TWI330503B - Constant current driving circuit and buck_boost led driving system using the same - Google Patents

Abstract

The invention relates to a constant current driving circuit and buck_boost LED driving system using the same. The constant current driving circuit comprises a PWM generator, an oscillator and an integrator. The PWM generator is used to generate a PWM control signal having a turn on time and a turn off time. The oscillator is used to control the turn on time. The integrator is used to integrate a sample voltage according to the turn off time, and output an integrated voltage to the PWM generator so as to control an output current to be a predetermined value. The constant current driving circuit of the invention can exactly control the output current to be a constant predetermined value. Therefore, the buck_boost LED driving system can output a constant output current to LED, and the number of the driving does not be limited so that the buck_boost LED driving system can be applied to that the output voltage is larger or smaller than the input voltage.

Description

1330503 IX. Description of the Invention: [Technical Field] The present invention relates to an LED driving system, and more particularly to a 疋 current driving circuit and a buck-boost type LED driving system using the same. [Prior Art] Referring to Fig. 1', there is shown a schematic diagram of a conventional boost LED driving system. The conventional step-up LED current driving system 1 〇 mainly includes a driving circuit 11, an inductor 12, a first kins diode 13 and a second kins diode 14. The driving circuit Η is used to control the energy storage of the inductor 12, and the inductor 12 outputs a driving current, so that the first kins diode 13 is turned on, and the driving current can drive the LEDs (light emitting diodes). Light Emitting Diode) 16, 17, 18 ° This known step-up LED current drive system can only be used for boost situations where the output voltage is greater than the input voltage, thus limiting the number of LEDs that can be driven. In addition, the response time of the conventional boost type LED current drive system is slow. Therefore, it is necessary to provide an innovative and progressive buck-boost LED drive system to solve the above problems. SUMMARY OF THE INVENTION An object of the present invention is to provide a constant current driving circuit including: a pulse width modulation generator, an oscillator, and an integrator. The pulse width modulation generator is configured to generate a pulse width modulation control signal, and the pulse width modulation control signal includes an on time and a off time. The oscillator is coupled to the pulse width modulation to generate a 'the oscillator' for controlling the on time. The integrator is coupled to the pulse width 105565.doc 1330503 modulation generator for processing a sampling voltage according to the wear time integration, and outputting an integrated voltage to the pulse width modulation generator to control an output current. The solid state is a set current. The constant current driving circuit of the present invention can eliminate variations in frequency variation and accurately control the output current to be a fixed set value. Another object of the present invention is to provide a buck-boost LED drive system for providing a fixed set current to at least one LED. The buck-boost LED driving system comprises: a constant current driving circuit, a switching circuit, an inductor and a sampling resistor. The constant current driving circuit comprises: a pulse width modulation generator, an oscillation benefit and an integrator. The pulse width modulation generator is configured to generate a pulse width modulation control signal. The pulse width modulation control signal includes an on time and a cutoff time. The vibrator is coupled to the pulse width modulation generator, and the oscillator is used to control the on time. The integrator is coupled to the pulse width modulation generator for processing a sampling voltage according to the cutting time integration, and outputting an integrated voltage to the pulse width modulation generator. The switch circuit is coupled to an input power source and the constant current drive circuit, and controls whether the switch circuit is turned on or not according to the pulse width modulation control signal. The inductor is coupled to the constant current driving circuit and the switching circuit for storing energy 'release energy at the wearing time' during the on time to output the set current. The sampling resistor is coupled to the constant current driving circuit and the inductor for providing the sampling voltage of the constant current driving circuit. The buck-boost LED driving system of the invention can output a fixed output current to the LED, and the number of the driven led can be arbitrarily adjusted by the user without being limited by the input voltage, so the buck-boost LED driving system of the invention I05565.doc 1330503 can be applied to the case where the output voltage is greater or less than the boost voltage of the input power supply. In addition, the buck-boost LED driving system of the present invention can be designed with a maximum current limit value and has an internal slow start function. Moreover, the buck-boost type LED driving system of the present invention is current mode control, and the response speed is fast. [Embodiment] Please refer to the circle 2' which shows a block diagram of the constant current drive circuit of the present invention. The constant current driving circuit 20 of the present invention comprises a pulse width modulation generator 21, an oscillator 22 and an integrator 23. The pulse width modulation (PWM) generator 21 is configured to generate a pulse width modulation control signal. The pulse width modulation control signal includes an on time (T0N) and a off time (TOFF). One cycle time (τ) is the turn-on time (T〇n) plus the cut-off time (T〇FF). The oscillator scillator 22 is coupled to the pulse width modulation generator 21 for controlling the on time (τ0 Ν). The integrator 23 is coupled to the pulse width modulation generator 21 for integrating a sampling voltage vSENSE according to the off time (toff), and outputting an integrated voltage to the pulse width modulation generator 21 to control one. The output current 1〇 is fixed to a set current. In the embodiment shown in Fig. 2, the output current is a current flowing through a sampling resistor Rsense. The output current is generated via a control circuit 24 in accordance with the pulse width modulation control signal. The relationship between the integrated voltage and the output current is as follows:

