Light source driving system and light source controller

Abstract

The utility model discloses a light source driving system and a light source controller. In a light source controller, a primary side controller controls power transferred from a primary winding of a transformer to a first secondary winding and a second secondary winding of the transformer according to a load of a system circuit, where the system circuit is powered by the second secondary winding. When a switching circuit connected to the first secondary winding is turned on, the switching circuit causes the first secondary winding to provide a portion of the power to a light source connected to the first secondary winding. And a secondary side controller connected with the switching circuit and the primary side controller, monitoring the state of the light source and controlling the switching circuit according to the state. The light source driving system can omit a direct-current / direct-current converter in an existing system, so that the cost is reduced, and the size of a printed circuit board is reduced. The light source driving system can also solve the problem that the system load change and the light source power mode in the existing system are possibly incompatible with each other.

Description

Technical Field

[0001] The utility model relates to the field of light source driving, in particular to a light source driving system and a light source controller based on a transformer. Background Art

[0002] Figure 1 Shown is a light source driving system 100 for driving a light source 108 in the prior art, wherein the light source 108 includes a light-emitting diode (LED) backlight. The light source driving system 100 is connected to a power supply V AC through a rectifier 120. The light source driving system 100 includes a transformer 110, a primary side controller 102, a secondary side controller 104, a DC / DC converter 118, and a system circuit 106.

[0003] The rectifier 120 rectifies an AC voltage V AC (e.g., an AC voltage from an AC power supply such as 220 volts, 110 volts, etc.) to provide rectified electrical energy to the transformer 110. The transformer 110 includes a primary winding 112, a first secondary winding 114, and a second secondary winding 116. The primary side controller 102 alternately turns on and off a switch Q PR connected to the primary winding 112, such that when the switch Q PR is off, the transformer 110 transfers electrical energy from the primary winding 112 to the secondary windings 114 and 116. The light source 108 is powered by the first secondary winding 114. The secondary side controller 104 and the system circuit 106 are powered by the second secondary winding 116.

[0004] When a current I 108 flows through the light source 108, the light source 108 can emit light. The secondary side controller 104 monitors the state of the light source 108 (e.g., whether the light source 108 receives sufficient electrical energy) and generates a control signal 122 according to this state. The primary side controller 102 controls the on and off of the switch Q PR according to the control signal 122, so that the light source 108 receives sufficient electrical energy, thereby maintaining the current I 108 flowing through the light source 108 at a target level. The user can increase or decrease the brightness of the light source 108 by increasing or decreasing this target level, which will cause an increase or decrease in the power transferred from the primary winding 112 to the secondary windings 114 and 116. The output power of the second secondary winding 116 (e.g., represented by the input voltage V INPUT of the DC / DC converter 118) will also change with the change of the target level of the current I 108 . Therefore, the light source driving system 100 further includes a DC / DC converter 118 for converting the output power of the second secondary winding 116 (e.g., represented by the voltage VINPUT is converted to a relatively stable voltage V SYS to supply power to the secondary side controller 104 and the system circuit 106.

[0005] However, a DC / DC converter (e.g., a component generally including an inductor, a high-power transistor, a feedback circuit, a comparator, a pulse width modulation signal generator, a high-power transistor driver, etc.) is generally relatively expensive and occupies a relatively large space on a printed circuit board.

[0006] In addition, the light source 108 may operate in a high-power mode (e.g., when it is set to emit light at a full brightness level) or in a low-power mode (e.g., when it is dimmed to a relatively low brightness level, such as 10% of the full brightness level). The primary side controller 102 controls the switch Q PR such that the power received by the first secondary winding 114 and the power received by the second secondary winding 116 increase when the light source 108 operates in the high-power mode and decrease when the light source 108 operates in the low-power mode. The load of the system circuit 106 (abbreviation: system load) changes in real time according to the actual situation, e.g., increases or decreases. Regardless of the mode in which the light source 108 operates, the system load may increase or decrease. Therefore, if the system circuit 106 is in a heavy load state when the light source 108 operates in the low-power mode, the second secondary winding 116 may not receive enough electrical energy to support the heavy load of the system circuit 106. Similarly, if the system circuit 106 is in a light load state when the light source 108 operates in the high-power mode, the power received by the second secondary winding 116 may be too high for the DC / DC converter 118 to correctly perform power conversion to support the light load of the system circuit 106. SUMMARY OF THE UTILITY MODEL

[0007] The technical problem to be solved by the present utility model is to provide one or more solutions for solving the problems of high cost and high power consumption due to the DC / DC converter in the existing light source driving system, and the problem that the change of the system load and the operating mode of the light source may be incompatible with each other.

[0008] To solve the above technical problems, the present utility model provides a light source driving system, which includes: a primary side controller configured to control the power transmitted from the primary winding of a transformer to a first secondary winding and a second secondary winding of the transformer according to the load of the system circuit, wherein the system circuit is powered by the second secondary winding; a switching circuit connected to the first secondary winding and configured to, when the switching circuit is turned on, cause the first secondary winding to supply a part of the power to a light source connected to the first secondary winding; and a secondary side controller connected to the switching circuit and the primary side controller and configured to monitor the state of the light source and control the switching circuit according to the state.

[0009] The present utility model also provides a light source controller, which includes: a monitoring terminal configured to monitor the state of a light source, wherein the light source is powered by the first secondary winding of a transformer, and the light source controller is powered by the second secondary winding of the transformer, and the transformer includes a primary winding, the first secondary winding and the second secondary winding; a driving terminal configured to provide a driving signal to control a switching circuit connected to the first secondary winding, wherein, when the driving signal turns on the switching circuit, the first secondary winding supplies a part of the power transmitted from the primary winding of the transformer to the first secondary winding and the second secondary winding to the light source; a synchronization terminal configured to detect the electrode polarity on the output terminal of the second secondary winding; and a control circuit connected to the monitoring terminal, the driving terminal and the synchronization terminal, wherein, when the control circuit detects a positive polarity on the synchronization terminal, the control circuit generates the driving signal according to the state of the light source, and when the control circuit does not detect the positive polarity on the synchronization terminal, the control circuit suspends generating the driving signal.

