TWI556679B - Driving circuit for driving light source and controller for controlling converter - Google Patents

Description

Light source driving circuit and power converter controller thereof

The invention relates to a driving circuit, in particular to a light source driving circuit and a controller.

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 the buck converter based on the preset peak current level. 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. Average current level (ie flow) The average current through the LED string 108 cannot be accurately controlled.

In order to solve the above technical problem, the present invention provides a light source driving circuit, comprising: a falling boost converter, receiving an input voltage and an input current and providing an energy for a load, the boost converter comprising: a switch for controlling the driving signal; and a current monitor coupled to the switch; and a controller coupled to the step-up converter to receive a first sensing signal indicative of a current flowing through the load, and The first sense signal generates the drive signal, controls the switch, and regulates the current through the load, wherein the current monitor provides a second sense signal indicative of a current flowing through the down-boost converter.

The present invention also provides a controller for controlling a boost converter, the boost converter receiving an input voltage and an input current, and providing a power for a load, comprising: a first sensing port, receiving the indication stream a first sensing signal of a current passing through the load; a monitoring signal receiving a monitoring signal indicating a current flowing through an energy storage unit, and when the monitoring signal is reduced to a predetermined current value, the controller is connected a switch, wherein the switch controls the current flowing through the energy storage unit; and a driving port, providing a driving signal to the switch according to the first sensing signal and the monitoring signal, and controlling the flow through the step-down conversion A current of the device regulates the current flowing through the load.

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

401‧‧‧Undervoltage lockout circuit

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, 1404‧‧‧Inductance

1406‧‧‧Power Converter

1408‧‧‧ Capacitance

1410‧‧‧ Controller

1412‧‧ ‧ diode

1414‧‧‧ Energy storage unit

1416‧‧‧ switch

1418‧‧‧ Current monitor

1420‧‧‧resistance

1424‧‧‧ Capacitance

1433‧‧‧Common node

1600‧‧‧Light source drive circuit

1700‧‧‧Light source drive circuit

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.

Figure 10 is a schematic illustration of a light source driving circuit in accordance with yet another embodiment of the present invention.

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

Figure 15 is a block diagram showing the structure of the controller shown in Figure 14 in accordance with an embodiment of the present invention.

Figure 16 is a circuit diagram showing a light source driving circuit according to another embodiment of the present invention.

Figure 17 is a circuit diagram showing a light source driving circuit according to still another embodiment of the present invention.

Figure 18 is a diagram showing signal waveforms generated or received by a light source driving circuit in accordance with one embodiment of the present invention.

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. Rather, the invention is to cover various modifications, equivalents, and equivalents of the invention as defined by the scope of the appended claims.

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.

The present invention provides a circuit that controls a power converter to power various loads (e.g., light sources). The circuit can include a current sensor for monitoring current flowing through the energy storage element (eg, an inductor), and a controller including a switch that can be coupled to the inductor to control the average current of the source to a target current value . The current sensor monitors the current flowing through the inductor regardless of whether the switch is on or off.

2 is a schematic diagram of a drive circuit 200 in accordance with an embodiment of the present invention. Light source drive circuit 200 includes a rectifier 204 that receives an input voltage from a power source 202 and provides an adjusted voltage 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 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 200 in accordance with an embodiment of the present 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. Diode 314 It 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 current flowing through inductor 302. In other words, the resistor 218 senses the 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 that the current flowing through the LED string 208 may be slightly different from the target current, but is still within an allowable range, so that the circuit component is not considered to be undesirable. The power transmitted from the inductor 304 to the controller 210 can be ignored and can be ignored.

In the example of FIG. 3, the controller 210 includes ZCD, GND, DRV, VDD, CS, COMP, and FB. The 埠ZCD is coupled to the inductor 304 for receiving a power condition indicative of the inductor 302 (eg, whether the current flowing through the inductor 302 is reduced to a preset current level) The detection signal AUX is normal, for example, "0". The detection signal AUX can also indicate whether the LED string 208 is in an open state. The 埠DRV is coupled to the switch 316 and generates a drive signal (eg, a pulse width modulation signal PWM1) to turn the switch 316 on or off.埠 VDD is coupled to inductor 304 and receives power from inductor 304. The 埠CS is coupled to the resistor 218 and receives a first signal ISEN indicative of the current flowing through the inductor 302. The 埠COMP is coupled through a capacitor 318 to a reference ground of the controller 210. The 埠FB is coupled through filter 212 to resistor 218 to receive a second signal IAVG indicative of the average current flowing through inductor 302. In the example of FIG. 3, 埠 GND (ie, the reference ground of controller 210) is coupled to a common node 333 between resistor 218, inductor 302, and 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 of 埠 GND (ie, the voltage at common node 333). Therefore, the pulse width modulation signal PWM1 of the 埠DRV output 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, and thus the circuit of the present invention can be applied to a power source having a relatively high voltage.

