JP2014007143A - Circuit and method for driving light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit for supplying power to a light source including a filter, a transformer, and a controller.SOLUTION: A filter receives and filters an input voltage to provide a stabilized voltage. A transformer converts the stabilized voltage into an output voltage, and supplies power to a light source. A controller generates a drive signal, and alternately operates a switch between a first state and a second state. The controller controls continuous times of the first state and the second state to modify a power factor of the circuit so that an input current reduces to a preliminarily-defined level during the second state and increases from the preliminarily-defined level to a maximum level proportional to the input voltage during the first state. The controller controls a ratio of the time in the first state and the time in the second state to adjust an output current to be flown in the light source to a target level.

Description

  This application claims the priority of Chinese Patent Application No. 201010119888.2 “Circuits and Methods for Driving Light Sources” filed with the Chinese National Intellectual Property Office on March 4, 2010. U.S. co-pending application filed February 10, 2012, which is a partial co-pending application of U.S. Patent Application No. 12 / 761,681 `` Circuits and Methods for Driving Light Sources '' This is a continuation-in-part of Application No. 13 / 371,351 “Circuits and Methods for Driving Light Sources”. No. 13 / 371,351 also applied for priority to Chinese Patent Application No. 201110453588,2 `` Circuit, Method and Controller for Driving LED Light Source '' filed with the Chinese National Intellectual Property Office on December 29, 2011. Insist.

  FIG. 1 shows a block diagram of a conventional circuit 100 for driving a light source, such as a light emitting diode (LED) string 108. Circuit 100 is powered by a power supply 102 that provides an input voltage VIN. Circuit 100 includes a step-down converter for providing a regulated voltage VOUT to LED string 108 under the control of controller 104. The step-down converter includes a diode 114, an inductor 112, a capacitor 116, and a switch 106. The resistor 110 is connected in series with the switch 106. When switch 106 is turned on, resistor 110 is coupled to inductor 112 and LED string 108 and can provide a feedback signal indicative of the current flowing through inductor 112. When switch 106 is turned off, resistor 110 is disconnected from inductor 112 and LED string 108 so that no current flows through resistor 110.

  The switch 106 is controlled by the controller 104. When switch 106 is turned on, current flows to ground through LED string 108, inductor 112, switch 106, and resistor 110. The current increases due to the inductance of the inductor 112. When the current reaches a predetermined maximum level of current, controller 104 turns switch 106 off. When switch 106 is turned off, current flows through LED string 108, inductor 112, and diode 114. The controller 104 can turn on the switch 106 again after a certain time. Therefore, the controller 104 controls the step-down converter based on a predetermined maximum current level. However, the average level of current flowing through the inductor 112 and the LED string 108 may vary depending on the inductance of the inductor 112, the input voltage VIN, and the voltage VOUT through the LED string 108. Thus, the average level of current flowing through the inductor 112 (average of current flowing through the LED string 108) may not be accurately controlled.

  In one embodiment, the circuit for supplying power to the light source includes a filter, a transformer, and a controller. The filter receives the input voltage and filters the input voltage to provide a regulated voltage. The transformer converts the regulated voltage into an output voltage and supplies power to the light source. The controller generates a drive signal and operates the switch alternately between the first state and the second state. The controller modifies the power factor of the circuit by controlling the duration of the first state and the second state, and the input current is reduced to a predetermined level during the second state, so that the first state During this period, the level is increased from a predetermined level to a maximum level proportional to the input voltage. The controller controls the ratio between the time in the first state and the time in the second state to adjust the output current flowing through the light source to a target level.

  The features and advantages of the claimed subject matter will become apparent as the following detailed description proceeds, and by reference to the drawings. In the drawings, like reference numerals designate like parts.

It is a block diagram of the conventional circuit for driving a light source. It is a block diagram of a drive circuit in an embodiment according to the present invention. It is a figure which shows the example of the schematic of the drive circuit in embodiment by this invention. FIG. 4 is a diagram illustrating an example of the controller of FIG. 3 in an embodiment according to the present invention. FIG. 5 is a diagram showing signal waveforms of signals associated with the controller of FIG. 4 in an embodiment according to the present invention. FIG. 4 is a diagram showing another example of the controller of FIG. 3 in the embodiment according to the present invention. FIG. 7 shows signal waveforms of signals associated with the controller of FIG. 6 in an embodiment according to the present invention. It is a figure which shows the other example of the schematic of the drive circuit in embodiment by this invention. It is another block diagram of the drive circuit in the embodiment according to the present invention. FIG. 9B is a diagram showing an example of a waveform of a signal generated or received by the drive circuit of FIG. 9A in the embodiment according to the present invention. It is a figure which shows the example of the schematic of the drive circuit in embodiment by this invention. FIG. 9B is a diagram showing an example of the controller of FIG. 9A in the embodiment according to the present invention. FIG. 4 is a diagram illustrating a waveform of a signal generated or received by a driving circuit in an embodiment according to the present invention. 4 is a flowchart of operations performed by a circuit for driving a load in an embodiment according to the present invention; It is another block diagram of the drive circuit in the embodiment according to the present invention. FIG. 6 shows another waveform of a signal generated or received by a drive circuit in an embodiment according to the present invention. FIG. 3 is an exemplary schematic diagram of a drive circuit in an embodiment according to the present invention. It is a figure which shows the example of the controller in embodiment by this invention. 4 is a flowchart of an example of an operation performed by a circuit for driving a light source in an embodiment according to the present invention.

  Reference will now be made in detail to embodiments of the invention. While the invention will be described in conjunction with these embodiments, it will be understood that these embodiments are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternative embodiments, modifications, and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims.

  Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, those skilled in the art will recognize that the invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention.

  Embodiments in accordance with the present invention provide circuits and methods for controlling power conversion devices that can be used to power various types of loads, eg, light sources. In one embodiment, the circuit can include an energy storage element, such as a current sensor operable to monitor the current flowing through the inductor, and controls a switch coupled to the inductor to control the average current of the light source. A controller operable to allow control of the current to a target current. The current sensor can monitor the current through the inductor whether the switch is on or off.

  FIG. 2 shows a block diagram of a drive circuit 200 in an embodiment according to the present invention. The drive circuit 200 includes a rectifier 204 that receives an input voltage from the power source 202 and provides the rectified voltage to the power converter 206. When power converter 206 receives the rectified voltage, it provides output power to load 208. The power conversion device 206 may be a step-down converter or a step-up converter. In one embodiment, the power converter 206 includes an energy storage element 214 and a current sensor 218 for sensing the electrical state of the energy storage element 214. The current sensor 218 provides the controller 210 with a first signal ISEN indicative of the instantaneous current flowing through the energy storage element 214. The drive circuit 200 may further include a filter 212 operable to generate a second signal IAVG indicative of the average current flowing through the energy storage element 214 based on the first signal ISEN. In one embodiment, the controller 210 receives the first signal ISEN and the second signal IAVG and controls the average current flowing through the energy storage element 214 to a target current level.

  FIG. 3 shows an example of a schematic diagram of a drive circuit 300 in an embodiment according to the present invention. Elements labeled the same as in FIG. 2 have similar functions. In the example of FIG. 3, the drive circuit 300 includes a rectifier 204, a power converter 206, a filter 212, and a controller 210. As an example, rectifier 204 is a bridge rectifier including diodes D1-D4. The rectifier 204 rectifies the voltage from the power source 202. The power converter 206 receives the rectified voltage from the rectifier 204 and provides output power to supply power to a load, such as the LED string 208.

