TWI505746B - Circuits and method for powering led light source and power converter thereof - Google Patents

Description

Power supply circuit, power converter and power supply method of light emitting diode light source

The invention relates to a power supply circuit, in particular to a power supply circuit, a power converter and a power supply method for a light-emitting diode light source.

FIG. 1 is a schematic diagram of a conventional light source driving circuit 100. The light source driving circuit 100 is for driving a light source (for example, the light emitting diode string 108). The light source driving circuit 100 supplies an input voltage VIN from a power source 102 to power the driving circuit 100. The light source driving circuit 100 includes a buck converter that provides an adjusted voltage VOUT to the LED string 108 under the control of a controller 104. The buck converter includes a diode 114, an inductor 112, a capacitor 116, and a switch 106. A resistor 110 is coupled in series with the switch 106. When the switch 106 is turned on, the resistor 110 is coupled to the inductor 112 and the LED string 108, and generates a feedback signal to indicate the current flowing through the inductor 112. When the switch 106 is turned off, the resistor 110 is disconnected from the inductor 112 and the LED string 108, so no current flows through the resistor 110.

Switch 106 is controlled by controller 104. When the switch 106 is turned on, a current flows through the LED string 108, the inductor 112, the switch 106, and the resistor 110 to ground. This current gradually increases under the action of the inductor 112. When the current increases to a predetermined peak current level, the controller 104 turns off the switch 106. When the switch 106 is turned off, a current flows through the LED string 108, the inductor 112, and the diode 114. The controller 104 can turn the switch 106 on again after a period of time. Therefore, the controller 104 controls based on the preset peak current level Buck converter. However, the average current level flowing through the inductor 112 and the LED string 108 varies with the inductance of the inductor 112, the input voltage VIN, and the voltage VOUT across the LED string 108, thus flowing through the inductor 112. The average current level (i.e., the average current flowing through the LED string 108) cannot be accurately controlled.

An object of the present invention is to provide a power supply circuit for a light emitting diode light source, comprising: a filter that receives an input voltage and filters the input voltage to provide a stable voltage; and a transformer coupled to the filter to stabilize the Converting the voltage into an output voltage, providing an electric energy for the light emitting diode light source; and a controller coupled to the switch, the filter and the transformer, generating a driving signal, and controlling the switch to operate alternately in the first Between a state and a second state, wherein the controller controls the switch such that an input current flowing through the filter increases during the first state and decreases during the second state, and wherein The controller controls a time ratio of the first state and the second state to adjust an output current flowing through the light emitting diode source to a target value.

The present invention also provides a power converter for providing an electric energy to a light emitting diode light source, comprising: a switch operable between a first state and a second state according to a pulse width modulation signal; a filter The switch is coupled to include an inductor and a capacitor, filtering an input voltage to provide a stable voltage, and a transformer including a primary winding coupled to the switch and a primary winding to convert the stable voltage to an output voltage Causing the light emitting diode source to provide the electrical energy, wherein adjusting the pulse width modulation A duty cycle of the signal to regulate the output current flowing through the light emitting diode source to a target value.

The present invention further provides a method for providing electrical energy to a light emitting diode light source, comprising: receiving an input voltage and an input current; filtering the input voltage to provide a stable voltage; converting the stable voltage to an output voltage; generating a driving signal, controlling a switch to alternately operate between a first state and a second state; controlling a duration of the switching operation in the first state and a duration of operation in the second state; and controlling the a time ratio of a state to the second state to adjust an output current flowing through the light emitting diode source to a target value.

A detailed description of the embodiments of the present invention will be given below. While the invention will be described in conjunction with the embodiments, it is understood that the invention is not limited to the embodiments. On the contrary, the invention is intended to cover various modifications, modifications and equivalents

In addition, in the following detailed description of the embodiments of the invention However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail in order to facilitate the invention.

2 is a schematic diagram of a drive circuit 200 in accordance with an embodiment of the present invention. The light source driving circuit 200 includes a rectifier 204 that can be from a power source 202 An input voltage is received and an adjusted voltage is provided to power converter 206. Power converter 206 receives the adjusted voltage and provides an output power to load 288. In an embodiment, power converter 206 can be a buck converter or a boost converter. In one embodiment, power converter 206 includes an energy storage component 214 and a current sensor 278 (eg, a resistor) for sensing the power condition of energy storage component 214. Current sensor 278 provides a first signal ISEN to controller 210 to indicate the instantaneous current flowing through energy storage element 214. The drive circuit 200 also includes a filter 212 that generates a second signal IAVG for indicating an 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 be a target current value level.

FIG. 3 is a circuit diagram of a light source driving circuit 300 according to an embodiment of the invention. Elements in Figure 3 having the same reference numerals as in Figure 2 have similar functions. In the example of FIG. 3, the light source driving circuit 300 includes a rectifier 204, a power converter 206, a filter 212, and a controller 210. Rectifier 204 can be a bridge rectifier including diodes D1-D4. Rectifier 204 adjusts the voltage from power source 202. Power converter 206 receives the voltage adjusted by rectifier 204 and provides an output power to power the load (e.g., LED string 208).

In the example of FIG. 3, the power converter 206 is a buck converter including a capacitor 308, a switch 316, a diode 314, a current inductor (eg, resistor 218), an inductor 302 coupled to each other, and an inductor. 304, and capacitor 324. The diode 314 is coupled between the switch 316 and the ground of the light source driving circuit 300. The capacitor 324 is coupled in parallel with the LED string 208. In an embodiment, the inductor 302 and the inductor 304 are electromagnetically coupled to each other. More specifically, the inductor 302 and the inductor 304 are coupled to a common node 333. In the example of FIG. 3, the common node 333 is interposed between the resistor 218 and the inductor 302. However, the invention is not limited to this architecture, and the common node 333 can also be located between the switch 316 and the resistor 218. The common node 333 provides a reference ground for the controller 210. In an embodiment, the reference ground of the controller 210 is different from the ground of the light source driving circuit 300. By turning on and off switch 316, the current flowing through inductor 302 can be adjusted to adjust the power supplied to light emitting diode string 208. Inductor 304 senses the power condition of inductor 302, for example, monitoring whether the current flowing through inductor 302 drops to a predetermined current level.

One end of the resistor 218 is coupled to a node between the switch 316 and the cathode of the diode 314, and the other end of the resistor 218 is coupled to the inductor 302. When switch 316 is turned "on" and "off", resistor 218 provides a first signal ISEN indicative of the instantaneous current flowing through inductor 302. In other words, the resistor 218 senses the instantaneous current flowing through the inductor 302 regardless of whether the switch 316 is turned "on" or "off". Filter 212 is coupled to resistor 218 and produces a second signal IAVG indicative of the average current flowing through inductor 302. In an embodiment, filter 212 includes a resistor 320 and a 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 be a target current level by turning on or off the switch 316. The capacitor 324 filters out the chopping current flowing through the LED string 208, thereby smoothing the current flowing through the LED string 208 and substantially equal to the average current flowing through the inductor 302. Thus, the current flowing through the LED string 208 can be substantially equal to the target current. Here, "substantially equal to the target current" means the current flowing through the LED string 208. Although there may be a slight difference from the target current, it is still within an allowable range, so that the undesired condition of the circuit components and the power transmitted from the inductor 304 to the controller 210 may be ignored.