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 decreased 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 two ends of the inductor 302 The voltage increases and the voltage of the detection signal AUX also increases accordingly. As a result, the current flowing into the controller 210 through the 埠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 埠 VDD. If the LED string 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 decrease. The voltage across inductor 304 and the voltage at VDD are also reduced accordingly. Therefore, when the switch 316 is in the off state, if the voltage at 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 埠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 埠CS, indicating the current flowing through the inductor 302. The detection signal AUX is received through the 埠ZCD, indicating whether the current flowing through the inductor 302 has dropped to a preset current level (eg, reduced to zero). The pulse width modulation signal generator 408 is coupled to the comparator 404 and the 埠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 埠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 voltage of the second signal 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 voltage of the second signal IAVG 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.

The controller 210 also includes an undervoltage lockout circuit 401 coupled to its 埠VDD for selectively activating one or more components within the controller 210 based on different electrical energy conditions. In one embodiment, if the voltage on 埠 VDD is higher than the first predetermined voltage, undervoltage lockout circuit 401 will activate all of the components in controller 210. If 埠VDD The voltage above is lower than the second predetermined voltage, and the undervoltage lockout circuit 401 will turn off all components in the controller 210. In one embodiment, the first predetermined voltage is higher than the second predetermined voltage.埠 VDD provides power to controller 210.

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 埠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 generates a pulse width modulation signal PWM1 based on the output of the comparator 604 and the reset signal RESET. The pulse width modulation signal PWM1 controls the conduction state of the switch 316 through the 埠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. 7 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. saw The voltage of the sawtooth wave signal SAW generated by the tooth wave 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 800 in accordance with 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 埠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 of 埠 VDD substantially constant. In the example of FIG. 8, the 埠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 control power converter to load Powered circuit. 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 is applicable to voltage sources having relatively high 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 source 202 generates an input AC voltage V _AC (eg, the AC input voltage V _AC has a sine wave signal) and an input AC current I _AC . The input alternating 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 input AC 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 a predetermined voltage value (eg, reduced to 0V).

Advantageously, controller 910 generates drive signal 962 based on sawtooth signal 960 and sense signal IAVG. Drive signal 962 controls the switch 316, 288 is flowing through the load current I _OUT is maintained at the target current value to improve the precision 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). When a value of the rectified current I _IN reaches the rectified voltage V _IN proportional to the rectified current I _IN fall below the 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, a sawtooth signal generator 902, and a controller 910. In one embodiment, the load includes a light emitting diode string 208. The invention is not limited in this regard, and the load 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 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 (eg, a pulse width modulation signal) on DRV埠 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)

Wherein, T _ON switch 316 represents the conduction time, △ I ₂₁₄ represents the current change amount I _214, L ₃₀₂ represents the inductance 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 parallel connection between the CS埠 and the reference ground of the controller 910 and parallel to each other. Resistor 1012 and capacitor 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 size and cost of the light source driving 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. The controller 910 includes an error amplifier 402, a comparator 404, and a pulse width modulation signal generator 408. The error amplifier 402 is between the average current sense signal IAVG and the reference signal SET representing the target current value. The difference produces an error signal VEA. 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 the 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 current I ₂₁₄ decreases the average current, to reduce the 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 rectified 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 AC current I _AC is substantially in phase with the input AC 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. FIG. 13 will be described in conjunction with FIGS. 9A through 12. 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 current flowing through the light emitting diode source is maintained at the target current value, the time during which the sawtooth signal is increased from the preset value to the error signal is constant.

Embodiments of the present invention provide a drive circuit that drives a load (e.g., a light emitting diode source). The drive circuit includes a power converter and a controller. The power converter converts the input voltage to an output voltage to provide power to the load. The power converter provides an inductive signal indicative of the flow of current through the load. The drive circuit further includes a sawtooth signal generator for generating a sawtooth signal based on the drive signal. Advantageously, the controller generates a drive signal based on the sensed signal and the sawtooth signal. The drive signal controls the current flowing through the energy storage element to regulate 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 power factor of the light source drive circuit.

FIG. 14 is a circuit diagram of a light source driving circuit 1400 according to an embodiment of the invention. Elements in Figure 14 that are numbered the same as Figures 2 and 3 have similar functions. In the example of FIG. 14, light source drive circuit 1400 includes rectifier 204, power converter 1406, filter 212, and controller 1410. For example, rectifier 204 can be a bridge rectifier including diodes D1-D4. Rectifier 204 adjusts the AC voltage from power source 202. Power converter 1406 receives the adjusted voltage output by rectifier 204 and produces an output power to power the load (e.g., LED string 208).

In the example of FIG. 14, power converter 1406 is a Buck-Boost converter that receives an input voltage and produces an output voltage that can be greater or less than the input voltage. With the step-down converter, the light source driving circuit 1400 can more flexibly adjust the output voltage according to different load requirements. In addition, the light source driving circuit 1400 having a step-down converter has relatively low total harmonic distortion and a relatively high power factor.