  In the example of FIG. 3, power conversion device 206 is a step-down converter including capacitor 308, switch 316, diode 314, current sensor 218 (eg, resistor), coupled inductors 302 and 304, and capacitor 324. The diode 314 is connected between the switch 316 and the ground of the drive circuit 300. The capacitor 324 is connected in parallel with the LED string 208. In one embodiment, inductors 302 and 304 are electrically and magnetically interconnected. More specifically, inductor 302 and inductor 304 are electrically connected to common node 333. In the example of FIG. 3, the common node 333 is between the resistor 218 and the inductor 302. However, the present invention is not limited to this, and the common node 333 can be disposed between the switch 316 and the register 218. Common node 333 provides a reference ground for controller 210. In one embodiment, the reference ground of controller 210 is different from the ground of drive circuit 300. By switching the switch 316 on and off, the current flowing through the inductor 302 can be adjusted, thereby adjusting the power provided to the LED string 208. The inductor 304 detects the electrical state of the inductor 302, for example, whether the current flowing through the inductor 302 is reduced to a predetermined current level.

  One end of resistor 218 is coupled to a node between switch 316 and the cathode of diode 314, and the other end is coupled to inductor 302. Resistor 218 provides a first signal ISEN that indicates the instantaneous current flowing through inductor 302 whether switch 316 is on or switch 316 is off. In other words, resistor 218 can detect the instantaneous current flowing through inductor 302 regardless of whether switch 316 is on or off. A filter 212 coupled to resistor 218 generates a second signal IAVG indicating the average current flowing through inductor 302. In one embodiment, filter 212 includes resistor 320 and capacitor 322.

  The controller 210 receives the first signal ISEN and the second signal IAVG and controls the average current flowing through the inductor 302 to a target current level by switching the switch 316 on and off. Capacitor 324 absorbs the ripple current flowing through LED string 208 so that the current flowing through LED string 208 is smoothed and substantially equal to the average current flowing through inductor 302. In this way, the current flowing through the LED string 208 has a level that is substantially equal to the target current level. As used herein, “substantially equal to the target current level” means that the current flowing through the LED string 208 may be slightly different from the target current level, but is a non-ideal factor of the circuit components This means that the ripple current generated by the current can be ignored and the power transferred from the inductor 304 to the controller 210 is in a negligible range.

  In the example of FIG. 3, the controller 210 has terminals ZCD, GND, DRV, VDD, CS, COMP, and FB. Terminal ZCD is coupled to inductor 304 to receive a detection signal AUX indicating whether the electrical state of inductor 302, e.g., the current flowing through inductor 302 decreases to a predetermined current level, e.g., zero. ing. The signal AUX can also indicate whether the LED string 208 is in an open circuit state. Terminal DRV is coupled to switch 316 and generates a drive signal, eg, pulse width modulation signal PWM1, to switch switch 316 on and off. Terminal VDD is coupled to inductor 304 for receiving power from inductor 304. Terminal CS is coupled to resistor 218 and is operable to receive a first signal ISEN indicating the instantaneous current flowing through inductor 302. Terminal COMP is connected to the reference ground of controller 210 through capacitor 318. Terminal FB is coupled to resistor 218 through filter 212 and is operable to receive a second signal IAVG indicative of the average current flowing through inductor 302. In the example of FIG. 3, the terminal GND, that is, the reference ground of the controller 210 is connected to the common node 333 between the resistor 218 and the inductors 302 and 304.

  The switch 316 may be an N-channel metal oxide semiconductor field effect transistor (NMOSFET). The conduction state of the switch 316 is determined based on the difference between the gate voltage of the switch 316 and the voltage at the terminal GND (the voltage at the common node 333). Therefore, switch 316 can switch the power supply on and off in accordance with pulse width modulation signal PWM1 from terminal DRV. When switch 316 is turned on, the reference ground of controller 210 is higher than the ground of drive circuit 300, making the present invention suitable for power supplies having relatively high voltages.

  In operation, when switch 316 is turned on, current flows through switch 316, resistor 218, inductor 302, and LED string 208 to the ground of drive circuit 300. When switch 316 is turned off, current continues to flow through resistor 218, inductor 302, LED string 208, and diode 314. An inductor 304 that is magnetically coupled to the inductor 302 detects whether the electrical state of the inductor 302, for example, whether the current flowing through the inductor 302 is reduced to a predetermined current level. Thus, in one embodiment, the controller 210 monitors the current flowing through the inductor 302 via the signal AUX, the signal ISEN, and the signal IAVG and controls the switch 316 with the pulse width modulation signal PWM1 to Allow the average current flowing through 302 to be controlled to the target current level. In this way, the current flowing through the LED string 208, filtered by the capacitor 324, can also be substantially equal to the target current level.

  In one embodiment, the controller 210 determines whether the LED string 208 is in an open circuit state based on the signal AUX. When LED string 208 is open, the voltage across capacitor 324 increases. When switch 316 is off, the voltage across inductor 302 increases and the voltage of signal AUX increases accordingly. As a result, the current flowing through the controller 210 via the terminal ZCD increases. Thus, the controller 210 monitors the signal AUX and if the current flowing through the controller 210 increases beyond the current threshold when the switch 316 is turned off, the controller 210 determines that the LED string 208 is in an open circuit state. .

  The controller 210 can also determine whether the LED string 208 is in a short-circuit state based on the voltage at the terminal VDD. When the LED string 208 is in a short-circuit state, when the switch 316 is turned off, both ends of the inductor 302 are connected to the ground of the drive circuit 300, so that the voltage across the inductor 302 decreases. In response, the voltage across inductor 304 and the voltage at terminal VDD decrease. If switch 316 is turned off and the voltage at terminal VDD decreases below the voltage threshold, controller 210 determines that LED string 208 is in a short circuit condition.

  FIG. 4 shows an example of the controller 210 of FIG. 3 in an embodiment according to the present invention. FIG. 5 shows signal waveforms of signals associated with the controller 210 of FIG. 4 in an embodiment according to the present invention. FIG. 4 is described in combination with FIG. 3 and FIG.

  In the example of FIG. 4, the controller 210 includes an error amplifier 402, a comparator 404, and a pulse width modulation signal generator 408. The error amplifier 402 generates an error signal VEA based on the difference between the reference signal SET and the signal IAVG. The reference signal SET can indicate a target current level. Signal IAVG may be received at terminal FB and may indicate an average current flowing through inductor 302. The error signal VEA can be used to adjust the average current flowing through the inductor 302 to a target current level. The comparator 404 is connected to the error amplifier 402 and compares the error signal VEA and the signal ISEN. Signal ISEN is received at terminal CS and indicates the instantaneous current flowing through inductor 302. Signal AUX is received at terminal ZCD to indicate whether the current flowing through inductor 302 is reduced to a predetermined current level, eg, zero. The pulse width modulation signal generator 408 is connected to the comparator 404 and the terminal ZCD, and can generate the pulse width modulation signal PWM1 based on the output of the comparator 404 and the signal AUX. Pulse width modulation signal PWM1 is applied to switch 316 via terminal DRV to control the conduction state of switch 316.