In the example of FIG. 3, the endpoints of controller 210 include ZCD, GND, DRV, VDD, CS, COMP, and FB. The terminal ZCD is coupled to the inductor 304 for receiving a detection signal AUX indicating the power condition of the inductor 302 (eg, whether the current flowing through the inductor 302 is reduced to a preset current level, for example, “0”). The detection signal AUX can also indicate whether the LED string 208 is in an open state. The terminal DRV is coupled to the switch 316 and generates a drive signal (eg, pulse width modulation signal PWM1) to turn the switch 316 on or off. Endpoint VDD is coupled to inductor 304 and receives power from inductor 304. The terminal CS is coupled to the resistor 218 and receives a first signal ISEN indicative of an instantaneous current flowing through the inductor 302. The terminal COMP is coupled to the reference ground of the controller 210 through the capacitor 318. The terminal FB is coupled through the filter 212 coupled to the resistor 218 to receive a second signal IAVG indicative of the average current flowing through the inductor 302. In the example of FIG. 3, the terminal GND (ie, the reference ground of the controller 210) is coupled to a common node 333 between the resistor 218, the inductor 302, and the inductor 304.

Switch 316 can be an N-channel metal oxide semiconductor field effect transistor (NMOSFET). The conduction state of switch 316 is determined based on a voltage difference between the gate voltage of switch 316 and the voltage at terminal GND (i.e., the voltage at common node 333). Therefore, the pulse width modulation signal PWM1 output from the terminal DRV determines the on or off state of the switch 316. When the switch 316 is turned on, the voltage level of the reference ground of the controller 210 is higher than the voltage level of the ground of the light source driving circuit 300, so the circuit of the present invention can be applied to have A relatively high voltage power supply.

In operation, when switch 316 is turned on, a current flows through switch 316, resistor 218, inductor 302, and LED string 208 to ground of light source drive circuit 300. When switch 316 is open, a current flows through resistor 218, inductor 302, LED string 208, and diode 314. The inductor 304 is magnetically coupled to the inductor 302 to detect the power condition of the inductor 302, for example, to detect if the current flowing through the inductor 302 has dropped to a preset current level. Therefore, the controller 210 monitors the current flowing through the inductor 302 through the detection signal AUX, the first signal ISEN, and the second signal IAVG, and controls the switch 316 through the pulse width modulation signal PWM1 to control the average current flowing through the inductor 302. A target current level. Therefore, the current flowing through the LED string 208 after being filtered by the capacitor 324 can also be substantially equal to the target current level.

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

The controller 210 can also determine whether the light emitting diode string 208 is in a short circuit state based on the voltage at the terminal VDD. If the LED 208 is short-circuited, when the switch 316 is in the off state, since both ends of the inductor 302 are coupled to the ground of the light source driving circuit 300, the voltage across the inductor 302 will be reduced. small. The voltage across inductor 304 and the voltage at terminal VDD are also reduced accordingly. Therefore, when the switch 316 is in the off state, if the voltage at the terminal VDD is lower than a voltage threshold, the controller 210 determines that the LED string 208 is in a short circuit state.

4 is a schematic diagram of the controller 210 shown in FIG. 3 in accordance with an embodiment of the present invention. FIG. 5 is a waveform diagram of the controller 210 shown in FIG. 4 in accordance with an embodiment of the present invention. Figure 4 will be described in conjunction with Figures 3 and 5.

In the example of FIG. 4, 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 a voltage difference between a reference signal SET and a second signal IAVG. The reference signal SET can indicate the target current level. The second signal IAVG is received through the terminal FB to indicate the average current flowing through the inductor 302. The error signal VEA can be used to adjust the average current flowing through the inductor 302 to the target current level. The comparator 404 is coupled to the error amplifier 402 and compares the error signal VEA with the first signal ISEN. The first signal ISEN is received through the terminal CS indicating the instantaneous current flowing through the inductor 302. The sense signal AUX is received through the endpoint ZCD indicating whether the current flowing through the inductor 302 has dropped to a predetermined current level (eg, reduced to zero). The pulse width modulation signal generator 408 is coupled to the comparator 404 and the terminal ZCD, and generates a pulse width modulation signal PWM1 based on the output of the comparator 404 and the detection signal AUX. The pulse width modulation signal PWM1 controls the conduction state of the switch 316 through the terminal DRV.

The pulse width modulation signal generator 408 generates a pulse width modulation signal PWM1 having a first level (eg, logic 1) to turn on the switch 316. When the switch 316 is turned on, a current flows through the switch 316, the resistor 218, the inductor 302, and the LED string 208 to the ground of the light source driving circuit 300. The current flowing through the inductor 302 gradually increases, so that the voltage of the first signal ISEN gradually increases. In an embodiment, when the switch 316 is turned on, the voltage of the detection signal AUX is a negative value. In one embodiment, within controller 210, comparator 404 compares error signal VEA with first signal ISEN. When the voltage of the first signal ISEN exceeds the voltage of the error signal VEA, the comparator 404 outputs a logic 0, otherwise the comparator 404 outputs a logic 1. In other words, the output of comparator 404 is a series of pulses. The pulse width modulation signal generator 408 generates a pulse width modulation signal PWM1 having a second level (e.g., logic 0) in response to the negative going output of the comparator 404, thereby turning off the switch 316. When the switch 316 is turned off, the voltage of the detection signal AUX becomes a positive value. When switch 316 is open, a current flows through resistor 218, inductor 302, LED string 208, and diode 314. The current flowing through the inductor 302 gradually decreases, so the voltage of the first signal ISEN gradually decreases. When the current flowing through the inductor 302 is reduced to a predetermined current level (eg, reduced to zero), the voltage of the detection signal AUX will generate a negative edge, and the pulse width modulation signal generator 408 will have the first state ( For example, the pulse width modulation signal PWM1 of logic 1) turns on the switch 316.

In one embodiment, the duty cycle ratio of the pulse width modulation signal PWM1 is determined by the error signal VEA. If the voltage of the second signal IAVG is less than the voltage of the reference signal SET, the error amplifier 402 increases the voltage of the error signal VEA to increase the duty cycle ratio of the pulse width modulation signal PWM1. Accordingly, the average current flowing through the inductor 302 increases until the voltage of the second signal IAVG increases to the voltage level of the reference signal SET. If the second signal When the voltage of the IAVG is greater than the voltage of the reference signal SET, the error amplifier 402 reduces the voltage of the error signal VEA to reduce the duty cycle ratio of the pulse width modulation signal PWM1, thereby reducing the average current flowing through the inductor 302 until the second signal IAVG The voltage is lowered to the voltage level of the reference signal SET. Therefore, the average current flowing through the inductor 302 can be maintained to be equal to the target current level.

FIG. 6 is a block diagram showing another architecture of the controller 210 shown in FIG. 3 according to an embodiment of the invention. FIG. 7 is a waveform diagram of the controller 210 shown in FIG. 6 in accordance with an embodiment of the present invention. Figure 6 will be described in conjunction with Figures 3 and 7.

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 a voltage difference between a reference signal SET and a second signal IAVG. The reference signal SET indicates a target current level. The second signal IAVG receives an average current indicative of the flow through the inductor 302 through the terminal FB. The error signal VEA can be used to adjust the average current flowing through the inductor 302 to be equal to the target current level. The sawtooth signal generator 606 generates a sawtooth signal SAW. The comparator 604 is coupled to the error amplifier 602 and the sawtooth signal generator 606, and compares the error signal VEA with the sawtooth signal SAW. The reset signal generator 608 generates a reset signal RESET and provides a reset signal RESET to the sawtooth signal generator 606 and the pulse width modulation signal generator 610. In response to the reset signal RESET, the switch 316 is turned "on". The pulse width modulation signal generator 610 is coupled to the comparator 604 and the reset signal generator 608, and based on the output of the comparator 604 and the reset signal RESET. A pulse width modulation signal PWM1 is generated. The pulse width modulation signal PWM1 controls the conduction state of the switch 316 through the terminal DRV.