[0010] By using the light source driving system provided by the present utility model, the power transmitted from the primary winding of the transformer to the secondary winding can be adjusted according to the size of the system load, thereby omitting the DC / DC converter in the existing system to reduce costs and the size of the printed circuit board. In addition, the light source driving system and the light source controller provided by the present utility model can control the switching circuit connected to the first secondary winding and the light source according to the state of the light source. Regardless of whether the system load is in a heavy load, normal load or light load state, the light source can be controlled to operate in a desired operating mode by controlling the switching circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The following description of some embodiments of the present utility model in conjunction with its drawings can further understand the purpose, specific structural features and advantages of the present utility model.

[0012] Figure 1 Shown is a schematic diagram of a module of a light source driving system of the prior art.

[0013] Figure 2A Shown is a schematic diagram of a module of a light source driving system according to an embodiment of the present invention.

[0014] Figure 2B Shown is a schematic circuit diagram of a light source driving system according to an embodiment of the present invention.

[0015] Figure 3 Shown is a schematic circuit diagram of a secondary side controller according to an embodiment of the present invention.

[0016] Figure 4 Shown is a waveform diagram of signals related to a secondary side controller according to an embodiment of the present invention and a state diagram of a switching circuit based on the states of the signals.

[0017] Figure 5 Shown is a schematic diagram of an operation flow of a light source driving system according to an embodiment of the present invention. Detailed implementation manners

[0018] The following will give a detailed reference to the embodiments of the present invention. Although the present invention is described and illustrated by these embodiments, it should be noted that the present invention is not limited to these embodiments. On the contrary, the present invention covers all alternatives, variations, and equivalents within the spirit and scope of the invention defined by the appended claims.

[0019] In addition, for a better illustration of the present invention, numerous specific details are given in the following detailed implementation manners. Those skilled in the art will understand that the present invention can be implemented without these specific details. In other instances, well-known methods, procedures, components, and circuits are not described in detail to highlight the gist of the present invention.

[0020] The term "including" and its variations used herein mean open inclusion, that is, "including but not limited to". Unless otherwise stated, the term "or" means "and / or". The term "based on" means "at least partially based on". The term "an embodiment" means "at least one embodiment". The terms "first", "second", etc. may refer to different or the same samples. The terms "connected" and "coupled" may mean "directly electrically connected", "indirectly electrically connected", or "coupled connection".

[0021] Embodiments of the present utility model provide a light source driving system based on a transformer. In the light source driving system according to an embodiment of the present utility model, the transformer includes a primary winding, a first secondary winding, and a second secondary winding. The transformer can transfer electrical energy from the primary winding to the first secondary winding and the second secondary winding. The first secondary winding can supply power to the light source. The second secondary winding can supply power to a controller for monitoring the light source or to a system circuit. If the load of the system circuit (hereinafter simply referred to as: system load) increases, the power transferred from the primary winding to the first and second secondary windings increases; if the system load decreases, the power transferred from the primary winding to the first and second secondary windings decreases. Therefore, the system circuit and the controller can receive a stable supply voltage and thus operate normally. The light source driving system further includes a switch circuit connected to the first primary winding. The controller can supply power from the first primary winding to the light source by turning on the switch circuit, or pause the supply of power from the first primary winding to the light source by turning off the switch circuit. Therefore, the controller can adjust the brightness of the light source by controlling the switch circuit (e.g., its duty cycle). In this way, the light source driving system according to the embodiments of the present utility model can eliminate the existing DC / DC converter in the light source driving system, thereby reducing the cost of the light source driving system and reducing the size of the printed circuit board. In addition, regardless of whether the system load is in a light load, normal load, or heavy load, the controller can adjust the brightness of the light source to a target level by increasing or decreasing the duty cycle of the switch circuit. More specifically, if the light source operates in a low-power mode when the system load is very heavy, the controller can set the duty cycle of the switch circuit very low; if the light source operates in a high-power mode when the system load is very light, the controller can set the duty cycle of the switch circuit very high. Therefore, regardless of the power mode of the light source and the level of the system load, the light source and the system circuit can operate normally.

[0022] Figure 2A Shown is a block diagram of a light source driving system 200 for driving a light source 208 according to an embodiment of the present utility model. As shown in FIG. 2, the light source driving system 200 is connected to a power supply V through a rectifier 220. AC The light source driving system 200 includes a power converter 210 (e.g., a transformer), a primary side controller 202, a secondary side controller 204, a switch circuit 228, a feedback circuit 224, and a system circuit 206. In one embodiment, the rectifier 220 rectifies an AC voltage V (e.g., an AC voltage from an AC power supply such as 220 volts, 110 volts, etc.) to supply rectified electrical energy to the transformer 210. The transformer 210 includes a primary winding 212, a first secondary winding 214, and a second secondary winding 216. The primary side controller 202 alternately turns on and off a switch Q connected to the primary winding 212. AC (e.g., an AC voltage from an AC power supply such as 220 volts, 110 volts, etc.) to supply rectified electrical energy to the transformer 210. The transformer 210 includes a primary winding 212, a first secondary winding 214, and a second secondary winding 216. The primary side controller 202 alternately turns on and off a switch Q connected to the primary winding 212. PR, such that the transformer 210 transfers electrical energy (e.g., represented by power P 210 ) from the primary winding 212 to the secondary windings 214 and 216. The light source 208 is powered by the first secondary winding 214. The secondary side controller 204 and the system circuit 206 can be powered by the second secondary winding 216.

