CN102413610A - Automatic current sharing non-isolated multi-path LED drive circuit - Google Patents
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Abstract
The invention discloses an automatic current sharing non-isolated multi-path LED drive circuit. The automatic current sharing non-isolated multi-path LED drive circuit comprises a driver circuit and an LED circuit, wherein, an output terminal of the driver circuit is connected with an input terminal of the LED circuit. The drive circuit direct current and a controller to drive on and off of two power switch tubes, and the power switch tubes are in series connection with a resonant inductor. The LED circuit is composed of at least two LED branch circuits which are in parallel connection. The LED branch circuits are composed of a blocking capacitor, two diodes, an energy storage capacitor, and a light emitting diode string which are connected. The LED drive circuit in the invention has a characteristic of automatic current sharing, and influence of inconsistent LED characteristic parameters on the drive circuit is inhibited. In addition, a circuit topology structure has the characteristics of simple structure and strong expansion capability, and LED current sharing of any number of branches can be realized conveniently.
Description
Technical Field
The invention relates to an LED drive circuit, in particular to an automatic current-sharing non-isolated multi-path LED drive circuit.
Background
With the continuous improvement of LED (Light-Emitting Diode) technology, LEDs have been characterized by high lighting efficiency, long service life, fast response, environmental protection, etc. as illumination Light sources, and have begun to replace traditional Light sources in a plurality of illumination fields. Although the power capacity of a single LED reaches 10W, the illumination scheme using a single LED still fails to meet the requirements in illumination situations requiring large area and high illumination. To solve this problem, the LEDs are often connected in parallel, series, or parallel-series. Considering that there is inconsistency in the characteristic parameters of LEDs, as shown in fig. 1; the requirement of LED driving voltage on safety regulations and the requirement of reliability, at present, in the application occasions with slightly larger power in industry, LEDs are mostly used in series-parallel connection, as shown in figure 2.
However, since each LED has a different characteristic curve, even if the voltages applied to the LEDs are uniform, there is a difference in current among the LEDs. This will make each LED be in under different operating conditions, then light reduce the life-span of heavily loaded branch road, make heavily loaded branch road damage. Therefore, current sharing measures must be adopted for each LED, and at present, the following LED current sharing measures are mainly adopted:
(1) and selecting the LED elements with more consistent performance characteristics for parallel use. This measure can reduce the imbalance of the current passing through the LED to some extent, but requires a great deal of personnel and equipment to select the LED, and makes the operation difficult in practice.
(2) Current sharing of a plurality of independent LEDs is achieved by using a mature IC chip. The LED driving circuit formed by the mode is complex, an optical coupler and an operational amplifier are required to be additionally arranged, and the cost is high. The current sharing control method is only suitable for current sharing control of 1-2 LEDs generally, and current sharing control of multiple paths of LEDs is difficult to meet.
(3) And a current control unit is connected in series in each LED branch. The working principle of this current sharing mode is shown in fig. 3. This method requires active devices (MOS transistors, triodes, etc.) to be connected in series in each branch, and these active devices are mostly operated in the amplification region. The multi-branch LED drive circuit formed by adopting the mode generally has the defects of high cost, large loss and complex control, and is adopted less and less at present.
(4) And each LED branch is connected with a resistor, an inductor or a capacitor element in series for current sharing. Fig. 4 shows a schematic diagram of a current sharing scheme, in which current sharing is implemented by using the resistance of the series resistors to be much larger than the on-resistance of the diodes. In order to solve the problem of low efficiency (most of the energy in the circuit is consumed by the series-connected resistor) in the series-connected resistor scheme, various schemes of serially connecting a capacitor and an inductor in a branch circuit are proposed. Since the capacitance and inductance do not consume power in use, they are considered to be an ideal current sharing scheme. In the scheme of adopting inductors as the current equalizing elements, the inductors need to be coupled with each other, and the design and the manufacture of the inductors are relatively complex, so that the scheme is difficult to be put into practical use. At present, in order to realize a scheme in which a capacitor is used as a current sharing element, an independent LLC resonant circuit is often used as a preceding stage circuit, so that the circuit topology is relatively complex, and the current sharing problem of only 2N (N =1,2, 3 … …) branches can be solved.