^OFF \VSENSE (1)

It is known from the formula (1) that the integral voltage vA has a parameter component of time, and after the wheel pulse is turned into the 105565.doc 1330503 pulse width modulation generator 21, the pulse width modulation generator 21 is adjusted to be close to a reference voltage VREF. . Then, the output current 1〇 is determined by the equation (2), which is determined by the integral voltage vA, the sampling resistor rsense, and the period 昱. The integral voltage Va, the sampling resistor Rsense, and the period T are constant values. Therefore, the output current is also 1〇. Is a fixed value. Furthermore, since the integral electric SVA has a parameter component of time, and the period is a function of time, the two are respectively in the numerator and the denominator of the formula (2), each of which can eliminate the variation when the frequency changes, and the sampling resistance Rsense is about It is ±1% error, so the shai output current 1〇 is a fine fixed current. Referring to Figure 3', there is shown a schematic circuit diagram of a constant current drive circuit of the present invention. The constant current driving circuit 30 of the present invention comprises: a pulse width modulation unit 31, an oscillation module 32, an integrator 33, a first proportional controller 34, an error amplifier 35, a second proportional controller 36, and a comparison. 37 and a flip-flop %. The integrator 3 3 integrates a sampling voltage Vsense according to the cutoff time (T〇FF), and outputs an integrated voltage VA to the first proportional controller 34 » the first proportional controller 34 is coupled to the integrator 33 is used between the error amplifier 35 to multiply the integrated voltage ¥8 by a first ratio κι. The first ratio K1 may be greater than 1 or less than 1 to amplify or reduce the integrated voltage; the first ratio K1 may also be equal to 1, that is, the first proportional controller 34 may be omitted, so that the integrator 33 is directly connected to The error amplifier 35. The error amplifier 35 is configured to compare the first proportional integrated voltage with a reference voltage VREF to output an error voltage to the second proportional controller 36. The second proportional controller 36 is coupled between the error amplifier 35 and the comparator 37 for multiplying the error voltage by a second ratio K2. The second ratio K2 may be greater than 1 or less than 1 to amplify or reduce the error voltage; the second ratio I05565.doc • 9· 1330503, the example K2 may also be equal to 1, that is, the second proportional controller 36 may be omitted. The error amplifier 35 is directly connected to the comparator 37. The comparator 37 is configured to compare the second proportional processing error voltage with the sampling voltage Vsense to output a reset signal to a reset terminal of the flip-flop 38. The flip-flop 38 is coupled to the comparator 37 and the oscillator 32. The flip-flop 38 receives the reset signal of the comparator 37 and the signal of the oscillator 32 for using the reset signal and the The signal of the oscillator 32 controls the on-time (T0N) of the pulse width modulation control signal. The pulse width modulation unit 31 generates a pulse width modulation control signal 'and transmits the off time (TOFF) of the pulse width modulation control signal to the integrator 33 ' according to the on time, so that the integrator 33 can The cutoff time integrates the sampled voltage. Referring to FIG. 2 and FIG. 3, the pulse width modulation generator 21 in FIG. 2 may be included in the pulse width modulation unit 31 of FIG. 3, the first proportional controller 34, the error amplifier 35, and the first The second proportional controller 36, the comparator 37 and the flip-flop 38. The constant current driving circuit 30 of FIG. 3 can make the integrated voltage approach the reference voltage VREF ' such that the integrated voltage vA in the equation (2) is the set value of the reference voltage 俾, and the output current can be accurately controlled. A fixed set value. Therefore, the constant current driving circuit 30 of the present invention can control the output current to be a fixed set value. Referring to Figure 4, there is shown a circuit diagram of a first practical example of an integrator of a constant current drive circuit of the present invention. The integrator 40 of the first embodiment includes an operational amplifier 41, a resistor 42, a charging capacitor 43, a wheel discharging capacitor 44, and five switching switches 51, 52, 53, 54, 55. The operational amplifier 41 has a first input 105565.doc • 10-1330503 'input (+), a second input (one) and an output, the first input being coupled to the sampling voltage Vsense. The resistor 42 is coupled to the second input end. The charging capacitor 43 is coupled between the second input terminal and the output terminal. The output capacitor is coupled to the output. 