[0023] In one embodiment, the primary side controller 202 (also referred to as the first controller) controls the power P transferred from the primary winding 212 to the first secondary winding 214 and the second secondary winding 216 according to the load of the system circuit (hereinafter simply referred to as: system load SL 206 ). As 210 shown, the feedback circuit 224 is coupled to the power supply terminal of the system circuit 206 and senses the supply voltage V Figure 2A of the system circuit 206. The feedback circuit 224 can generate a control signal 222 according to the supply voltage V SYS . The primary side controller 202 can periodically turn on and off the switch Q SYS according to the control signal 222, and increase or decrease the duty cycle of the switch Q PR . Herein, the "duty cycle of the switch" refers to the ratio of the time the switch is on to the period time during one on and off cycle of the switch. For example, if the supply voltage V PR decreases (e.g., indicating an increase in the system load SL SYS ), the control signal 222 can control the primary side controller 202 (e.g., by increasing the duty cycle of the switch Q 206 ) to increase the power P transferred in the transformer 210 PR . If the supply voltage V 210 increases (e.g., indicating a decrease in the system load SL SYS ), the control signal 222 can control the primary side controller 202 (e.g., by decreasing the duty cycle of the switch Q 206 ) to decrease the power P transferred in the transformer 210 PR . In this way, the second secondary winding 216 can provide a relatively stable voltage V 210 to power the system circuit 206. This relatively stable voltage V SYS can also be used to power the secondary side controller 204, thus eliminating the need for an additional power supply circuit dedicated to powering the secondary side controller 204. SYS

[0024] Additionally, in one embodiment, when the switch circuit 228 is turned on, the switch circuit 228 can cause the first secondary winding 214 to transfer a portion of the power P 210 of the power P 208It is provided to the light source 208. The secondary side controller 204 (also referred to as: the second controller) can monitor the state of the light source 208 and control the switching circuit 228 according to this state. For example, the secondary side controller 204 can periodically turn on and off the switching circuit 228 and control the duty cycle of the switching circuit 228 according to the state of the light source 208. Herein, the "duty cycle of the switching circuit" described in this article refers to the ratio of the on-time of the switching circuit in a cycle of on and off to the cycle time.

[0025] More specifically, in one embodiment, if the light source 208 receives sufficient power, the light source 208 is in a normal power state and can emit light with a target brightness level. If the light source 208 does not receive sufficient power, the light source 208 is in an underpower state and may not be able to emit light with a target brightness level. Therefore, the secondary side controller 204 is used to control the light source 208 to be in a normal power state.

[0026] In one embodiment, the status signal 226 (e.g., a voltage signal) from the light source 208 can indicate whether the light source 208 is in a normal power state, and the status signal 226 is monitored by the secondary side controller 204. For example, if the status signal 226 is at a preset reference level, the light source 208 is in a normal power state. In one embodiment, if the status signal 226 is less than the reference level, the secondary side controller 204 increases the duty cycle of the switching circuit 228; or, if the status signal 226 is greater than the reference level, the secondary side controller 204 decreases the duty cycle of the switching circuit 228. In this way, the status signal 226 is adjusted to the reference level to make the light source 208 in a normal power state.

[0027] Although Figure 2A the illustrated system circuit 206 and the secondary side controller 204 are separate, the present invention is not limited thereto. In some embodiments of the present invention, the system circuit 206 may include the secondary side controller 204 and other circuits powered by the second secondary winding 216. The "load of the system circuit 206" or "system load SL" described in this article 206 may include the total load of the secondary side controller 204 and the other circuits.

[0028] In one embodiment, the system circuit 206 (e.g., including the controller 204) has a minimum operating power P MIN206 (e.g., which depends on the minimum operating voltage and minimum operating current of the system circuit 206). Therefore, even when the system circuit 206 is in a light load state, the operating power of the system circuit 206 (e.g., represented by P 206 ) is still greater than the minimum operating power P MIN206. The light source 208 has a maximum operating power P MAX208 (e.g., which depends on the maximum operating voltage and maximum operating current of the light source 208). Thus, even when the light source 208 operates in the high power mode, the operating power of the light source 208 (e.g., represented by P 208 ) is less than the maximum operating power P MAX208 . In one embodiment, the turns ratio of the secondary windings 214 and 216 (e.g., the ratio of the number of turns N 214 of the first secondary winding 214 to the number of turns N 216 of the second secondary winding 216) can be set such that if the operating power P 206 of the system circuit 206 is equal to the minimum operating power P MIN206 , the first secondary winding 214 can also provide a power P MAX208 not less than the maximum operating power P 208 to the light source 208. More specifically, if the turns ratio N 214 / N 216 is large enough, when the second secondary winding 216 receives relatively low power from the primary winding 212 to maintain the system circuit 206 in the light load state, the first secondary winding 214 can receive sufficient power from the primary winding 212 to support the light source 208 operating in the high power mode.

[0029] In addition, in one embodiment, when the system circuit 206 is in the heavy load state, the second secondary winding 216 receives relatively high power from the primary winding 212, which causes the first secondary winding 214 to receive relatively high power from the primary winding 212. If the light source 208 is set to operate in the low power mode, the secondary side controller 204 can reduce the duty cycle of the switching circuit 228 to a relatively low value, such that the light source 208 receives relatively low power from the first secondary winding 214.

[0030] Therefore, the light source driving system 200 according to the embodiment of the present invention can omit the DC / DC converter in the existing light source driving system 100, thereby reducing the cost of the light source driving system 200 and reducing the size of its printed circuit board. In addition, under the control of the primary side controller 202, regardless of whether the system circuit 206 is in the light load, normal load or heavy load state, the second secondary winding 216 can provide the required power for the system circuit 206. In addition, regardless of the load condition of the system circuit 206, the secondary side controller 204 can control the duty cycle of the switching circuit 228 such that the light source 208 operates in the desired operating mode.