In one embodiment, the reset signal RESET is a pulse signal having a fixed frequency. In another embodiment, the reset signal RESET is a pulse signal that causes the switch 316 to be in an off state for a constant period of time. The reset signal RESET is such that the time when the pulse width modulation signal PWM1 in FIG. 5 is logic 0 is a constant.

In operation, pulse width modulation signal generator 610 generates a pulse width modulation signal PWM1 having a first state (eg, logic 1) to turn on switch 316 and to respond to reset signal RESET. When the switch 316 is turned on, a current flows through the switch 316, the resistor 218, the inductor 302, and the LED string 208 to the ground of the light source driving circuit 300. The voltage of the sawtooth wave signal SAW generated by the sawtooth signal generator 606 is increased from an 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 state (eg, logic 0) to turn off the switch 316, and The voltage of the sawtooth signal SAW is reset to the initial level INI until the sawtooth signal generator 606 receives the next pulse of the reset signal RESET. Upon receiving the next pulse of the reset signal RESET, the voltage of the sawtooth signal SAW will gradually increase from the initial level INI again in response to the pulse.

In one embodiment, the duty cycle ratio of the pulse width modulation signal PWM1 is determined by the error signal VEA. If the voltage of the second signal IAVG is less than the voltage of the reference signal SET, the error amplifier 602 increases the voltage of the error signal VEA to increase the duty cycle ratio of the pulse width modulation signal PWM1. Accordingly, the average current flowing through the inductor 302 increases until the voltage of the second signal IAVG increases to the voltage level of the reference signal SET. If the voltage of the second signal IAVG is greater than the voltage level of the reference signal SET, the error amplifier 602 reduces the voltage of the error signal VEA to reduce the duty cycle ratio of the pulse width modulation signal PWM1. Accordingly, the average current flowing through the inductor 302 decreases until the voltage of the second signal IAVG drops to the voltage level of the reference signal SET. Therefore, the average current flowing through the inductor 302 can be maintained to be equal to the target current level.

FIG. 8 is a schematic diagram of a light source driving circuit light source driving circuit 800 according to another embodiment of the present invention. Elements in Figure 8 having the same reference numerals as in Figures 2 and 3 have similar functions.

The terminal VDD of the controller 210 is coupled to the rectifier 204 through the switch 804 and receives the output voltage adjusted by the rectifier 204. A Zener diode 802 coupled between the switch 804 and the reference ground of the controller 210 is used to maintain the voltage at the terminal VDD substantially constant. In the example of FIG. 8 , the terminal ZCD of the controller 210 is electrically coupled to the inductor 302 and receives a detection signal AUX indicating the power condition of the inductor 302 . The detection signal AUX may indicate whether the current flowing through the inductor 302 has decreased to a preset current level (eg, whether it is reduced to zero). The common node 333 can provide a reference ground for the controller 210.

In summary, the present invention provides a circuit that controls a power converter to power a load. In one embodiment, the power converter provides a substantially constant current to a load, such as a string of light emitting diodes. In another embodiment, the power converter provides a current to charge the battery. The current provided by the circuit of the present invention to the load or battery can be more accurately controlled than the conventional circuit of FIG. Moreover, the circuit of the present invention can be applied to have a phase A voltage source for higher voltages.

FIG. 9A is a block diagram showing a light source driving circuit 900 in accordance with another embodiment of the present invention. Elements in Figure 9A numbered the same as Figures 2 and 3 have similar functions. In an embodiment, light source drive circuit 900 includes a filter 920 coupled to power source 202, a rectifier 204, a power converter 906, a load 288, a sawtooth signal generator 902, and a controller 910. The power supply 202 produces an AC input voltage V _AC (eg, the AC input voltage V _AC has a sinusoidal signal) and an AC input current I _AC . The AC input current I _AC flows into the filter 920. Current I _AC ' flows out of filter 920 and flows into rectifier 204. The rectifier 204 receives the AC input voltage V _AC through the filter 920 and provides a rectified voltage V _IN and a rectified current I _IN on the power line 912. The power line 912 is coupled between the rectifier 204 and the power converter 906. Power converter 906 converts rectified voltage V _IN to an output voltage V _OUT to provide power to load 288. The controller 910 is coupled to the power converter 906 for controlling the power converter 906 to regulate the current I _OUT flowing through the load 288 and correct the power factor of the light source driving circuit 900.

Controller 910 generates a drive signal 962. In one embodiment, power converter 906 includes a switch 316. Drive signal 962 controls switch 316 to regulate current I _OUT flowing through load 288. Power converter 906 also generates an induced signal IAVG indicative of current I _OUT flowing through load 288.

In one embodiment, the sawtooth signal generator 902 coupled to the controller 910 generates a sawtooth signal 960 based on the drive signal 962. For example, drive signal 962 can be a pulse width modulated signal. In one embodiment, the sawtooth signal 960 is increased when the drive signal 962 is at a logic high level; when the drive signal 962 is at a logic low level, the sawtooth signal 960 is lowered to The preset voltage value (for example, reduced to 0V).

Advantageously, controller 910 generates drive signal 962 based on sawtooth signal 960 and sense signal IAVG. The drive signal 962 controls the switch 316 to maintain the current I _OUT flowing through the load 288 at the target current value to improve the accuracy of the current control. In addition, the drive signal 962 controls the switch 316, and the average current I _{IN_AVG of the} regulated rectified current I _IN is substantially in phase with the rectified voltage V _IN to correct the power factor of the light source drive circuit 900. In the present invention, substantially in phase means that the two waveforms are theoretically in phase, however, in practical applications, due to the presence of capacitance in the circuit, there is a slight phase difference between the two waveforms. The operation of light source drive circuit 900 will be further described in Figure 9B.

Figure 9B is a waveform diagram of signals in the light source driving circuit 900 of Figure 9A in accordance with one embodiment of the present invention, and Figure 9B will be described in conjunction with Figure 9A. FIG. 9B depicts waveforms of the input AC voltage V _AC , the rectified voltage V _IN , the rectified current I _IN , the average current I _{IN — AVG of the} rectified current, the current I _AC ', and the input AC current I _AC .

For convenience of description, the input AC voltage V _AC is a sinusoidal waveform, but is not limited thereto. The rectifier 204 rectifies the input AC voltage V _AC . In the embodiment of Figure 9B, the rectified voltage V _IN has a rectified sinusoidal waveform, i.e., the forward waveform of the input AC voltage V _AC remains, and its negative waveform is converted to a corresponding forward waveform.

In one embodiment, the drive signal 962 generated by the controller 910 controls the rectified current I _IN . The rectified current I _{IN increases} from a predetermined value (for example, 0 amps). After the rectified current I _IN reaches a value proportional to the rectified voltage V _IN , the rectified current I _IN drops to a preset value. As shown in FIG. 9B, the waveform of the average current I _{IN_AVG} of the rectified current I _IN is substantially in phase with the waveform of the rectified voltage V _IN .

The rectified current I _IN flows out of the rectifier 204 and flows into the power converter 906. The rectified current I _IN is the current rectified by the current I _AC ' flowing into the rectifier 204. As shown in FIG. 9B, when the input AC voltage V _AC is positive, the forward waveform of the current I _AC ' is similar to the forward waveform of the rectified current I _IN ; when the input current voltage V _AC is negative, the current I _AC The negative waveform of ' corresponds to the waveform of the rectified current I _IN .

In one embodiment, the input AC current I _AC is equal or proportional to the average of the current I _AC ' through a filter 920 coupled between the power source 202 and the rectifier 204. Therefore, as shown in FIG. 9B, the waveform of the input alternating current I _AC is substantially in phase with the waveform of the input alternating current voltage V _AC . In theory, the input AC current I _{AC is in} phase with the input AC voltage V _AC . However, in practical applications, there may be a slight phase difference between the input alternating current I _AC and the input alternating voltage V _AC due to the presence of capacitance in the filter 920 and the power converter 906. In addition, the input AC current I _AC is also substantially similar to the input AC voltage V _AC waveform. Therefore, the power factor of the light source driving circuit 900 is corrected, thereby improving the power supply quality of the light source driving circuit 900.