In summary, in the existing multi-path LED current sharing methods, the current sharing method using resistors has the problems of large circuit loss, single-cycle operation of LEDs and pulsating direct current of circuit current in the current sharing method using capacitors, the current sharing method using transformers (inductors) has the disadvantages of complex circuit and difficult expansion, and the linear current sharing method using each group of LEDs connected in series with active devices has the disadvantages of high circuit cost and complex control, so that these current sharing methods cannot solve the current sharing problem of parallel operation of multiple groups of LEDs.
Disclosure of Invention
The invention aims to provide an automatic current-sharing non-isolated multi-path LED drive circuit by considering the problems and aiming at the characteristic that an LED drive circuit does not need to be isolated in certain application occasions. The driving circuit has a simple structure and a non-isolation effect with an automatic current-sharing characteristic. The drive circuit combines the resonance capacitor in the LLC circuit with the external blocking capacitor and cancels an isolation transformer in a common current equalizing circuit, so that the drive circuit has the characteristics of less element number and internal automatic current equalizing; the driving circuit can also solve the problem of parallel connection of any number of branches, and has good expansion capability.
The purpose of the invention is realized by the following technical scheme:
a non-isolated multi-path LED driving circuit capable of automatically equalizing current comprises a driver circuit and an LED circuit, wherein the output end of the driver circuit is connected with the input end of the LED circuit.
The driver circuit comprises a direct-current power supply Vc, a controller, a first power switch tube Q1, a second power switch tube Q2 and a resonant inductor Lr; the positive electrode of the direct-current power supply Vc is connected with the source electrode of the first power switch tube Q1, the negative electrode of the direct-current power supply Vc is connected with the drain electrode of the second power switch tube Q2, the controller controls the switching states of the first power switch tube Q1 and the second power switch tube Q2, and the drain electrode of the first power switch tube Q1 is connected with the source electrode of the second power switch tube Q2 and connected with the resonant inductor Lr in series.
The LED circuit comprises a branch circuit or a plurality of parallel branch circuits, and the branch circuit comprises a first blocking capacitor Cb1, a first diode D1, a second diode D2, a first energy storage capacitor C1 and a first LED string LED 1; the first blocking capacitor Cb1 is connected with the resonant inductor Lr, the first blocking capacitor Cb1 is respectively connected with the anode of the first diode D1 and the cathode of the second diode D2, the cathode of the first diode D1 is connected with the anode of the first energy storage capacitor C1 and the cathode of the first light emitting diode string LED1, the cathode of the second diode D2 is grounded with the cathode of the first energy storage capacitor C1, and a current detection resistor Rm is connected between the cathode of the light emitting diode string and the cathode of the direct current power supply Vc.
The parameters of the first blocking capacitor Cb1, the first diode D1, the second diode D2, the first energy storage capacitor C1 and the first light emitting diode string LED1 on each LED branch circuit are the same, or at least any one of the parameters of the first blocking capacitor Cb1, the first diode D1, the second diode D2, the first energy storage capacitor C1 and the first light emitting diode string LED1 on each LED branch circuit is different.
The driver circuit comprises a direct-current power supply Vc, a controller, a first power switch tube Q1, a second power switch tube Q2 and a resonant inductor Lr; the positive electrode of the direct-current power supply Vc is connected with the source electrode of the first power switch tube Q1, the negative electrode of the direct-current power supply Vc is connected with the drain electrode of the second power switch tube Q2, the controller controls the switching states of the first power switch tube Q1 and the second power switch tube Q2, and the drain electrode of the first power switch tube Q1 is connected with the source electrode of the second power switch tube Q2 and connected with the resonant inductor Lr in series.
The LED circuit comprises a branch circuit or a plurality of parallel-connected branch circuits, and the branch circuit comprises a first blocking capacitor Cb1 and an alternating current equivalent resistor connected in series with the first blocking capacitor Cb1
(ii) a AC equivalent resistance
Comprises the following steps:
wherein: m is the number of the LED lamp beads on the LED branch,
for the equivalent resistance of the LED lamp bead, one end of a first blocking capacitor Cb1 is connected with the resonance inductor Lr, and the other end of the first blocking capacitor Cb1 is connected with the alternating current equivalent resistance
And (4) connecting.
The resonant inductor Lr and the first blocking capacitor Cb1 are utilized to form a resonant circuit, the resonant circuit works near a resonant point, and the current flowing through the first blocking capacitor Cb1 is close to a sine wave.
The rated working current of the LED can be set by changing the values of the resonant inductor Lr and the first blocking capacitor Cb 1.
The current detection resistor Rm is connected in series in the LED branch circuit, so that a current feedback link in current closed-loop control directly comes from a direct current link, and the method is simple and reliable.