In one embodiment, power converter 1406 includes a capacitor 1408, a switch 1416, a resistor 1420, an energy storage unit 1414, a current monitor 1418 (eg, a resistor), a diode 1412, and a capacitor 1424. Power converter 1406 receives the input voltage and input current and provides energy to LED string 208. Switch 1416 is controlled by a drive signal. The controller 1410 receives the sense signal IAVG indicating the current flowing through the LED string 208 and generates a drive signal to control the switch 1416 based on the sense signal IAVG and to regulate the current flowing through the LED string 208.

More specifically, in an embodiment, the energy storage unit 1414 is coupled between the switch 1416 and the ground of the light source driving circuit 1400. The energy storage unit 1414 is also coupled to a common node 1433 between the switch 1416 and the current monitor 1418. The common node 1433 provides a reference ground for the controller 1410. In one embodiment, the reference ground of controller 1410 is different from the ground of light source drive circuit 1400. In the example of FIG. 14, energy storage unit 1414 includes an inductor 1402 and an inductor 1404. The inductor 1402 is coupled between the reference ground of the controller 1410 and the ground of the light source driving circuit 1400. Inductor 1404 electromagnetically coupled to inductor 1402 monitors the condition of inductor 1402. More specifically, both inductor 1402 and inductor 1404 are coupled to a common node 1433.

Switch 1416 controls the current flowing through energy storage unit 1414. Coupled to the switch A resistor 1420 between the 1416 and the energy storage unit 1414 provides a sense signal VSEN to the controller 1410, which senses the state of the energy storage unit 1414. If the voltage of the sense signal VSEN is greater than a preset voltage value (eg, 1.1V), the controller 1410 turns off the switch 1416.

One end of the current monitor 1418 is connected to the common node 1433, and the other end is connected to the diode 1412. Resistor 1418 provides an induced signal ISEN indicative of the current flowing through power converter 1406, for example, indicating the current flowing through diode 1412 when switch 1416 is open. When the switch 1416 is turned on, no current flows through the diode 1412 because the diode 1412 is reverse biased. The sense signal IAVG indicating the current flowing through the LED string 208 is obtained from the sense signal ISEN. More specifically, the filter 212 coupled between the current monitor 1418 and the controller 1410 generates an induced signal IAVG indicative of the current flowing through the LED string 208 based on the sense signal ISEN. In one embodiment, filter 212 includes a resistor 320 and a capacitor 322. In the example of FIG. 14, the sense signal ISEN indicates the current flowing through the power converter 1406, such as the current flowing through the diode 1412. The average current flowing through the diode 1412 is equal to the current flowing through the LED string 208. However, in other alternative embodiments, the sense signal ISEN may indicate the current flowing through other components of the power converter 1406, and is not limited to the embodiment shown in FIG.

The controller 1410 receives the sense signal IAVG and transmits or lowers the switch 1416 such that the average current flowing through the diode 1412 is equal to a target current value. The capacitor 1424 filters out the chopping of the current flowing through the LED string 208, thereby making the current flowing through the LED string 208 relatively stable and equal to the average current flowing through the diode 1412. Therefore, the current flowing through the LED string 208 is made equal to the target current value. Here, "equal to the target current value" means that the current flowing through the LED string 208 can be slightly different from the target current value but within the range, so that current ripple caused by undesired circuit elements can be ignored.

In the example of FIG. 14, the controller 1410 includes ZCD, GND, DRV, VDD, CS, COMP, and FB. The 埠FB is coupled to the current monitor 1418 through the filter 212 and receives an induced signal IAVG indicative of the average current flowing through the diode 1412. The average current flowing through the diode 1412 is equal to the current flowing through the LED string 208. As such, the 埠FB receives an induced signal IAVG indicative of the current flowing through the LED string 208.埠ZCD and electricity The sense 1404 is coupled for receiving a monitoring signal AUX indicative of a condition of the energy storage unit 1414 (eg, whether current flowing through the inductor 1402 is reduced to a first predetermined current value, such as zero amperes). The current of the energy storage unit 1414 is controlled by a switch 1416. If the current flowing through the inductor 1402 is reduced to a first predetermined current value (eg, zero amps), the controller 1410 turns on the switch 1416. The monitor signal AUX can also indicate whether the LED string 208 is in an open state. The DRV is coupled to the switch 1416 and generates a drive signal (eg, a pulse width modulation signal PWM1) based on the sense signal IAVG and the monitor signal AUX. The pulse width modulation signal PWM1 controls the current flowing through the power converter 1406, such as the current flowing through the diode 1412, thereby adjusting the current flowing through the LED string 208. In one embodiment, the pulse width modulation signal PWM1 has a first state (eg, a logic high) and a second state (eg, a logic low). If the pulse width modulation signal PWM1 is in the first state, the switch 1416 is turned on; conversely, if the pulse width modulation signal PWM1 is in the second state, the switch 1416 is turned off. When the drive signal is in the first state, the current flowing through the inductor 1402 increases; and when the drive signal is in the second state, the current flowing through the inductor 1402 decreases.埠 VDD is coupled to inductor 1404 and receives power from inductor 1404. The 埠CS is coupled to the resistor 1420 and receives a sensing signal VSEN indicating the state of the energy storage unit 1414 (eg, whether the energy stored in the energy storage unit 1414 is increased to a preset energy value). The 埠COMP is coupled to the reference ground of the controller 1410 via a capacitor 318. In the example of FIG. 14, 埠 GND (ie, the reference ground of controller 1410) is coupled to a common node 1433 between current monitor 1418, inductor 1402, and inductor 1404.