FIG. 10 is a schematic diagram of a light source driving circuit 1000 in accordance with still another embodiment of the present invention. Elements in Figure 10 that are numbered the same as Figures 2, 3, and 9A have similar functions. Figure 10 will be described in conjunction with Figures 4, 5 and 9A.

In the example of FIG. 10, the light source driving circuit 1000 includes a filter 920 coupled to the power source 202, a rectifier 204, a power converter 906, a load 288, a sawtooth signal generator 902, and a controller 910. In one embodiment, load 288 includes a light emitting diode string 208 (eg, a light emitting diode chain). The invention is not limited in this regard, and the load 288 may include other types of light sources or other types of loads (eg, battery packs). The filter 920 can be an inductor-capacitor filter including a pair of inductors and a pair of capacitors, but is not limited thereto. In one embodiment, controller 910 includes a plurality of ports, for example, ZCD埠, GND埠, DRV埠, VDD埠, FB埠, COMP埠, and CS埠.

In one embodiment, power converter 906 includes an input capacitor 1008 coupled to power line 912. The input capacitor 1008 reduces the chopping of the rectified voltage V _IN to smooth the waveform of the rectified voltage V _IN . In one embodiment, input capacitor 1008 has a relatively small capacitance value (eg, less than 0.5 microfarads) to help eliminate or reduce distortion of the rectified voltage V _IN waveform. Additionally, in one embodiment, since the capacitance of the input capacitor 1008 is small, the current flowing through the input capacitor 1008 can be ignored. Thus, when switch 316 is turned "on", current I ₂₁₄ flowing through switch 316 is substantially equal to the rectified current I _IN flowing from rectifier 204.

Power converter 906 is similar to the operation of power converter 206 in FIG. In one embodiment, the energy storage component 214 includes an inductor 302 and an inductor 304 that is electromagnetically coupled to the inductor 304. Inductor 302 is coupled to switch 316 and light emitting diode string 208. Therefore, current I ₂₁₄ flows through inductor 302 depending on the on state of switch 316. More specifically, in one embodiment, controller 910 generates a drive signal 962 (e.g., a pulse width modulation signal) on DRV to control switch 316 to be turned "on" or "off". When switch 316 is closed, current I ₂₁₄ flows from power line 912, through switch 316 and inductor 302, and increases. Current I ₂₁₄ can be derived from equation (1): ΔI ₂₁₄ = (V _IN - V _OUT ) * T _ON / L ₃₀₂ (1)

Where T _ON represents the time when the switch 316 is turned on, ΔI ₂₁₄ represents the amount of change of the current I ₂₁₄ , and L ₃₀₂ represents the inductance value of the inductor 302. In one embodiment, controller 910 controls drive signal 962 such that T _ON is a constant value. Therefore, when the output voltage V _OUT is substantially constant, in a time interval T _ON, the current I ₂₁₄ is the amount of change △ I of the rectified voltage ₂₁₄ is proportional to V _IN. In one embodiment, when current I _{214 is} lowered to a preset value (eg, 0 amps), switch 316 is closed. Therefore, the peak value of the current I ₂₁₄ is proportional to the rectified voltage V _IN .

When switch 316 is open, current I ₂₁₄ flows from ground and flows through diode 314 and inductor 302 into current LED string 208. Accordingly, the current I _{214 is} lowered according to the formula (2): ΔI ₂₁₄ = (-V _OUT ) * T _OFF / L ₃₀₂ (2)

Where T _OFF represents the off time of the switch 316.

In one embodiment, current I _{IN is} equal to current I ₂₁₄ when switch 316 is on, and current I _IN is equal to 0 amps when switch 316 is open.

Inductor 304 senses the condition of inductor 302, for example, whether the current flowing through inductor 302 drops to a preset current value, such as 0 amps. In conjunction with FIG. 5, in one embodiment, the monitor signal AUX is low when the switch 316 is closed and the monitor signal AUX is high when the switch 316 is open. When the current I ₂₁₄ flowing through the inductor 302 is lowered to a preset current value, the voltage of the monitor signal AUX produces a negative edge. The ZCD of the controller 910 is coupled to the inductor 304 for receiving the monitoring signal AUX.

In one embodiment, power converter 906 includes an output filter 1024. Output filter 1024 can be a capacitor having a relatively large capacitance value (eg, greater than 400 microfarads). Therefore, the current I _OUT flowing through the LED string 208 represents the average value of the current I ₂₁₄ .

Resistor 218 produces a current sense signal ISEN indicative of the current flowing through inductor 302. In one embodiment, filter 212 is a resistor-capacitor filter comprising a resistor 320 and a capacitor 322. The filter 212 removes the chopping in the current sense signal ISEN to generate an average current sense signal IAVG of the current sense signal ISEN. Therefore, in the embodiment of FIG. 10, the average current sense signal IAVG represents the current I _OUT flowing through the LED string 208. The 埠FB of the controller 910 is used to receive the average current sense signal IAVG.

The sawtooth signal generator 902 is coupled to the DRV埠 and CS埠. The sawtooth signal generator 902 generates a sawtooth signal 960 on CS埠 based on the DRV drive signal 962. For example, the sawtooth signal generator 902 includes a resistor 1016 and a diode 1018 coupled between the DRV埠 and the CS埠 and connected in parallel with each other, and further includes a resistor 1012 and a capacitor coupled between the CS埠 and the ground and connected in parallel with each other. 1014. In operation, the sawtooth signal 960 varies according to the drive signal 962. More specifically, in one embodiment, drive signal 962 is a pulse width modulated signal. When the drive signal 962 is at a logic high level, the current I1 flows out of the DRV, passes through the resistor 1016, and flows into the capacitor 1014. Therefore, the capacitor 1014 is charged, and the voltage V _{960 of the} sawtooth signal 960 is increased. When the drive signal 962 is at a logic low level, the current I2 flows out of the capacitor 1014, passes through the diode 1018, and flows into the DRV. Therefore, the capacitor 1014 is discharged and the voltage V _{960 is} lowered to 0 volts. The sawtooth signal generator 902 may also include other components and is not limited to the embodiment shown in FIG.

In one embodiment, controller 910 is integrated on an integrated circuit die. Resistors 1016 and 1012, diode 1018, and capacitor 1014 are peripheral circuit components of the integrated circuit die. In another embodiment, the sawtooth signal generator 902 and controller 910 can also be integrated on an integrated circuit die. In this embodiment, the CS埠 can be omitted, thereby reducing the light. The size and cost of the source drive circuit 1000. The power converter 906 can also have other configurations and is not limited to the embodiment shown in FIG.

FIG. 11 is a block diagram showing the structure of the controller 910 of FIG. 9A according to an embodiment of the present invention. Elements in Figure 11 that are numbered the same as Figures 4 and 9A have similar functions. Figure 11 will be described in conjunction with Figures 4, 5, 9A and 10.

In one embodiment, controller 910 has a similar structure to controller 210 of FIG. 4, except that CS埠 receives sawtooth signal 960 instead of current sense signal ISEN. The controller 910 generates a drive signal 962 based on the sawtooth signal 960, the average current sense signal IAVG, and the monitor signal AUX. Controller 910 includes error amplifier 402, comparator 404, and pulse width modulation signal generator 408. The error amplifier 402 generates an error signal VEA based on the difference between the average current sense signal IAVG and the reference signal SET indicating the target current value. Comparator 404 compares sawtooth signal 960 and error signal VEA to produce comparison signal S. The pulse width modulation signal generator 408 generates a drive signal 962 based on the comparison signal S and the monitor signal AUX.