The controller generates a PWM driving signal with a duty ratio of about 50% according to the voltage returned by the current detection resistor Rm, and controls the switching states of the first power switch Q1 and the second power switch Q2.
The impedance of the first blocking capacitor Cb1 in the alternating current loop is far larger than that of the alternating current equivalent resistor formed by each LED branch circuit, so that the condition that the current of each LED branch circuit is inconsistent due to the inconsistency of the internal parameters of the LED is restrained.
Compared with the prior art, the invention has the advantages that:
(1) the driving circuit has the inherent current balancing capability (the balancing mechanism is shown in figures 6 and 7), and the influence of the inconsistency of the LED parameters on the circuit can be well inhibited.
(2) The driving circuit adopts a capacitor without energy loss as a current equalizing element, and the energy loss of the driving circuit is small.
(3) The current feedback link in the current closed-loop control is directly derived from the direct current link, and is simple and reliable.
(4) The driving circuit has good expandability and can be conveniently expanded to any number of branches.
(5) The drive circuit can be controlled by a general IC and has wide application range.
The invention is a multi-path LED drive circuit which has simple structure, internal current balance capability, convenience and practicability.
Drawings
Fig. 1 LED characteristic curve.
FIG. 2 is a schematic diagram of the LED series-parallel operation.
The current sharing scheme of the current control unit connected in series in the branch of fig. 3.
The current sharing scheme of serially connected resistor elements in the branch of fig. 4.
Fig. 5 is a topological structure diagram of the present invention.
Fig. 6 is an equivalent model of the driving circuit according to the present invention.
FIG. 7 is a schematic diagram of a current sharing mechanism according to the present invention.
Detailed Description
Fig. 5 shows a topology diagram of the present invention. In fig. 5, only 2 LED branches are shown, and in practical use, a circuit consistent with the LED branch may be connected in series at the connection between the resonant inductor Lr and the first blocking capacitor Cb1, so that the driving circuit provided by the present invention may be used to drive any number of LED branches.
Fig. 6 shows an equivalent model of the driving circuit proposed by the present invention, and in fig. 6,
（i=1,2…n) The AC equivalent resistance value of the LED branch circuit is shown.
Fig. 7 is a schematic diagram of a current sharing scheme according to the present invention, in fig. 7,
and
（
) Are respectively the firstStrip branch andthe impedance of the branch,
Is the equivalent impedance of the first blocking capacitor Cb1 and the second blocking capacitor Cb2 in the ac loop. When the circuit is in operation
Strip branch andbranch (
) The ratio of the current amplitudes of (a) to (b) is:
when the AC impedance of the blocking capacitor is much greater than the equivalent resistance of the LED string, i.e.
Formula (1) can be simplified as:
such asEquation (2) is further simplified as:
therefore, the automatic current-sharing non-isolated multi-path LED driving circuit provided by the invention can ensure that the current flowing through each branch is consistent as long as the blocking capacitors are ensured to have the same value and the alternating current impedance of the blocking capacitors is far greater than the alternating current equivalent resistance of the LED branches.
As shown in fig. 5, the present invention provides an automatic current-sharing non-isolated multi-channel LED driving circuit, which includes a driver circuit and an LED circuit, wherein an output terminal of the driver circuit is connected to an input terminal of the LED circuit.
The driving circuit comprises a direct-current power supply Vc, a controller, a first power switch tube Q1, a second power switch tube Q2 and a resonant inductor Lr; the positive electrode of the direct-current power supply Vc is connected with the source electrode of the first power switch tube Q1, the negative electrode of the direct-current power supply Vc is connected with the drain electrode of the second power switch tube Q2, the controller controls the switching states of the first power switch tube Q1 and the second power switch tube Q2, and the drain electrode of the first power switch tube Q1 is connected with the source electrode of the second power switch tube Q2 and connected with the resonant inductor Lr in series.