4 and 5 are used to explain the timing of the switches. The switching switches are respectively coupled to the first input terminal, the second input terminal and the output terminal for controlling the switching of the switching switches according to the pulse width modulation control signal. The first switch (S1) 51 is coupled between the first input terminal and the sampling voltage VSENSE, and the first switch 51 is open (OFF) during the on time (t〇n). The cut-off time (t〇ff) is the short-circuit (ON) of the first switch. The second switch (S2) 52 is coupled between the first input terminal and a ground terminal at the on-time ( τΟΝ) The second switch 52 is short-circuited (ON). The second switch 52 is open (OFF) at the off time (t〇ff), and the third switch (S3) 53 is coupled to the The second input terminal and the output terminal are connected in parallel with the charging capacitor 43. The third switching switch 53 is short-circuited at a pulse time before the wearing time (toff) of each cycle. N), at other times, the third switch 53 is open (OFF). The fourth switch (S4) 54 is coupled between the output and the output capacitor, and the off time of each cycle (toff The fourth switch 54 is short-circuited (ON) at one pulse time, and the fourth switch 54 is open at other times (〇F The fifth switching switch (S5) 55 is coupled between the second input end and the ground end, and the fifth switching is performed at one pulse time after the cutting time (T〇ff) of each period The switch 55 is short-circuited (ON). The fifth switch 55 is open (〇FF) at other times. 105565.doc -II . 1330503 Therefore, the first changeover switch 51 is short-circuited at the off time (Toff), so that The operation voltage is amplified, the resistor 42 and the charging capacitor 43 integrate the sampling voltage Vsense, and the integrated voltage is stored in the charging capacitor 43. After the integration, the fourth switching switch 54 and the fifth switching switch 55 are short-circuited for one pulse time. The integrated voltage of the charging capacitor is transmitted to the output capacitor 44. And, before the next cycle, the second switching switch 53 is short-circuited for one pulse time to release the integrated voltage of the charging capacitor 43. Therefore, the circuit of FIG. 4 can be used for integration. The sampling voltage is processed. Referring to Fig. 6, there is shown a circuit diagram of a second embodiment of the integrator of the constant current driving circuit of the present invention. The integrator 6〇 of the second embodiment comprises: an operational amplifier 61, a resistor 62, and a An electric capacitor 63, a turn-out capacitor, and seven switch switches, 73' 74, 75, 76, 77. The integrated state 60 circuit of the second embodiment is different from the integrator 4 〇 circuit of the first embodiment of FIG. 4 described above. The integrator 6〇 circuit of the second embodiment further includes a sixth switch (S6) 76 and a seventh switch (S7) 77 for canceling the offset voltage voltage). The sixth switch 76 The sixth switching switch 76 is connected to the charging capacitor 63 and the output terminal, and the sixth switching switch 76 is open at a pulse time before the cutoff time (t〇ff) of each cycle, and the sixth switching switch 76 is used at other times. Is a short circuit. The seventh switch 77 is coupled between the sixth switch 76 and the ground, and the seventh switch 77 is short-circuited at a pulse time before the cut-off time (T0FF) of each cycle. The seventh changeover switch 77 is an open circuit. When the square operational amplifier 61 has the offset voltage v 〇 s, the charging capacitor 63 is similarly integrated. Therefore, the charging voltage is charged with an inverted voltage at each cycle to eliminate the error in integration, as shown in the following equation: I05565.doc -12- 1330503