Switch 1416 can be an N-channel metal oxide semiconductor field effect transistor (NMOSFET). The conduction state of switch 1416 is determined by the voltage difference between the gate voltage of switch 1416 and the voltage of 埠 GND (ie, the voltage of common node 1433). Therefore, the pulse width modulation signal PWM1 of the 埠DRV output determines the state of the switch 1416. When the switch 1416 is turned on, the reference ground of the controller 1410 is higher than the ground of the light source driving circuit 1400, so that the circuit of the present invention can be applied to a power source having a higher voltage.

In operation, when switch 1416 is turned on, current flows through switch 1416, resistor 1420, and inductor 1402 to the ground of light source drive circuit 1400. When the switch 1416 is turned off, current flows through the inductor 1402, the LED string 208, the diode 1412, and the current monitor. 1418. Current monitor 1418 provides an induced signal ISEN indicative of the current flowing through diode 1412. The sense signal IAVG indicating the current flowing through the LED string 208 is obtained from the sense signal ISEN. Thus, in one embodiment, controller 1410 controls switch 1416 via pulse width modulation signal PWM1 based on sense signal IAVG such that the average current flowing through diode 1412 is equal to the preset current value. Therefore, after filtering by the capacitor 1424, the current flowing through the LED string 208 is also equal to the preset current value.

In one embodiment, the controller 1410 determines whether the LED string 208 is in an open state based on the monitor signal AUX. If the LED string 208 is open, the voltage across the capacitor 1424 increases. When the switch 1416 is in the off state, the voltage across the inductor 1402 increases, and the voltage of the monitor signal AUX also increases. Therefore, the current flowing into the controller 1410 through the 埠ZCD increases. Therefore, the controller 1410 determines whether the LED string 208 is open by detecting whether the signal AUX and the current flowing through the inductor 1402 exceed the second preset current value (for example, 300 microamps) when the switch 1416 is in the off state. status.

In one embodiment, the controller 1410 determines whether the LED string 208 is in a short circuit condition based on the sensing signal VSEN. If the LED string 208 is shorted, the energy stored in the energy storage unit 1414 increases, and the voltage of the sensing signal VSEN also increases. As a result, the voltage of 埠CS increases. Therefore, the controller 1410 determines whether the LED string 208 is in a short-circuit state by whether the voltage of the sensing signal VSEN exceeds a preset voltage value (for example, 1.1 V).

Figure 15 is a block diagram showing the structure of the controller 1410 shown in Figure 14 in accordance with an embodiment of the present invention. Elements in Figure 15 that are numbered the same as in Figure 4 have similar functions. Figure 15 will be described in conjunction with Figure 14.

In the example of FIG. 15, controller 1410 includes error amplifier 402, comparator 404, and pulse width modulation signal generator 408. The error amplifier 402 generates an error signal VEA at 埠COMP based on the reference signal SET and the sense signal IAVG. The reference signal SET indicates the target current value. The sense signal IAVG is received through the 埠FB, indicating the average current flowing through the diode 1412. The average current flowing through the diode 1412 is equal to the target current value by the action of the error signal VEA. Comparator 404 is coupled to error amplifier 402 and will The error signal VEA is compared with the sense signal VSEN. The sensing signal VSEN is received through the 埠CS, indicating the state of the energy storage unit 1414. The monitor signal AUX is received through the 埠ZCD to indicate whether the current flowing through the inductor 1402 is reduced to a first predetermined current value (eg, reduced to zero amps). The pulse width modulation signal generator 408 is coupled to the 埠ZCD and the comparator 404, and generates a pulse width modulation signal PWM1 according to the error signal VEA and the monitoring signal AUX. The pulse width modulation signal PWM1 controls the conduction state of the switch 1416 through the 埠DRV.

