An LED driver low-temperature startup device

Abstract

The present invention relates to a low-temperature startup device for an LED driver, which includes a power supply VCC, a control optocoupler, a current-limiting resistor, an operational amplifier, and an output current control circuit of an LED controller. One end of the control optocoupler is connected to the power supply VCC through the current-limiting resistor, the other end of the control optocoupler is connected to the output end of the operational amplifier, and the input end of the operational amplifier is connected to the output current control circuit of the LED controller; when the LED driver starts up, the output current control circuit of the LED controller controls the operational amplifier to reduce the output current of the LED driver, so that the LED driver operates at a low power. After reaching the set time, the output current control circuit of the LED controller controls the operational amplifier to normally output the output current of the LED driver, so that the LED driver operates at the set normal power. Compared with the prior art, the present invention has the advantages of small volume, low price, and strong operability.

Description

Technical Field

[0001] The present invention relates to an LED driver starting device, and more particularly to a device for starting an LED driver at low temperatures. Background Art

[0002] For applications in extremely cold regions, it is often necessary for an LED driver to start up and operate at -60 °C, such as in Russia. This poses a great challenge to the LED driver. For example, for the electrolytic capacitors used in the LED driver, since the electrolytic solution of the electrolytic capacitor almost freezes at low temperatures, the capacitance of the electrolytic capacitor drops sharply, and at the same time, the internal resistance increases. Generally, the role of the electrolytic capacitor in the circuit is filtering and energy storage. The decrease in capacitance and the increase in internal resistance are fatal to the function of the electrolytic capacitor. Eventually, the LED driver cannot start well at low temperatures, manifested as large output ripple or protective restart, etc. The common solution is to use capacitors with a larger capacitance and select more special low-temperature capacitors. First, the cost of the electrolytic capacitor is proportional to its capacitance. A higher capacitance means a higher cost. Second, the lowest temperature that the low-temperature electrolytic capacitor can withstand is -40 °C, and it is more difficult to start at lower temperatures. Therefore, at lower temperatures, only expensive thin-film capacitors can be selected, and the cost is even more expensive. Summary of the Invention

[0003] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide an LED driver low-temperature starting device with a small volume, low price, and strong operability.

[0004] The purpose of the present invention can be achieved through the following technical solutions:

[0005] An LED driver low-temperature starting device includes a power supply VCC, a control optocoupler for achieving constant current, a current-limiting resistor, an operational amplifier, and an LED controller output current control circuit. One end of the control optocoupler is connected to the power supply VCC through the current-limiting resistor, the other end of the control optocoupler is connected to the output end of the operational amplifier, and the input end of the operational amplifier is connected to the LED controller output current control circuit;

[0006] When the LED driver starts, the LED controller output current control circuit controls the operational amplifier to reduce the output current of the LED driver, so that the LED driver operates at a low power. After reaching the set time, the LED controller output current control circuit controls the operational amplifier to normally output the output current of the LED driver, so that the LED driver operates at the set normal power.

[0007] Preferably, the output current control circuit of the LED controller includes a triode Q1, resistors R1, R2, R3, R4, R5, R6, and a capacitor C1. One end of the base of the triode Q1 is connected to one end of the resistor R1, one end of the resistor R2, and one end of the capacitor C1. The other end of the resistor R1 is connected to the power supply VCC. The emitter of the triode Q1 is connected to one end of the resistor R3. The other end of the resistor R3 is connected between the resistors R4 and R5. The resistors R4, R5, and R6 are connected in series in sequence. The positive input terminal of the operational amplifier is connected between the resistors R5 and R6. The negative input terminal of the operational amplifier is the output current detection terminal of the LED driver. The other end of the resistor R2, the other end of the capacitor C1, the collector of the triode Q1, and the other end of the resistor R6 are respectively grounded.

[0008] Preferably, the resistor R1 is an NTC thermistor.

[0009] Preferably, how much the rated current of the LED driver is reduced is adjusted by the resistor R3.

[0010] Preferably, the output current control circuit of the LED controller includes a triode Q2, resistors R11, R12, R13, R14, R15, and a capacitor C2. One end of the base of the triode Q2 is connected to one end of the resistor R14, one end of the resistor R15, and one end of the capacitor C2. The emitter of the triode Q2 is connected to one end of the resistor R13. The other end of the resistor R13 and the other end of the resistor R14 are respectively connected to the power supply VCC. The collector of the triode Q2 is respectively connected to the negative input terminal of the operational amplifier and one end of the resistor R12. The other end of the resistor R12 is respectively connected to the output current detection terminal of the LED driver and one end of the resistor R11. The other end of the resistor R11, the other end of the resistor R15, and the other end of the capacitor C2 are respectively grounded.

[0011] Preferably, the resistor R14 is an NTC thermistor.

[0012] Preferably, the reduction amplitude of the output power of the LED driver depends on the ratio of R13 to R12.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] 1) Small volume, only ordinary electrolytic capacitors are needed, and the volume is smaller compared with thin film capacitors.

[0015] 2) Inexpensive, the electrolytic capacitors, crystal triodes, and optocouplers used in the present invention are all relatively inexpensive devices.

