TWI392208B - Driving circuit of light source and methods of powering led light source - Google Patents

Description

Light source driving circuit and method for supplying power to light emitting diode light source

The present invention relates to a drive circuit, and more particularly to a circuit and method for powering a light emitting diode (LED) light source.

In a display system, a drive circuit drives one or more light sources to illuminate the display. For example, in a liquid crystal display (LCD) using a light emitting diode (LED) as a backlight, an LED array is used to illuminate the liquid crystal display. An LED array typically includes one or more strings of LEDs, each string of LEDs comprising a set of LEDs coupled in series.

1 is a block diagram of a conventional light source driving circuit 100. The light source driving circuit 100 drives the LED chain 106, and includes a converter circuit 102, a switch controller 104, and a switching regulator 108. Converter circuit 102 receives an input voltage V _IN and provides an output voltage V _OUT to LED chain 106 on a power supply line 141. Switching regulator 108 includes an inductor L1 coupled in series with LED chain 106. The switching regulator 108 also includes a switch S1 and a diode D1 for controlling the current flowing through the inductor L1. More specifically, switch controller 104 provides a pulse width modulation (PWM) signal 130 to turn switch S1 on or off. When the switch S1 is closed, the diode D1 is reversely biased, and a current flows through the power line 141, the LED chain 106, the inductor L1, the switch S1, and a resistor R _SEN in sequence. The output voltage V _OUT supplies power to the LED chain 106 and charges the inductor L1. When the switch S1 is turned off, the diode D1 is forward biased, and current flows sequentially through the inductor L1, the diode D1, the power supply line 141, and the LED chain 106. Inductor L1 is discharged to power LED chain 106. Therefore, by adjusting the duty cycle of the pulse width modulation signal 130 to adjust the average value of the current flowing through the inductor L1, the current flowing through the LED chain 106 is adjusted.

However, when switch S1 is turned off, the anode voltage of diode D1 rises above the output voltage V _OUT to bias bias diode D1 in the forward direction. Thus, the voltage across switch S1 is substantially equal to the output voltage V _OUT . When the switch S1 is closed, the voltage across the diode D1 is substantially equal to the output voltage V _OUT . Therefore, the switching voltages of the switching elements (for example, the switches S1 and the diodes D1) used in the conventional light source driving circuit 100 must be larger than the output voltage V _OUT . Otherwise, when the operating voltage is approximately equal to the output voltage V _OUT , the switching element is damaged. When the number of LEDs in the LED chain 106 is increased to achieve higher brightness, the output voltage V _OUT increases. Therefore, a switching element having a higher rated voltage increases the power consumption and cost of the conventional driving circuit 100.

An object of the present invention is to provide a light source driving circuit comprising: a converter circuit for supplying a first output voltage to a light emitting diode light source on a first power line, and providing less than the first power line a second output voltage of the output voltage; an energy storage component coupled to the light emitting diode light source to regulate a current flowing through the light emitting diode light source; and a switching element coupled to the converter circuit And the energy storage component, the energy storage component is charged when the switching component operates in a first state, and the energy storage component is discharged when the switching component operates in a second state, wherein the converter circuit provides the And a second output voltage to maintain an operating voltage across the switching element less than the first output voltage in the first state and the second state.

The present invention also provides a light source driving circuit, comprising: a converter circuit, providing a first output voltage on a first power line to supply power to a plurality of light emitting diode sources, and providing less than a second power line a second output voltage of the first output voltage; and a plurality of switching regulators coupled to the converter circuit to adjust a plurality of currents flowing through the plurality of light emitting diode sources, each of the switching regulators including a switching element, when the switching element operates in a first state, an energy storage component is charged, and when the switching component operates in a second state, the energy storage component discharges, by adjusting the charging and discharging of the energy storage component The time ratio adjusts a current flowing through a corresponding light emitting diode source, the converter circuit provides the second output voltage to maintain an operating voltage across the switching element less than the first state and the second state The first output voltage.

The invention also provides a method for supplying a light emitting diode, comprising: providing a first output voltage on a first power line to supply power to a light emitting diode source; and providing a second power line on the second power line that is smaller than the first output voltage a second output voltage; when a switching element operates in a first state, charging an energy storage component; when the switching component operates in a second state, the energy storage component is discharged; adjusting the switching component in the first state and Maintaining a current flowing through the light emitting diode light source by a duration ratio of the second state; and providing the second output voltage to maintain one of the two ends of the switching element in the first state and the second state The operating voltage is less than the first output voltage.

A detailed description of the embodiments of the present invention will be given below. Although the invention will be described in connection with the embodiments, it should be understood that this is not intended to mean the invention Limited to these 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.

2 is a block diagram of a load drive circuit 200 in accordance with an embodiment of the present invention. In one embodiment, the load is a light source 206. The load driving circuit 200 includes a converter circuit 202, a switch controller 204, a switching regulator 208, and a current sensor 210. Converter circuit 202 receives an input voltage V _IN, generates an output voltage _V OUT_H on a power line 241, and generates an output voltage _V OUT_H less than the other output voltage V _{OUT_L} power source line 242 on the other. The output voltage V _{OUT — H is} used to drive the light source 206. The output voltage V _{OUT — L is} used to reduce the operating voltage of one or more switching elements in the switching regulator 208.