  In operation, the pulse width modulation signal generator 408 can generate a pulse width modulation signal PWM1 having a first level (eg, logic 1) to turn on the switch 316. When switch 316 is turned on, current flows through switch 316, resistor 218, inductor 302, and LED string 208 to the ground of drive circuit 300. As the current flowing through the inductor 302 increases, the voltage of the signal ISEN increases. In one embodiment, when switch 316 is turned on, signal AUX has a negative voltage level. In the controller 210, the comparator 404 compares the error signal VEA with the signal ISEN. In one embodiment, if the voltage of the signal ISEN increases beyond the voltage of the error signal VEA, the output of the comparator 404 is logic 0, otherwise the output of the comparator 404 is logic 1 . In other words, the output of the comparator 404 includes a series of pulses. In response to the falling edge of the output of the comparator 404, the pulse width modulation signal generator 408 generates a pulse width modulation signal PWM1 having a second level (eg, logic 0), and turns off the switch 316. When switch 316 is turned off, the voltage of signal AUX changes to a positive voltage level. When switch 316 is turned off, current flows through resistor 218, inductor 302, LED string 208, and diode 314. As the current flowing through the inductor 302 decreases, the voltage of the signal ISEN decreases. When the current flowing through inductor 302 decreases to a predetermined current level (eg, zero), a falling edge occurs in the voltage of signal AUX. Upon receiving the falling edge of signal AUX, pulse width modulation signal generator 408 generates pulse width modulation signal PWM1 having a first level (eg, logic 1) to turn on switch 316.

  In one embodiment, the duty cycle of the pulse width modulation signal PWM1 is determined by the error signal VEA. When the voltage of the signal IAVG is lower than the voltage of the signal SET, the error amplifier 402 increases the voltage of the error signal VEA so that the duty cycle of the pulse width modulation signal PWM1 can be increased. Therefore, the average current flowing through the inductor 302 increases until the voltage of the signal IAVG reaches the voltage of the signal SET. When the voltage of the signal IAVG is higher than the voltage of the signal SET, the error amplifier 402 decreases the voltage of the error signal VEA so that the duty cycle of the pulse width modulation signal PWM1 can be decreased. Thus, the average current flowing through inductor 302 decreases until the voltage of signal IAVG falls to the voltage of signal SET. In this way, the average current flowing through the inductor 302 can be maintained to be substantially equal to the target current level.

  FIG. 6 shows another example of the controller 210 of FIG. 3 in an embodiment according to the present invention. FIG. 7 shows waveforms of signals associated with the controller 210 of FIG. 6 in an embodiment according to the present invention. FIG. 6 is described in combination with FIG. 3 and FIG.

  In the example of FIG. 6, the controller 210 includes an error amplifier 602, a comparator 604, a sawtooth signal generator 606, a reset signal generator 608, and a pulse width modulation signal generator 610. The error amplifier 602 generates an error signal VEA based on the reference signal SET and the signal IAVG. The reference signal SET indicates a target current level. Signal IAVG is received at terminal FB and represents the average current flowing through inductor 302. Error signal VEA is used to adjust the average current flowing through inductor 302 to a target current level. The sawtooth signal generator 606 generates a sawtooth signal SAW. The comparator 604 is connected to the error amplifier 602 and the sawtooth signal generator 606, and compares the error signal VEA and the sawtooth signal SAW. The reset signal generator 608 generates a reset signal RESET that is applied to the sawtooth signal generator 606 and the pulse width modulation signal generator 610. The switch 316 can be turned on in response to the reset signal RESET. The pulse width modulation signal generator 610 is connected to the comparator 604 and the reset signal generator 608, and generates a pulse width modulation (PWM) signal PWM1 based on the outputs of the comparator 604 and the reset signal RESET. Pulse width modulation signal PWM1 is applied to switch 316 via terminal DRV to control the conduction state of switch 316.

  In one embodiment, the reset signal RESET is a pulse signal having a constant frequency. In another embodiment, the reset signal RESET is a pulse signal configured such that the time Toff during which the switch 316 is off is constant. For example, in FIG. 5, the time during which the pulse width modulation signal PWM1 is logic 0 can be constant.

  In operation, the pulse width modulation signal generator 610 generates a pulse width modulation signal PWM1 having a first level (eg, logic 1) in response to a pulse of the reset signal RESET and turns on the power of the switch 316. . When switch 316 is turned on, current flows through switch 316, resistor 218, inductor 302, and LED string 208 to the ground of drive circuit 300. The sawtooth signal SAW generated by the sawtooth signal generator 606 begins to increase from the initial level INI in response to the pulse of the reset signal RESET. When the voltage of the sawtooth signal SAW increases to the voltage of the error signal VEA, the pulse width modulation signal generator 610 generates a pulse width modulation signal PWM1 having a second level (logic 0) and turns off the switch 316 . The sawtooth signal SAW is reset to the initial level INI until the next pulse of the reset signal RESET is received by the sawtooth signal generator 606. The sawtooth signal SAW starts to increase from the initial level INI again in response to the next pulse.

  In one embodiment, the duty cycle of the pulse width modulation signal PWM1 is determined by the error signal VEA. When the voltage of the signal IAVG is lower than the voltage of the signal SET, the error amplifier 602 increases the voltage of the error signal VEA so that the duty cycle of the pulse width modulation signal PWM1 can be increased. Therefore, the average current flowing through the inductor 302 increases until the voltage of the signal IAVG reaches the voltage of the signal SET. When the voltage of the signal IAVG is higher than the voltage of the signal SET, the error amplifier 602 decreases the voltage of the error signal VEA so that the duty cycle of the pulse width modulation signal PWM1 can be decreased. Thus, the average current flowing through inductor 302 decreases until the voltage of signal IAVG falls to the voltage of signal SET. In this way, the average current flowing through the inductor 302 can be maintained to be substantially equal to the target current level.

  FIG. 8 shows another example of a schematic diagram of a drive circuit 800 in an embodiment according to the present invention. Elements labeled the same as in FIGS. 2 and 3 have similar functions.

  Terminal VDD of controller 210 is coupled to rectifier 204 through switch 804 to receive the rectified voltage from rectifier 204. Zener diode 802 is coupled between switch 804 and the reference ground of controller 210 and maintains the voltage at terminal VDD at a substantially constant level. In the example of FIG. 8, the terminal ZCD of the controller 210 receives the signal AUX indicating whether the electrical state of the inductor 302, for example, whether the current through the inductor 302 is reduced to a predetermined current level, for example, zero. The inductor 302 is electrically connected. Node 333 can provide a reference ground for controller 210.

  Accordingly, embodiments in accordance with the present invention provide circuits and methods for controlling a power converter that can be used to power various types of loads. In one embodiment, the power converter provides a substantially constant current for supplying power to a load, such as a light emitting diode (LED) string. In other embodiments, the power conversion device provides a substantially constant current to charge the battery. Advantageously, compared to the conventional drive circuit in FIG. 1, the average current to the load or battery can be controlled more accurately. Furthermore, the circuit according to the invention may be suitable for a power supply having a relatively high voltage.

FIG. 9A shows another block diagram of a drive circuit 900 in an embodiment according to the present invention. Elements labeled the same as in FIGS. 2 and 3 have similar functions. In the example of FIG. 9A, drive circuit 900 includes a current filter 920 coupled to power supply 202, rectifier 204, power converter 906, load 208, sawtooth signal generator 902, and controller 910. The power source 202 generates an _AC input voltage V _AC having a sinusoidal waveform and an AC input current I _AC , for example. The AC input current I _AC flows to the current filter 920, and the current I _AC ′ flows from the current filter 920 to the rectifier 204. The rectifier 204 receives the _AC input voltage V _AC through the current filter 920, and couples the rectified AC voltage V _IN and the rectified AC current I _IN between the rectifier 204 and the power converter 906. Provided with power line 912. The power converter 906 converts the voltage V _IN into the output voltage V _OUT and supplies power to the load 208. A controller 910 coupled to the power converter 906 controls the power converter 906 to adjust the current I _OUT through the load 208 to correct the power factor of the drive circuit 900.