[0016] 3) Without affecting normal use, when LED lights using an LED driver are applied under low-temperature conditions, they are basically outdoors. In the present invention, the starting instantaneous power and brightness of the LED driver low-temperature starting device are slightly lower than normal, but it does not affect normal use because it is not completely dark when starting. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the specific implementation circuit of Embodiment 1 of the present invention;

[0018] Figure 2 It is the specific implementation circuit of Embodiment 2 of the present invention; DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] The biggest bottleneck for low-temperature startup is the electrolytic capacitor, and the selection of the capacitance value of the electrolytic capacitor basically depends on the output power of the LED driver. That is to say, a large power requires a large electrolytic capacitor capacity, and a small power requires a relatively small electrolytic capacitor capacity. At the same time, the internal impedance of the electrolytic capacitor decreases rapidly as the temperature of the capacitor rises, and the capacitance rises rapidly at the same time. At low temperatures, when the electrolytic capacitor is loaded in the LED driver, this internal impedance is equivalent to being connected in series in the high-frequency circuit. As long as the temperature of the electrolytic capacitor rises rapidly after the power supply starts, the internal impedance of the electrolytic capacitor will be reduced, which is a virtuous cycle. Therefore, as long as the LED driver is allowed to operate at a reduced power for a period of time under low-temperature conditions, the electrolytic capacitor can quickly reach the performance at normal temperature, thus meeting the normal working requirements. Starting from the above idea, in the present invention, when the LED driver starts, the output power is relatively low, and after a period of time, the output power rises to the set normal power. In this way, the low power at startup allows the required electrolytic capacitor capacity to be relatively low, and the large internal impedance has limited influence. After working for a period of time, the performance of the electrolytic capacitor returns to the normal value as its temperature rises, and the output of the LED driver also rises to the normal power, thus solving the startup problem.

[0021] Embodiment 1

[0022] Such as Figure 1As shown in the figure, an LED driver low-temperature startup device includes a power supply VCC, a control optocoupler for achieving constant current, a current-limiting resistor, an operational amplifier, and an LED controller output current control circuit. One end of the control optocoupler is connected to the power supply VCC through the current-limiting resistor, the other end of the control optocoupler is connected to the output end of the operational amplifier, and the input end of the operational amplifier is connected to the LED controller output current control circuit;

[0023] The LED controller output current control circuit includes a triode Q1, resistors R1, R2, R3, R4, R5, R6, and a capacitor C1. The base of the triode Q1 is respectively connected to one end of the resistor R1, one end of the resistor R2, and one end of the capacitor C1. The other end of the resistor R1 is connected to the power supply VCC. The emitter of the triode Q1 is connected to one end of the resistor R3. The other end of the resistor R3 is connected between the resistors R4 and R5. The resistors R4, R5, and R6 are connected in series in sequence. The positive input terminal of the operational amplifier is connected between the resistors R5 and R6. The negative input terminal of the operational amplifier is the output current detection terminal of the LED driver; the other end of the resistor R2, the other end of the capacitor C1, the collector of the triode Q1, and the other end of the resistor R6 are respectively grounded.

[0024] The + input terminal of the operational amplifier U1A is the constant current reference setting value of the driver. This setting value is obtained by dividing the reference voltage Vref through R4, R5, and R6. The — input terminal of U1A is the output current detection terminal of the driver. When the LED driver starts up, VCC divides the voltage through R1 and R2 to charge C1. At startup, the b-stage voltage of Q1 is very low, so Q1 is in the saturation conduction state. R3 is in parallel with R5 and R6, so that the constant current setting value of the driver will decrease, and the output current of the driver will decrease, achieving the original intention of reducing the power operation of the driver. The amount of reduction in the rated current depends on the resistance value of R3. As time goes by, the capacitor C1 will be gradually filled, Q1 will change from saturation conduction to the amplification region, and finally enter the cut-off region, and R3 is completely disconnected, and the output current of the driver returns to the original setting value. This scheme makes the output current reference follow the voltage on C1 and slowly and smoothly rise, so that the output current of the LED driver will also rise gradually and smoothly. Intuitively, the output brightness of the LED lamp will slowly become brighter, without flickering and step changes.

[0025] If the function of reducing power during startup is not required at room temperature, the circuit can be optimized by replacing R1 with an NTC thermistor. At low temperature, the resistance value of R1 is very large, and the time constant of R1C1 is very large, and the power reduction time during startup is very long. At room temperature, R1 is very small, so the power reduction time is very short.

[0026] Embodiment 2

[0027] AsFigure 2 As shown in the figure, an LED driver low-temperature startup device includes a power supply VCC, a control optocoupler for achieving constant current, a current-limiting resistor, an operational amplifier, and an LED controller output current control circuit. One end of the control optocoupler is connected to the power supply VCC through the current-limiting resistor, the other end of the control optocoupler is connected to the output end of the operational amplifier, and the input end of the operational amplifier is connected to the LED controller output current control circuit;

[0028] The LED controller output current control circuit includes a triode Q2, resistors R11, R12, R13, R14, R15, and a capacitor C2. The base of the triode Q2 is respectively connected to one end of the resistor R14, one end of the resistor R15, and one end of the capacitor C2. The emitter of the triode Q2 is connected to one end of the resistor R13. The other end of the resistor R13 and the other end of the resistor R14 are respectively connected to the power supply VCC. The collector of the triode Q2 is respectively connected to the negative input end of the operational amplifier and one end of the resistor R12. The other end of the resistor R12 is respectively connected to the output current detection end of the LED driver and one end of the resistor R11. The other end of the resistor R11, the other end of the resistor R15, and the other end of the capacitor C2 are respectively grounded.