[0031] Figure 2B Shown is a circuit schematic diagram of the light source driving system 200 according to an embodiment of the present invention. The following is combined with Figure 2A for Figure 2Bis described. In one embodiment, the light source 208 includes light-emitting diode strings S1, S2, ……, SN (where N is a natural number), and each light-emitting diode string includes one or more light-emitting diodes. The positive terminals T of the light-emitting diode strings S1, S2, ……, SN PST can receive power P from a first secondary winding 214 208 . The secondary-side controller 204 may include monitoring terminals ISEN1, ISEN2, ……, ISENN, which are respectively coupled to the negative terminals T of the light-emitting diode strings S1, S2, ……, SN NGT1 , T NGT2 , ……, T NGTN , for monitoring the states of the light-emitting diode strings S1, S2, ……, SN. The secondary-side controller 204 may further include a driving terminal DRV, a power input terminal V IN , a synchronization terminal SYNC, an adjustment terminal EN_PWM, and an input / output terminal LPF.

[0032] In one embodiment, when the light source 208 receives sufficient power (for example: the light source 208 is in the above normal power state), the currents I 1 , I 2 ,... and I N flowing through the light-emitting diode strings S1, S2, ……, SN can all be adjusted to a target level, so that the light emitted by the light-emitting diode strings S1, S2, ……, SN all reaches the target brightness. In one embodiment, since the currents I 1 , I 2 , ……, I N flow through the monitoring terminals ISEN1, ISEN2, ……, ISENN respectively, the voltages V NGT1 , V NGT2 , ……, V NGTN on the monitoring terminals ISEN1, ISEN2, ……, ISENN (or the negative terminals T of the light-emitting diode strings S1, S2, ……, SN ISEN1 , V ISEN2 , ……, V ISENN )( Figure 2B not shown in NGT1 , T NGT2 , ……, T NGTN can represent the state of the light source 208. Therefore, the monitoring terminals ISEN1, ISEN2, ……, ISENN can be configured to monitor the state of the light source 208 by sensing the voltages V ISEN1 , V ISEN2 , ……, V ISENN on the negative terminals T of the light-emitting diode strings S1, S2,... and SN.

[0033] In one embodiment, when the light source 208 receives sufficient power, the voltages V ISEN1 , V ISEN2 , ……, V ISENN each can be greater than or equal to a threshold voltage, and the currents I 1 , I 2 , ……, I N can be adjusted to a target level. If the light source 208 does not receive sufficient power, one or more of the voltages V ISEN1 , V ISEN2 , ……, V ISENN are less than the threshold voltage, and one or more of the currents I 1 , I 2 , … and I N are below the target level. Embodiments of the present utility model provide a preset reference level V REF (for example: a reference level slightly greater than or equal to the threshold voltage) for comparison with the voltage minV ISEN , where the voltage minV ISEN is a voltage selected from the voltages V ISEN1 , V ISEN2 , ……, V ISENN . The control circuit in the secondary side controller 204 can control the duty cycle of the switching circuit 228 according to the comparison result, so that the voltage minV ISEN is adjusted to the reference level V REF . In one embodiment, the voltage minV ISEN includes the minimum voltage among the voltages V ISEN1 , V ISEN2 , ……, V ISENN . In this way, the voltages V ISEN1 , V ISEN2 , ……, V ISENN can be adjusted to be greater than or equal to the reference level V REF . In one embodiment, if the voltage minV ISEN is less than the reference level V REF , the secondary side controller 204 can increase the duty cycle of the switching circuit 228; if the voltage minV ISEN is greater than the reference level V REF , the secondary side controller 204 can decrease the duty cycle of the switching circuit 228. In this way, the secondary side controller 204 can maintain the light source 208 in a normal power state. In one embodiment, Figure 2A the status signal 226 shown includes the voltages V ISEN1 , V ISEN2 , ……, V ISENN .

[0034] In one embodiment, the drive end DRV is configured to provide a drive signal S DRV to control the switching circuit 228. By way of example, the drive signal S DRV may include a pulse signal such as a pulse-width modulation (PWM) signal. The falling edge (or rising edge) of the drive signal S DRV can turn on the switching circuit 228, and its rising edge (or falling edge) can turn off the switching circuit 228.

[0035] Taking Figure 2B as an example, the switching circuit 228 may include a p-channel metal–oxide–semiconductor field-effect transistor 218 (p-MOS transistor), a resistor R6, a diode D3, and a capacitor C6. The resistor R6 is connected between the gate and the source of the p-MOS transistor 218. The positive and negative electrodes of the diode D3 are respectively connected to the gate and the source of the p-MOS transistor 218. The capacitor C6 is connected between the gate of the p-MOS transistor 218 and the drive end DRV. In one embodiment, if the source-gate voltage V SG of the p-MOS transistor 218 is greater than the conduction threshold V TH (for example, V SG >V TH >0), then the p-MOS transistor 218 can conduct. In Figure 2B the example, the source of the p-MOS transistor 218 is connected to the reference ground GND. Therefore, if the voltage V G218 applied to the gate of the p-MOS transistor 218 is negative and this negative voltage V G218 is lower than the negative threshold -V TH , then the p-MOS transistor 218 can conduct. In Figure 2B the example, the falling edge of the drive signal S DRV can make the gate voltage V G218 of the p-MOS transistor 218 lower than the negative threshold -V TH , and the rising edge of the drive signal S DRV can make the gate voltage V G218 higher than the negative threshold -V TH . Therefore, the switching circuit 228 can be turned on by the falling edge of the drive signal S DRV and turned off by the rising edge of the drive signal S DRV . Additionally, in the initial default case, when no signal is generated at the drive end DRV, the p-MOS transistor 218 is off, so the switching circuit 228 is off. Although Figure 2BThe switch circuit 228 shown includes a circuit structure composed of components 218, R6, D3 and C6, but the present invention is not limited thereto. In other embodiments, the switch circuit 228 may have other different circuit structures and include other types of components. For example, the switch circuit 228 may include an n-channel metal oxide semiconductor field effect transistor (abbreviated as: n-MOS tube).