The LED circuit is formed by connecting two LED branch circuits in parallel, the first LED branch circuit is composed of a first blocking capacitor Cb1, a first diode D1, a second diode D2, a first energy storage capacitor C1 and a first light-emitting diode string LED1, the first blocking capacitor Cb1 is connected with the resonant inductor Lr, the first blocking capacitor Cb1 is respectively connected with the anode of the first diode D1 and the cathode of the second diode D2, the cathode of the first diode D1 is connected with the anode of the first energy storage capacitor C1 and the cathode of the first light-emitting diode string LED1, and the cathode of the second diode D2 is grounded with the cathode of the first energy storage capacitor C1; the second LED branch circuit is composed of a second blocking capacitor Cb2, a third diode D3, a fourth diode D4, a second energy storage capacitor C2 and a second light emitting diode string LED2, the second blocking capacitor Cb2 is connected to the resonant inductor Lr, the second blocking capacitor Cb2 is respectively connected to the anode of the third diode D3 and the cathode of the fourth diode D4, the cathode of the third diode D3 is connected to the anode of the second energy storage capacitor C2 and the cathode of the second light emitting diode string LED2, and the cathode of the third diode D3 is grounded to the cathode of the second energy storage capacitor C2.
When the two LED branch circuits are connected in parallel, the negative electrode of the first LED string LED1 is connected with the negative electrode of the second LED string LED 2; a current detection resistor Rm is connected between the cathode of the first LED string LED1 of the first LED branch circuit and the cathode of the direct-current power supply Vc; the controller detects the voltage across the current detection resistor Rm.
As shown in fig. 6, the equivalent circuit of the automatic current-sharing non-isolated multi-channel LED driving circuit of the present invention. As shown in fig. 7, the present invention relates to a current balancing mechanism of an automatic current-sharing non-isolated multi-channel LED driving circuit.
The specific implementation steps of the equivalent circuit of the LED branch circuit are as follows:
1. according to the LED lamp bead curve provided by the manufacturer, the curve is searched to calculate the rated current of the LED lamp bead under the typical parameters
LED equivalent resistor
And the rated voltage of the LED lamp bead at the moment
。
2. And calculating the number M of the LED lamp beads to be driven by the whole driving circuit and the number N of the LED branches according to the brightness requirement and the limit of the number of the single-loop LED strings.
3. The operating angular frequency of the driving circuit is set according to the types of the first power switch Q1 and the second power switch Q2 and the material of the magnetic element used by the resonant inductor Lr
。
4. Calculating the AC equivalent resistance of the circuit composed of the half-wave rectifier circuit and the LED by using the formula (5)
。
5. Determination of the current supply voltage using equation (6)
Whether the requirements are met.
6. Using equation (7) and operating frequency
Calculating the values of the resonant inductance Lr and the blocking capacitance Cb;
wherein,
in order to be a frequency offset coefficient,
。
7. verification of the resonance factor in a resonant tank using equation (8)
Whether the requirements are met, if so
If too large or too small, the frequency shift coefficient in equation (7) is required
The correction is carried out until a satisfactory result is obtained.
8. Calculating the numerical values of the first energy storage capacitor C1 and the second energy storage capacitor C2 by using a formula (9);
wherein, in the formula:
the voltage difference of the first energy storage capacitor C1 is equal to the maximum current fluctuation rate of the LED (the parameter is 5% and below of the rated working current);
is the duty cycle of the driving circuit.
9. Through the voltage returned by the current detection resistor Rm, the controller generates a PWM driving signal with a duty ratio of about 50% to control the switching states of the first power switch Q1 and the second power switch Q2.
10. And if the voltage returned by the detection resistor Rm is detected to be too large, the frequency of the PWM driving signal generated by the controller is increased, otherwise, the frequency of the PWM driving signal generated by the controller is reduced.
Claims (4)
1. The non-isolated multi-path LED driving circuit capable of automatically equalizing current is characterized by comprising a driver circuit and an LED circuit, wherein the output end of the driver circuit is connected with the input end of the LED circuit.
2. The non-isolated multi-path LED driving circuit capable of automatically current sharing according to claim 1, wherein the driver circuit comprises a direct current power supply Vc, a controller, a first power switch tube Q1, a second power switch tube Q2, a resonant inductor Lr; the positive electrode of a direct-current power supply Vc is connected with the source electrode of a first power switch tube Q1, the negative electrode of the direct-current power supply Vc is connected with the drain electrode of a second power switch tube Q2, a controller controls the switching states of the first power switch tube Q1 and the second power switch tube Q2, and the drain electrode of the first power switch tube Q1 is connected with the source electrode of a second power switch tube Q2 and connected with a resonant inductor Lr in series;
the LED circuit comprises a branch circuit or a plurality of parallel branch circuits, and the branch circuit comprises a first blocking capacitor Cb1, a first diode D1, a second diode D2, a first energy storage capacitor C1 and a first LED string LED 1; the first blocking capacitor Cb1 is connected with the resonant inductor Lr, the first blocking capacitor Cb1 is respectively connected with the anode of the first diode D1 and the cathode of the second diode D2, the cathode of the first diode D1 is connected with the anode of the first energy storage capacitor C1 and the cathode of the first light emitting diode string LED1, the cathode of the second diode D2 is grounded with the cathode of the first energy storage capacitor C1, and a current detection resistor Rm is connected between the cathode of the light emitting diode string and the cathode of the direct current power supply Vc.
