JP2011228584A - Led driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED driving device capable of protecting LEDs even if an LED unit is short-circuited.SOLUTION: An LED driving device includes: power supply means 10 that outputs an alternating current; a first LED group that has a plurality of series-connected LEDs 1a-1e and is connected to an output side of a rectifying smoothing circuit that has first rectifying elements D1, D11 and first smoothing elements C1, C11 and is connected to an output of the power supply means 10; and short-circuit detection part D4, Tr, R1 that detects short circuit in the first LED group by being activated when voltage at an input side of the rectifying smoothing circuit becomes larger than voltage at an output side of the rectifying smoothing circuit.

Description

  The present invention relates to an LED driving device that drives a plurality of LEDs connected in series.

  Conventionally, for example, Patent Document 1 is known as an LED driving device that lights a plurality of LEDs (Light Emitting Diodes) connected in series.

 As shown in FIG. 8, Patent Document 1 discloses an LED lamp device that can quickly suppress overcurrent and protect an LED when a short circuit occurs in an LED assembly.

 In FIG. 8, the resistor 130 detects the energization current of the LED unit 110 through the transistor 140. A power supply 142 having a voltage Vref2 corresponding to an overcurrent determination value is connected to the non-inverting terminal of the operational amplifier 141. When a short circuit occurs in some LEDs of the LED unit 110, the current increases and an increased voltage is generated across the resistor 130.

 When the voltage across the resistor 130 becomes equal to or higher than the voltage Vref2 corresponding to the overcurrent determination value, the output of the operational amplifier 141 decreases, and the decreased output is output to the base of the transistor 140. For this reason, the current flowing between the collector and the emitter of the transistor 140 is limited, and the overcurrent flowing in the LED unit 110 is suppressed.

JP 2007-188692 A

  However, in the LED lamp device disclosed in Patent Document 1, an operational amplifier 141 for detecting a short circuit of the LED is provided, and the LED lamp device is expensive. In addition, each LED unit 110 must be provided with an operational amplifier 141 for detecting a short circuit and a transistor 140 for suppressing overcurrent, which has become more expensive as the number of LED units 110 increases.

  The subject of this invention is providing the cheap LED drive device which can suppress overcurrent rapidly and can protect LED, when a short circuit generate | occur | produces in an LED unit.

 In order to solve the above-described problems, an LED drive device according to the present invention is an LED drive device that rectifies and smoothes an alternating current and supplies the alternating current to the LED, and includes a resonance-type power supply unit that outputs the alternating current, and the power A first rectifying / smoothing circuit connected to the output of the supply means and having a first rectifying element and a first smoothing element; a first rectifying / smoothing circuit connected to the output side of the first rectifying / smoothing circuit; and a plurality of LEDs connected in series. 1 LED group and a short-circuit detecting unit that detects a short circuit of the first LED group by operating when the voltage on the input side of the first rectifying and smoothing circuit becomes larger than the voltage on the output side of the first rectifying and smoothing circuit It is characterized by having.

  According to the present invention, when a short circuit of the load occurs, that is, when the voltage on the input side of the first rectifying / smoothing circuit becomes larger than the voltage on the output side of the first rectifying / smoothing circuit, the short-circuit detecting unit operates. Thus, a short circuit of the first LED group is detected. Therefore, when a short circuit failure occurs in the LED unit, it is possible to quickly suppress an overcurrent, protect the LED, and provide an LED driving device that is inexpensive.

It is a block diagram of the LED drive device of Example 1 of this invention. It is a block diagram of the LED drive device of Example 2 of this invention. It is a block diagram of the LED drive device of Example 3 of this invention. It is a block diagram of the LED drive device of Example 4 of this invention. It is a figure which shows transition of the voltage at the time of the power supply starting in the point A and the point B of the LED drive device of Example 4. FIG. It is the block diagram which employ | adopted the half-wave rectifier circuit in the secondary side of the trans | transformer of the LED drive device of each Example. It is the block diagram which employ | adopted the full wave rectifier circuit in the secondary side of the trans | transformer of the LED drive device of each Example. It is a figure which shows the specific example of the conventional LED drive device.

  Hereinafter, an LED drive device according to an embodiment of the present invention will be described in detail with reference to the drawings. The present invention employs a voltage doubler rectification method for the LED drive section and does not use the conventional short-circuit detection operational amplifier 141 shown in FIG.

  FIG. 1 is a configuration diagram of an LED driving apparatus according to Embodiment 1 of the present invention. In the power supply means 10, in order to supply a sinusoidal alternating current, a series circuit of a switching element QH made of a MOSFET and a switching element QL made of a MOSFET is connected to both ends of the DC power supply Vin.

  A series resonance circuit of a primary winding Np of the transformer T and a current resonance capacitor Cri is connected to a connection point between the switching element QH and the switching element QL. The transformer T has a leakage inductance Lr1. Lp is the exciting inductance of the transformer T. By alternately turning on and off the switching element QL and the switching element QH, a sinusoidal alternating current resonated by the leakage inductance Lr1 and the current resonance capacitor Cri or Lr1, Lp and Cri is supplied from the winding Ns of the transformer T. it can.

