TW201332263A - Current balancing device - Google Patents

Abstract

A current balancing device drives at least two sets of LED lamp to illuminate and includes a Zeta-type converter, a differential transformer and two sets of rectifier circuit. The technical characteristics of the present invention is that the equivalent leakage inductance of the differential transformer replaces the output inductance of the Zeta-type converter, and an energy transmission capacitor can demagnetize the differential transformer and recycle energy therefrom so as to avoid power loss and increase the overall efficiency.

Description

Current balancing device

The present invention relates to a current balancing circuit, and more particularly to a current balancing device that recovers excitation energy to avoid power loss and improve overall efficiency.

The existing LED driving device is driven by a constant voltage source as shown in Fig. 1, or driven by a constant current source as shown in Fig. 2, as follows.

Referring to Figure 1, LED with fixed-voltage driving device 9 is the LED - each cathode terminal grounded LED _n of, LED ~ after each of the male terminal LED _n are respectively connected in series a current limiting resistor (Ballast Resistor) in parallel with a total input terminal, and load the constant voltage source V _in total to the input terminal, but when the constant voltage source V _in voltage or a forward voltage of each LED ~ LED _n are changes in the current flowing through the LED ~ LED _n will also change Therefore, its shortcoming is that the flow stability is poor.

Referring to FIG. 2, a constant current LED driving device 8 includes a constant voltage source V _in , an input capacitor C _in , a buck converter, an output inductor L _{o ,} and an output capacitor C _o , and finally outputs a constant current to an LED string. Since the brightness of the LED element is proportional to the current, a plurality of LED elements are connected in series to each other so that the current of each LED element is uniform, thereby avoiding the problem of current instability.

However, multiple sets of parallel LED strings require more complicated driving circuits. Taking a current-balanced driving device as an example, when the load is unbalanced, the voltage across the differential transformer of the driving device is not zero, so the existing method is used. The reset diode is added as a demagnetization element, and a demagnetization resistor or a dipole is added to the demagnetization path to complete the demagnetization, but power loss is reduced to reduce the overall efficiency.

Accordingly, it is an object of the present invention to provide a current balancing device that recovers excitation energy to avoid power loss and improve overall efficiency.

Therefore, the current balancing device of the present invention drives at least two groups of light emitting diode strings to illuminate, the current balancing device comprises a differential transformer and two sets of rectifier circuits, the differential transformer comprising an input end, a transformer body and two An output end, the input end receives a DC power source to cause the transformer body to generate excitation and output a driving current at each of the output ends, the differential transformer has an equivalent leakage inductance; the two sets of rectifier circuits are respectively coupled to the differential transformer Each of the output terminals drives each group of light emitting diode strings to illuminate, and each of the rectifier circuits includes a reset diode for demagnetizing the differential transformer to demagnetize the differential transformer, and The rectifying unit that supplies the light-emitting diode strings of each group after the driving current is rectified.

The technical feature of the current balancing device of the present invention is that the current balancing device further includes a Zeta-type converter in front of the current balancing device, which has a power switch, a storage inductor, an energy transfer capacitor, and a second a pole element and an output inductor, the power switch, the energy storage inductor and the energy transfer capacitor each have a first end and a second end, the first end of the power switch is connected to a power source and controls current conduction/non-conduction The first end of the energy storage inductor and the first end of the energy transfer capacitor are connected to the second end of the power switch, and the first end of the energy transfer capacitor is connected to the energy storage inductor. The first end of the energy transfer capacitor is connected to the cathode end of the diode element, the second end of the energy storage inductor and the anode end of the diode element are grounded, and the energy transfer capacitance and the The connection of the diode element outputs the DC power source to the input end of the differential transformer, and replaces the output inductance of the original Zeta-type converter by the equivalent leakage inductance of the differential transformer, and cooperates with the energy transfer capacitor The magnetizing inductance of the differential transformer is demagnetized and recovers energy.

The effect of the current balancing device of the present invention is that the output inductance of the Zeta-type converter is replaced by the equivalent leakage inductance of the differential transformer, and the energy transfer capacitance is used as the demagnetization element to demagnetize and recover the magnetizing inductance of the differential transformer. Energy, avoiding power loss and increasing overall efficiency and increasing its current sharing accuracy.