The current sensor 210 is coupled to the light source 206 to generate a sense signal 234 indicative of the current flowing through the light source 206. In one embodiment, switch controller 204 generates a switch control signal 230 and a feedback signal 232 based on sense signal 234. In one embodiment, switch controller 204 compares sense signal 234 with a reference signal REF indicative of a desired current value. Based on a comparison result, the switch controller 204 generates a switch control signal 230. Thus, the switch control signal 230 controls the switching regulator 208 to adjust the current flowing through the source 206 to the current desired value. The feedback signal 232 indicates the desired forward voltage of the source 206 when the current flowing through the source 206 has a current desired value. Therefore, the converter circuit 202 receives the feedback signal 232 and adjusts the output voltage V _{OUT — H} to meet the power supply requirements of the light source 206 .

In one embodiment, light source 206 includes one or more strings of light emitting diodes. Each string of LED chains includes one or more LEDs coupled in series. In one embodiment, the switching regulator 208 includes an energy storage component 220 and a switching component 222. The energy storage component 220 is coupled to the light source 206, and the current flowing through the energy storage component 220 determines the current flowing through the light source 206.

In one embodiment, switching element 222 is coupled to power line 241, power line 242, and a reference node 244. For example, if reference node 244 is connected to ground, reference voltage V _{REF of} reference node 244 is zero. The switching element 222 controlled by the switch control signal 230 can operate in a plurality of operating states, and the switching element 222 can selectively connect the power line 241, the power line 242, and the reference node 244 to the buffer of the energy storage element 220. The current flowing through the energy storage element 220 constitutes a different current path.

More specifically, the operating state of the switching element 222 includes a switch closed state and a switch open state. In the closed state of the switch, the switching element 222 conducts current through two of the power line 241, the power line 242, and the reference node 244. An operating voltage having a first voltage value increases the current flowing through the energy storage element 220, thereby charging the energy storage element 220. In the off state of the switch, the switching element 222 conducts current through the other two of the power line 241, the power line 242, and the reference node 244. The operating voltage having the second voltage value reduces the current flowing through the energy storage element 220, and thus the energy storage element 220 discharges. Therefore, by adjusting the duration of the switch on state and the switch off state, The current flowing through the source 206 (eg, the average) is adjusted. The operation of the switching regulator 208 will be further described with respect to Figures 3, 6, and 7.

3 is a schematic diagram of a load drive circuit 300 in accordance with an embodiment of the present invention. In one embodiment, the load is a light source 206. Elements in Figure 3 that are numbered the same as in Figure 2 have similar functions. Figure 3 will be described in conjunction with Figure 2.

In the example shown in FIG. 3, light source 206 includes an LED chain that is coupled in series by a plurality of LEDs. The load drive circuit 300 includes a converter circuit 202, a switch controller 204, a switching regulator 208, and a current sensor 210. Current sensor 210 includes a resistor R3 for generating a sense signal 234 indicative of the LED current flowing through LED chain 206. In one embodiment, sense signal 234 is the voltage across resistor R3. The switch controller 204 generates a switch control signal 230 (eg, a pulse width modulation signal) and a feedback signal 232 based on the sense signal 234.

In one embodiment, converter circuit 202 includes a converter controller 302 and a dual converter 304. The converter controller 302 receives the feedback signal 232, wherein the feedback signal 232 indicates that when the LED current reaches a current desired value, the converter controller 302 accordingly generates a control signal 310 for the forward voltage required by the LED chain 206. The dual converter 304 receives the input voltage V _IN and generates output voltages V _{OUT — H} and V _{OUT — L} according to the control signal 310 . For example, based on the feedback signal 232, the converter controller 302 adjusts the control signal 310 to raise or lower the output voltage _{VOUT_H} , thereby adjusting the LED current to the current desired value.

In one embodiment, the output voltage V _{OUT — H} output by the dual converter 304 is equal to the output voltage V _{OUT — L} plus one of the voltage differences V _DIFF between the two. Therefore, V _{OUT_H} =V _{OUT_L} +V _DIFF (1)

As shown in equation (1), if the voltage difference V _DIFF is a positive value, V _{OUT — L is} smaller than V _{OUT — H} . The operation of the dual converter 304 will be further described with respect to Figures 4A, 4B and 5.

Switching regulator 208 is used to regulate the LED current flowing through LED chain 206. In the embodiment shown in FIG. 3, the switching regulator 208 is a buck converter. The energy storage element 220 in the switching regulator 208 includes an inductance L3 coupled to the LED chain 206. The switching element 222 in the switching regulator 208 includes a switch S3 and a diode D3. For example, the switch S3 can be an N-type metal oxide semiconductor (MOS) transistor. The anode of the diode D3 is coupled to a common node together with the drain of the switch S3, and the common node is coupled to the power line 241 through the inductor L3 and the LED chain 206. The cathode of the diode D3 is connected to the power supply line 242. The source of the switch S3 is connected to ground through a resistor R3.