In operation, when the pulse width modulation signal PWM1 is in the first state (eg, logic 1), the switch 1416 is turned "on". When the switch 1416 is turned on, current flows through the switch 1416, the resistor 1420, and the inductor 1402 to the ground of the light source driving circuit 1400. The current flowing through the inductor 1402 gradually increases, so that the voltage of the induced signal VSEN gradually increases. In one embodiment, the voltage of the monitor signal AUX is negative when the switch 1416 is turned on. Inside controller 1410, comparator 404 compares error signal VEA to sense signal VSEN. When the voltage of the sense signal VSEN exceeds the voltage of the error signal VEA, the output of the comparator 404 is a logic 0, otherwise the output of the comparator 404 is a logic 1. In other words, the output of comparator 404 is a series of pulses. Under the effect of the negative edge of the output of comparator 404, pulse width modulation signal generator 408 generates a pulse width modulation signal PWM1 having a second state (e.g., logic 0) to open switch 1416. In one embodiment, when switch 1416 is open, the voltage of monitor signal AUX is positive. When the switch 1416 is turned off, current flows through the inductor 1402, the LED string 208, the diode 1412, and the current monitor 1418. The current flowing through the inductor 1402 gradually decreases, and thus the voltage of the induced signal VSEN gradually decreases. If the monitor signal AUX indicates that the current flowing through the inductor 1402 is reduced to a first predetermined current value (eg, to zero amps), the pulse width modulation signal PWM1 switches to the first state (eg, logic 1). More specifically, when the current flowing through the inductor 1402 is reduced to a first predetermined current value (eg, reduced to zero amperes), the voltage of the monitor signal AUX produces a negative edge. Under the effect of the negative edge of the monitor signal AUX, the pulse width modulation signal generator 408 generates a pulse width modulation signal PWM1 having a first state (eg, logic 1) to turn on the switch 1416.

In one embodiment, when switch 1416 is open, monitor signal AUX indicates that current flowing through inductor 1402 increases to a second predetermined current value (eg, 300 microamps), and pulse width modulation signal PWM1 remains at second Status (for example, logic 0). Controller 1410 It is judged that the light emitting diode string 208 is in an open state. In one embodiment, if the voltage of the sense signal VSEN exceeds a predetermined voltage value (eg, 1.1V), the controller 1410 determines that the light-emitting diode string 208 is in a short-circuit condition. When the controller 1410 determines that the LED string 208 is in an open state or a short circuit state, the pulse width modulation signal PWM1 remains in the second state (eg, logic 0) to open the switch 1416 until such an abnormal state no longer exists.

In one embodiment, the duty cycle of the pulse width modulation signal PWM1 is determined by the error signal VEA. If the voltage of the sense 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 of the pulse width modulation signal PWM1, thereby increasing the average current flowing through the diode 1412. Until the voltage of the sense signal IAVG increases to the voltage of the reference signal SET. If the voltage of the sense signal 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 of the pulse width modulation signal PWM1, thereby reducing the average current flowing through the diode 1412. Until the voltage of the sense signal IAVG is reduced to the voltage of the reference signal SET. Thus, the average current flowing through the diode 1412 can be adjusted to be equal to the target current value.

FIG. 16 is a circuit diagram of a light source driving circuit 1600 according to another embodiment of the present invention. Elements in Figure 16 that are numbered the same as Figure 14 have similar functions. The circuit diagram of the light source driving circuit 1600 of FIG. 16 is similar to the circuit diagram of the light source driving circuit 1400 of FIG. 14, except for the setting of the power converter 1406. In the example of FIG. 16, energy storage unit 1414 includes only inductor 1402. In one embodiment, the power converter 1406 can also include a Zener diode D5 coupled between the inductor 1402 and the controller 1410. Zener diode D5 forms a bias potential shifter to apply a potential shift (bias) to the supply voltage of controller 1410, which in turn provides appropriate power from inductor 1402 to controller 1410 via 埠VDD.

Figure 17 is a circuit diagram of a light source driving circuit 1700 in accordance with still another embodiment of the present invention. Elements in Figure 17 that are numbered the same as Figures 9A, 10 and 14 have similar functions. The circuit diagram of the light source driving circuit 1700 in FIG. 17 is similar to the circuit diagram of the light source driving circuit 1000 in FIG. 10 except for the setting of the power converter 1406.

In one embodiment, power converter 1406 includes a capacitor 1408 that is coupled to power line 912. The capacitor 1408 reduces the chopping of the rectified voltage V _IN to smooth the waveform of the rectified voltage V _IN . In one embodiment, capacitor 1408 has a relatively small capacitance value to help eliminate or reduce distortion of the rectified voltage V _IN waveform. Moreover, in one embodiment, since the capacitance 1408 is small, the current flowing through the capacitor 1408 is negligible. Thus, when switch 1416 is turned on, current I ₁₄₀₂ flowing through switch 1416 is substantially equal to rectified current I _IN flowing from rectifier 204.