The foregoing and other objects, features, and advantages of the invention are set forth in the <RTIgt;

Before the present invention is described, it should be noted that not all types of power converters having output inductors are suitable for use as a front stage circuit as a current balancing device, as explained below.

Referring to Fig. 3, a Cuk converter 71 utilizes an electrical inductor L ₂ as an energy transfer element, but the reason why the Cuk converter 71 cannot be applied to a current balancing device is that the Cuk converter 71 is a negative voltage output.

Referring to FIG. 4, a single-ended primary inductor converter (Sepic) 72 uses an inductor L2 as an energy transfer element, but since the inductor L _{2 of the} Sepic converter is directly grounded, it cannot be replaced by the equivalent leakage inductance of the transformer. This inductor L ₂ .

From the above results, it is understood that the possibility of using the Cuk converter 71 or the single-ended primary inductor 72 as the pre-stage circuit of the current balancing device is eliminated.

Referring to FIG. 5, a Zeta converter 73 having similar components to FIGS. 3 and 4 has a power switch S, a storage inductor L, an energy transfer capacitor C, a diode component D _p and an output inductor L _{o .} Since the output inductor L _o is a positive voltage output, the present invention replaces the output inductance L _o with the equivalent leakage inductance of the transformer 5 ( FIG. 6 ), and has obtained similar components as those of FIGS. 3 and 4 . The power converter can't achieve the effect.

Referring to FIG. 6, a preferred embodiment of the current balancing device 100 of the present invention includes a Zeta-type converter 10 in the front stage, a differential transformer 5, and two sets of rectifier circuits 601 and 602. The rectifier circuits 601 and 602 respectively Electrically connecting each of the LED strings LS ₁ and LS ₂ , the rectifier circuit 601 includes a reset diode D _f1 and a rectifying unit 61 , and the rectifying circuit 602 includes a reset diode D _f2 and a rectifying unit 62 ; The components of the device 100 are described below.

The Zeta-type converter 10 has a power switch S, an energy storage inductor L, an energy transfer capacitor C and a diode element D. The power switch S, the energy storage inductor L and the energy transfer capacitor C each have a first end. 11, 21, 31 and a second end 12, 22, 32, the first end 11 of the power switch S is connected to a power source V _in and controls the current conduction/non-conduction to be outputted to the second end 12 thereof, the energy storage inductor The first end 21 of the L and the first end 31 of the energy transfer capacitor C are connected to the second end 12 of the power switch S. The first end 31 of the energy transfer capacitor C is connected to the first end 21 of the energy storage inductor L, and the energy transfer The second end 32 of the capacitor C is connected to the cathode end 41 of the diode element D, the second end 22 of the storage inductor L and the anode end 42 of the diode element are grounded.

The differential transformer 5 includes an input terminal 50, a transformer body 500 and two output terminals 51, 52. The transformer body 500 has a transformer T and primary and secondary windings N ₁ and N ₂ , and the input terminal 50 receives the DC power supply. The transformer body 500 is excited and outputs a driving current I _o1 , I _o2 (see FIG. 7 ) at each of the output terminals 51 , 52 . The two sets of rectifier circuits 601 and 602 are respectively coupled to the respective output ends 50 of the differential transformer 5 and driven. Each group of LED strings LS ₁ and LS _{2 is} illuminated, and the reset diodes D _f1 and D _f2 demagnetize the differential transformer 5 to reset the differential transformer 5, and each of the rectifying units 61 and 62 is driven by each. The currents I _o1 and I _{o2 are} rectified and supplied to each group of LED strings LS ₁ and LS ₂ , and each of the rectifying units 61 and 62 includes a diode D _o1 , D _o2 and a capacitor C _o1 , C _o2 , and senses. The resistor R _s can be used in conjunction with the feedback sampling circuit for detecting current, which is not described here because it is not the focus of the present invention.