Switching element 222 is selectively coupled to ground, power line 241 or power line 242 to inductor L3 in accordance with switch control signal 230. More specifically, the switch control signal 230 can be a pulse width modulated (PWM) signal. When the switch control signal 230 is at a logic high level, the switching element 222 operates in a switch closed state, at which time the switch S3 is closed and the diode D3 is reverse biased. Therefore, the TA end of the inductor L3 is electrically coupled to the power line 241, and the other end TB of the inductor L3 is electrically coupled to the ground. Then, the current I1 flows through the power source line 241, the LED chain 206, the inductor L3, the resistor R3, and the ground, and then flows from the ground through the double converter 304 to the power source line 241. The operating voltage of the inductor L3 is the first voltage value. Inductor L3 is charged and its current rises.

When the switch control signal 230 is at a logic low level, the switching element 222 operates in a switch open state, at which time the switch S3 is open and the diode D3 is forward biased. The TA end is electrically coupled to the power line 241, and the TB end is electrically coupled to the power line 242. Therefore, the current I2 passes through the power line 241, the LED chain 206, the inductor L3, the diode D3, and the power line 242, and then flows from the power line 242 through the double converter 304 to the power line 241. The operating voltage of the inductor L3 is a second voltage value, and the second voltage value is determined by the voltages V _{OUT — H} and V _{OUT — L} . Inductor L3 discharges and its current drops.

Accordingly, in one embodiment, the inductor current rises when the switch control signal 230 is logic high, and the inductor current decreases when the switch control signal 230 is logic low. In the example shown in FIG. 3, the current through LED source 206 is substantially equal to the average current flowing through inductor L3. As a result, by controlling the duty cycle of the switch control signal 230, the switch controller 204 can adjust the LED current flowing through the LED source 206 to the desired current value.

Advantageously, during the switch closed state of switching element 222, voltage V _D3 across the diode is less than V _{OUT — H} (eg, V _D3 is approximately equal to V _{OUT — L} ). During the switch-off state of the switching element 222, the voltage V _D3 across the diode is also less than V _{OUT — H} . That is to say, by using the output voltage V _{OUT_L} of the double converter 304, the operating voltage across the switch S3 and the diode D3 remains smaller than V _{OUT_H} in the switch closing and switching off states. Therefore, the rated voltage of these components is lowered, thereby reducing the power consumption and cost of the driving circuit 300.

4A and 4B are schematic diagrams of a converter circuit 202 in accordance with an embodiment of the present invention. The components numbered in Figures 4A and 4B are the same as those of Figures 2 and 3. 4A and 4B will be described with reference to Figs. 2 and 3.

In the example shown in FIGS. 4A and 4B, the dual converter 304 includes a resistor 402, a switch 416, a transformer T1, diodes 410 and 412, and capacitors 408 and 414. Transformer T1 includes a primary coil 404, a core 405, and a primary coil 406. The dual converter 304 generates an output voltage V _{OUT — L} and a voltage difference V _{DIFF , respectively} . More specifically, as shown in FIG. 4A, the primary coil 404, the diode 412, the capacitor 414, and the switch 416 of the transformer T1 constitute a switching mode boost converter 452. Converter controller 302 generates a drive signal 460 to control switch 416. In one embodiment, drive signal 460 is a pulse width modulated signal with a duty cycle of D _DUTY that alternately closes or opens switch 416. Therefore, the switch mode boost converter 452 converts the input voltage V _IN into an output voltage V _{OUT — L} . If the resistance of resistor 402 can be ignored, the output voltage V _{OUT_L} on power line 242 can be calculated from equation (2): V _{OUT_L} = V _IN / (1-D _DUTY ) (2)

Further, as shown in FIG. 4B, the transformer T1, the diode 410, the capacitor 408, and the switch 416 constitute a switch mode flyback converter 454. The flyback converter 454 alternately turns the switch 416 on or off according to the drive signal 460, converting the input voltage V _IN into a voltage difference V _DIFF . The voltage difference V _DIFF can be expressed as: V _DIFF =V _IN *(N ₄₀₆ /N ₄₀₄ )* D _DUTY /(1-D _DUTY ) (3)

Where N ₄₀₆ /N ₄₀₄ represents the turns ratio of the secondary coil 406 to the primary coil 404.

In one embodiment, since the coil 406 is connected to the non-polar end of the power line 242, the output voltage equals the output voltage _V OUT_H V _{OUT_L} a voltage difference V _DIFF, as in equation (1) shown in FIG. Therefore, based on equations (1), (2), and (3), V _{OUT_H} = V _{OUT_L} * (1 + D _DUTY * (N ₄₀₆ / N ₄₀₄ )) (4)

As shown in equation (4), as long as the duty cycle D _{DUTY is} greater than zero, the output voltage V _{OUT — H is} greater than the output voltage V _{OUT — L} . In addition, according to equations (2) and (4), by adjusting the duty cycle D _{DUTY of the} drive signal 460, the output voltage V _{OUT_H} and the output voltage V _{OUT_L} are adjusted accordingly.

The advantage is that the boost converter 452 shown in FIG. 4A and the flyback converter 454 shown in FIG. 4B have common elements such as the primary coil 404 and the switch 416, which reduces the number of components in the circuit. Therefore, the size of the converter circuit 202 is reduced, and the cost of the load driving circuit 200/300 is lowered.