3. The self-current-sharing non-isolated multi-channel LED driving circuit according to claim 2, wherein the parameters of the first blocking capacitor Cb1, the first diode D1, the second diode D2, the first energy-storage capacitor C1 and the first LED string LED1 on each LED branch circuit are the same as each other, or at least any one of the parameters of the first blocking capacitor Cb1, the first diode D1, the second diode D2, the first energy-storage capacitor C1 and the first LED string LED1 on each LED branch circuit is different.
4. The non-isolated multi-path LED driving circuit capable of automatically current sharing according to claim 1, wherein the driver circuit comprises a direct current power supply Vc, a controller, a first power switch tube Q1, a second power switch tube Q2, a resonant inductor Lr; the positive electrode of a direct-current power supply Vc is connected with the source electrode of a first power switch tube Q1, the negative electrode of the direct-current power supply Vc is connected with the drain electrode of a second power switch tube Q2, a controller controls the switching states of the first power switch tube Q1 and the second power switch tube Q2, and the drain electrode of the first power switch tube Q1 is connected with the source electrode of a second power switch tube Q2 and connected with a resonant inductor Lr in series;
the LED circuit comprises a branch circuit or a plurality of parallel-connected branch circuits, and the branch circuit comprises a first blocking capacitor Cb1 and an alternating current equivalent resistor connected in series with the first blocking capacitor Cb1
(ii) a AC equivalent resistance
Comprises the following steps:
wherein: m is the number of the LED lamp beads on the LED branch,for the equivalent resistance of the LED lamp bead, one end of a first blocking capacitor Cb1 is connected with the resonance inductor Lr, and the other end of the first blocking capacitor Cb1 is connected with the alternating current equivalent resistance
And (4) connecting.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105491724A (en) * | 2015-12-31 | 2016-04-13 | 华南理工大学 | Current-sharing controlled-switch capacitor control-based dimmable LED drive circuit |
| CN106535393A (en) * | 2016-10-26 | 2017-03-22 | 广东工业大学 | Control method of resonant LED current-sharing circuit |
| CN113709941A (en) * | 2021-09-09 | 2021-11-26 | 深圳市优仕拓科技有限公司 | Circuit of high PF value non-isolation multichannel intelligent power supply |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN201918900U (en) * | 2010-06-18 | 2011-08-03 | 阳菊村 | Driving power source used for LED (light-emitting diode) fluorescent lamp |
| CN202335004U (en) * | 2011-11-16 | 2012-07-11 | 广东工业大学 | Automatic current-equalizing non-isolation multi-circuit light emitting diode (LED) drive circuit |
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN201918900U (en) * | 2010-06-18 | 2011-08-03 | 阳菊村 | Driving power source used for LED (light-emitting diode) fluorescent lamp |
| CN202335004U (en) * | 2011-11-16 | 2012-07-11 | 广东工业大学 | Automatic current-equalizing non-isolation multi-circuit light emitting diode (LED) drive circuit |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105491724A (en) * | 2015-12-31 | 2016-04-13 | 华南理工大学 | Current-sharing controlled-switch capacitor control-based dimmable LED drive circuit |
| CN105491724B (en) * | 2015-12-31 | 2017-10-20 | 华南理工大学 | Based on the Dimmable LED drive circuit for flowing gate-controlled switch Capacity control |
| CN106535393A (en) * | 2016-10-26 | 2017-03-22 | 广东工业大学 | Control method of resonant LED current-sharing circuit |
| CN106535393B (en) * | 2016-10-26 | 2018-05-15 | 广东工业大学 | A kind of mode of resonance LED flow equalizing circuit control methods |
| CN113709941A (en) * | 2021-09-09 | 2021-11-26 | 深圳市优仕拓科技有限公司 | Circuit of high PF value non-isolation multichannel intelligent power supply |
| CN113709941B (en) * | 2021-09-09 | 2024-03-08 | 深圳市优仕拓科技有限公司 | Circuit of non-isolated multichannel intelligent power supply of high PF value |
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