The power converter 1406 in FIG. 17 is similar in operation to the power converter 1406 in FIG. In one embodiment, current I ₁₄₁₂ flows through diode 1412 and current I ₁₄₀₂ flows through inductor 1402, depending on the on state of switch 1416. More specifically, controller 910 generates a drive signal 962 (e.g., a pulse width modulation signal) on DRV to control switch 1416 to be turned "on" or "off". When the switch 1416 is turned on, the current I ₁₄₀₂ flows from the power line 912 and flows through the switch 1416, the resistor 1420, and the inductor 1402 to the ground of the light source driving circuit 1700. Since the diode 1412 is reverse biased, no current flows through the diode 1412. During the turn-on of the switch 1416, the current I ₁₄₀₂ can be gradually increased according to the equation (3): ΔI ₁₄₀₂ = V _IN * T _ON / L ₁₄₀₂ (3)

Wherein, T _ON represents a time switch 1416 is turned on, the current I △ I represents the amount of change _{1402 1402 1402} L represents the inductance value of the inductor 1402, and the drop can be ignored from the switch 1416 to the voltage of the resistor 1420. In one embodiment, controller 910 controls drive signal 962 such that time period T _ON in each switching cycle of switch 1416 is a constant value. Therefore, the current I of the amount of change △ I ₁₄₀₂ and ₁₄₀₂ is proportional to the rectified voltage V _IN. In one embodiment, when current I _{1402 is} reduced to a first predetermined value (eg, zero amps), switch 1416 is closed. Therefore, the peak value of the current I ₁₄₀₂ is proportional to the rectified voltage V _IN .

At each switching cycle, switch 1416 is turned off after the _ON time period is turned on. When the switch 1416 is turned off, current flows through the inductor 1402, the LED string 208, the diode 1412, and the current monitor 1418. Correspondingly, the current I _{1412 is} reduced according to equation (4): ΔI ₁₄₁₂ = ΔI ₁₄₀₂ = V _OUT * T _OFF / L ₁₄₀₂ (4)

Where T _OFF represents the time when switch 1416 is open, ΔI ₁₄₁₂ represents the amount of change in current I ₁₄₁₂ , and the voltage drop from diode 1412 to current monitor 1418 can be ignored. In one embodiment, when switch 1416 is turned on, rectified current I _{IN is} equal to current I ₁₄₀₂ , and when switch 1416 is turned off, rectified current I _{IN is} equal to zero amperes.

In one embodiment, power converter 1406 includes a capacitor 1424. Capacitor 1424 can be a capacitor having a relatively large capacitance. Therefore, the current I _OUT flowing through the LED string 208 represents the average value of the current I ₁₄₁₂ .

The controller 910 of FIG. 17 is similar to the operation of the controller 910 of FIG. In FIG. 17, the 埠 of the controller 910 includes ZCD, GND, DRV, VDD, CS, COMP, and FB. The 埠ZCD is coupled to the inductor 1404 for receiving a monitoring signal AUX indicative of the condition of the inductor 1402 (eg, whether the current flowing through the inductor 1402 is reduced to a first predetermined current value, such as zero amps). The monitor signal AUX can also indicate whether the LED string 208 is in an open state. The GND is coupled to a common node 1433 between the current monitor 1418, the inductor 1402, and the inductor 1404. The 埠DRV is coupled to the switch 1416 and generates a drive signal 962 (eg, a pulse width modulation signal) to turn the switch 1416 on or off.埠 VDD is coupled to inductor 1404 and receives power from inductor 1404. The 埠COMP is coupled to the reference ground of the controller 910 through the capacitor 318. The 埠FB is coupled to the current monitor 1418 via the filter 212 and receives an induced signal IAVG indicative of the current I _OUT flowing through the LED string 208.

The sawtooth signal generator 902 coupled to the controller 910 is configured to generate a sawtooth signal 960 on the CS frame according to 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 parallel connection between the CS埠 and the reference ground of the controller 910 and parallel to each other. Resistor 1012 and capacitor 1014. 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. Thus, capacitor 1014 is discharged and voltage V _{960 is} reduced to zero volts. The sawtooth signal generator 902 may also include other components and is not limited to the embodiment shown in FIG.

Advantageously, controller 910 generates drive signal 962 based on sawtooth signal 960 and sense signal IAVG. Adjusting a drive signal flows through the light emitting diode 962 current I _OUT string body 208 to a target current value and the average current I _{IN I} IN_AVG the rectified voltage V _IN with the substance by controlling the rectified current in phase to correct the power factor of the drive circuit 1700.

Figure 18 is a diagram showing signal waveforms generated or received by a light source driving circuit (e.g., driving circuit 1700) in accordance with one embodiment of the present invention. FIG. 18 will be described in conjunction with FIG. 4, FIG. 9A, FIG. 9B, and FIG. Figure 18 depicts the rectified voltage V _IN, the rectified current I _IN, the rectified current I _IN average current _I IN_AVG, the current flowing through the inductor 1402 of the I _1402, flowing through the LED string 208 of the diode current I _OUT, indicative of flow through the two The sense signal ISEN of the current I ₁₄₁₂ of the polar body 1412, the error signal VEA, the sawtooth signal 960, and the drive signal 962. The light source drive circuit 1700 with a step-down converter has relatively low total harmonic distortion and a relatively high power factor.

As shown in FIG. 18, the rectified voltage V _IN is a rectified sine wave signal. At time t1, drive signal 962 becomes a logic high. Therefore, the switch 1416 is turned on, and the current I ₁₄₀₂ flowing through the inductor 1402 is increased. Since the diode 1412 is reverse biased, no current flows through the diode 1412. At the same time, the sawtooth signal 960 increases during the first state of the drive signal 962 (eg, a logic high).

