter switching frequency Value

3. If the voltage measurement value is greater than the voltage value corresponding to the curve, increase the inverter switching frequency, otherwise reduce the inverter switching frequency.

The difference between the voltage value corresponding to the curve and the voltage measurement value in the step 3 is too large, which may be caused by the fact that the number of lamps that actually work normally is reduced due to damage of a certain lamp tube, and may also be caused by other circuit interference. . Because the actual number of lamps reduced will cause the equivalent capacitance C of the lamp series and the equivalent impedance R of the lamp to change, the function of the output voltage and frequency of the transformer corresponding to Equation 2 will change accordingly, Figure 9 It shows the relationship between the voltage and frequency of a series of different lamps and capacitors.

In order to keep the lamp current constant, the output voltage and frequency of the transformer must satisfy the equation at the same time.

1. However, if a certain lamp is broken, the frequency of the oscillation circuit rises due to the change of the curve of Equation 2, and the current transformer output voltage will leave the operating point corresponding to the current oscillation frequency in Equation 1, that is, the output voltage of the current transformer even if Without change, Equation 1 is still not satisfied, and the current flowing through the lamp suddenly increases, possibly burning the lamp. Figure 10 shows the curves represented by Equation 1 and Equation 2 in the same coordinate system. The curve of Equation 1 has two intersections with each curve of Equation 2, one lower than the resonant frequency and one higher than The resonant frequency, which means that the output voltage and frequency of the transformer satisfy both Equation 1 and Equation 2, and the actual operating point is chosen to be higher than the resonant frequency.

When the relationship between the output voltage and the frequency of the transformer changes from A to B due to the change in the number of lamps, as long as the output voltage and frequency of the transformer change from the intersection with curve A to the intersection with curve B, the current of the lamp will constant. For example, when multiple lamps in parallel are broken, the curve corresponding to Equation 2 goes up to the right, indicating that the circuit oscillation frequency will be higher if the output voltage of the transformer is to be kept constant. However, as can be seen from Figure 9, even if the transformer output voltage is constant, the current flowing through other normally operating lamps is already greater than the current before the lamp is broken. Therefore, it is necessary to reduce the transformer output voltage V _tr , but to what extent, it is necessary to satisfy the circuit itself represented by Equation 1. Attributes, in order to stabilize the current to a suitable position, accurately control the current of the lamp, so that its light is stable. Decreasing the transformer output voltage v _tr , by increasing the inverter switching frequency until the detected voltage measurement falls on the preset relationship that satisfies Equation 1, and vice versa, reducing the inverter switching frequency until the detection The voltage measurement falls on the preset relationship that satisfies Equation 1. Specifically, if the voltage measurement value is greater than the voltage value corresponding to the curve, the inverter switching frequency is increased, otherwise the inverter switching frequency is lowered. In practice, it may not be necessary to strictly control the transformer output voltage to fall on the voltage and frequency relationship between the lamp and the capacitor series circuit when the required single lamp current value is constant. The output voltage is close to falling on the relationship curve. For example, the maximum error between the voltage value corresponding to the curve and the voltage measurement value at a certain oscillation frequency is preset, for example, plus or minus 5%, at present When the difference between the voltage value corresponding to the curve and the voltage measurement value is greater than 5%, the switching frequency of the inverter is adjusted to adjust the output voltage of the transformer. In other words, the curve is at the current frequency. When the difference between the corresponding voltage value and the voltage measurement value is too large, the output voltage of the transformer is adjusted so as to be close to the preset voltage and frequency relationship curve, and the "close" can be an error range of 5%. Inside.

By judging the output voltage and frequency of the transformer operating on curve A, curve B or other curves, the number of lamps driven by the transformer can also be inferred. Because the different intersections of the two curves above the resonant frequency correspond to the different number of lamps that are connected to the oscillating circuit and operate normally, the normal state is obtained according to the working state of the lamp at different intersections of the two curves. The number of lamps that work.