Resistor 402 provides a current sense signal 462 that indicates the current flowing through primary coil 404. Converter controller 302 receives current sense signal 462 and determines if dual converter 304 is in an abnormal or undesired state, such as an overcurrent condition. Converter controller 302 controls dual converter 304 to prevent it from entering an abnormal or undesired state. For example, when current sense signal 462 indicates that dual converter 304 is in an over current condition, converter controller 302 turns off switch 416 through drive signal 460.

FIG. 5 shows a schematic diagram of a converter circuit 202 in accordance with another embodiment of the present invention. Elements in Figure 5 that are numbered the same as Figures 2 through 4 have similar functions. Figure 5 will be described in conjunction with Figures 2 and 3.

In the example shown in FIG. 5, the dual converter 304 includes a transformer T2, diodes 510 and 512, capacitors 514 and 516, a switch 518, and a resistor 402. The transformer T2 includes a primary coil 504, a core 505, a secondary coil 506, and an auxiliary coil 508. Converter controller 302 generates drive signal 460 (e.g., a pulse width modulation signal) to alternately close or open switch 518. The primary coil 504, the core 505, the secondary coil 506, the switch 518, the diode 510, and the capacitor 514 constitute a first flyback converter. The first flyback converter converts the input voltage V _IN into a voltage difference V _DIFF '. The voltage difference V _DIFF ' can be expressed as: V _DIFF '=V _IN *(N ₅₀₆ /N ₅₀₄ )* D _DUTY /(1-D _DUTY ) (5)

Where N ₅₀₆ /N ₅₀₄ represents the turns ratio of the secondary coil 506 to the primary coil 504.

Similarly, primary coil 504, core 505, auxiliary coil 508, switch 518, diode 512, and capacitor 516 form a second flyback converter. The second flyback converter converts the input voltage V _IN into an output voltage V _{OUT — L} . The output voltage V _{OUT_L} can be expressed as: V _{OUT_L} = V _IN * (N ₅₀₈ /N ₅₀₄ )* D _DUTY /(1-D _DUTY ) (6)

Where N ₅₀₈ /N ₅₀₄ represents the turns ratio of the auxiliary coil 508 to the primary coil 504.

Since the non-polar end of the secondary coil 506 is connected to the power supply line 242, according to equation (1), the output voltage V _{OUT_H} is equal to the output voltage V _{OUT — L} plus the voltage difference V _DIFF . Based on equations (1), (5), and (6), the output voltage V _{OUT_H} can be calculated from equation (7): V _{OUT_H} = V _{OUT_L} * (1 + N ₅₀₆ / N ₅₀₈ ) (7)

As shown in equation (7), the output voltage V _{OUT — H is} greater than the output voltage V _{OUT — L} . As shown in equations (6) and (7), the output voltage V _{OUT — H} and the output voltage V _{OUT — L} are adjusted according to the duty cycle D _{DUTY of the} drive signal 460 .

Advantageously, the first flyback converter and the second flyback converter share some common components, which reduces the size of the converter circuit 202 and reduces the cost of the drive circuit 200.

As discussed in Figure 3, when the switching element 222 is in a closed state During the period (eg, switch S3 is closed), current I1 flows from ground through dual converter 304 to power line 241. When the switching element 222 is in the switch off state (eg, the switch S3 is open), the current I2 flows from the power line 242 through the dual converter 304 to the power line 241. If the dual converter 304 shown in FIGS. 4A and 4B is used, the secondary coil 406 transfers the current I1 from ground through the capacitor 414 to the power supply line 241 in the switch closed state. In the open state of the switch, the secondary coil 406 transfers the current I2 from the power line 242 to the power line 241. If a dual converter 304 as shown in FIG. 5 is used, in the switch closed state, secondary coil 506 transfers current I1 from ground through capacitor 516 to power supply line 241. In the open state of the switch, the secondary coil 506 transfers the current I2 from the power line 242 to the power line 241. The dual converter 304 can include other structures and is not limited to the embodiments of Figures 4A, 4B, and 5.

FIG. 6 shows a schematic diagram of a load drive circuit 600 in accordance with another embodiment of the present invention. In one embodiment, the load is a light source 206. Elements in Figure 6 that are numbered the same as Figures 2 and 3 have similar functions. Figure 6 will be described in conjunction with Figures 2 through 5.

In the example shown in FIG. 6, current sensor 210 includes a resistor R6 and an error amplifier 602. Error amplifier 602 receives the voltage across resistor R6, which in turn produces a sense signal 234 indicative of the current flowing through LED chain 206. In an embodiment, the switching regulator 208 coupled between the current sensor 210 and the LED chain 206 is a buck converter structure. Switching regulator 208 includes switching element 222 and energy storage element 220. In one embodiment, energy storage component 220 includes an inductance L6 coupled to LED chain 206. The switching element 222 includes a switch S6 and a diode D6. In one embodiment, the switch S6 can be a P-type metal oxide semiconductor transistor. Anode D6 anode and power line 242 connected. The cathode of diode D6 and the drain of switch S6 are coupled together to a common node that is coupled to ground through inductor L6 and LED chain 206. The source of the switch S6 is connected to the power line 241 through the current sensor 210.