T〇FF \(VsENSE ^05) X ^ R χ 7;--V〇s :c _ ^OS^OFF ~VOS ' T〇FF SENSE X ^ 4 〇 —RC RC J〇FF "~RC

-Wos^

It is known from equation (3) that when (T0FF/RC) = 1, the error caused by the offset voltage can be effectively eliminated. Therefore, the circuit of the integrator 60 of the second embodiment can effectively eliminate the error caused by the offset voltage, making the integration result more accurate.

Referring to Figure 8, there is shown a schematic view of a first embodiment of a buck-boost LED drive system of the present invention. The step-up and step type LED driving system 80 of the first embodiment comprises: a certain current driving circuit 20, a switching circuit 81, an inductor 82, a sampling resistor 83, a buffer capacitor 84 and a diode 85. The buck-boost LED drive system 80 is configured to provide a fixed set current to at least one of the LEDs 88, 89, and the like. The constant current driving circuit 20 can refer to the constant current driving circuit 20 of FIG. The constant current driving circuit 20 outputs a pulse width modulation control signal to the switching circuit 81, and the sampling resistor (Rsense) 83 obtains the sampling power Vsense. The switch circuit 81 is coupled to an input power supply VIN and the constant current drive circuit 20, and controls whether the switch circuit 81 is turned on or not according to the pulse width modulation control signal of the constant current drive circuit 20. In this embodiment, the switch circuit 81 can be a transistor, preferably a PMOS transistor. The inductor 82 is coupled to the constant current driving circuit 20 and the switching circuit 81 for storing energy during the on time, and discharging energy at the off time to rotate a set current. The sampling resistor (Rsense) 83 is coupled to the constant current driving circuit 20 and the inductor 82 for providing 105565.doc -13 - 1330503. The sampling voltage Vsense β of the constant current driving circuit 20 is the lifting voltage type LED driving system. The 80 further includes a buffer capacitor 84 and a diode 85. The snubber capacitor 84 is coupled to the LEDs 88, 89, that is, the snubber capacitor 84 is connected in parallel with the LEDs. The diode 85 is coupled between the snubber capacitor 82 and the inductor 84. The diode 85 can be a Zener diode. The buck-boost LED drive system 80 further includes a comparison capacitor 86 and an input capacitor 87. The comparison capacitor 86 is coupled between the constant current driving circuit 20 and a ground terminal. The input capacitor 87 is coupled between the input power source Vin and the ground. As described above, the constant current drive circuit 20 can output a fixed output current, so that the buck-boost LED drive system 80 can output a fixed output current 1 至 to the LEDs 88, 89. And the sampling resistor 83 can apply a precision resistor ' to accurately control the output current. In addition, the number of the LEDs can be arbitrarily adjusted by the user without being limited by the magnitude of the input voltage. Therefore, the buck-boost LED driving system 80 of the present invention can be applied to an output voltage having a voltage greater or lower than that of the input power source. Since the output current of the constant current driving circuit 20 is cycle-dependent and is cycle by cycle current limit, the user can design a maximum current limit value. Furthermore, with reference to FIG. 3 and FIG. 8, since the output of the error amplifier 35 of the constant current driving circuit 30 is connected to the comparison capacitor 86, the pulse width modulation control signal can be slowly increased to have an internal slow start. (internal soft start) effect. Since the buck-boost type LED driving system 80 of the present invention is current mode control, the response speed is fast. Referring to Figure 9, there is shown a schematic diagram of a second embodiment 105565.doc - 14-1330503 of the buck-boost LED drive system of the present invention. The buck-boost LED driving system 90 of the second embodiment comprises: a certain current driving circuit 20, a switching circuit 91, an inductor 92, a sampling resistor 93, a comparison capacitor 94 and an input capacitor 95. The difference between the step-up and step type LED driving system 80 of the first embodiment described above is that the snubber capacitor 84 and the diode 85 are omitted from the step-up and step type LED driving system 90 of the second embodiment. In the case where the snubber capacitor 84 and the diode 85 are omitted, the buck-boost LED driving system 90 of the second embodiment can further be used in addition to the above-described effects of the step-up and step type LED driving system 80 of the first embodiment. Reduce the required components to reduce costs. However, the above embodiments are merely illustrative of the principles and effects of the invention and are not intended to limit the invention. Therefore, those skilled in the art can modify and change the above embodiments without departing from the spirit of the invention, and should be within the scope of the invention. The scope of the invention should be as set forth in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a conventional step-up type LED driving system; FIG. 2 is a block diagram of a constant current driving circuit of the present invention; FIG. 3 is a schematic diagram showing a circuit of a constant current driving circuit of the present invention; BRIEF DESCRIPTION OF THE DRAWINGS FIG. 5 is a schematic diagram of a switching switch of a circuit of a first embodiment of a constant current driving circuit according to the present invention; FIG. 6 is a schematic diagram of a switching circuit of a constant current driving circuit of the present invention; FIG. 7 is a schematic diagram of a circuit of a switch of a second embodiment of an integrator of a constant current drive circuit according to the present invention; 105565.doc 15 1330503 圊8 is a buck-boost type LED drive system of the present invention A schematic diagram of a circuit of a first embodiment; and FIG. 9 is a schematic diagram of a circuit of a second embodiment of a buck-boost LED driving system of the present invention. [Major component symbol description] 10 conventional boost type LED current drive system 11 drive circuit 12 inductor 13 first kins diode 14 second kinner diode 20 constant current drive circuit 21 of the present invention pulse width modulation generator 22 Oscillator 23 Integrator 24 Control circuit 30 Constant current drive circuit 31 Pulse width modulation unit 32 Oscillator 33 Integrator 34 First proportional controller 35 Error amplifier 36 Second proportional controller 37 tb comparator 38 Positive and negative device 105565 .doc • 16- 1330503