The ideal differential transformer 5 does not have a leakage inductance. Considering that the actual differential transformer 5 generates a leakage inductance, the circuit of the present invention is designed to replace the Zeta-type converter by the equivalent leakage inductance of the differential transformer 5. 10 output inductors, to save components and improve performance.

Referring to FIG. 7, the Zeta-type converter 10 of the preferred embodiment outputs a DC power source v _D to the differential transformer 5 from the junction of the energy transfer capacitor C and the diode element D, and the output inductor L cooperates with the energy transfer capacitor C. The differential transformer 5 demagnetizes and recovers energy; in addition, the current flowing through the power switch S is represented by i _in , the current flowing through the storage inductor L is represented by i _L , and the voltage is represented by v _L , and the voltage transfer capacitor C is cross-voltage In the case of v _C , the current flowing through the energy transfer diode _{D is} represented by i _D ; in the differential transformer 5 of the preferred embodiment, the cross-pressure of the primary and secondary windings N ₁ and N ₂ is v ₁ , v ₂ indicates that the magnetizing inductance of the transformer T is expressed by L _m , and one of the transformers T and the secondary side leakage inductances L _r1 and L _{r2 are} represented by v _Lr1 and v _Lr2 across the transformer, and flow through one of the transformers T and the secondary side leakage. The currents of the senses L _r1 and L _{r2 are} represented by i _Lr1 , i _Lr2 ; the currents flowing through the reset diodes D _f1 and D _{f2 are} represented by i _Df1 , i _Df2 ; the voltages rectified by the respective rectifying units 61 , 62 are V _o1 and V _{o2 are} indicated.

In order to facilitate the analysis, the following assumptions are made: the power switch S and the energy transfer diode D are both regarded as ideal components, that is, the switching time of the power switch S, the on-resistance and the energy transfer diode D are in turn. The reverse recovery time is negligible; the energy storage inductor L and the energy transfer capacitor C do not consider parasitic resistance; each LED string LS ₁ and LS _{2 is} equivalent to an ideal diode, knee voltage and The series connection of internal resistance; the main circuit architecture operates in discontinuous conduction mode; the turns ratio of one of the transformer T and the secondary side is 1:1 and the leakage inductance is equal.

The following modes of operation of the preferred embodiment are described below with reference to FIG. 8 to FIG. 13 , which are mainly based on the conduction and cut-off of the power switch and the diode and the different states of the transformer T and the energy storage component, and the present invention can be The current balancing device 100 is divided into six modes in a period T _s [ t ₀ t t ₁ ], [ t ₁ t t ₂ ], [ t ₂ t t ₃ ], [ t ₃ t t ₄ ], [ t ₄ t t ₅ ], [ t ₅ t t ₀ + T _s ] is used for circuit analysis, and the component numbers represent the meanings as shown in the description of FIG. 7 .

Mode 1: Referring to Figure 8, power switch S is turned on, the output diode D _{o 1} and D _{o 2} is turned on, the input power supply V _in L magnetizing of the inductor, so the rise i _L linearly; Meanwhile, the input power supply V _in the energy The transfer capacitor C supplies energy to the load terminal, so the energy transfer capacitor C is in a discharged state. Due to the different process factors of each LED light-emitting component, even under the same current drive, the operating voltage of each LED light-emitting component will be slightly different. It is assumed that V _{o 1} < V _{o 2} , the transformer T is Startup, the magnetizing inductance is equivalent to the primary side, and the exciting current flows in by the dot. Since the forward current of the transformer T is much larger than the excitation current, the current value flowing through one of the differential transformers T and the secondary side are very similar, that is, the voltage across the voltage v _{Lr 1} Cross-pressure v _{Lr 2} , so it can be assumed that the trans-voltage v _{Lr 1} = the trans-voltage v _{Lr 2} , the following expression can be known from the Khr-Hoff voltage law:

V _in + v _C = v _{Lr 1} + v ₁ + V _{o 1} = v _{Lr 2} - v ₂ + V _{o 2} Equation 1