Switching element 222 selectively connects ground, power line 241, and power line 242 to inductor L6 in accordance with switch control signal 230 (eg, a pulse width modulation signal). More specifically, when the switch control signal 230 is logic low, the switching element 222 operates in a switch closed state, at which time the switch S6 is closed and the diode D6 is reverse biased. Therefore, the power line 241 and the ground are electrically coupled to the inductor L6. Current I1' flows through power line 241, resistor R6, switch S6, inductor L6, LED chain 206, and ground, and then flows from ground through dual converter 304 to power line 241. Since the current flows from the TA terminal of the inductor L6 to the TB terminal, the output voltage V _{OUT_H charges} the inductor L6, so the current I1' rises.

In addition, when the switch control signal 230 is logic high, the switching element 222 operates in the switch open state, at which time the switch S6 is open and the diode D6 is forward biased. Therefore, the power line 242 and the ground are electrically coupled to the inductor L6. Current I2' flows through power line 242, diode D6, inductor L6, LED chain 206, and ground, and then flows from ground through dual converter 304 to power line 242. The inductor L6 discharge supplies power to the LED chain 206, and the current (I2') flowing from the TA terminal to the TB terminal is gradually reduced. Similar to the drive circuit 300 shown in FIG. 3, the switch controller 204 adjusts the LED current to the current desired value by adjusting the duty cycle of the switch control signal 230.

The advantage is that during the switch closed state, the voltage V _D6 across the diode _{D6 is} less than the output voltage V _{OUT — L} . During the switch off state, the voltage across switch S6 is approximately equal to the difference between output voltage V _{OUT — H} minus output voltage V _{OUT — L} . That is to say, by using the output voltage voltage V _{OUT_L} , the operating voltage across the switch S6 and the diode D6 remains smaller than the output voltage V _{OUT — H} when the switch is turned on and the switch is turned off. Therefore, the rated voltage of the switch S6 and the diode D6 is lowered, and the power consumption and cost of the drive circuit 300 are lowered.

The dual converter 304 in the example shown in FIGS. 4A, 4B, and 5 can also be used in the drive circuit 600. If the dual converter 304 shown in Figs. 4A and 4B is used, in the switch closed state, the secondary coil 406 transfers the current I1' from the ground through the capacitor 414 to the power supply line 241. In the off state of the switch, current I2' flows from ground through capacitor 414 to power line 242. If a dual converter 304 as shown in Fig. 5 is used, in the closed state of the switch, the secondary winding 506 transfers the current I1' from ground through the capacitor 516 to the power supply line 241. In the off state of the switch, current I2' flows from ground through capacitor 516 to power line 242.

FIG. 7 shows a schematic diagram of a load drive circuit 700 in accordance with another embodiment of the present invention. Elements in Figure 7 that are numbered the same as Figures 2 and 3 have similar functions. Figure 7 will be described in conjunction with Figures 2 through 5.

In the example shown in FIG. 7, switching regulator 208 coupled to LED chain 206 is a boost converter configuration. The reserve element 220 includes an inductance L7 connected to a power supply line 241. The switching element 222 includes a switch S7 and a diode D7. In one embodiment, the switch S7 can be an N-type metal oxide semiconductor transistor. The anode of the diode D7 and the drain of the switch S7 are coupled together to a common node, and the common node is connected to the power line 241 through the inductor L7. The source of switch S7 is coupled to power line 242. The anode of diode D7 is coupled to ground through LED chain 206 and sensor 210.

Switching element 222 selectively connects ground, power line 241, and power line 242 to inductor L7 in accordance with switch control signal 230 (eg, a pulse width modulation signal). More specifically, when the switch control signal 230 is logic high In the bit position, the switching element 222 operates in the switch closed state, at which time the switch S7 is closed and the diode D7 is reverse biased. Therefore, the power line 241 and the power line 242 are electrically coupled to the inductor L7. The current I1" flows through the power line 241, the inductor L7, the switch S7, and the power line 242, and then flows from the power line 242 through the double converter 304 to the power line 241. The current flows from the TA end of the inductor L7 to the TB terminal. The inductor L7 is Charging, current I1" rises. Since the diode D7 is reverse biased, the capacitor C7 supplies power to the LED chain 206.

Further, when the switch control signal 230 is at a logic low level, the switching element 222 operates in a switch-off state, at which time the switch S7 is open and the diode D7 is forward biased. Therefore, the power line 241 and the ground are electrically coupled to the inductor L7. Current I2" flows through power line 241, inductor L7, diode D7, LED chain 206, and ground, and then flows from ground through dual converter 304 to power line 241. Current flows from the TA terminal of inductor L7 to the TB terminal. I2" drops, inductor L7 discharges power to LED chain 206 and charges capacitor C7. Thus, by adjusting the duty cycle of the switch control signal 230, the switch controller 204 adjusts the LED current.