40 Integral First Embodiment 41 Operational Amplifier 42 Resistor 43 Charging Capacitor 44 Output Capacitor 51 First Switching Switch 52 Second Switching Switch 53 Third Switching Switch 54 Fourth Switching Switch 55 Fifth Switching Switch 60 Second of Integrator Embodiment 61 Operational amplifier 62 Resistor 63 Charging capacitor 64 Output capacitor 71 First changeover switch 72 Second changeover switch 73 Third changeover switch 74 Fourth changeover switch 75 Fifth changeover switch 76 Sixth changeover switch 77 Seventh changeover switch 80 81st switch circuit embodiment of a profiled LED drive system 105565.doc 1330503

82 Inductor 83 Sampling Resistor 84 Buffer Capacitor 85 Diode Body 86 Comparing Capacitor 87 Input Capacitor 88, 89 LED 90 Bucket-Up LED Driver System Second Embodiment 91 Switching Circuit 92 Inductance 93 Sampling Resistor 94 Comparing Capacitor 95 Input Capacitor 96, 97 LED

105565.doc 18-

Claims (1)

1330503 X. Patent application scope: 1. A constant current driving circuit, comprising: a pulse width modulation generator for generating a pulse width modulation control signal, the pulse width modulation control signal comprising an on time and a load An oscillator is coupled to the pulse width modulation generator for controlling the on time; and an integrator coupled to the pulse width modulation generator for determining the off time The integration process a sampling voltage and output an integrated voltage to the pulse width modulation generator ' to control an output current to be fixed to a set current. 2. The current drive circuit of claim 1, wherein the pulse width modulation generator comprises: an error amplifier 'coupled to the integrator for comparing the integrated voltage with a reference voltage to output an error voltage a comparator coupled to the error amplifier for comparing the error voltage with the sampled voltage to output a reset signal; a flip-flop 'coupled to the comparator and the oscillator for The reset signal and the control of the oscillator to generate the pulse width modulation control signal. 3. The current drive circuit of claim 2, wherein the pulse width modulation generator further comprises a first proportional controller coupled between the integrator and the error amplifier for multiplying the integrated voltage by A first ratio. 4. The current drive circuit of claim 2, wherein the pulse width modulation generator further comprises a second proportional controller coupled between the error amplifier and the comparator to multiply the error voltage by a second ratio. 5. The current drive circuit of claim 1, wherein the integrator comprises: 105565.doc 1330503 an operational amplifier having a first input terminal 'a second input terminal and one wheel output terminal' coupled to the first input terminal a sampling resistor; a resistor coupled to the second input terminal; a charging capacitor coupled between the second input terminal and the wheel terminal; a turn-off capacitor coupled to the output terminal; Switching switches respectively coupled to the first input end and the second input The input end and the output end are configured to control whether the switch is turned on or not according to the pulse width modulation control signal. 6. The current driving circuit of claim 5, wherein the switching switch comprises: a first switching switch coupled between the first input terminal and the sampling voltage, wherein the first switching is performed during the conduction time. In the open circuit, the first switching open relationship is a short circuit at the off time; the second switching switch is coupled to the first input end and a ground end The second switching open relationship is a short circuit during the turn-on time, and the second switching open relationship is an open circuit at the off time; - the third switching switch is consuming between the second input end and the output end, The third switching-on relationship is a short circuit before the cut-off time, and the third switching-off relationship is an open circuit at other times; - the fourth switching switch is connected between the output terminal and the output capacitor, and the axis-off time After the -pulse time, the fourth switch-on_ is a short circuit, and the fourth switch-on relationship is open at other times; and - the fifth switch is connected to the second input terminal and the ground terminal After the time, one of the pulse switches is divided into a short circuit, and the fifth switch is open at other times. 105565 doc 1330503. The constant current driving circuit of claim 6, wherein the switching switch further comprises: a sixth switching switch coupled between the charging capacitor and the output terminal, before the cutoff time - pulse The sixth switching relationship is an open circuit, and the sixth switching open relationship is a short circuit at other times; and/or a seventh switching switch is coupled between the sixth switching switch and the grounding end, before the deadline The seventh switching-on relationship is a short circuit for one pulse time. The seventh switching-on relationship is an open circuit at other times. 