Since the single-chip calculator is used to control the multi-lamp driving circuit, the output voltage is detected by adjusting the frequency or pulse width of the inverter, and the equation 1 is checked. By approximating, the lamp current can be accurately controlled indirectly, and the lamp can be realized. Intelligent closed-loop control of current. Since the lamp voltage varies with temperature, the lamp voltage that is checked into the above formula is temperature compensated.

As can be seen from Fig. 9, since the resonance frequency is related to the number of lamps, when the lamp is open, the resonance frequency rises. When the resonance frequency exceeds the switching frequency of the inverter, the inverter circuit operates in a capacitive mode. At this time, the characteristics of the zero-voltage turn-on of the power transistor in the inverter will be lost, which will endanger the safety of the power transistor. At the same time, V _tr will become a positive exponential function of f, and the control law is completely reversed. If the original control law is continued, V _tr will rise to the resonance voltage peak to damage the circuit or reduce V _tr to the most Small values cause the system to not work.

A method for stabilizing a circuit in an extreme case according to an embodiment of the present invention includes: determining whether a output voltage of the transformer is a negative exponential function of an inverter switching frequency, and if so, continuing to perform step 3 of the above-described lamp driving method of the present invention The step of changing the switching frequency of the inverter, otherwise the inverter output frequency is rapidly changed to the maximum value set by the system, and then gradually decreased to the voltage and frequency values corresponding to the relationship curve. This extra measure ensures that the drive circuit remains stable in extreme cases. In addition to the above methods, the embodiment of the present invention may also cause the inverter to stop operating, then restart and adjust to the steady state operating point.

In the circuit of Figure 7, the current of each cold cathode fluorescent tube is determined by the transformer Tl, T2 output voltage, frequency and series connected capacitance Cn. The impedance of the cold cathode fluorescent tube itself is not so great, therefore, the current of each cold cathode fluorescent tube is substantially equal as long as the series capacitance Cn is equal, and the current of the cold cathode fluorescent tube is constant at the same frequency. The output voltage of the transformer is controlled.

Experiments show that when the output voltage of the transformer is 2.13 times the steady-state operating voltage of the lamp, even if the steady-state voltage of the lamp has a difference of 10%, the lamp current is only 3% difference. Therefore, based on the difference in lamp steady-state voltage and the desired current balance, the output voltages of the transformers T1, T2 required in this solution can be derived. In other words, the maximum allowable error between multiple lamp currents is 3%, which corresponds to a minimum of 2.13 for the quotient of the transformer output voltage and the steady-state operating voltage of the lamp. In the case where the series capacitor has a fixed capacitance value and the operating frequency can be fixed, the lamp current is controlled only by one parameter of the transformer output voltage. Therefore, the present invention can be easily controlled by controlling the output voltages of the transformers T1 and T2. The lamp current is at an optimum level.

It can be seen from the above analysis that the lamp current of the present invention is controlled by the transformer output voltage and is automatically balanced when the series capacitor and operating frequency are selected, thus satisfying the characteristics that the lamp current is stable and substantially equal;

Since the transformer output voltage is higher and higher than the breakdown voltage of the lamp, the transformer T1,

T2 is designed to operate at high voltage output, so there is no additional problem of requiring high voltage breakdown of the lamp;

Due to the transformer leakage inductance and capacitive resonance operation, the lamp current is sinusoidal;

Since the lamp current of the present invention is controlled by the transformer output voltage, and the transformer output is high Pressure, therefore, when a certain lamp is open, as long as the output voltage and frequency of the control transformer meet the above Equation 1, other lamp work will not be affected, and it is not necessary to stop the operation of the inverter circuit, thereby ensuring that the backlight will not be affected by one. Only the open circuit of the lamp is completely disabled, the redundancy of the system is increased, and the reliability and service life are improved.