In one embodiment, when the monitor signal AUX indicates that the current I ₂₁₄ flowing through the inductor 302 drops to a preset value (eg, 0 amps), the drive signal 962 switches to a first potential (eg, a logic high) to close Switch 316. When the sawtooth signal 960 reaches the error signal VEA, the drive signal 962 switches to a second potential (eg, a logic low) to turn off the switch 316. Advantageously, since CS埠 receives the sawtooth signal 960 instead of the current sense signal ISEN, the peak value of the current I ₂₁₄ flowing through the inductor 302 is not limited by the error signal VEA. Therefore, as described in the formula (1), the current I ₂₁₄ flowing through the inductor 302 changes according to the rectified voltage V _IN . For example, the peak value of current I ₂₁₄ is proportional to the rectified voltage V _IN rather than to the error signal VEA.

The controller 910 controls the drive signal 962 to maintain the current I _OUT at the target current value represented by the reference signal SET. For example, if the current I _{OUT is} greater than the target current value (eg, due to a change in the rectified voltage V _IN ), the error amplifier 402 reduces the error signal VEA to shorten the time T _ON at which the switch 316 is closed. Therefore, the average current of current I ₂₁₄ is reduced to reduce current I _OUT . Similarly, if the current I _{OUT is} less than the target current value, the controller 910 extends the time T _{ON at} which the switch 316 is closed to increase the current I _OUT .

Figure 12 is a diagram showing signal waveforms generated or received by a light source driving circuit (e.g., light source driving circuit 900 or 1000) in accordance with an embodiment of the present invention. Figure 12 will be described in conjunction with Figures 4, 9A, 9B and 10. Figure 12 depicts the rectified voltage V _IN, the rectified current I _IN, the rectified current I _IN average current _I IN_AVG, flowing through the light-emitting diode current I _OUT string 208, the current flowing through the inductor 302 represents the inductive signal ISEN ₂₁₄ of I The error signal VEA, the sawtooth signal 960, and the drive signal 962.

As shown in FIG. 12, the rectified voltage V _IN is a rectified sine wave signal. At time t1, drive signal 962 becomes a logic high. Thus, switch 316 is closed, indicating that the induced signal ISEN of current I ₂₁₄ flowing through inductor 302 is increased. At the same time, the sawtooth signal 960 is increased in accordance with the drive signal 962.

At time t2, the sawtooth signal 960 is added to the error signal VEA. Accordingly, controller 910 adjusts drive signal 962 to a logic low level and sawtooth signal 960 to a voltage of zero volts. The drive signal 962 turns off the switch 316, so the sense signal ISEN drops. In other words, the sawtooth signal 960 and the error signal VEA determine the time T _{ON at which} the drive signal 962 is logic high.

At time t3, current I _{214 is} reduced to a preset current value (eg, 0 amps), whereby controller 910 adjusts drive signal 962 to a logic high to close switch 316.

In one embodiment, the current I _OUT flowing through the LED string 208 is equal or proportional to the average of the current I ₂₁₄ during one cycle of the rectified voltage V _IN . In conjunction with the description of FIG. 11, controller 910 adjusts current I _OUT to a target current value represented by reference signal SET. In addition, as shown in FIG. 12, the induced signal ISEN indicating the current I ₂₁₄ has the same waveform during the period from t1 to t4 and during the period from t5 to t6. Therefore, the average value of the current I ₂₁₄ during t1 to t4 is equal to the average value during t5 to t6. Therefore, the current I _{OUT is} maintained at the target current value. In one embodiment, T _{ON is} determined by the sawtooth signal 960 and the error signal VEA. Since the time during which the sawtooth signal 960 rises from 0 volts to the error signal VEA is equal during each period of the drive signal 962, T _ON is constant. According to the formula (1), within a time T _ON, the current I ₂₁₄ is the amount of change △ I of the rectified voltage ₂₁₄ is proportional to V _IN. Therefore, as shown in FIG. 12, the peak value of the induced signal ISEN is proportional to the input voltage V _IN .

In one embodiment, when switch 316 is closed, the waveform of current I _IN is similar to the waveform of current I ₂₁₄ , and when switch 316 is open, current I _IN is equal to 0 amps. In the period t1 to t6, and the average current _I IN_AVG substantial rectifying the rectified voltage V _IN is in phase with current I _IN. As described in connection with FIG. 9B, the input current I _{AC is} substantially in phase with the input voltage V _AC , thereby correcting the power factor of the light source driving circuit, thereby improving the power supply quality.

13 is a flowchart 1300 of a method for driving a load driving circuit (eg, light source driving circuit 900 or 1000 for driving light emitting diode string 208) in accordance with an embodiment of the present invention. Figure 13 will be combined with Figure 9A Description will be made to FIG. The specific steps covered in Figure 13 are only examples. That is, the present invention is also applicable to the steps of performing other reasonable steps or improving FIG.

In step 1302, an input voltage (eg, rectified voltage V _IN ) and an input current (eg, rectified current I _IN ) are received. In step 1304, the input voltage is converted to an output voltage to provide electrical energy to a load (eg, a light emitting diode source). In step 1306, 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 regulate the current flowing through the load.

In step 1308, a first induced signal (eg, average current sense signal IAVG) representative of the current flowing through the load is received. In one embodiment, the first sensed signal is obtained by filtering a second sensed signal indicative of current flowing through the energy storage element. In step 1310, a sawtooth signal is generated based on the drive signal.

In step 1312, the driving signal is controlled by the sawtooth wave signal and the first sensing signal to adjust the current flowing through the load to the target current value, and the average current through the control input current is substantially in phase with the input voltage to correct the light source driving circuit. Power factor. In one embodiment, an error signal is generated based on a difference between the first sensed signal and the reference signal, the reference signal representing a target current value flowing through the light emitting diode source. The sawtooth signal and the error signal are compared and a monitoring signal indicative of the condition of the energy storage element is received. If the monitoring signal indicates that the current flowing through the energy storage element is reduced to a preset value, the driving signal is switched to the first state, and the driving signal is switched to the second state according to the comparison value of the sawtooth wave signal and the error signal. When the drive signal is in the first state, the current flowing through the energy storage element is increased; and when the drive signal is in the second state, the current flowing through the energy storage element is reduced. In one embodiment, if the light flows through the light emitting diode The current of the source is maintained at the target current value, and the time during which the sawtooth signal is increased from the preset value to the error signal is constant.

FIG. 14A is a block diagram showing a light source driving circuit 1400 according to another embodiment of the present invention. Elements in Figure 14A numbered the same as Figures 2, 3 and 9A have similar functions. Figure 14B is a diagram showing signal waveforms generated or received by the light source driving circuit 1400 shown in Figure 14A in accordance with the present invention. 14A and 14B will be described in conjunction with Figs. 9A and 9B.

In the example of FIG. 14A, light source drive circuit 1400 includes a current filter 1402 coupled to a power source 202, a rectifier 204, a power converter 1406, a light source 1408, and a controller 1410. Power source 202 produces an AC input voltage V _AC (eg, V _AC has a sinusoidal signal) and an AC input current I _AC . The AC input current I _AC flows into the current filter 1402. Current I _AC ' flows out of current filter 1402 and flows into rectifier 204. Rectifier 204 receives AC input voltage V _AC through current filter 1402 and provides rectified voltage V _IN and rectified current I _IN on power line 912. The power line 912 is coupled between the rectifier 204 and the power converter 1406.