The advantage is that during the switch closed state, the voltage V _D7 across the diode _{D7 is} less than the output voltage V _{OUT — H} . During the switch off state, the voltage across switch S7 is less than the output voltage V _{OUT — H} . That is to say, by using the output voltage voltage V _{OUT_L} , the operating voltage across the switch S7 and the diode D7 remains smaller than the output voltage V _{OUT — H} in the switch closed state and the switch open state. Therefore, the rated voltage of the switch S7 and the diode D7 is smaller than the output voltage V _{OUT — H} , which reduces the power consumption and cost of the driving circuit 700. The dual converter 304 of the example shown in FIGS. 4A, 4B, and 5 can also be used for the load driving circuit 700. If the dual converter 304 shown in Figures 4A and 4B is used, in the closed state of the switch, the secondary winding 406 passes the current I1" from the power supply line 242 through the capacitor 414 to the power supply line 241. In the open state of the switch, the current I2" From ground through capacitor 414 to power line 241. If a dual converter 304 as shown in FIG. 5 is used, in the closed state of the switch, secondary coil 506 transfers current I1 from power line 242 through capacitor 516 to power line 241. In the off state of the switch, current I2 flows from ground through capacitor 516 to power line 241. Switching regulator 208 can be other configurations as long as the structure is within the scope of the claims, and is not limited to the buck converter structure of Figures 3 and 6, and the boost converter structure of Figure 7.

FIG. 8 is a circuit diagram of a load drive circuit 800 in accordance with an embodiment of the present invention. The components numbered in Figure 8 and Figure 2 have similar functions. FIG. 8 will be described in conjunction with FIGS. 2, 3, 6, and 7.

The load driving circuit 800 includes a converter circuit 202 for generating an output voltage _V OUT_H power supply line 241, and produces an output voltage V _{OUT_L} power supply line 242. In the example shown in FIG. 8, the load driving circuit 800 is used to drive a plurality of strings of LED chains. Although the example of FIG. 8 only shows three strings of LED chains 806_1, 806_2, and 806_3, the load driving circuit 800 may include other numbers of LED chains, and is not limited thereto. Each string of LED chains is connected to the circuit in a manner similar to the load drive circuit 300 of FIG. For example, the LED chain 806_1 is connected to a switching regulator including a diode D8_1, a switch S8_1, and an inductor L8_1. The LED chain 806_2 is connected to a switching regulator including a diode D8_2, a switch S8_2, and an inductor L8_2. The LED chain 806_3 is connected to a switching regulator including a diode D8_3, a switch S8_3, and an inductor L8_3.

The load drive circuit 800 also includes a plurality of switch controllers 804_1, 804_2, and 804_3 for controlling flow through the LED chains 806_1 through 806_3, respectively. LED current. For example, the switch controllers 804_1 to 804_3 compare the sense signals ISEN_1 to ISEN_3 and the reference signal REF indicating the current expectation value, respectively, and generate the switch control signals PWM_1 to PWM_3 to adjust the LED current to the preset current value. That is, the switch controllers 804_1 through 804_3 are capable of balancing the current flowing through the LED chains 806_1 through 806_3, so the LED chains 806_1 through 806_3 can provide balanced brightness.

The switch controllers 804_1 through 804_3 also generate error signals VEA_1, VEA_2, and VEA_3, each error signal indicating the desired forward voltage of the LED chains 806_1 through 806_3 when the current flowing through the LED chains 806_1 through 806_3 reaches a preset current value. The load driving circuit 800 further includes a feedback selection circuit 812 that receives the error signals VEA_1 to VEA_3 and determines which of the LED chains 806_1 to 806_3 has the largest forward voltage. As a result, feedback selection circuit 812 generates a feedback signal 810 indicating the LED current of the LED chain having the largest forward voltage. In one embodiment, converter circuit 202 adjusts output voltage _{VOUT_H} based on feedback signal 810 to meet the power requirements of the LED chain having the largest forward voltage. Since the output voltage V _{OUT_H} can meet the power supply requirements of the LED chain with the largest forward voltage, it can also meet the power supply requirements of other LED chains. The load drive circuit 800 can have other configurations, for example, each of the LED chains 806_1 through 806_3 is driven by the circuit shown in FIG. 6 or 7.

The advantage is that the output voltage of the switching element associated with the LED chain _drops due to the output voltage V _{OUT — L} on the power line 242. Therefore, the power consumption and cost of the load driving circuit 800 are degraded.

FIG. 9 shows an operational flow diagram 900 of a load drive circuit (e.g., load drive circuit 200) in accordance with an embodiment of the present invention. Figure 9 will be combined with the figure 2 to 8 are described. Although Figure 9 discloses certain specific steps, these steps are merely examples. The present invention is suitable for performing other steps similar or equivalent to those of FIG.

In step 902, the first power supply line provides a first output voltage (eg, output voltage _{VOUT_H} ) to power the light source (eg, LED chain 206).

In step 904, the second power line provides a second output voltage (eg, output voltage _{VOUT_L} ) that is less than the first output voltage.

In step 906, when the switching element (eg, switching element 222) is operating in the first state, the energy storage element (eg, energy storage element 220) is charged.

In step 908, when the switching element (eg, switching element 222) is operating in the second state, the energy storage element (eg, energy storage element 220) is discharged.