Since one of the transformers T and the secondary side have a ratio of turns of 1:1 and the leakage inductance is equal, the crossover voltage v ₁ = the voltage across the pressure v ₂ and the voltage across the pressure v _{Lr 1} = the voltage across the pressure v _{Lr 2} , so Equation 1 can be used. After simplification, it can be seen from Equation 2 that the voltage across the primary winding N ₁ of the transformer T is ( V _{o 2} - V _{o 1} )/2, and this voltage is positive, so the exciting inductance L _m is excited and the transformer T The leakage inductances L _{r 1} and L _{r 2} of the primary and secondary sides are in an excited state. This mode ends when the power switch S is turned off.

v ₁ = v ₂ =( V _{o 2} - V _o1 )/2 Equation 2

Mode 2: Referring to FIG. 9, the power switch S is turned off, the diode D is turned on, and the inductor L releases the stored energy to the energy transfer capacitor C, so i _L decreases linearly, and the energy transfer capacitor C is in a charged state; The leakage inductances L _{r 1} and L _{r 2} of the primary and secondary sides of the transformer T release the excitation energy of the previous state to the load terminal, so the leakage inductances L _{r 1} and L _{r 2} are demagnetized. According to Kirchhoff's voltage law, the following expressions can be known:

v _{Lr 1} + v ₁ + V _{o 1} = v _{Lr 2} - v ₂ + V _{o 2} Equation 3

Simplify formula 3 to get:

v ₁ = v ₂ =( V _{o 2} - V _o1 )/2 Equation 4

Since V _{o 2} > V _{o 1} and it can be known from Equation 4 that the voltage across the primary winding N ₁ of the transformer T is still positive, L _{m is} still excited. Therefore, when the leakage inductances L _{r 1} and L _{r 2} of the primary and secondary sides of the transformer T are demagnetized to zero, this mode ends.

Mode 3: Referring to Figure 10, the power switch S is still off, the diode D is turned on, the inductor L continues to release energy on the energy transfer capacitor C, the output diodes D _{o 1} and D _{o 2 are} cut off and the load end energy Provided by output capacitors C _{o 1} and C _{o 2} . Therefore, the primary side of the transformer T has no freewheeling path and the excitation current of the transformer T must be freewheeling, and its freewheeling direction is the inflow of the dot, so the magnetizing inductance L _m is equivalent to the second by the relationship of the square of the turns. The side is L _m ' , so the excitation current flows from the secondary side to make a freewheeling action. Since the diode D and the reset diodes D _f1 and D _{f2 are} turned on, the voltage across the transformer T is zero, so the inductor current i _{L is made} to the diode D , the reset diodes D _f1 and D _f2 Dividing, at this time, the i _m ' of the transformer T is a certain value, so the magnetic flux of the excitation is a certain value. At this time, since the negative current transfer current of one of the transformers T and the secondary side is smaller than the previous forward current, the excitation current should not be ignored, since the reset diode current i _{Df 2 is} only more than i _{Df 1} A certain value of i _m ' component, so i _{Df 1} and i _{Df 2} both have equal current slopes and i _{Df 2} falls slower to zero than i _{Df 1} . The following expressions can be known from Kirchhoff's voltage law:

v _C + v _L = v _D =0 Equation 5

In this stage, since the inductor L continues to release energy to the energy transfer capacitor C, the capacitor voltage v _C will rise slowly, and Equation 5 shows that when v _C + v _L >0, the pole Body D will be cut off and this mode ends.

Mode 4: Referring to FIG. 11, the power switch S and the diode D are cut off, and the demagnetization path of the energy storage inductor L is demagnetized by resetting the two paths of the diodes D _{f 1} and D _{f 2} , and the energy transfer capacitor C In the state of charge, the load end energy is still provided by the output capacitor. The following expressions can be known from Kirchhoff's voltage law:

v _{Lr 1} + v ₁ = v _{Lr 2} - v ₂ Equation 6

Since one of the transformers T and the secondary side have a ratio of turns of 1:1 and the leakage inductance is equal, v ₁ = v ₂ and v _{Lr 1} = v _{Lr 2} , so v ₁ = v ₂ =0, two of the transformers T The end-span voltage is zero, and the magnetizing inductor current still performs the freewheeling action, so the magnetic flux of the exciting magnet is a certain value.