Controller 910 generates drive signal 962. In one embodiment, power converter 906 includes a switch 316 that is controlled by drive signal 962. In this way, the current I _OUT flowing through the load 208 is adjusted by the drive signal 962. In one embodiment, the power converter 906 further generates a sense signal IAVG that indicates the current I _OUT through the load 208.

  In one embodiment, the sawtooth signal generator 902 coupled to the controller 910 generates a sawtooth signal 960 with the drive signal 962. For example, the drive signal 962 may be a pulse width modulation (PWM) signal. In one embodiment, the sawtooth signal 960 increases when the drive signal 962 is logic high, and the sawtooth signal 960 is a predetermined voltage level when the drive signal 962 is logic low. For example, falls to zero volts.

Advantageously, the controller 910 generates the drive signal 962 based on signals including the sawtooth signal 960 and the detection signal IAVG. Drive signal 962 controls switch 316 to maintain current I _OUT through load 208 at a target level, thus improving current control accuracy. Furthermore, the drive signal 962 controls the switch 316, and adjusted so that the average current I _{IN_AVG} power I _IN is substantially tuned to the input voltage V _IN, modifies the power factor of the drive circuit 900. The operation of the drive circuit 900 is further described in FIG. 9B.

FIG. 9B shows an example of the waveform of a signal associated with the drive circuit 900 of FIG. 9A in an embodiment according to the present invention. FIG. 9B is described in combination with FIG. 9A. FIG. 9B shows the AC input voltage V _AC , the rectified AC voltage V _IN , the rectified AC voltage I _IN , the current I _AC ′, and the AC input current I _AC .

Without being limited thereto, for the sake of illustration, the AC input voltage V _AC has a sinusoidal waveform. The rectifier 204 rectifies the AC input voltage V _AC . In the example of FIG. 9B, the rectified AC voltage V _IN has a rectified sine waveform, the AC input voltage V _AC positive wave remains, and the AC input voltage V _AC negative wave corresponds to the positive wave. Converted into waves.

In one embodiment, drive signal 962 generated by controller 910 controls current I _IN . In one embodiment, current I _IN increases from a predetermined level, eg, zero amperes. After current I _IN reaches a level proportional to the AC input voltage V _IN which is rectified, current I _IN drops to a predetermined level. Therefore, as shown in FIG. 9B, the waveform of the average current I _{IN_AVG} of the current I _IN substantially tunes to the waveform of the rectified AC voltage V _IN .

A current I _IN flowing from the rectifier 204 to the power converter 906 is a current obtained by rectifying the current I _AC ′ flowing to the rectifier 204. As shown in FIG.9B, when the AC input voltage V _AC is positive, the current I _AC ′ has a positive wave similar to the positive wave of the current I _IN , and when the AC input voltage V _AC is negative, It has a negative wave corresponding to the negative wave of the current _IIN .

In one embodiment, by using a current filter 920 between the power source 202 and the rectifier 204, the alternating input current I _AC is equal to or proportional to the average current of the current I _AC ′. Therefore, as shown in FIG. 9B, the waveform of the _AC input current I _AC substantially tunes to the waveform of the _AC input voltage V _AC . Ideally, the _AC input voltage V _AC and AC input current I _AC are tuned. However, in practical applications, there may be a slight phase difference due to the capacitors in current filter 920 and power converter 906. Further, the waveform shape of the _AC input current I _AC is similar to the waveform shape of the AC input voltage V _AC . Therefore, the power factor of the drive circuit 900 is corrected, and the power quality of the drive circuit 900 is improved.

  FIG. 10 shows an example of a schematic diagram of a drive circuit 1000 in an embodiment according to the present invention. Elements labeled the same as in FIGS. 2, 3, and 9A have similar functions. FIG. 10 is described in combination with FIG. 4, FIG. 5, and FIG. 9A.

  In the example of FIG. 10, the drive circuit 1000 includes a current filter 920 coupled to the power supply 202, a rectifier 204, a power converter 906, a load 208, a sawtooth signal generator 902, and a controller 910. In one embodiment, load 208 includes an LED light source, such as an LED string. The present invention is not so limited, and the load 208 can include other types of light sources, or other types of loads such as battery packs. The current filter 920 may be, but is not limited to, an inductor-capacitor (L-C) filter including a set of inductors and a set of capacitors. In one embodiment, the controller 910 includes a plurality of terminals such as a ZCD terminal, a GND terminal, a DRV terminal, a VDD terminal, an FB terminal, a COMP terminal, and a CS terminal.

In one embodiment, power converter 906 includes an input capacitor 1008 coupled to power line 912. Input capacitor 1008 reduces the ripple of the rectified AC voltage V _IN, to smooth the waveform of the rectified AC voltage V _IN. In one embodiment, the capacitor 1008 has a relatively small capacitance, eg, less than 0.5 μF, and thus serves to eliminate or reduce any distortion of the rectified AC voltage _VIN . Further, in one embodiment, the current flowing through capacitor 1008 may be ignored because of the relatively small capacitance. Thus, the current I _IN flowing through switch 316 is approximately equal to the current from rectifier 204 when switch 316 is on.

The power conversion device 906 operates in the same manner as the power conversion device 206 in FIG. In one embodiment, energy storage element 214 includes inductors 302 and 304 that are magnetically and electrically interconnected. Inductor 302 is coupled to switch 316 and LED light source 208. Thus, current I ₂₁₄ flows through inductor 302 according to the conduction state of switch 316. More specifically, in one embodiment, the controller 910 generates a drive signal 962, eg, a PWM signal, through the DRV terminal to switch the switch 316 to an on state or an off state. When switch 316 is turned on, current I ₂₁₄ flows from power line 912 through switch 316 and inductor 302. The current I ₂₁₄ increases while switch 316 is on and can be given by equation (1):
△ I ₂₁₄ = (V _IN -V _OUT ) * T _ON / L ₃₀₂ (1)
In the above equation, T _ON represents the time when the switch 316 is turned on, ΔI ₂₁₄ represents the change in the current I ₂₁₄ , and L ₃₀₂ represents the inductance of the inductor 302. In one embodiment, the controller 910 controls the drive signal 962 to keep the T _ON time constant. Therefore, change △ I ₂₁₄ of the current I ₂₁₄ during the time T _ON, if V _OUT is substantially constant proportional to the input voltage V _IN. In one embodiment, switch 316 is turned on when current I ₂₁₄ decreases to a predetermined level, such as zero amperes. Thus, the maximum level of current I ₂₁₄ is proportional to input voltage V _IN .

When switch 316 is turned off, current I ₂₁₄ flows from ground through diode 314 and inductor 302 to LED light source 208. Therefore, the current I ₂₁₄ decreases according to equation (2):
△ I ₂₁₄ = (-V _OUT ) * T _OFF / L_ ₃₀₂ (2)
Thus, in one embodiment, current I _IN is substantially equal to current I ₂₁₄ while switch 316 is in the on state and equal to zero amperes while switch 316 is in the off state.

Inductor 304 detects whether the electrical state of inductor 302, for example, the current flowing through inductor 302, decreases to a predetermined level (eg, zero amperes). As described in connection with FIG. 5, in one embodiment, the detection signal AUX has a negative level when the switch 316 is turned on and has a positive level when the switch 316 is turned off. When current I ₂₁₄ through inductor 302 decreases to a predetermined level, a falling edge occurs in the voltage of signal AUX. The ZCD terminal of the controller 910 connected to the inductor 304 is used to receive the detection signal AUX.