In step 910, the current flowing through the source is adjusted by adjusting the ratio of the duration of charge and discharge of the energy storage element. In one embodiment, the energy storage element comprises an inductance. In one embodiment, the switching element comprises a transistor and a diode.

In step 912, the second output voltage maintains the operating voltage across the switching element less than the first output voltage during the first state and the second state. In one embodiment, during the first state, the current of the energy storage element is turned on, charging the energy storage element through the first power line and the reference node; during the second state, the current of the energy storage element is conducting, passing the first power source The line and the second power line discharge the energy storage element. In another embodiment, during the first state, the current of the energy storage element is turned on, charging the energy storage element through the first power line and the reference node; during the second state, the current of the energy storage element is conducting, passing The second power line and the reference node discharge the energy storage element. In still another embodiment, during the first state, the current of the energy storage element is turned on, charging the energy storage element through the first power line and the second power line; during the second state, the current of the energy storage element is turned on, The first power line and the reference node discharge the energy storage element.

A drive circuit for powering a load is provided in accordance with an embodiment of the present invention. For convenience of explanation, the present invention supplies power to a light source of a light emitting diode chain. However, the invention is not limited to powering the light source, but can also be used to power other types of loads. The drive circuit includes a converter circuit, an energy storage element, and a switching element. The converter circuit provides a first output voltage on the first power line to drive the light source and a second output voltage on the second power line that is less than the first output voltage. When the switching element operates in the first state, the energy storage element is charged, and when the switching element operates in the second state, the energy storage element is discharged. The current flowing through the light source can be adjusted by adjusting the duration ratio of the first state to the second state.

Advantageously, due to the second output voltage on the second power line, the operating voltage across the switching element remains less than the first output voltage during the first state and the second state. Therefore, the rated voltage of the switching element is lowered, and the power consumption and cost of the driving circuit are lowered.

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 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 intended to be illustrative and not restrictive, and the scope of the invention is defined by the appended claims

100‧‧‧Light source drive circuit

102‧‧‧ converter circuit

104‧‧‧Switch controller

106‧‧‧LED chain

108‧‧‧Switching regulator

130‧‧‧ Pulse width modulation (PWM) signal

141‧‧‧Power cord

200‧‧‧Load drive circuit

202‧‧‧ converter circuit

204‧‧‧Switch controller

206‧‧‧Light source

208‧‧‧Switching regulator

210‧‧‧ Current Sensor

220‧‧‧ energy storage components

222‧‧‧Switching elements

230‧‧‧Switch control signal

232‧‧‧Return signal

234‧‧‧Sensing signal

241, 242‧‧‧ power cord

244‧‧‧ reference node

300‧‧‧Load drive circuit

302‧‧‧ Converter Controller

304‧‧‧Dual converter

310‧‧‧Control signal

402‧‧‧resistance

404‧‧‧Primary coil

405‧‧‧ iron core

406‧‧‧secondary coil

408‧‧‧ Capacitance

410, 412‧‧‧ diode

414‧‧‧ Capacitance

416‧‧‧ switch

452‧‧‧Boost Converter

454‧‧‧Reverse converter

460‧‧‧ drive signal

462‧‧‧ Current sensing signal

504‧‧‧Primary coil

505‧‧‧ iron core

506‧‧ level coil

508‧‧‧Auxiliary coil

510, 512‧‧‧ diode

514, 516‧‧‧ capacitor

518‧‧‧ switch

600‧‧‧Load Drive Circuit

602‧‧‧Error amplifier

700‧‧‧Load Drive Circuit

800‧‧‧Load drive circuit

804_1, 804_2, 804_3‧‧‧ switch controller

806_1, 806_2, 806_3‧‧‧LED chain

810‧‧‧Return signal

812‧‧‧Feedback selection circuit

900‧‧‧Flowchart

902~912‧‧‧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. among them:

Figure 1 is a block diagram showing a conventional light source driving circuit.

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

3 is a block diagram of a load driving circuit in accordance with an embodiment of the present invention.

4A and 4B are schematic diagrams of a converter circuit in accordance with an embodiment of the present invention.

FIG. 5 is a schematic diagram of a converter circuit in accordance with another embodiment of the present invention.

6 is a schematic diagram of a load driving circuit in accordance with another embodiment of the present invention.

FIG. 7 is a schematic diagram of a load driving circuit according to another embodiment of the present invention.

Figure 8 is a circuit diagram of a load driving circuit in accordance with an embodiment of the present invention.

9 is a flow chart showing the operation of a load driving circuit in accordance with an embodiment of the present invention.