At time t2, when the sawtooth signal 960 is added to the error signal VEA, the drive signal 962 switches to the second state (eg, a logic low). Under the action of the negative edge of the drive signal 962, the sawtooth signal 960 drops to zero volts and the sense signal ISEN increases to the peak of the current I ₁₄₀₂ . Drive signal 962 turns off switch 1416, and current begins to flow through inductor 1402 and diode 1412, so current I ₁₄₀₂ and sense signal ISEN drop. 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 to turn the switch 1416 on.

At time t3, current I ₁₄₀₂ and current I _{1412 are} reduced to a first predetermined current value (eg, zero amps), and thus controller 910 adjusts drive signal 962 to a logic high to turn on switch 1416.

In one embodiment, the current I _OUT flowing through the LED string 208 is equal or proportional to the average of the current I ₁₄₁₂ 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. 18, the induced signal ISEN indicating the current I ₁₄₁₂ 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 ₁₄₁₂ 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. In one embodiment, since the time during which the sawtooth signal 960 rises from zero volts to the error signal VEA is equal during each cycle of the drive signal 962, T _ON is constant. According to equation (3), within a time T _ON, current I is the amount of change △ I of the ₁₄₀₂ and ₁₄₀₂ is proportional to the rectified voltage V _IN. Therefore, as shown in FIG. 18, the peak value of the induced signal ISEN (i.e., the peak value of the current I ₁₄₀₂ ) is proportional to the rectified voltage V _IN .

In one embodiment, when switch 1416 is turned on, the waveform of rectified current I _IN is similar to the waveform of current I ₁₄₀₂ , and when switch 1416 is turned off, rectified current I _{IN is} equal to zero amperes. 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. In conjunction with FIG. 9B, controller 910 corrects the power factor of light source drive circuit 1700 to cause input AC current I _AC to be substantially in phase with input AC voltage V _AC .

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 appended claims. It should be understood by those of ordinary skill in the art that the present invention may be applied in the form of the form, structure, arrangement, ratio, material, element, element, and other aspects in the actual application without departing from the invention. Changed. Therefore, the embodiments disclosed herein are intended to be illustrative and not limiting, and the scope of the invention is defined by the scope of the appended claims and their legal equivalents.

202‧‧‧Power supply

204‧‧‧Rectifier

208‧‧‧Lighting diode strings

212‧‧‧ filter

318‧‧‧ Capacitance

320‧‧‧resistance

322‧‧‧ Capacitance

1400‧‧‧Light source drive circuit

1402, 1404‧‧‧Inductance

1406‧‧‧Power Converter

1408‧‧‧ Capacitance

1410‧‧‧ Controller

1412‧‧ ‧ diode

1414‧‧‧ Energy storage unit

1416‧‧‧ switch

1418‧‧‧ Current monitor

1420‧‧‧resistance

1424‧‧‧ Capacitance

1433‧‧‧Common node

Claims (25)