[0036] In one embodiment, the synchronization terminal SYNC is configured to detect the output terminal T of the second secondary winding 216. OUT2 When a positive polarity is detected at the synchronization terminal SYNC, the secondary side controller 204 can detect the positive polarity according to the state of the light source 208 (for example, including the voltage V ISEN1 、V ISEN2 ,……,V ISENN ) to generate the driving signal S DRV When no positive polarity is detected on the synchronization terminal SYNC, the secondary side controller 204 may pause or stop generating the driving signal S DRV .

[0037] More specifically, in one embodiment, when the switch Q connected to the primary winding 212 PR When turned on, the primary current I P can flow through the primary winding 212. Since the primary current I P This increases the magnetic flux in transformer 210, causing transformer 210 to store magnetic energy. PR During the on-time, the output terminal T of the second secondary winding 216 OUT2 The polarity of is negative, and no current is generated in the secondary windings 214 and 216. PR When the transformer 210 is turned off after being turned on for a period of time, it releases magnetic energy to the secondary windings 214 and 216, so that a secondary current I S1 and I S2 During the period when the transformer 210 releases magnetic energy, the output terminal T of the second secondary winding 216 OUT2 The polarity is positive. If the switch circuit 228 is turned on, the first secondary winding 214 can supply power to the light source 208 (for example, including power P 208 In this case, a driving signal S DRV To control the switch circuit 228, thereby controlling the power P 208 The size of the switch Q PR During the on-time (e.g. when the output terminal T OUT2 When no positive polarity is detected on the first secondary winding 214, the first secondary winding 214 does not supply power to the light source 208. Therefore, the secondary side controller 204 may pause or stop generating the driving signal S DRV, to reduce power consumption.

[0038] In one embodiment, the adjustment terminal EN_PWM is configured to receive an adjustment signal APWM, wherein the adjustment signal APWM is used to indicate the target level of the current flowing through the light source 208 (e.g., including I 1 , I 2 , ……, I N ). When the voltages on the monitoring terminals ISEN1, ISEN2, ……, ISENN indicate that the light source 208 is in the above normal power state, the secondary side controller 204 adjusts the current of the light source 208 (e.g., including I 1 , I 2 , ……, I N ) to the target level. More specifically, as described above, when the voltages on the monitoring terminals ISEN1, ISEN2, ……, ISENN are equal to or approximately equal to the above reference level V REF , it indicates that the light source 208 is in the normal power state and the received electrical power is sufficient. Therefore, the secondary side controller 204 can adjust the currents I 1 , I 2 , ……, I N of the light emitting diode strings S1, S2, ……, SN to the target level.

[0039] Figure 3 Shown is a circuit schematic diagram of the secondary side controller 204 according to an embodiment of the present invention. The following will be described in conjunction with Figure 2A and Figure 2B for Figure 3 . As Figure 3 shown, the secondary side controller 204 may include a selector 332, an error amplifier 334, a ramp signal generator 336, a comparison circuit 338, a converter 330, and an adjustment circuit 348. The secondary side controller 204 may also include a group of transistors Q 1 , Q 2 , ……, Q N (e.g., metal oxide semiconductor field effect transistors) and a group of sense resistors R S1 , R S2 , ……, R SN .

[0040] As described above for Figure 2B , the negative terminals T NGT1 , T NGT2 , ……, T NGTN of the light emitting diode strings S1, S2, ……, SN are respectively coupled to the monitoring terminals ISEN1, ISEN2, ……, ISENN. In one embodiment, each negative terminal T NGT1 , T NGT2 , ……, TNGTN through corresponding transistors Q 1 , Q 2 , ……, Q N and corresponding sense resistors R S1 , R S2 , ……, R SN coupled to the reference ground GND. For example, the negative terminal T of the light-emitting diode string S1 NGT1 is coupled to the reference ground GND through transistor Q 1 and resistor R S1 . The voltage V across the two ends of resistor R S1 can represent the current I flowing through the light-emitting diode string S1 RS1 (e.g., in a linear proportional relationship with the current I 1 ). Similarly, the negative terminal T of the light-emitting diode string S2 1 is coupled to the reference ground GND through transistor Q2 and resistor R NGT2 . The voltage V across the two ends of resistor R S2 can represent the current I flowing through the light-emitting diode string S2 S2 (e.g., in a linear proportional relationship with the current I RS2 ). Therefore, the voltages V 2 , V 2 , ……, V S1 , R S2 , ……, R SN across R RS1 , V RS2 , ……, V RSN (not shown in Figure 3 ) can respectively represent the currents I 1 , I 2 , ……, I N flowing through the light-emitting diode strings S1, S2, ……, SN.

[0041] In one embodiment, the converter 330 includes a PWM duty cycle to analog dimming converter, which can be abbreviated as: PWM to ADIM converter. More specifically, the converter 330 can receive an adjustment signal APWM through the adjustment terminal EN_PWM. The adjustment signal APWM can include a PWM signal. The converter 330 can convert the duty cycle of the PWM signal APWM into an adjustment voltage V Figure 3 through a circuit (e.g., including an integrator, not shown in ADJ ). For example, if the duty cycle of the signal APWM increases, the adjustment voltage V ADJ can increase; if the duty cycle of the signal APWM decreases, the adjustment voltage V ADJIt can be reduced. The duty cycle of the PWM signal (e.g., signal APWM) described herein represents the ratio of the time the PWM signal is in the logic high state within one cycle to that cycle.