In one embodiment, power converter 906 includes an output filter 1024. The output filter 1024 may be a relatively large capacitor, for example having a capacitance greater than 400 μF. In this way, the current I _OUT through the LED light source 208 represents the average level of the current I ₂₁₄ .

The current sensor 218 generates a current detection signal ISEN indicating the current flowing through the inductor 302. In one embodiment, the signal filter 212 is a resistor-capacitor (RC) filter that includes a resistor 320 and a capacitor 322. The signal filter 212 removes the ripple of the current detection signal ISEN and generates the average detection signal IAVG of the current signal ISEN. Therefore, in the example of FIG. 10, the average detection signal IAVG indicates the current I _OUT flowing through the LED light source 208. In one embodiment, terminal FB of controller 910 receives detection signal IAVG.

A sawtooth signal generator 902 coupled to the DRV terminal and the CS terminal is operable to generate a sawtooth signal 960 at the CS terminal by a drive signal 962 on the DRV terminal. As an example, sawtooth signal generator 902 includes a resistor 1016 and a diode 1018 connected in parallel between terminals DRV and CS, and a resistor 1012 and a capacitor connected in parallel between terminal CS and ground. 1014 is further included. During operation, the sawtooth signal 960 varies according to the drive signal 962. More specifically, in one embodiment, drive signal 962 is a PWM signal. When the drive signal 962 is logic high, the current l1 flows from the DRV terminal through the resistor 1016 to the capacitor 1014. Accordingly, the capacitor 1014 is charged and the voltage V ₉₆₀ of the sawtooth signal 960 increases. When drive signal 962 is logic low, current l2 flows from capacitor 1014 through diode 1018 to the DRV terminal. Accordingly, capacitor 1014 is discharged and voltage V ₉₆₀ is reduced to zero volts. The sawtooth signal generator 902 can include other components and is not limited to the example shown in FIG.

  In one embodiment, the controller 910 is integrated into an integrated circuit (IC) chip. Resistors 1016 and 1012, diode 1018, and capacitor 1014 are peripheral components of the IC chip. Alternatively, both the sawtooth signal generator 902 and the controller 910 are integrated into a single IC chip. Since the terminal CS can be removed in this state, the size and cost of the drive circuit 1000 can be further reduced. The power conversion device 906 can have other configurations and is not limited to the example of FIG.

  FIG. 11 shows an example of the controller 910 of FIG. 9A in an embodiment according to the present invention. Elements labeled the same as in FIGS. 4 and 9A have similar functions. FIG. 11 is described in combination with FIG. 4, FIG. 5, FIG. 9A, and FIG.

  In one embodiment, the controller 910 has a configuration similar to the controller 210 of FIG. 4 except that the CS terminal receives a sawtooth signal 960 instead of the current sense signal ISEN. Controller 910 generates drive signal 962 in accordance with signals including sawtooth signal 960, detection signal IAVG, and detection signal AUX. The controller 910 includes an error amplifier 402, a comparator 404, and a pulse width modulation (PWM) signal generator 408. The error amplifier 402 amplifies the difference between the detection signal IAVG and the reference signal SET indicating the target current level, and generates an error signal VEA. The comparator 404 compares the sawtooth signal 960 and the error signal VEA to generate a comparison signal S. The PWM signal generator 408 generates the drive signal 962 according to the comparison signal S and the detection signal AUX.

In one embodiment, the drive signal 962 has a first level, eg, logic high, when the detection signal AUX indicates that the current I ₂₁₄ through the inductor 302 falls to a predetermined level, eg, zero amperes. Then, switch 316 is turned on. The drive signal 962 has a second level, eg, logic low, to turn off the switch 316 when the sawtooth signal 960 reaches the error signal VEA. Advantageously, the maximum level of current I ₂₁₄ through inductor 302 is not limited by error signal VEA because the CS terminal receives sawtooth signal 960 instead of sense signal ISEN. Therefore, the current I ₂₁₄ through the inductor 302 varies depending on the input voltage V _IN as shown in the equation (1). For example, the maximum level of current I ₂₁₄ is adjusted to be proportional to input voltage V _IN rather than error signal VEA.

Controller 910 controls drive signal 962 to maintain current I _OUT at the target current level represented by reference signal SET. For example, if the current I _OUT is greater than the target level, for example due to a change in the input voltage V _IN , the error amplifier 402 decreases the error signal VEA and shortens the time T _ON when the switch 316 is on. Therefore, the average level of current I ₂₁₄ decreases and current I _OUT decreases. Similarly, if current I _OUT is less than the target level, controller 910 increases time T _ON and increases current I _OUT .

FIG. 12 shows the waveform of a signal generated or received by a drive circuit, eg, drive circuit 900 or 1000, in an embodiment according to the present invention. FIG. 12 is described in conjunction with FIGS. 4, 9A, 9B, and 10. FIG. FIG. 12 shows a rectified AC voltage V _IN , a rectified AC current I _IN , an average current I _{IN_AVG} of the current I _IN, a current I _OUT flowing through the LED light source 208, and a current I ₂₁₄ flowing through the inductor 302. A detection signal ISEN, an error signal VEA, a sawtooth signal 960, and a drive signal 962 are shown.

As shown in the example of FIG. 12, the input voltage V _IN is a rectified sinusoidal waveform. At time t1, the drive signal 962 changes to logic high. Accordingly, the switch 316 is turned on, and the detection signal ISEN indicating the current I ₂₁₄ through the inductor 302 is increased. On the other hand, the sawtooth signal 960 increases according to the drive signal 962.

At time t2, the sawtooth signal 960 reaches the error signal VEA. Accordingly, controller 910 adjusts drive signal 962 to a logic low. The sawtooth signal 960 falls to zero volts. The drive signal 962 turns off the switch 316, thereby decreasing the sense signal ISEN. In other words, the sawtooth signal 960 and the error signal VEA determine the time T _ON when the drive signal 962 is logic high and turn on the switch 316.

At time t3, current I ₂₁₄ decreases to a predetermined current level, eg, zero amperes. Accordingly, controller 910 adjusts drive signal 962 to logic high and turns on switch 316.

In one embodiment, the current I _OUT flowing through the LED light source 208 is equal to or proportional to the average level of the current I ₂₁₄ over the cycle of the input voltage V _IN . As described in connection with FIG. 11, the current I _OUT is adjusted to the target current level represented by the reference signal SET. Further, as shown in FIG. 12, the detection signal ISEN indicating the current I ₂₁₄ between t1 and t4 has the same waveform as that between t5 and t6. Therefore, the average level of the current I ₂₁₄ between t1 and t4 is equal to the average level of the current I ₂₁₄ between t5 and t6. Therefore, the current I _OUT is maintained at the target level. In one embodiment, the time T _ON is determined by the sawtooth signal 960 and the error signal VEA. In one embodiment, the time T _ON is constant because the time for the sawtooth signal 960 to rise from zero volts to the error signal VEA is the same in each cycle of the drive signal 962. Based on equation (1), change △ I ₂₁₄ of the current I ₂₁₄ during the time T _ON is proportional to the input voltage V _IN. Therefore, as shown in FIG. 12, the maximum level of the detection signal ISEN is proportional to the input voltage V _IN .

In one embodiment, current I _IN has a waveform similar to that of current I ₂₁₄ when switch 316 is turned on and is substantially equal to zero amps when switch 316 is turned off. The average current I _{IN_AVG} substantially tunes to the input voltage V _IN between times t1 and t6. As described in connection with FIG. 9B, the AC input current I _AC substantially tunes to the _AC input voltage V _AC and modifies the power factor of the drive circuit 900 to improve power quality.