It can be seen that the present invention fully satisfies the four conditions that need to be met by the cold cathode fluorescent multi-lamp driving circuit; and, has better technical effects than the prior art, that is, realizes the intelligent closed-loop control of the above-mentioned lamp current; Stable, not susceptible to faults; At the same time, less transformers are used to reduce costs; system redundancy is increased, reliability and service life are improved; switching transistors in inverter circuits can easily achieve zero voltage Switch, energy consumption is reduced; and automatic detection of lamp failure is realized.

The above is a detailed description of a lamp driving circuit and a method thereof provided by the present invention, which are for explaining and explaining the principles of the present invention. It is to be understood that the specific embodiments of the present invention are not limited thereto. It will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is defined by the claims.

Claims

Rights request

A multi-lamp current control method, each of the lamps is connected in series with a capacitor, and the plurality of lamps connected in series are connected in parallel and connected to an output winding of the driving transformer, and the characteristics thereof In that, the method includes:

The multi-lamp current control method according to claim 1, wherein an inverter is connected to an input end of the transformer, and the output voltage of the adjustment transformer is realized by controlling an inverter switching frequency.

The multi-lamp current control method according to claim 2, wherein the transformer output terminal further has a voltage dividing detection capacitor connected in parallel, wherein the controlling the inverter output voltage by controlling the inverter switching frequency comprises: :

Obtaining a transformer output voltage measurement value by measuring the voltage division detecting capacitor voltage; comparing a voltage value determined by the voltage measurement value with a predetermined voltage and frequency relationship curve corresponding to a current inverter switching frequency;

If the voltage measurement value is greater than the voltage value corresponding to the curve, increase the inverter switching frequency, otherwise reduce the inverter switching frequency.

The multi-lamp current control method according to claim 3, further comprising: before the step of changing the switching frequency of the inverter, further comprising:

Determine whether the output voltage of the transformer is a negative exponential function of the inverter switching frequency. If yes, continue to change the inverter switching frequency. Otherwise, the inverter switching frequency is quickly changed to the maximum value set by the system, and then gradually Decrease to the voltage and frequency values corresponding to the relationship curve or control the inverter to stop working.

The multi-lamp current control method according to claim 1, further comprising: obtaining the lamp quantity information of the normal operation according to the position of the curve corresponding to the current working point.

6. a multi-lamp driving circuit, each of the plurality of lamps being connected in series with a capacitor, a plurality of tubes connected in series with a capacitor and coupled to an output winding of the driving transformer, wherein the driving circuit has an operating state control unit, and the working state control unit comprises:

The multi-lamp driving circuit according to claim 6, further comprising: an inverter connected to the input end of the transformer;

At least two series-connected voltage-dividing detection capacitors are connected in parallel to the output of the transformer, the at least two voltage-dividing detection capacitors are grounded, the leakage inductance of the transformer and the capacitance and voltage division of all the series-connected lamps The detecting capacitor constitutes a resonant circuit;

The control module controls the output voltage of the transformer by adjusting the switching frequency of the inverter.

The multi-lamp driving circuit according to claim 7, further comprising: a voltage detecting unit, configured to obtain a partial pressure value of the voltage dividing detecting capacitor, and obtain the divided voltage a value is input to the working state control unit;

The working state control unit determines, according to the obtained partial pressure value, whether the output voltage of the transformer is a voltage corresponding to the relationship curve at a current inverter switching frequency.

The multi-lamp driving circuit according to claim 8, wherein the working state control unit further comprises:

a voltage comparison unit, configured to compare the input voltage detection value with a voltage value corresponding to the relationship curve at the current inverter switching frequency, and output a frequency control signal to the inverter to control the switching frequency according to the comparison result, if the voltage The measured value is greater than the voltage value corresponding to the relationship curve, and the control module issues a frequency control signal that increases the switching frequency of the inverter, and otherwise issues a frequency control signal that reduces the switching frequency of the inverter.

The multi-lamp driving circuit according to claim 8, wherein the storage unit further stores different operating points on the relationship curve corresponding to different number of lamps participating in the resonant circuit and working normally. The data, the control module obtains the data of the number of the lamps according to the current working point.