[0042] In one embodiment, the adjustment circuit 348 can apply the adjustment voltage V 1 、Q 2 、……、Q N to the resistors R ADJ 、R S1 、……、R S2 、……、R SN by controlling the transistors Q 1 、I 2 、……、I N such that the currents I Figure 3 flowing through the LED strings S1, S2, ……, SN are adjusted to the target level. More specifically, as Figure 3 shown, the adjustment circuit 348 can include operational amplifiers BF1, BF2, ……, BFN (also referred to as: buffers BF1, BF2, ……, BFN). The operational amplifier BF1 compares the adjustment voltage V ADJ with the voltage V S1 of the resistor R RS1 and controls the transistor Q 1 based on the comparison result. In this way, the voltage V S1 of the resistor R RS1 can be clamped at the level of the adjustment voltage V ADJ . In other words, the operational amplifier BF1 can apply the adjustment voltage V ADJ to the resistor R S1 . Similarly, the operational amplifiers BF2, BF3, ……, BFN can apply the adjustment voltage V ADJ to the resistors R S2 、R S3 、……、R SN . In one embodiment, the resistors R S1 、R S2 、……、R SN are configured to have the same resistance value R S . Therefore, when the adjustment voltage V ADJ is applied to the resistors R S1 、R S2 、……、R SN , the currents I 1 、I 2 、……、I N flowing through the LED strings S1, S2, ……, SN can be configured to have the same current level V ADJ / R S . In one embodiment, the above-mentioned current I1 , I 2 , ……, I N The target levels of ADJ / R S include the current level V 1 , I 2 , ……, I N to be substantially equal.

[0043] In one embodiment, although the currents I 1 , I 2 , ……, I N are configured to have the same current level (e.g., V ADJ / R S ), in actual situations, there may be differences between the currents I 1 , I 2 , ……, I N due to the non-ideality of circuit elements such as the resistors R S1 , R S2 , ……, R SN , operational amplifiers BF1, BF2, ……, BFN, etc. However, as long as the differences are relatively small and negligible, such differences are allowed.

[0044] In one embodiment, the transistors Q 1 , Q 2 , ……, Q N can also be configured to have the same characteristics (e.g., the same material, the same aspect ratio, etc.). The light-emitting diode strings S1, S2, ……, SN can also be configured to have the same number of light-emitting diodes and the same type of light-emitting diodes. Therefore, if the currents I 1 , I 2 , ……, I N flow through the light-emitting diode strings S1, S2, ……, SN at substantially the same current level, then the voltages V NGT1 , V NGT2 , ……, V NGTN at the negative terminals T ISEN1 , V ISEN2 , ……, V ISENN of the light-emitting diode strings S1, S2, ……, SN can also be substantially the same. Therefore, one voltage can be selected from the voltages V ISEN1 , V ISEN2 , ……, V ISENN to represent all the voltages V ISEN1 , V ISEN2 , ……, V ISENN。The selected voltage can also indicate the state of the light source 208. In one embodiment, the selector 332 can select the minimum voltage minV ISEN1 from voltages V ISEN2 , V ISENN , …, and V ISEN , and output a signal minISEN indicating the minimum voltage minV ISEN . For example, the selector 332 can transfer the minimum voltage minV ISEN from its input terminal to its output terminal, so the signal minISEN is the minimum voltage minV ISEN . As another example, the selector 332 can receive the minimum voltage minV ISEN and generate a signal minISEN that is linearly proportional to the minimum voltage minV ISEN . Thus, the selector 332 can output a signal minISEN indicating the state of the light source 208.

[0045] In one embodiment, the error amplifier 334 can compare the signal minISEN with a reference signal DRreg and generate a compensation signal V CPS based on the difference between the signal minISEN and the reference signal DRreg. For example, if the signal minISEN is greater than the reference signal DRreg, the compensation signal V CPS can increase, or if the signal minISEN is less than the reference signal DRreg, the compensation signal V CPS can decrease. The ramp signal generator 336 is coupled to the SYNC terminal and can be enabled by the positive polarity detected on the SYNC terminal. When the ramp signal generator 336 is enabled, the ramp signal generator 336 can generate a ramp signal V RAMP . By way of example, the ramp signal generator 336 can include a High-frequency Oscillator (HFOSC) that generates a series of ramp voltages V RAMP at a preset frequency. The comparison circuit 338 can compare the compensation signal V CPS with the ramp signal V RAMP to generate a drive signal S DRV .

[0046] Taking Figure 3 as an example, the comparison circuit 338 can include a comparator 340 and an inverting driver 342. The positive input terminal of the comparator 340 receives the compensation signal V CPS , and its negative input terminal receives the ramp signal V RAMP . Thus, the comparison result signal S CPRmay include a PWM signal whose duty cycle increases when the signal minISEN is less than the reference signal DRreg, or decreases when the signal minISEN is greater than the reference signal DRreg. The inverting driver 342 receives the comparison result signal S CPR and generates a drive signal S CPR that is inverted with respect to the comparison result signal S DRV . As described above, in one embodiment, the switch circuit 228 may be turned on by the falling edge of the drive signal S DRV and turned off by the rising edge of the drive signal S DRV . Thus, the switch circuit 228 may be turned on by the rising edge of the comparison result signal S CPR and turned off by the falling edge of the comparison result signal S CPR . In other words, if the duty cycle of the comparison result signal S CPR increases, the duty cycle of the switch circuit 228 may increase, or if the duty cycle of the comparison result signal S CPR decreases, the duty cycle of the switch circuit 228 may decrease. Therefore, if the signal minISEN is less than the reference signal DRreg, the duty cycle of the comparison result signal S CPR will increase, thereby increasing the signal minISEN. If the signal minISEN is greater than the reference signal DRreg, the duty cycle of the comparison result signal S CPR will decrease, thereby decreasing the signal minISEN. As a result, the signal minISEN can be adjusted to the level of the reference signal DRreg. In one embodiment, the above reference level V REF may include the reference signal DRreg or may be indicated by the reference signal DRreg. Thus, the voltages V ISEN1 , V ISEN2 , ……, V ISENN can be adjusted to the reference level V REF , and the light source 208 can be controlled to be in the normal power state.