  FIG. 13 shows a flowchart 1300 of operations performed by a circuit for driving a load, eg, a circuit 900 or 1000 for driving an LED light source 208, in an embodiment according to the present invention. FIG. 13 is described in combination with FIG. 9A to FIG. Although specific steps are disclosed in FIG. 13, such steps are examples. That is, the present invention is well suited to performing various other steps or variations of the steps listed in FIG.

At block 1302, an input voltage, such as a rectified alternating voltage V _IN , and an input current, such as a rectified alternating current I _IN are received. At block 1304, the input voltage is converted to an output voltage to supply power to a load such as an LED light source. At block 1306, the current flowing through the energy storage element, eg, energy storage element 214, is controlled in accordance with a drive signal, eg, drive signal 962, to adjust the current through the LED light source.

  At block 1308, a first sensing signal indicative of current through the LED light source, eg, IAVG, is received. In one embodiment, the first sense signal is generated by filtering a second sense signal indicative of current through the energy storage element. At block 1310, a sawtooth signal is generated based on the drive signal.

  At block 1312, the drive signal is controlled based on the signal including the sawtooth signal and the first sense signal to adjust the current through the LED light source to a target level so that the average current of the input current is substantially tuned to the input voltage. The power factor of the drive circuit is corrected by controlling so as to. In one embodiment, an error signal is generated that indicates the difference between the first detection signal and a reference signal that indicates a target level of current through the LED light source. The sawtooth signal is compared with the error signal. A detection signal indicative of the electrical state of the energy storage element is received. The drive signal is switched to the first state when the detection signal indicates that the current through the energy storage element decreases to a predetermined level, and the second state according to the result of the comparison between the sawtooth signal and the error signal. Can be switched to. The current through the energy storage element increases when the drive signal is in the first state and decreases when the drive signal is in the second state. In one embodiment, when the current through the LED light source is maintained at a target level, the time for the sawtooth signal to increase from the predetermined level to the error signal is constant.

  FIG. 14A shows another block diagram of the drive circuit 1400 in the embodiment according to the present invention. Elements labeled the same as in FIGS. 2, 3, and 9A have similar functions. FIG. 14B shows a waveform of a signal generated or received by the drive circuit 1400 in an embodiment according to the present invention. 14A and 14B will be described in combination with FIGS. 9A and 9B.

In the example of FIG. 14A, drive circuit 1400 includes current filter 920, rectifier 204, power converter 1406, light source 1408, and controller 1410 coupled to power supply 202. The power source 202 generates an _AC input voltage V _AC having a sinusoidal waveform and an AC input current I _AC, for example. The AC input current I _AC flows to the current filter 920, and the current I _AC ′ flows from the current filter 920 to the rectifier 204. Rectifier 204 receives the ac input voltage V _AC via a current filter 920, a rectifier 204 and the AC voltage is rectified by a power line 912 that is coupled between the power converter 1406 V _IN and rectified alternating current Provide I _IN .

In one embodiment, power converter 1406 includes a voltage filter 1420, a transformer 1422, and a switch 1424. Voltage filter 1420 receives the voltage V _IN, and filters the voltage V _IN to generate a regulated voltage V _REG. For example, a relatively high frequency harmonic component of voltage V _IN is eliminated or eliminated. Therefore, as shown in FIG. 14B, the waveform of the stabilization voltage V _REG is more stable than the waveform of the voltage V _IN . The transformer 1422 converts the stabilized voltage V _REG into the output voltage V _OUT and supplies power to the light source 1408. Therefore, the waveform of the output voltage V _OUT is not affected by the form of the input voltage V _IN such as a sine waveform. Thus, the ripple of the current I _OUT through the light source 1408 caused by the form of the input voltage V _IN is reduced or eliminated, further reducing line frequency interference of light emitted by the light source 1408.

The controller 1410 generates the drive signal 1462 to operate the switch 1424 in the first state or the second state, further control the input current I _IN flowing through the filter 1420, and the output current I _OUT flowing through the light source 1408. To control. In one embodiment, transformer 1422 provides a sense signal 1464 that is indicative of output current I _OUT . Based on the detection signal 1464, the controller 1410 controls the ratio of the time T _ON and the time T _OFF of the switch 1424 to adjust the current I _OUT to the target level.

In one embodiment, the input current I _IN increases while switch 1424 is operating in the first state and decreases while switch 1424 is operating in the second state. While operating in the second state, the controller 1410 controls the duration of the second state so that the input current I _IN decreases to a predetermined level, eg, ground. The controller 1410 further controls the time of the first state so that the input current I _IN increases from the predetermined level to a level proportional to the input voltage V _IN . Therefore, the average current I _{IN_AVG} the current I _IN is substantially tuned to the input voltage V _IN. Similar to the description for FIG. 9B, the current I _AC is substantially tuned to the input voltage V _AC . Ideally, the _AC input voltage V _AC and AC input current I _AC are tuned. However, in practical applications, there may be a slight phase difference due to the capacitors in current filter 920 and power converter 1406. Further, the waveform shape of the _AC input current I _AC is similar to the waveform shape of the AC input voltage V _AC . Therefore, the power factor of circuit 1400 is corrected.

Advantageously, by switching a single switch 1424 between the first state and the second state, the power factor of the circuit 1400 is corrected and the output current I _OUT is adjusted to the target level. Thus, both the power quality of circuit 1400 and the accuracy of current control are improved. Since only a single switch 1424 is used for control, the size and cost of the circuit 1400 can be reduced.

  FIG. 15 shows an exemplary schematic diagram of a drive circuit 1500 in an embodiment according to the present invention. Elements labeled the same as in FIGS. 2, 3, 9A, and 14A have similar functions. FIG. 15 is described in combination with FIG. 14A and FIG. 14B. In one embodiment, the controller 1410 includes a plurality of pins such as a VIN pin, a COMP pin, a GND pin, a DRV pin, a CS pin, a VDD pin, a ZCD pin, and an FB pin.

In one embodiment, voltage filter 1420 includes inductor 1512, diodes D15 and D16, and capacitor C15. The transformer 1422 may be a flyback converter including a primary winding 1504, a secondary winding 1506, an auxiliary winding 1508, and a core 1502. Switch 1424 is coupled to diode D16 and primary winding 1504 and operates in a first state, such as an on state, and a second state, such as an off state, to control the current I _IN flowing through inductor 1512. The current I _OUT flowing through the LED light source 1408 is controlled.

In one embodiment, the controller 1410 generates a drive signal 1462, eg, a pulse width modulated signal, to control the switch 1424. More specifically, in one embodiment, if drive signal 1462 is electrically high, such as during on-time T _ON , switch 1424 is turned on and diode D15 is reverse biased to D16 is forward biased. The transformer 1422 is powered by the regulated voltage V _REG . Current I _PRI flows through primary winding 1504, switch 1424, and ground. The current I _PRI increases and stores energy in the core 1502. Further, current I _IN flows through inductor 1512, diode D16, and switch 1424, and increases to charge inductor 1512, which can be given as equation (3):
△ I _IN = V _IN * T _CH / L ₁₅₁₂ (3)
In the above equation, T _CH represents the charging time during which the inductor 1512 is charged while the switch 1424 is on, ΔI _IN represents the change in the current I _IN , and L ₁₅₁₂ represents the inductance of the inductor 1512. In one embodiment, time T _CH is equal to time T _ON when switch 1424 is on.