8. A buck-boost LED driving system for providing a fixed set current to at least one LED, comprising: a constant current driving circuit comprising: a pulse width modulation generator, an oscillator and an integrator, The pulse width modulation generator is configured to generate a pulse width modulation control signal, where the pulse width modulation control signal includes an on time and a off time; the oscillator is coupled to the pulse width modulation generator, the oscillator For controlling the on-time; the integrator is coupled to the pulse width modulation generator for integrating a sampling voltage according to the off-time, and outputting an integrated voltage to the pulse width modulation generator; 'Coupling to a wheel-in power supply and the constant current driving circuit, controlling whether the switching circuit is turned on or not according to the pulse width modulation control signal; an inductor coupled to the constant current driving circuit and the switching circuit for The conduction time stores energy, and the energy is released during the wearing time to rotate the set current; and a sampling resistor is coupled to the constant current driving circuit and the inductor to provide the setting The sampling voltage of the current drive circuit. 9. The buck-boost LED driving system of claim 8, further comprising: 105565.doc 1330503 a snubber capacitor coupled to the led; and a diode coupled between the snubber capacitor and the inductor. 10. The buck-boost LED driving system of claim 8, further comprising: a comparison capacitor coupled between the constant current driving circuit and a ground; and an input capacitor coupled to the input power source and the ground Between the ends. 11. The buck-boost LED driving system of claim 8, wherein the pulse width modulation generator of the constant current driving circuit comprises: an error amplifier coupled to the integrator for integrating the integrated voltage with a reference Comparing a voltage to output an error voltage; a comparator coupled to the error amplifier for comparing the error voltage with the sampling voltage to output a reset signal; a flip-flop coupled to the comparator And the oscillator is configured to generate the pulse width modulation control signal according to the reset signal and the control of the oscillator. 12. The buck-boost LED driving system of claim η, wherein the pulse width modulation generator further comprises a first proportional controller coupled between the integrator and the error amplifier for integrating the integrated voltage Multiply by a first ratio. 13. The buck-boost LED driving system of claim 11, wherein the pulse width modulation generator further comprises a second proportional controller coupled between the error amplifier and the comparator for using the error The voltage is multiplied by a second ratio. The step-up type LED driving system of claim 8, wherein the integrator of the constant current driving circuit comprises: an operational amplifier having a first input terminal, a second input terminal and an output terminal, the first input terminal Coupling to the sampling voltage; I05565.doc -4· 1330503 resistor is coupled to the second input terminal; a charging capacitor coupled between the second input terminal and the output terminal; a round-out capacitor, coupled And the plurality of switch switches are respectively coupled to the first input end, the second input end, and the output end, respectively, for controlling the conduction of the switch according to the pulse width modulation control signal no. For example, the (4) switch includes: a first switch, coupled to the first input terminal and the sampling voltage, the first switchover is turned on at the turn-on time The relationship is an open circuit, the first switching open relationship is a short circuit at the cutoff time; a second switching switch is coupled between the first input end and a ground end: the second switching open relationship is a short circuit during the conduction time The second switching open relationship is an open circuit at the deadline; The third switching switch is coupled between the second input end and the wheel end, and the third switching open relationship is a short circuit at a pulse time before the cutoff time, and the third switching open relationship is an open circuit at other times. a fourth switching switch coupled between the output terminal and the output capacitor, wherein the fourth switching-on relationship is a short circuit after one of the off-times, and the fourth switching-off relationship is an open circuit at other times; and The fifth (4) (4) is connected between the second input end and the ground end, and after the wearing time, the fifth switching open relationship is a short circuit, and the fifth switching open relationship is an open circuit at other times. The buck-boost LED driving system of claim 15, wherein the b-switching switch 105565.doc I33〇5〇3 comprises: - a sixth switching switch, being lightly connected between the charging capacitor and the output terminal, One of the pulse times before the time is the sixth switch-on relationship is an open circuit, and the other time is the sixth switch-on relationship is a short circuit; and the seventh seventh switch is coupled to the sixth switch and the ground end, ' Before the cut-off time, the seventh switching-on relationship of the pulse time is short, and the seventh switching-off relationship is open. I05565.doc