[0047] Although Figure 3 the illustrated comparison circuit 338 includes a comparator 340 and an inverting driver 342, the present invention is not limited thereto. In other embodiments, the comparison circuit 338 may include other circuit configurations. By way of example, the comparison circuit 338 may include a comparator and a driver (a non-inverting driver) not shown in Figure 3 . In this example, the positive input terminal of the comparator receives a ramp signal V RAMP , and its negative input terminal receives a compensation signal V CPS . The driver receives the comparison result of the comparator and generates a drive signal S DRV accordingly. In this example, the drive signal S DRVThe switch circuit 228 can also be controlled such that the voltages V ISEN1 、V ISEN2 、……、V ISENN are adjusted to the reference level V REF , thereby controlling the light source 208 to be in the normal power state.

[0048] Figure 4 Shown are the waveforms of the signals DRreg, minISEN, V RAMP 、V CPS 、S CPR and S DRV related to the secondary side controller 204 according to an embodiment of the present invention, as well as the state diagram of the switch circuit 228 based on the states of these signals. The following will be described in conjunction with Figure 2A 、 Figure 2B and Figure 3 for Figure 4 .

[0049] As Figure 4 shown, during the time period from t0 to t1, the signal minISEN is less than the reference signal DRreg (for example: indicating that the minimum voltage of the voltages V ISEN1 、V ISEN2 、……、V ISENN on the monitoring terminals ISEN1, ISEN2,..., ISENN is less than the reference level V REF ). Therefore, the compensation signal V CPS output by the error amplifier 334 increases. When the compensation signal V CPS is greater than the ramp signal V RAMP , the comparison result signal S CPR can be in the logic high state, and the drive signal S DRV can be in the logic low state. When the compensation signal V CPS is less than the ramp signal V RAMP , the comparison result signal S CPR can be in the logic low state, and the drive signal S DRV can be in the logic high state. The switch circuit 228 can be turned on by the falling edge 446 of the drive signal S DRV or the rising edge 444 of the comparison result signal S CPR . The switch circuit 228 can also be turned off by the rising edge of the drive signal S DRV or the falling edge of the comparison result signal S CPR . During the time period from t0 to t1, the compensation signal V CPS increases, so the duty cycle of the comparison result signal S CPR increases, resulting in an increase in the duty cycle of the switch circuit 228. Therefore, the signal minISEN increases.

[0050] During the time period from t1 to t2, the signal minISEN is adjusted to the level of the reference signal DRreg (e.g., representing voltages V ISEN1 , V ISEN2 , ……, V ISENN equal to or slightly greater than the reference level V REF ). The compensation signal V CPS can be at a relatively stable level, and the duty cycle of the switching circuit 228 can be relatively stable (e.g., substantially unchanged).

[0051] During the time period from t2 to t3, the signal minISEN is greater than the reference signal DRreg (e.g., representing that the minimum voltage of the voltages V ISEN1 , V ISEN2 , ……, V ISENN on the monitoring terminals ISEN1, ISEN2, …, ISENN is greater than the reference level V REF ). Therefore, the compensation signal V CPS output by the error amplifier 334 decreases, causing the duty cycle of the comparison result signal S CPR to decrease. As a result, the duty cycle of the switching circuit 228 decreases, causing the signal minISEN to decrease.

[0052] Therefore, the signal minISEN can be adjusted to the level of the reference signal DRreg. That is to say, the voltages V ISEN1 , V ISEN2 , ……, V ISENN on the monitoring terminals ISEN1, ISEN2, ……, ISENN can be adjusted to be equal to or slightly greater than the reference level V REF . In this way, the light source 208 can be maintained in a normal power state to receive sufficient power, so that the light emitted by the light source 208 can reach the target brightness.

[0053] Figure 5 Shown is a schematic diagram of the operation process of the light source driving system 200 according to an embodiment of the present invention. The following will be described in conjunction with Figure 2A , Figure 2B , Figure 3 and Figure 4 for Figure 5 . Those skilled in the art can understand that Figure 5 the specific steps covered are only examples. That is to say, the present invention is applicable to other reasonable processes or steps for improving Figure 5 .

[0054] In step 502, the primary side controller 202 controls the power P transmitted from the primary winding 212 of the transformer 210 to the first secondary winding 214 and the second secondary winding 216 of the transformer 210 according to the load of the system circuit 206210 Among them, the system circuit 206 is powered by the second secondary winding 216.

[0055] In step 504, the secondary side controller 204 supplies a part P208 of the power P210 from the first secondary winding 214 to the light source 208 by turning on the switch circuit 228 connected to the first secondary winding 214 and the light source 208.

[0056] In step 506, the secondary side controller 204 monitors the state of the light source 208. For example, the monitoring methods include: monitoring the negative terminals T NGT1 、T NGT2 、... and T NGTN of the light emitting diode strings S1, S2,... and SN ISEN1 、V ISEN2 、……、V ISENN .

[0057] In step 508, the secondary side controller 204 controls the switch circuit 228 according to the state of the light source 208, so that the light source 208 remains in the normal power state.

[0058] Therefore, in one embodiment, regardless of whether the system circuit 206 is in a light load, a normal load or a heavy load, the light source 208 can receive sufficient power to support the light emitting diode strings to emit light at a target brightness level. In addition, the light source driving system 200 can eliminate the DC / DC converter 118 in the existing light source driving system 100, thereby reducing the cost of the light source driving system 200 and reducing the size of the printed circuit board.

[0059] The terms and expressions used herein are for illustrative purposes and not restrictive. Using these terms and expressions does not exclude any equivalents (or partial equivalents) of the features illustrated and described herein from the scope of the utility model. Various modifications may exist within the scope of the claims, and other modifications, variations and substitutions may also exist. Therefore, the claims are intended to cover all such equivalents.