For example, when the drive signal 1462 is electrically low, such as during the off time T _OFF , the switch 1424 is turned off, the diode D15 is forward biased, and the diode D16 is reverse biased. The transformer 1422 is discharged to supply power to the LED light source 208. Accordingly, the current I _SE flowing through the secondary winding 1506 is reduced. In addition, current I _IN flows through inductor 1512, diode D15, and capacitor C15 and decreases according to equation (4) to discharge inductor 1512:
△ I _IN = (V _IN- V _REG) * T _DISCH / L ₁₅₁₂ (4)
In the above equation, T _DISCH represents the time during which the inductor 1512 is discharged while the switch 1424 is off. Since the discharge of the inductor 1512 ends when the current I _IN decreases to zero amperes, the time T _DISCH may be different from the off-state time T _OFF .

In one embodiment, inductor 1512 and capacitor C15 constitute an inductor-capacitor (LC) filter. An LC filter filters out high frequency harmonic components of voltage V _IN . In this way, the ripple in the waveform of the regulated voltage V _REG caused by the form of the voltage V _IN is reduced. The transformer 1422 converts the regulated voltage V _REG to the output voltage V _OUT , which is also independent of the voltage V _IN .

In one embodiment, auxiliary winding 1508 is coupled to controller 1410 via a ZCD pin. The auxiliary winding 1508 provides a current sense signal 1466 that indicates whether the current I _SE falls to a predetermined level, eg, zero amperes. The FB pin of the controller 1410 receives a detection signal 1464 indicating the current I _OUT flowing through the LED light source 208. In one embodiment, controller 1410 controls the duty cycle of drive signal 1462 based on signals including current detection signal 1466 and detection signal 1464 to adjust current I _OUT to a target current level. The operation of controller 1410 will be further described in connection with FIG.

In one embodiment, the controller 1410 further controls the times T _ON and T _OFF of the drive signal 1462 to modify the power factor of the circuit 1500. More specifically, in one embodiment, the controller 1410 sets the OFF state time T _OFF longer than the time threshold value T _TH . By rewriting equation (4), the discharge time of inductor 1512 can be given as:
T _DISCH = △ I _IN * L ₁₅₁₂ / (V _IN -V _REG ) (5)
As shown in FIG. 14B, ΔI _IN may be different in different cycles of the drive signal 1462. In one embodiment, the time threshold T _TH may be set to an amount equal to or longer than the maximum discharge time T _{DISCH_MAX} of the inductor 1512. Thus, the time during which switch 1424 is off is sufficient to reduce current I _IN to zero amperes. In addition, controller 1410 maintains time T _ON at the same value. Therefore, according to equation (3), the current I _IN increases from a predetermined level to a maximum level proportional to the input voltage V _IN . Accordingly, as described in relation to FIGS. 14A and 14B, the power factor of circuit 1500 is corrected, and the power quality of circuit 1500 is improved.

  FIG. 16 shows an example of the controller 1410 of FIG. 14A in an embodiment according to the present invention. Elements labeled the same as in FIGS. 4 and 9A have similar functions. FIG. 16 is described in combination with FIG. 4, FIG. 5, FIG. 10, and FIG.

  In one embodiment, the controller 1410 has a similar configuration to the controller 910 of FIG. 11 except that the controller 1410 further includes a sawtooth signal generator 1602 that generates a sawtooth signal 1660. In one embodiment, the sawtooth signal generator 1602 operates similarly to the sawtooth signal generator 902 shown in FIG. The sawtooth signal 1660 increases when the drive signal 1462 turns on the switch 1424 and falls to zero amperes when the drive signal 1462 turns off the switch 1424.

Controller 1410 generates drive signal 1462 according to signals including sawtooth signal 1660, detection signal 1464, and detection signal 1466. The controller 1410 further includes an error amplifier 402, a comparator 404, and a pulse width modulation (PWM) signal generator 408. The error amplifier 402 amplifies the difference between the detection signal 1464 and the reference signal SET indicating the target current level, and generates an error signal VEA. The comparator 404 compares the sawtooth signal 1660 and the error signal VEA to generate a comparison signal S. The PWM signal generator 408 generates a drive signal 1462 according to the comparison signal S and the detection signal AUX. T _ON corresponds to the amount of time it takes for the sawtooth signal 1660 to increase from a predetermined level to the error signal VEA.

In one embodiment, the drive signal 1462 is used to turn on the switch 1424 when the detection signal 1466 indicates that the current I _se through the secondary winding 1506 falls to a predetermined level, eg, zero amperes. It can have an electrically high level. The drive signal 1462 can also have an electrically low level to turn off the switch 1424 when the sawtooth signal 1460 reaches the error signal VEA.

Controller 1410 controls drive signal 1462 to maintain current I _OUT at the target current level represented by reference signal SET. For example, if the current I _OUT is greater than the target level due to, for example, unwanted noise, the error amplifier 402 decreases the error signal VEA and shortens the time T _ON when the switch 316 is on. Accordingly, the duty cycle of drive signal 1462 decreases and current I _OUT decreases. Similarly, if current I _OUT is less than the target level, controller 1410 increases the duty cycle of drive signal 1462 to increase current I _OUT . In one embodiment, time T _ON is maintained at a constant value when current I _OUT is maintained at a target level.

  FIG. 17 shows a flowchart 1700 of an example of operations performed by a circuit for driving a light source 1408 in an embodiment according to the present invention. FIG. 17 is described in combination with FIG. 14A to FIG. Although specific steps are disclosed in FIG. 17, such steps are examples. That is, the present invention is well suited to performing various other steps or forms of steps listed in FIG.

At block 1702, an input current, eg, input current I _IN , and an input voltage, eg, input voltage V _IN are received. At block 1704, the input voltage is filtered to provide a regulated voltage, eg, regulated voltage V _REG . At block 1706, the regulated voltage is converted to an output voltage, eg, output voltage _VOUT , to provide power to the LED light source. At block 1708, a drive signal, eg, drive signal 1462, is generated to operate a switch, eg, switch 1424, alternately between a first state and a second state. The input current increases during the first state and decreases during the second state.

  At block 1710, the duration of operation in the first state and the duration of operation in the second state are controlled so that the input current is reduced to a predetermined level during operation in the second state, for example, zero amperes. During operation in the first state, the level is increased from a predetermined level to a maximum level proportional to the input voltage.

  At block 1712, the time ratio, ie, the ratio of the amount of time in the first state to the amount of time in the second state, is controlled to adjust the output current flowing through the LED light source to a target level.

  Embodiments according to the present invention provide a drive circuit for driving a load, eg, an LED light source. The drive circuit includes a filter, a transformer, and a controller. The filter receives the input voltage and filters the input voltage to provide a regulated voltage. The transformer converts the regulated voltage into an output voltage and supplies power to the LED light source. The controller generates a drive signal and operates the switch alternately between the first state and the second state. The controller controls the duration of operation in the first state and the duration of operation in the second state so that the input current is reduced to a predetermined level during operation in the second state, During operation, the level is increased from a predetermined level to a maximum level proportional to the input voltage. The controller further controls the time ratio (first state time to second state time) to adjust the output current flowing through the LED light source to a target level. Advantageously, the ripple of output current flowing through the LED light source caused by the form of the input voltage is reduced or eliminated, further reducing the line frequency interference of the light emitted by the light source. Furthermore, the power factor of the drive circuit is corrected, the power quality of the drive circuit is improved, and the power control accuracy of the drive circuit is also improved.