[0029] The operational amplifier U2A controls the input voltage of its inverting input terminal (-) to be equal to its non-inverting (+) Iref voltage through the current of the control optocoupler. VCC divides the voltage through R13 and R12, and this voltage is superimposed on the voltage drop of the output current of the LED driver on R11. The sum of these two parts of the voltage is equal to the output current setting reference of the LED driver. By controlling the conduction state of Q2, the output current is controlled, and finally the purpose of controlling the power is achieved.

[0030] VCC divides the voltage through R14 and R15, and charges C2 through R14. The voltage of C2 rises slowly. When just powered on, the voltage of C2 is almost zero, and Q2 is in a saturated conduction state. As the voltage of C2 rises, the conduction state of Q2 changes from saturated conduction, amplification to finally cut-off. In this way, the output power of the LED driver starts to be lower, and the reduced amplitude depends on the ratio of R13 and R12. Finally, when Q2 is cut off, the power output of the driver returns to normal.

[0031] If the function of not starting and reducing power at normal temperature is not considered, similar to Embodiment 1, replacing R14 with an NTC thermistor can achieve the purpose of not reducing power in a normal temperature environment.

[0032] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. An LED driver low-temperature startup device, characterized in that, It includes a power supply VCC, a control optocoupler for achieving constant current, a current-limiting resistor, an operational amplifier, and an output current control circuit of an LED controller. One end of the control optocoupler is connected to the power supply VCC through the current-limiting resistor, the other end of the control optocoupler is connected to the output end of the operational amplifier, and the input end of the operational amplifier is connected to the output current control circuit of the LED controller; When the LED driver starts, the output current control circuit of the LED controller controls the operational amplifier to reduce the output current of the LED driver, so that the LED driver operates at low power. After reaching the set time, the output current control circuit of the LED controller controls the operational amplifier to normally output the output current of the LED driver, so that the LED driver operates at the set normal power; The output current control circuit of the LED controller includes a triode Q1, resistors R1, R2, R3, R4, R5, R6, and a capacitor C1. The base of the triode Q1 is respectively connected to one end of the resistor R1, one end of the resistor R2, and one end of the capacitor C1. The other end of the resistor R1 is connected to the power supply VCC. The emitter of the triode Q1 is connected to one end of the resistor R3. The other end of the resistor R3 is connected between the resistors R4 and R5. The resistors R4, R5, and R6 are connected in series in sequence. The positive input end of the operational amplifier is connected between the resistors R5 and R6. The negative input end of the operational amplifier is the output current detection end of the LED driver; The other end of the resistor R2, the other end of the capacitor C1, the collector of the triode Q1, and the other end of the resistor R6 are respectively grounded; The resistor R1 is an NTC thermistor; When the LED driver starts, the power supply VCC charges the capacitor C1 through the voltage division of the resistors R1 and R2. At startup, the b-stage voltage of the triode Q1 is very low, and the triode Q1 is in a saturated conduction state. The resistor R3 is in parallel with R5 and R6. In this way, the constant current setting value of the driver will decrease, and the output current of the driver will decrease, achieving low-power operation of the driver; As time goes by, the capacitor C1 will be gradually filled, the triode Q1 will change from saturated conduction to the amplification region, and finally enter the cut-off region, and the resistor R3 will be completely disconnected, and the output current of the driver will return to the original set value.

2. The low-temperature startup device of an LED driver according to claim 1, characterized in that, How much the rated current of the LED driver is reduced is adjusted by the resistor R3.

3. The low-temperature startup device of an LED driver according to claim 1, wherein The LED controller output current control circuit described above includes a triode Q2, a resistor R11, a resistor R12, a resistor R13, a resistor R14, a resistor R15, and a capacitor C2. The base of the triode Q2 is connected to one end of the resistor R14, one end of the resistor R15, and one end of the capacitor C2 respectively. The emitter of the triode Q2 is connected to one end of the resistor R13. The other end of the resistor R13 and the other end of the resistor R14 are connected to the power supply VCC respectively. The collector of the triode Q2 is connected to the negative input terminal of the operational amplifier and one end of the resistor R12 respectively. The other end of the resistor R12 is connected to the output current detection terminal of the LED driver and one end of the resistor R11 respectively. The other end of the resistor R11, the other end of the resistor R15, and the other end of the capacitor C2 are grounded respectively.

4. The low-temperature startup device of an LED driver according to claim 3, characterized in that, The resistor R14 is an NTC thermistor.

5. The low-temperature startup device of an LED driver according to claim 3, characterized in that, The reduction amplitude of the output power of the LED driver depends on the ratio of R13 to R12.

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