In one embodiment, power converter 1406 includes voltage filter 1420, transformer 1422, and switch 1424. Voltage filter 1420 receives voltage V _IN and filters voltage V _IN to produce a regulated voltage V _REG . For example, harmonic components having a relatively high frequency in voltage V _IN are excluded or eliminated. Therefore, as shown in FIG. 14B, the waveform of the stable voltage V _REG is more stable than the waveform of the voltage V _IN . Transformer 1422 converts regulated voltage V _REG to output voltage V _OUT to provide power to light source 1408. Therefore, the waveform of the output voltage V _OUT is not affected by variations in the input voltage V _IN (eg, sine wave). Accordingly, the chopping of the current I _OUT flowing through the light source 1408, which is caused by the change in the input voltage V _IN , is reduced or eliminated, thereby further reducing the horizontal frequency interference of the light emitted by the light source 1408.

Controller 1410 generates drive signal 1462 to control switch 1424 to operate in a first state or a second state, thereby further controlling input current I _IN flowing into voltage filter 1420 and output current I _OUT flowing through light source 1408. In one embodiment, transformer 1422 provides an inductive signal 1464 indicative of output current _IOUT . Based on the sense signal 1464, the controller 1410 controls the ratio of the on time T _ON and the off time T _OFF of the switch 1424 to adjust the output current I _OUT to a target value.

In one embodiment, during operation of switch 1424 in the first state, input current I _IN increases, and during operation of switch 1424 in the second state, input current I _IN decreases. During the second state, the controller 1410 controls the duration of the second state to allow the input current I _{IN to} decrease to a preset value (eg, zero). The controller 1410 further controls the duration of the first state to allow the input current to increase from a preset value to a value proportional to the input voltage V _IN . Input current I _{IN I} IN_AVG average current and input voltage V _IN substantial phase. Similar to the discussion of FIG. 9B, the input current I _AC voltage V _AC with substantial phase. Ideally, the AC input voltage V _AC and the AC input current I _AC are in phase. However, in practical applications, due to the presence of a capacitor in the current filter 1402 and the power converter 1406, a slight phase difference may result. Further, the waveform 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 light source driving circuit 1400 can be corrected.

Advantageously, by switching the switch 1424 alternately between the first state and the second state, the power factor of the light source drive circuit 1400 can be corrected and the output current I _{OUT can be} adjusted to a target value. Therefore, the power supply quality and the accuracy of current control of the light source driving circuit 1400 are improved. Since only the switch 1424 is controlled, the size and cost of the light source driving circuit 1400 are reduced.

FIG. 15 is a circuit diagram of a light source driving circuit 1500 according to another embodiment of the present invention. Elements in Figure 15 that are numbered the same as Figures 2, 3, 9A and 14A have similar functions. Figure 15 will be described in conjunction with Figures 14A and 14B. In one embodiment, controller 1410 includes multiple endpoints, such as VIN endpoints, COMP endpoints, GND endpoints, DRV endpoints, CS endpoints, VDD endpoints, ZCD endpoints, and FB endpoints.

In one embodiment, voltage filter 1420 includes an inductor 1512, diodes D15 and D16, and a capacitor C15. Transformer 1422 can be a flyback converter including primary winding 1504, secondary winding 1506, auxiliary winding 1508, and magnetic core 1502. The switch 1424 is coupled to the diode D16 and the primary winding 1504 and operates in a first state (eg, an on state) and a second state (eg, an off state) to control an input current I _IN flowing through the inductor 1512. And an output current I _OUT flowing through the light source 1408.

In one embodiment, controller 1410 generates drive signal 1462 (eg, a pulse width modulation signal) to control switch 1424. More specifically, in one embodiment, when the drive signal 1462 has a logic high potential (eg, during the on state, T _ON ), the switch 1424 is turned on, the diode D15 is reverse biased, and the diode D16 is positive. Offset. The regulated voltage V _REG supplies power to the transformer 1422. Current I _PRI flows through primary winding 1504, switch 1424 to ground. The current I _{PRI is} increased to store energy in the magnetic core 1502. In addition, the input current I _IN flows through the inductor 1512, the diode D16, and the switch 1424, and the input current I _IN increases to charge the inductor 1512. The input current I _IN can be derived from equation (3): ΔI _IN =V _IN * T _CH /L ₁₅₁₂ (3)

Where T _CH represents the charging time during which the inductor 1512 is charged during the on state of the switch 1424. ΔI _IN represents the amount of change in the input current I _IN , and L ₁₅₁₂ represents the inductance value of the inductor 1512. In one embodiment, when switch 1424 is turned on, duration _TCH is equal to duration _TON .

When the drive signal 1462 has a logic low (eg, during the off state _TOFF ), the switch 1424 is turned off, the diode D15 is forward biased, and the diode D16 is reverse biased. The discharge of the transformer 1422 provides electrical energy to the LED string 208. Therefore, the current I _SE flowing through the secondary winding 1506 is reduced. In addition, the input current I _IN flows through the inductor 1512, the diode D15, and the capacitor C15, and according to the formula (4), the input current I _IN decreases to discharge the inductor 1512: ΔI _IN = (V _IN - V _REG )* T _DISCH /L ₁₅₁₂ (4)

Where T _DISCH represents the duration of discharge of the inductor 1512 during the off state of the switch 1424. Since the discharge of the inductor 1512 is terminated once the input current I _{IN is} reduced to 0 amps, the time T _DISCH and the time T _OFF may be different for the off state.

In one embodiment, inductor 1512 and capacitor C15 form an inductive-capacitor filter. The inductor-capacitor filter filters the high frequency harmonic components of the input voltage V _IN . Thus, the _{chopping of the} waveform of the stable voltage V _REG caused by the change in the input voltage V _IN is thus reduced. The transformer 1422 converts the stable voltage V _REG into an output voltage V _OUT .

In one embodiment, the auxiliary winding 1508 is coupled to the controller 1410 through the ZCD terminal. The auxiliary winding 1508 provides a monitoring signal 1466 indicating whether the current I _SE drops to a preset value (eg, 0 amps). The FB endpoint of controller 1410 receives an inductive signal 1464 indicating the output current I _OUT flowing through LED string 208. In one embodiment, the controller 1410 controls the duty cycle of the drive signal 1462 based on the monitor signal 1466 and the sense signal 1464 to adjust the output current I _OUT flowing through the LED string 208 to the target current value. The operation of controller 1410 will be further described in FIG.

In one embodiment, controller 1410 also controls the duration of drive signals 1462T _ON and T _OFF to correct the power factor of light source drive circuit 1500. More specifically, in one embodiment, the controller 1410 will shut down duration T _OFF state is set to a time greater than the threshold value T _TH. By rewriting equation (4), the discharge time of inductor 1512 can be derived from equation (5): T _DISCH = _{ΔI IN} * L ₁₅₁₂ / (V _IN - V _REG ) (5)

As shown in FIG. 14B, ΔI _IN may be different in different cycle periods of the drive signal 1462. In one embodiment, the time threshold T _TH may be set to be equal to or greater than the amount of the maximum discharge time T _{DISCH — MAX} of the inductor 1512. Thus, the duration of the switch 1424 in the off state is sufficient to allow the input current I _{IN to} decrease to 0 amps. In addition, controller 1410 maintains the duration of T _ON at the same value. Thus, according to equation (3), the input current I _IN is increased from a preset value to a peak proportional to the input voltage V _IN . Therefore, as described in FIGS. 14A and 14B, the power factor of the light source driving circuit 1500 is corrected to improve the power supply quality of the light source driving circuit 1500.

Figure 16 is a block diagram showing the structure of the controller 1410 shown in Figure 14A, in accordance with an embodiment of the present invention. Figure 16 is the same as Figure 4 and Figure 9A. The components have similar functions. Figure 16 will be described in conjunction with Figures 4, 5, 10 and 11.