  Although the foregoing description and drawings represent embodiments of the present invention, various additions, modifications, and substitutions may be made without departing from the spirit and scope of the principles of the invention as defined in the appended claims. It will be appreciated that may be performed. The present invention can be used with many modifications of shapes, structures, configurations, proportions, materials, elements, and components specifically adapted to specific environments and operational requirements without departing from the principles of the present invention, or One skilled in the art will appreciate that it can be used in the practice of the invention. Accordingly, the embodiments disclosed herein are illustrative in all respects and should not be construed as limiting, and the scope of the present invention is defined by the appended claims and their legal It is shown by the equivalent, and is not limited to the above description.

100 Conventional circuit
102 Power supply
104 controller
106 switch
108 LED string
110 registers
112 inductor
114 diode
116 capacitors
200 Drive circuit
202 power supply
204 Rectifier
206 Power converter
208 Load, LED light source, LED string
210 controller
212 filters
214 Energy storage element
218 resistor, current sensor
300 Drive circuit
302 inductor
304 inductor
308 Capacitor
314 diode
316 switch
320 registers
322 capacitors
324 capacitors
333 common node
402 Error amplifier
404 comparator
408 Pulse width modulation signal generator
602 error amplifier
604 comparator
606 sawtooth signal generator
608 Reset signal generator
610 Pulse width modulation signal generator
800 drive circuit
802 Zener diode
804 switch
900 Drive circuit
902 Sawtooth signal generator
906 Power converter
910 controller
912 Power line
920 current filter
960 sawtooth signal
962 Drive signal
1000 drive circuit
1008 Input capacitor
1016 registers
1012 registers
1014 capacitor
1018 diode
1024 output filter
1300 flowchart
1400 Drive circuit
1406 Power converter
1408 light source
1410 controller
1420 Voltage filter, voltage regulator
1422 transformer
1424 switch
1462 Drive signal
1464 Detection signal
1466 Current detection signal
1500 drive circuit
1502 core
1504 Primary winding
1506 Secondary winding
1508 Auxiliary winding
1512 inductor
1602 sawtooth signal generator
1660 sawtooth signal
1700 flowchart

Claims (20)

A circuit for supplying power to a light emitting diode (LED) light source,
A filter that receives an input voltage and filters the input voltage to provide a regulated voltage;
A transformer connected to the filter, converting the stabilized voltage into an output voltage and supplying power to the LED light source;
A controller coupled to the filter and a switch further coupled to the transformer, generating a drive signal and operating the switch alternately between a first state and a second state, and flowing through the filter A controller, wherein the input current increases during the first state and decreases during the second state;
The controller controls the duration of operation in the first state and the duration of operation in the second state, so that the input current decreases to a predetermined level during operation in the second state. , So as to increase from the predetermined level during operation in the first state to a maximum level proportional to the input voltage;
A circuit in which the controller controls the ratio of the time in the first state and the time in the second state to adjust the output current flowing through the LED light source to a target level. The filter is
An inductor coupled to the switch through a first diode and coupled to a capacitor through a second diode;
The input current flows through the inductor, the first diode, and the switch during operation in the first state, and the inductor, the second diode, and the capacitor during operation in the second state The circuit of claim 1, flowing through.   3. The circuit of claim 2, wherein the inductor and the capacitor constitute an inductor-capacitor (LC) filter that filters out multiple harmonic components of the input voltage to generate the regulated voltage. The transformer is
A primary winding for receiving the stabilizing voltage;
A secondary winding for providing the output voltage to the LED light source;
The current flowing through the primary winding and the switch increases during operation in the first state, and the current flowing through the secondary winding decreases during operation in the second state. The circuit according to 1.   2. The duration of operation in the first state is a time sufficient for the input current to rise from the predetermined level to the level proportional to the input voltage. circuit.   2. The circuit of claim 1, wherein the duration of operation in the second state is sufficient for the input current to decrease to the predetermined level. The controller is
A generator for generating a sawtooth signal in accordance with the drive signal;
An error amplifier that generates an error signal based on a detection signal indicative of the output current through the LED light source and based on a reference signal indicative of the target level of the output current;
2. The circuit according to claim 1, comprising a comparator coupled to the error amplifier and configured to compare the sawtooth signal and the error signal to control the drive signal.   8. The circuit of claim 7, wherein a sawtooth signal increases during the first state of the switch and the switch is switched to the second state when the sawtooth signal reaches the error signal.   9. The circuit of claim 8, wherein the period during which the sawtooth signal increases from a predetermined level to the error signal is constant when the current through the LED light source is maintained at the target level. A rectifier for receiving an alternating input current (AC) and an alternating input voltage and providing the input current;
The circuit of claim 1, wherein the controller modifies a power factor so that the AC input current is substantially tuned to the AC input voltage. A power conversion device for supplying power to a light emitting diode (LED) light source,
A switch that operates in a first state and a second state according to a pulse signal;
A filter coupled to the switch, comprising an inductor and a capacitor, for filtering the input voltage to provide a regulated voltage, wherein the input current flows through the inductor and the switch during the first state. The input current increases from a predetermined level to a maximum level proportional to the input voltage, and during the second state, the input current flows through the inductor and the capacitor, and the input current is A filter that reduces to the predetermined level;
A transformer having a primary winding connected to the switch, having a secondary winding, converting the stabilized voltage into an output voltage and supplying power to the LED light source, During the state, the transformer is powered by the regulated voltage, increasing the current flowing through the primary winding and the switch, and during the second state, powering the LED light source The transformer is discharged to provide a reduced current flowing through the secondary winding, and
A power conversion device that adjusts an output current flowing through the LED light source to a target level by adjusting a duty cycle of the pulse signal. The transformer is
Further comprising an auxiliary winding for generating a current detection signal indicating whether the current through the secondary winding decreases to a predetermined level;
12. The power conversion device according to claim 11, wherein the switch is switched from the second state to the first state in response to the current detection signal.   12. The power conversion device according to claim 11, wherein a duration time of the second state is longer than a time period during which the input current decreases to the predetermined level.   12. The power conversion device according to claim 11, wherein the duration of the first state is maintained at a constant value. A method for supplying power to a light emitting diode (LED) light source, receiving an input voltage and an input current;
Filtering the input voltage to provide a regulated voltage;
Converting the stabilization voltage into an output voltage and supplying power to the LED light source;
Generating a drive signal and alternately operating the switch between a first state and a second state, wherein the input current increases during the first state and the second state Decrease between the steps and
By controlling the duration of operation in the first state and the duration of operation in the second state, the input current is reduced to a predetermined level during operation in the second state, Increasing from the predetermined level during operation in a first state to a maximum level proportional to the input voltage;
Controlling the ratio between the time in the first state and the time in the second state to adjust the output current flowing through the LED light source to a target level. Receiving the regulated voltage by a primary winding of a transformer;
Providing the output voltage to the LED light source by a secondary winding of the transformer;
Increasing the current flowing through the primary winding and the switch during operation in the first state; and
16. The method of claim 15, further comprising reducing current flowing through the secondary winding during operation in the second state.   16. The method of claim 15, wherein the duration of operation in the first state is sufficient time for the input current to rise from the predetermined level to the level proportional to the input voltage. .   16. The method of claim 15, wherein the duration of operation in the second state is a time sufficient for the input current to decrease to the predetermined level. Generating a sawtooth signal in accordance with the drive signal;
Generating an error signal based on a detection signal indicating the output current through the LED light source and based on a reference signal indicating the target level of the output current;
Comparing the sawtooth signal and the error signal to control the drive signal;
16. The method of claim 15, further comprising switching the switch from the first state to the second state in response to the sawtooth signal reaching the error signal.   The method according to claim 19, wherein when the current through the LED light source is maintained at the target level, a period during which the sawtooth signal generated according to the drive signal increases from a predetermined level to the error signal is constant. The method described.

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