Claims

1. A light source driving system, comprising: a primary-side controller configured to control power transmitted from a primary winding of a transformer to a first secondary winding and a second secondary winding of the transformer according to a load of a system circuit powered by the second secondary winding; a switch circuit connected to the first secondary winding, configured so that when the switch circuit is turned on, the switch circuit causes the first secondary winding to provide a portion of the power to a light source connected to the first secondary winding; as well as A secondary-side controller connected to the switch circuit and the primary-side controller is configured to monitor a state of the light source and control the switch circuit according to the state.

2. The light source driving system according to claim 1, characterized in that: The secondary side controller comprises: A driving end configured to provide a driving signal to control the switch circuit; and A synchronization end is configured to detect the electrical polarity at the output end of the second secondary winding, wherein when the secondary side controller detects the positive polarity at the synchronization end, the secondary side controller generates the drive signal according to the state of the light source, and when the secondary side controller does not detect the positive polarity at the synchronization end, the secondary side controller suspends generating the drive signal.

3. The light source driving system according to claim 2, characterized in that: The secondary side controller further comprises: an error amplifier configured to generate a compensation signal based on a difference between a reference signal and a signal indicative of the state of the light source; a ramp signal generator connected to the synchronization terminal, configured to be enabled by the positive polarity detected on the synchronization terminal, wherein when the ramp signal generator is enabled, the ramp signal generator generates a ramp signal; and A comparison circuit connected to the error amplifier and the ramp signal generator is configured to compare the compensation signal with the ramp signal to generate the driving signal.

4. The light source driving system according to claim 1, characterized in that: If the load increases, the primary-side controller increases the power, and if the load decreases, the primary-side controller decreases the power.

5. The light source driving system according to claim 1, characterized in that: The secondary side controller comprises: a monitoring terminal configured to monitor the state of the light source; and The regulating end is configured to receive a regulating signal indicating a target level of current flowing through the light source, wherein when the state indicates that the light source is in a normal power state, the secondary side controller regulates the current to the target level.

6. The light source driving system according to claim 5, characterized in that: The secondary side controller is configured to control the switching circuit to maintain the light source in the normal power state, wherein if the voltage on the monitoring terminal is less than a reference level, the secondary side controller increases the duty cycle of the switching circuit, and if the voltage on the monitoring terminal is greater than the reference level, the secondary side controller reduces the duty cycle of the switching circuit.

7. The light source driving system according to claim 5, characterized in that: The light source includes a light-emitting diode string, which includes at least one light-emitting diode, wherein the positive terminal of the light-emitting diode string is configured to receive the portion of the power, and the negative terminal of the light-emitting diode string is coupled to a reference ground through a transistor and a resistor, and is further characterized in that the monitoring terminal is configured to monitor the state of the light source by sensing the voltage on the negative terminal.

8. The light source driving system according to claim 7, characterized in that: The regulating signal comprises a pulse width modulation signal, and the secondary side controller further comprises: a converter configured to convert the duty cycle of the pulse width modulation signal into a regulated voltage; and A regulating circuit connected to the converter is configured to control the transistor so as to apply the regulating voltage to the resistor so that the current flowing through the LED string is regulated to the target level.

9. A light source controller, comprising: A monitoring terminal configured to monitor a state of a light source, wherein the light source is powered by a first secondary winding of a transformer, and the light source controller is powered by a second secondary winding of the transformer, wherein the transformer comprises a primary winding, the first secondary winding, and the second secondary winding; a driving end configured to provide a driving signal to control a switch circuit connected to the first secondary winding, wherein when the driving signal turns on the switch circuit, the first secondary winding provides a portion of the power transmitted from the primary winding of the transformer to the first secondary winding and the second secondary winding to the light source; a synchronization terminal configured to detect an electrical polarity at an output terminal of the second secondary winding; and A control circuit connected to the monitoring end, the driving end and the synchronization end, wherein when the control circuit detects positive polarity at the synchronization end, the control circuit generates the driving signal according to the state of the light source, and when the control circuit does not detect the positive polarity at the synchronization end, the control circuit suspends generating the driving signal.

10. The light source controller according to claim 9, characterized in that: The control circuit comprises: an error amplifier configured to generate a compensation signal based on a difference between a reference signal and a signal indicative of the state of the light source; a ramp signal generator connected to the synchronization terminal, configured to be enabled by the positive polarity, wherein when the ramp signal generator is enabled, the ramp signal generator generates a ramp signal; and A comparison circuit connected to the error amplifier and the ramp signal generator is configured to compare the compensation signal with the ramp signal to generate the driving signal.

11. The light source controller according to claim 9, characterized in that: The light source controller further comprises: The regulating end is configured to receive a regulating signal indicating a target level of current flowing through the light source, wherein when the state indicates that the light source is in a normal power state, the control circuit regulates the current to the target level.

12. The light source controller according to claim 11, characterized in that: The control circuit is configured to control the switching circuit to maintain the light source in the normal power state, wherein if the voltage on the monitoring terminal is less than a reference level, the control circuit increases the duty cycle of the switching circuit, and if the voltage is greater than the reference level, the control circuit reduces the duty cycle of the switching circuit.

13. The light source controller according to claim 11, characterized in that: The monitoring terminal is configured to monitor the state of the light source by sensing the voltage on the negative terminal of the light emitting diode string in the light source, wherein The negative terminal is coupled to a reference ground through a transistor and a resistor.

14. The light source controller according to claim 13, characterized in that: The regulating signal comprises a pulse width modulation signal, and the control circuit further comprises: a converter configured to convert the duty cycle of the pulse width modulation signal into a regulated voltage; and A regulating circuit connected to the converter is configured to control the transistor so as to apply the regulating voltage to the resistor so that the current flowing through the LED string is regulated to the target level.

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