In one embodiment, controller 1410 has a similar structure to controller 910 of FIG. 11 except that it includes sawtooth signal generator 1602 that produces sawtooth signal 1660. In one embodiment, the operation of the sawtooth signal generator 1602 is similar to the sawtooth signal generator 902 shown in FIG. When the drive signal 1462 turns on the switch 1424, the sawtooth signal 1660 ramps up, and when the drive signal 1462 turns off the switch 1424, the sawtooth signal 1660 drops to 0 amps.

Controller 1410 generates drive signal 1462 based on sawtooth signal 1660, sense signal 1464, and monitor signal 1466. Controller 1410 also includes error amplifier 402, comparator 404, and pulse width modulation (PWM) signal generator 408. Error amplifier 402 amplifies the difference between sensed signal 1464 and reference signal SET indicative of the target current value to produce error signal VEA. Comparator 404 compares sawtooth signal 1660 with error signal VEA to produce a comparison signal S. The pulse width modulation signal generator 408 generates a drive signal 1462 based on the comparison signal S and a monitor signal 1466. T _ON corresponds to the time when the sawtooth signal 1660 is increased from the preset value to the error signal VEA.

In one embodiment, when the monitor signal 1466 indicates that the current I _SE flowing through the secondary winding 1506 has dropped to a preset value (eg, 0 amps), the drive signal 1462 has a logic high potential to turn on the switch 1424. When the sawtooth signal 1660 reaches the error signal VEA, the drive signal 1462 has a logic low to turn off the switch 1424.

The controller 1410 controls the drive signal 1462 to maintain the output current _IOUT at the target current value represented by the reference signal SET. For example, if the output current I _{OUT is} greater than the target value (eg, due to undesired noise), the error amplifier 402 will reduce the error signal VEA to shorten the on-state duration T _{ON of the} switch 1424. Therefore, the duty cycle of the drive signal 1462 is reduced to reduce the output current I _OUT . Likewise, if the output current I _{OUT is} less than the target value, the controller 1410 will increase the duty cycle of the drive signal 1462 to increase the output current I _OUT . In one embodiment, if the output current I _{OUT is} maintained at the target value, the duration T _{ON is} maintained at a constant value.

17 is a flow chart 1700 of a method of driving a light source in accordance with an embodiment of the present invention. Figure 17 will be described in conjunction with Figures 14A-16. The specific steps covered in Figure 17 are by way of example only. That is, the present invention is also applicable to the steps of performing other reasonable steps or improving FIG.

In step 1702, an input current (for example, input current I _IN ) and an input voltage (eg, input voltage V _IN ) are received. In step 1704, the input voltage is filtered to provide a regulated voltage (eg, a regulated voltage V _REG ). In step 1706, the regulated stable voltage is an output voltage (eg, output voltage _VOUT ) to provide electrical energy to the light source. In step 1708, a drive signal (eg, drive signal 1462) is generated to control the switch (eg, switch 1424) to alternate between the first state and the second state. The input current increases during the first state and decreases during the second state. In step 1708, step 1710 can be further included.

In step 1710, controlling the duration of the operation in the first state and the duration of operation in the second state such that the input current is reduced to a preset value (eg, 0 amps) during the second state operation, and at During a state operation, it increases from a preset value to a peak that is proportional to the input voltage.

In step 1712, the time ratio of the first state to the second state is controlled to adjust the output current through the light source to a target value.

Embodiments of the present invention provide a load (e.g., light emitting diode source) drive circuit. 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 to an output voltage to provide power to the light-emitting diode source. The drive signal control switch generated by the controller alternately operates between the first state and the second state. The controller controls the duration of the switch operation in the first state and the duration of operation in the second state such that the input current decreases to a preset value during the second state operation and from the preset value during the first state operation Increase to a peak that is proportional to the input voltage. The controller also controls a time ratio of the first state time to the second state time to adjust an output current flowing through the light emitting diode source to a target value. Advantageously, the chopping of the output current flowing through the illuminating diode source resulting from the change in input voltage is reduced or eliminated, further reducing the horizontal frequency interference of the light emitted by the source. In addition, the power factor of the driving circuit is corrected to improve the power quality of the driving circuit, and the current control accuracy of the driving circuit is also improved.

The above detailed description and the accompanying drawings are only typical embodiments of the invention. It is apparent that various additions, modifications, and substitutions are possible without departing from the spirit and scope of the invention as defined by the scope of the invention. It should be understood by those skilled in the art that the present invention may be changed in form, structure, arrangement, ratio, material, element, element, and other aspects without departing from the scope of the invention. Therefore, the embodiments disclosed herein are for illustration and not limitation, the scope of the invention The scope of the appended patent application and its legal equivalents are defined without limitation to the foregoing description.

100‧‧‧Light source drive circuit

102‧‧‧Power supply

104‧‧‧ Controller

106‧‧‧Switch

108‧‧‧Lighting diode strings

110‧‧‧resistance

112‧‧‧Inductance

114‧‧‧dipole

116‧‧‧ Capacitance

200‧‧‧ drive circuit

202‧‧‧Power supply

204‧‧‧Rectifier

206‧‧‧Power Converter

208‧‧‧Lighting diode strings

210‧‧‧ Controller

212‧‧‧ filter

214‧‧‧ Energy storage components

218‧‧‧resistance

278‧‧‧ Current sensor

288‧‧‧load

300‧‧‧Light source drive circuit

302, 304‧‧‧Inductance

308‧‧‧ Capacitance

314‧‧‧ diode

316‧‧‧ switch

318‧‧‧ Capacitance

320‧‧‧resistance

322‧‧‧ Capacitance

324‧‧‧ Capacitance

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‧‧‧Light source drive circuit

802‧‧ ‧ Zener diode

804‧‧‧ switch

900‧‧‧Light source drive circuit

902‧‧‧Sawtooth signal generator

906‧‧‧Power Converter

910‧‧‧ Controller

912‧‧‧Power cord

920‧‧‧ filter

960‧‧‧Sawtooth signal

962‧‧‧Drive signal

1000‧‧‧Light source drive circuit

1008‧‧‧ input capacitor

1012‧‧‧resistance

1014‧‧‧ Capacitance

1016‧‧‧resistance

1018‧‧‧dipole

1024‧‧‧ output filter

1300‧‧‧flow chart

1302~1312‧‧‧Steps

1400‧‧‧Light source drive circuit

1402‧‧‧ Current filter

1406‧‧‧Power Converter

1408‧‧‧Light source

1410‧‧‧ Controller

1420‧‧‧voltage filter

1422‧‧‧Transformer

1424‧‧‧Switch

1462‧‧‧Drive signal

1464‧‧‧Induction signal

1466‧‧‧Monitoring signal

1500‧‧‧Light source drive circuit

1502‧‧‧ magnetic core

1504‧‧‧Primary winding

1506‧‧‧Secondary winding

1508‧‧‧Auxiliary winding

1512‧‧‧Inductance

1602‧‧‧Sawtooth signal generator

1660‧‧‧Sawtooth signal

1702, 1704, 1706, 1708, 1710, 1712‧‧ steps

The technical method of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments to make the features and advantages of the present invention more obvious. Wherein: Figure 1 shows a schematic diagram of a conventional light source driving circuit.

2 is a schematic diagram of a driving circuit in accordance with an embodiment of the present invention.

3 is a circuit diagram of a light source driving circuit according to an embodiment of the invention.

4 is a schematic diagram of the controller shown in FIG. 3 in accordance with an embodiment of the present invention.