Mode 5: Referring to Figure 12, the power switch S and the diode D are turned off. At this stage, the inductor L has released the energy, the reset diode D _{f 1 is} turned off, and the load end energy is still output capacitors C _{ο 1} and C _{ο 2} provided. At this time, since the reset diode D _{f 1 is} turned off, no current is transmitted on the primary and secondary sides of the transformer T , and the current flowing through the secondary side is the exciting current, so the L _m ' of the transformer T is reset via The polar body D _{f 2} is demagnetized. On the demagnetization circuit, since the magnetizing inductance L _m ' is much larger than the inductance L and the leakage inductance L _{r 2} , the capacitance voltage v _C will mostly straddle the exciting inductance L _m '. At this time, the magnetizing inductance L _m ' will release energy to the energy transfer capacitor C across the capacitor voltage v _C , the energy transfer capacitor C is in a state of charge, and the reset diode D _{f 2 is} turned on, wherein the inductor current i _L is There is still a current component, which is still the demagnetizing current of the magnetizing inductance. When L _m ' is released, the reset diode D _{f 2} is turned off, and the next mode is entered.

Model 6: Referring to Figure 13, a power switch S, diode D and a reset diode D _{f 1} is turned off, the energy load terminal of the output capacitor C _{o 1} still and C _{o 2} provided; in this case the transformer T _m L ' In the last mode, the energy has been released, so the reset diode D _{f 2 is} turned off; when the power switch S is turned on again, the mode ends, and the next mode returns to the mode one state.

In order to verify the actual situation, two sets of light-emitting diode strings LS ₁ and LS ₂ with the same/different internal resistance are set in the experiment. The different internal resistance is to increase the internal resistance of the light-emitting diode string LS ₂ by 3Ω. Further, the current sharing effect is observed after the action of the current balancing device 100 of the present invention.

Table 1-1 and Table 1-2 show two groups of LEDs with the same internal resistance, LS ₁ and LS ₂ , with an input voltage of 24 volts and a load of 20% (light load) and 100% (full load). In the test results without increasing the internal resistance of 3Ω, refer to Figure 14 for the relevant waveforms of output voltage and output current.

Table 2-1 and Table 2-2 show the internal resistance of a group of LED strings LS _{2 with} an input voltage of 24 volts and a load of 20% (light load) and 100% (full load). As a result, Table 2 shows that the current error rate at light load is +0.57%, -0.57%, and the current error rate at full load is +0.42%, -0.42%. See Figure 15 for the waveforms of output voltage and output current. It can be verified that the present invention does have a good current sharing effect.

In addition to the dual-channel current balancing device 100, it is well known to those skilled in the art that as long as a multi-channel (eg, four-channel) current balancing device is suitable for the circuit architecture of the present invention, when the current is not balanced by two channels Device 100 is a limitation.

In summary, the current balancing device 100 of the present invention is effective in that the equivalent leakage inductance of the differential transformer 5 is designed as the output inductance of the Zeta-type converter 10, and the energy transfer capacitor C is used as the demagnetization element for the difference. The dynamic transformer 5 demagnetizes and recovers energy, avoids power loss, improves overall efficiency, and increases its current sharing accuracy, so that the object of the present invention can be achieved.

The above is only the preferred embodiment of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent changes and modifications made by the scope of the invention and the description of the invention are All remain within the scope of the invention patent.

[知知]

9. . . Constant voltage LED driver

8. . . Constant current LED driver

[This creation]

100. . . Current balancing device

10. . . Zeta-type converter

11, 21, 31. . . First end

12, 22, 32. . . Second end

41. . . Cathode end

42. . . Anode end

5. . . Differential transformer

50. . . Input

500. . . Transformer body

51, 52. . . Output

61, 62. . . Rectifier unit

601, 602. . . Rectifier circuit

71. . . Cuk converter

72. . . Single-ended primary inductor

73. . . Zeta converter

C. . . Energy transfer capacitor

C _o1 , C _o2 . . . capacitance

D. . . Diode component

D _f1 , D _f2 . . . Reset diode

D _o1 , D _o2 . . . Dipole

L. . . Energy storage inductor

LS ₁ , LS ₂ . . . Light-emitting diode string

N ₁ , N ₂ . . . First and second side winding

R _s . . . Sense resistor

S. . . Power switch

T. . . transformer

V _in . . . power supply

1 is a circuit diagram illustrating a constant voltage LED driving device;