200‧‧‧Load drive circuit

202‧‧‧ converter circuit

204‧‧‧Switch controller

206‧‧‧Light source

208‧‧‧Switching regulator

210‧‧‧ Current Sensor

220‧‧‧ energy storage components

222‧‧‧Switching elements

230‧‧‧Switch control signal

232‧‧‧Return signal

234‧‧‧Sensing signal

241, 242‧‧‧ power cord

244‧‧‧ reference node

Claims (20)

A light source driving circuit includes: a converter circuit that supplies a first output voltage to a light emitting diode light source on a first power line, and provides a first less than the first output voltage on a second power line a second output voltage; an energy storage component coupled to the light emitting diode light source to regulate a current flowing through the light emitting diode light source; and a switching element coupled to the converter circuit and the energy storage component, When the switching element operates in a first state, the energy storage component is charged, and when the switching component operates in a second state, the energy storage component is discharged, wherein the converter circuit provides the second output voltage to In the first state and the second state, an operating voltage across the switching element is maintained to be less than the first output voltage. The light source driving circuit of claim 1, wherein during the first state, the switching element conducts a current flowing through the energy storage element through the first power line and a reference node, in the second During the state, the current flowing through the energy storage element by the switching element flows through the first power line and the second power line. The light source driving circuit of claim 1, wherein during the first state, the switching element conducts a current flowing through the energy storage element through the first power line and a reference node, in the second During the state, the current flowing through the energy storage element by the switching element flows through the second power line and the reference node. The light source driving circuit of claim 1, wherein during the first state, the switching element conducts a flow through the energy storage element A current flows through the first power line and the second power line. During the second state, the current of the switching element conducting the energy storage element flows through the first power line and a reference node. The light source driving circuit of claim 1, further comprising: a transformer having a primary coil and a primary coil, the primary coil receiving an input voltage, the secondary coil being provided at a first turn of the secondary coil The first output voltage and the second output voltage are provided at a second turn of the secondary coil. The light source driving circuit of claim 1, further comprising: a transformer having a primary coil, a primary coil and an auxiliary coil, the secondary coil and the auxiliary coil being coupled to a common node, the primary coil receiving An input voltage, the secondary coil provides the first output voltage at a first turn of the secondary coil, the auxiliary coil providing the second output voltage at the common node. The light source driving circuit of claim 1, wherein the energy storage component comprises an inductor, and the switching component comprises a switch and a diode. The light source driving circuit of claim 1, wherein the second output voltage changes according to a change in the first output voltage. A light source driving circuit comprising: a converter circuit, providing a first output voltage on a first power line to supply power to a plurality of light emitting diode sources, and providing less than the first output voltage on a second power line a second output voltage; And a plurality of switching regulators coupled to the converter circuit to adjust a plurality of currents flowing through the plurality of light emitting diode light sources, each of the switching regulators comprising a switching element, wherein the switching element operates in a In one state, an energy storage component is charged, and when the switching component operates in a second state, the energy storage component is discharged, and the duration of charging and discharging of the energy storage component is adjusted to pass through a corresponding light emitting diode. a current of the body light source, the converter circuit providing the second output voltage to maintain an operating voltage across the switching element less than the first output voltage in the first state and the second state. The light source driving circuit of claim 9, further comprising: a plurality of switch controllers coupled to the plurality of switch regulators, the plurality of switch controllers receiving a plurality of sensing signals, the plurality of sensing signals Directing a plurality of currents flowing through the plurality of light emitting diode light sources, and comparing the plurality of sensing signals with a reference signal indicating a current expected value, and generating a plurality of switches according to at least one comparison result of the plurality of comparison results And a plurality of switching regulators that receive the plurality of switching control signals to adjust each current flowing through the plurality of light emitting diode sources to the current desired value. The light source driving circuit of claim 9, wherein during the first state, a current of the switching element that conducts the energy storage element flows through the first power line and a reference node, during the second state, The current flowing through the energy storage element by the switching element flows through the first power line and the second power line. The light source driving circuit of claim 9, wherein during the first state, a current of the switching element conducting the energy storage element flows through the first power line and a reference node during the second state The current that the switching element turns on the energy storage element flows through the second power line and the reference node. The light source driving circuit of claim 9, wherein during the first state, a current of the switching element conducting the energy storage element flows through the first power line and the second power line, in the second During the state, the current of the switching element conducting the energy storage element flows through the first power line and a reference node. The light source driving circuit of claim 9, wherein the energy storage element comprises an inductor, and the switching element comprises a switch and a diode. A method for supplying a light source of a light emitting diode includes: providing a first output voltage on a first power line to supply power to a light emitting diode source; and providing a second power line on the second power line smaller than the first output voltage An output voltage; when a switching element operates in a first state, charging an energy storage component; when the switching component operates in a second state, the energy storage component is discharged; adjusting the switching component in the first state and the first a duration of the two states to adjust a current flowing through the light emitting diode source; and providing the second output voltage to be in the first state and the second state The operating voltage across the switching element is maintained to be less than the first output voltage. The method of claim 15, further comprising: conducting a current through the energy storage element through the first power line and a reference node to charge the energy storage element; and conducting the current flow of the energy storage element The energy storage element is discharged through the first power line and the second power line. The method of claim 15, further comprising: conducting a current through the energy storage element through the first power line and a reference node to charge the energy storage element; and conducting the current flow of the energy storage element The energy storage element is discharged through the second power line and the reference node. The method of claim 15, further comprising: conducting a current through the energy storage element through the first power line and the second power line to charge the energy storage element; and turning on the energy storage element A current flows through the first power line and a reference node, and the energy storage element is discharged. The method of claim 15, wherein the energy storage component comprises an inductor. The method of claim 15, wherein the switching element comprises a transistor and a diode.