Figure 5 is a waveform diagram of the controller shown in Figure 4 in accordance with an embodiment of the present invention.

FIG. 6 is a block diagram showing another architecture of the controller shown in FIG. 3 according to an embodiment of the invention.

Figure 7 is a waveform diagram of the controller shown in Figure 6 in accordance with an embodiment of the present invention.

FIG. 8 is a schematic diagram of a light source driving circuit light source driving circuit according to another embodiment of the present invention.

FIG. 9A is a schematic diagram of a light source driving circuit according to another embodiment of the present invention.

Fig. 9B is a diagram showing signal waveforms in the light source driving circuit of Fig. 9A according to an embodiment of the present invention.

FIG. 10 shows a light source driving electric power according to still another embodiment of the present invention. Schematic diagram of the road.

Figure 11 is a block diagram showing the structure of the controller of Figure 9A in accordance with an embodiment of the present invention.

Figure 12 is a diagram showing signal waveforms generated or received by a light source driving circuit in accordance with an embodiment of the present invention.

Figure 13 is a flow chart of a method for driving a drive circuit of a load in accordance with an embodiment of the present invention.

FIG. 14A is a block diagram showing a light source driving circuit according to another embodiment of the present invention.

Figure 14B is a diagram showing signal waveforms generated or received by the light source driving circuit shown in Figure 14A in accordance with the present invention.

Figure 15 is a circuit diagram showing a light source driving circuit according to another embodiment of the present invention.

Figure 16 is a block diagram showing the structure of the controller shown in Figure 14A in accordance with an embodiment of the present invention.

17 is a flow chart of a method of driving a light source in accordance with an embodiment of the present invention.

1400‧‧‧Light source drive circuit

1402‧‧‧ Current filter

1406‧‧‧Power Converter

1408‧‧‧Light source

1410‧‧‧ Controller

1420‧‧‧voltage filter

1422‧‧‧Transformer

1424‧‧‧Switch

1462‧‧‧Drive signal

1464‧‧‧Induction signal

1466‧‧‧Monitoring signal

Claims (23)

A power supply circuit for a light emitting diode light source, comprising: a filter that receives an input voltage and filters the input voltage to provide a stable voltage; a transformer coupled to the filter to convert the stable voltage into an output voltage Causing a light source to provide an electrical energy; and a controller coupled to a switch, the filter and the transformer to generate a driving signal to control the switch to alternately operate in a first state and a second Between states, wherein the controller controls the switch such that an input current flowing through the filter increases during the first state and decreases during the second state, and wherein the controller controls the a time ratio of the first state to the second state to adjust an output current flowing through the light emitting diode source to a target value, wherein the input current is reduced to a predetermined value during the second state And increasing from the preset value to a peak proportional to the input voltage during the first state. The power supply circuit of claim 1, further comprising: an inductor coupled to the switch through a first diode, coupled to a capacitor through a first diode, wherein the input current is in the first During a state, the inductor, the first diode, and the switch pass through, and during the second state of operation, the inductor, the second diode, and the capacitor pass. The power supply circuit of claim 2, wherein the inductor and the capacitor form an inductor-capacitor filter that filters a plurality of harmonic components of the input voltage to generate the stable voltage. The power supply circuit of claim 1, wherein the transformer comprises: a primary winding that receives the stable voltage; and a primary winding that supplies the output voltage to the light emitting diode source, wherein the primary winding flows through the primary winding A current with the switch increases during the first state, and a current flowing through the secondary winding decreases during the second state. The power supply circuit of claim 1, wherein the duration of the first state is sufficient to allow the input current to increase from the predetermined value to be proportional to the input voltage. The power supply circuit of claim 1, wherein the duration of the second state is sufficient to allow the input current to decrease to the predetermined value. The power supply circuit of claim 1, wherein the controller further comprises: a signal generator for generating a sawtooth wave signal according to the driving signal; and an error amplifier for generating an error signal based on an inductive signal and a reference signal And a comparator coupled to the error amplifier to compare the sawtooth signal with the error signal to control the driving signal. The power supply circuit of claim 7, wherein the sensing signal indicates the output current flowing through the light emitting diode source, and the reference signal indicates the target value of the output current. The power supply circuit of claim 7, wherein during the first state, the sawtooth wave signal is increased until the sawtooth wave signal reaches To the error signal. The power supply circuit of claim 7, wherein when the output current flowing through the light emitting diode source is maintained at the target value, the sawtooth wave signal is increased from a preset value to one of the error signals. The duration is constant. The power supply circuit of claim 1, further comprising: a rectifier receiving an input alternating current and an input alternating current, and providing the input current, wherein the controller corrects a power factor such that the input alternating current is The input AC voltage is substantially in phase. A power converter for supplying an electric energy to a light emitting diode light source, comprising: a switch operating between a first state and a second state according to a pulse width modulation signal; a filter coupled to the switch Included as an inductor and a capacitor, filtering an input voltage to provide a stable voltage; and a transformer including a primary winding coupled to the switch and a primary winding, converting the stable voltage to an output voltage for the illumination The diode light source provides the electrical energy, wherein a duty cycle of the pulse width modulation signal is adjusted to adjust an output current flowing through the light emitting diode source to a target value, and wherein, during the first state An input current flows through the inductor and the switch, and the input current increases from a predetermined value to a peak proportional to the input voltage, and wherein during the second state, the input current flows through the Inductance and the capacitance, the input current is reduced Small to the preset value. The power converter of claim 12, wherein during the first state, the transformer stores electrical energy via the stable voltage, and a current flowing through the primary winding and the switch is increased, and wherein During the second state, the transformer discharges electrical energy to provide the electrical energy to the light emitting diode source, and a current flowing through the secondary winding is reduced. The power converter of claim 12, wherein the transformer further comprises: an auxiliary winding, generating a current monitoring signal indicating whether a current flowing through the secondary winding is reduced to the preset value, wherein The switch switches from the second state to the first state in response to the current monitoring signal. The power converter of claim 12, wherein the duration of the second state is greater than the time at which the input current decreases to the predetermined value. The power converter of claim 12, wherein the duration of the first state is maintained at a constant value. A method for providing an electric energy to a light emitting diode light source, comprising: receiving an input voltage and an input current; filtering the input voltage to provide a stable voltage; converting the stable voltage into an output voltage; generating a driving signal, Controlling a switch to alternately operate between a first state and a second state; controlling a time ratio of the first state and the second state to adjust an output flowing through the light emitting diode source Current to a target value; and controlling a duration of the switch operation in the first state and a duration of operation in the second state, and wherein the input current is reduced to a predetermined value during the second state operation And increasing from the preset value to a peak proportional to the input voltage during the first state operation. The method of claim 17, further comprising: receiving the stable voltage using a primary winding of a transformer; providing the output voltage to the light emitting diode source by using a primary winding of the transformer; during the first state a current flowing through the primary winding and the switch is increased; and during the second state, a current flowing through the secondary winding is decreased. The method of claim 17, wherein the duration of the first state is sufficient to allow the input current to increase from the predetermined value to be proportional to the input voltage. The method of claim 17, wherein the duration of the second state is sufficient to allow the input current to decrease to the predetermined value. The method of claim 17, further comprising: generating a sawtooth wave signal according to the driving signal; generating an error signal based on an inductive signal and a reference signal; comparing the sawtooth wave signal with the error signal to control The drive signal; and switching the switch from the first state to the second state to respond to the sawtooth signal reaching the error signal. The method of claim 21, wherein the sensing signal The output current flowing through the light emitting diode source is indicated, and the reference signal indicates the target value of the output current. The method of claim 22, wherein if the current flowing through the light emitting diode source is maintained at the target value, the sawtooth wave signal is increased from a predetermined value to a duration of the error signal. Constant.