2 is a circuit diagram illustrating a constant current LED driving device;

Figure 3 is a circuit diagram illustrating a Cuk converter;

4 is a circuit diagram illustrating a single-ended primary inductor converter;

Figure 5 is a circuit diagram illustrating a Zeta-type converter;

Figure 6 is a circuit diagram showing a preferred embodiment of the current balancing device of the present invention;

Figure 7 is a circuit diagram showing the components of the preferred embodiment of the current balancing device of the present invention and their current and voltage;

Figure 8 is a circuit diagram showing a preferred embodiment of the present invention in mode one;

Figure 9 is a circuit diagram showing the second embodiment of the preferred embodiment of the present invention;

Figure 10 is a circuit diagram showing the preferred embodiment of the present invention in mode three;

Figure 11 is a circuit diagram showing the fourth embodiment of the preferred embodiment of the present invention;

Figure 12 is a circuit diagram showing the fifth embodiment of the preferred embodiment of the present invention;

Figure 13 is a circuit diagram showing the mode of the preferred embodiment of the present invention;

Figure 14 is a waveform diagram showing the output voltage and output current of two sets of light-emitting diode strings of the same internal resistance;

Fig. 15 is a waveform diagram showing the output voltage and output current of two sets of light-emitting diode strings of different internal resistances.

100. . . Current balancing device

10. . . Zeta-type converter

11, 21, 31. . . First end

12, 22, 32. . . Second end

41. . . Cathode end

42. . . Anode end

5. . . Differential transformer

50. . . Input

500. . . Transformer body

51, 52. . . Output

61, 62. . . Rectifier unit

601, 602. . . Rectifier circuit

C. . . Energy transfer capacitor

C _o1 , C _o2 . . . capacitance

D. . . Diode component

D _f1 , D _f2 . . . Reset diode

D _o1 , D _o2 . . . Dipole

L. . . Energy storage inductor

LS ₁ , LS ₂ . . . Light-emitting diode string

N ₁ , N ₂ . . . First and second side winding

R _s . . . Sense resistor

S. . . Power switch

T. . . transformer

V _in . . . power supply

Claims (2)

A current balancing device for driving at least two groups of light emitting diode strings to emit light, the current balancing device comprising a differential transformer and two sets of rectifier circuits, the differential transformer comprising an input end, a transformer body and two output ends, The input end receives a DC power source to cause the transformer body to generate excitation and output a driving current at each of the output ends, the differential transformer has an equivalent leakage inductance; the two sets of rectifier circuits are respectively coupled to the differential transformer The output terminal drives each group of light emitting diode strings to illuminate, and each of the rectifier circuits includes a reset diode for demagnetizing the differential transformer to demagnetize the differential transformer, and a rectifying current for the driving current a rectifying unit for supplying each group of light emitting diode strings; wherein the current balancing device further comprises a Zeta-type converter in front of the current balancing device, the Zeta-type converter having a power switch, An energy storage inductor, an energy transfer capacitor, a diode component, and an output inductor, the power switch, the energy storage inductor, and the energy transfer capacitor each have a first end and a The first end of the power switch is connected to a power source and controls the current conduction/non-conduction to be outputted to the second end thereof, and the first end of the energy storage inductor and the first end of the energy transfer capacitor are connected to the power a second end of the switch, the first end of the energy transfer capacitor is connected to the first end of the energy storage inductor, and the second end of the energy transfer capacitor is connected to the cathode end of the diode element, and the energy storage inductor is The two ends and the anode end of the diode element are grounded, and the DC power source is output from the connection of the energy transfer capacitor and the diode element to the input end of the differential transformer, and the equivalent leakage of the differential transformer The sense replaces the output inductor and cooperates with the energy transfer capacitor to demagnetize the differential transformer and recover energy. The current balancing device of claim 1, wherein the rectifying unit comprises a diode and a capacitor.