A light source driving circuit comprising: a falling boost converter that receives an input voltage and an input current and provides an energy for a load, the boost converter comprising: a switch controlled by a driving signal; and a current a monitor coupled to the switch; and a controller coupled to the step-down converter, receiving a first sensing signal indicating a current flowing through the load, and generating the driving signal according to the first sensing signal, Controlling the switch and adjusting the current through the load, wherein the current monitor provides a second sense signal indicative of a current flowing through the step-up converter, the step-up converter further comprising: a reserve The energy unit is coupled between the switch and a ground of the light source driving circuit, wherein a current flowing through the energy storage unit is controlled by the switch; and a resistor coupled to the switch and the energy storage Between the units, a voltage sensing signal is provided to the controller, wherein the voltage sensing signal indicates a state of the energy storage unit, and when a voltage of the voltage sensing signal is greater than a predetermined voltage value, The controller turns off switch. The light source driving circuit of claim 1, wherein a reference ground of the controller is different from the ground of the light source driving circuit. The light source driving circuit of claim 2, wherein the energy storage unit is coupled to a common node between the switch and the current monitor, and the common node provides the reference ground of the controller. The light source driving circuit of claim 1, wherein the energy storage unit comprises: a first inductor coupled to a reference ground of the controller and the light source driving circuit And a second inductor electromagnetically coupled to the first inductor to monitor a state of the first inductor. The light source driving circuit of claim 1, wherein the energy storage unit comprises: a first inductor coupled between a reference ground of the controller and the ground of the light source driving circuit, wherein the lowering The boost converter further includes a Zener diode coupled between the first inductor and the controller. The light source driving circuit of claim 1, wherein the controller receives a monitoring signal indicating a condition of the energy storage unit, the driving signal having a first state and a second state, wherein the monitoring Signaling that the current flowing through the energy storage unit is reduced to a first predetermined value, the driving signal is switched to the first state, and wherein the monitoring signal indicates flowing through the storage when the switch is turned off The current of the energy unit is increased to a second predetermined value, and the drive signal is maintained in the second state. The light source driving circuit of claim 6, wherein the current flowing through the energy storage unit increases when the driving signal is in the first state. The light source driving circuit of claim 6, wherein the current flowing through the energy storage unit is lowered when the driving signal is in the second state. The light source driving circuit of claim 1, further comprising: a filter coupled between the current monitor and the controller, generating the first sensing signal according to the second sensing signal; wherein the control The device further includes an error amplifier that generates an error signal based on the first sensing signal and a reference signal indicative of a target current value. A light source driving circuit as claimed in claim 9, wherein the falling through the rising The current of the voltage converter includes a current flowing through a diode of the step-down converter, and wherein an average current flowing through the diode is equal to the current flowing through the load. A light source driving circuit comprising: a falling boost converter that receives an input voltage and an input current and provides an energy for a load, the boost converter comprising: a switch controlled by a driving signal; and a current a controller coupled to the switch; a controller coupled to the step-down converter, receiving a first sensing signal indicating a current flowing through the load, and generating the driving signal according to the first sensing signal, and controlling The switch and adjusting the current through the load, wherein the current monitor provides a second sensed signal indicative of a current flowing through the step-up converter; wherein the controller further comprises: an error amplifier, Generating an error signal according to the first sensing signal and a reference signal indicating a target current value; a filter coupled between the current monitor and the controller, and generating the first sensing according to the second sensing signal And a sawtooth signal generator coupled to the controller to generate a sawtooth signal according to the driving signal, wherein the controller is based on the sawtooth wave signal The error signal generating and the driving signal, the current flowing through the load is adjusted to the target current value, wherein the controller controls an average current of the input current with the input voltage in phase with the substance. The light source driving circuit of claim 11, wherein the driving signal has a first state and a second state, wherein the sawtooth wave signal increases during the first state, when the sawtooth wave signal is increased to The bit of the error signal The drive signal is switched to the second state. The light source driving circuit of claim 11, wherein when the current flowing through the load is maintained at the target current value, the sawtooth wave signal rises from a predetermined potential to a predetermined period of the error signal. It is constant. The light source driving circuit of claim 11, wherein the sawtooth signal generator comprises: a diode coupled in parallel with a first resistor between a first node and a second node; and a a capacitor coupled in parallel with a second resistor between the second node and a reference ground of the controller, wherein the first node receives the driving signal, and the second node provides the sawtooth signal, the controller This reference ground is different from the ground of the light source driving circuit. The light source driving circuit of claim 1, further comprising: a rectifier receiving an AC input voltage and an AC input current, providing the input voltage and the input current, wherein the controller controls the AC input current and the The AC input voltage is essentially in phase. A controller for controlling a step-down converter, the boost converter is configured to receive an input voltage and an input current, and provide a power for a load, comprising: a first sensing port, receiving a signal indicating that the load flows through the load a first sensing signal of the current; a monitoring signal, receiving a monitoring signal indicating a current flowing through an energy storage unit, and when the monitoring signal is reduced to a predetermined current value, the controller turns on a switch, wherein The switch controls the current flowing through the energy storage unit; and a driving port, providing a driving signal according to the first sensing signal and the monitoring signal To the switch, a current flowing through the step-down converter is controlled to regulate the current flowing through the load. The controller of claim 16 further includes: a compensation 埠 providing an error signal. The controller of claim 17, further comprising: an error amplifier that generates the error signal based on the first sensing signal and a reference signal indicative of a target current value. The controller of claim 18, further comprising: a pulse width modulation signal generator coupled to the error amplifier, and generating the driving signal according to the error signal and the monitoring signal. The controller of claim 16, wherein the driving signal has a first state and a second state, and when the driving signal is in the first state, the current flowing through the energy storage unit increases; When the drive signal is in the second state, the current flowing through the energy storage unit decreases. The controller of claim 16, wherein the controller receives a sawtooth signal that changes according to the driving signal, wherein the controller generates the driving signal regulating stream according to the first sensing signal and the sawtooth signal. The current through the load to a target current value and an average current that controls the input current is substantially in phase with the input voltage. The controller of claim 21, wherein the driving signal has a first state and a second state, wherein the sawtooth wave signal increases during the first state; when the sawtooth wave signal increases to an error The signal is leveled and the drive signal is switched to the second state. The controller of claim 22, wherein the error signal is generated based on the first sensing signal and a reference signal indicating the target current value. A controller as claimed in claim 23, wherein when flowing through the load The current is maintained at the target current value, and the time period during which the sawtooth wave signal rises from a predetermined potential to the level of the error signal is constant. The controller of claim 16, wherein the controller receives a voltage sensing signal indicating a state of the energy storage unit, and when the voltage of the voltage sensing signal is greater than a predetermined voltage value, the controller disconnects the switch.