 One end of the secondary winding Ns is connected to the anode of the diode D3 and one end of the capacitor C11, and the cathode of the diode D3 is connected to the other end of the secondary winding Ns via the capacitor C3. The other end of the capacitor C11 is connected to the anode of a diode D1 that half-wave rectifies the alternating current and the cathode of the diode D11. A capacitor C1 is connected between the cathode of the diode D1 and the other end of the secondary winding Ns, and a load LD1 (LED1a to LED1e) is connected in parallel to one end of the capacitor C1. The anode of the diode D11 is connected to the other end of the secondary winding Ns and the other ends of the capacitors C1 and C3. Capacitors C1 and C11 and diodes D1 and D11 constitute a half-wave double voltage rectification circuit and a first rectification smoothing circuit.

 A series circuit of a diode D4 and a resistor R1 is connected between a connection point A between the diode D3 and the capacitor C3 and a connection point B between the diode D1 and the capacitor C1. One end of the resistor R1 is connected to the emitter of the transistor Tr, and the other end of the resistor R1 is connected to the base of the transistor Tr. A cutoff circuit 3 is connected to the collector of the transistor. The cutoff circuit 3 detects that the diode D4 is turned on when the load LD1 is short-circuited and the transistor Tr is turned on, and stops the operation of the entire power supply circuit.

 The diodes D3 and D4, the capacitor C3, the resistor R1, and the transistor Tr constitute a short-circuit detection unit, and the short-circuit detection unit and the cutoff circuit 3 constitute a protection circuit when a load is short-circuited.

 Also, one end of the resistor Rs and one end of the input terminal of the PFM circuit 1 are connected to the load LD1, and the other end of the resistor Rs and the other end of the input terminal of the PFM circuit 1 are grounded. The resistor Rs collectively detects the current flowing through the load LD1 and outputs a current detection value to the PFM circuit 1. The PFM circuit 1 compares the current detection value with the internal reference voltage, and controls the on / off frequency of the switching element QH and the switching element QL based on the error output so that the current flowing through the load is constant.

 Next, the operation of the LED driving device according to the present invention will be described. First, the operation during normal operation will be described. When the load LD1 is operating normally without being short-circuited, a voltage that is ½ of the point B is applied to the point A shown in FIG. For this reason, the diode D4 does not conduct.

 Next, when the load LD1 is short-circuited, the potential at the point B becomes substantially equal to the ground potential (zero potential). For this reason, since the potential at the point A becomes higher than the potential at the point B, the diode D4 becomes conductive, and a current flows through the resistor R1. For this reason, the transistor Tr is turned on, and a current flows between the emitter and collector of the transistor Tr. The cutoff circuit 3 operates when the transistor Tr is turned on, and stops the operation of the entire power supply circuit of the LED driving device.

 Thus, according to the LED driving device of Example 1, the load LD1 is driven by the voltage rectified by the voltage doubler rectification method, so that the potential at the point A is lower than the potential at the point B during normal operation. When the load LD1 is short-circuited, the potential at the point A becomes higher than the potential at the point B. Therefore, the short-circuit detection unit operates to detect a short-circuit of the load LD1, and the cutoff circuit 3 stops the operation of the entire power supply circuit. For this reason, the operational amplifier 141 for detecting a short circuit becomes unnecessary. Therefore, it is possible to provide an inexpensive LED driving device that can quickly suppress overcurrent and protect the LED when a short circuit failure occurs in the load LD1.

 FIG. 2 is a configuration diagram of an LED drive device according to a second embodiment of the present invention. The LED drive device of Example 2 shown in FIG. 2 is provided with one LED unit and one rectifying / smoothing circuit corresponding to the LED unit in addition to the configuration shown in FIG.

 That is, one end of the capacitor C12 is connected to one end of the secondary winding Ns, and the anode of the diode D2 for half-wave rectifying the alternating current and the cathode of the diode D12 are connected to the other end of the capacitor C12. A capacitor C2 is connected between the cathode of the diode D2 and the other end of the secondary winding Ns, and a load LD2 (LED2a to LED2e) is connected in parallel to one end of the capacitor C2. The anode of the diode D12 is connected to the other end of the secondary winding Ns and the other end of the capacitor C2. Capacitors C2 and C12 and diodes D2 and D12 constitute a half-wave double voltage rectifier circuit and a second rectifier smoothing circuit.

 A series circuit of a diode D5 and a resistor R1 is connected between a connection point A between the diode D3 and the capacitor C3 and a connection point C between the diode D2 and the capacitor C2. A transistor Tr is connected to the resistor R1. The cutoff circuit 3 detects that when at least one of the loads LD1 and LD2 is short-circuited, at least one of the diodes D4 and D5 corresponding to the short-circuited load is turned on and the transistor Tr is turned on, and the power supply of the LED driving device The operation of the entire circuit can be stopped.

 Thus, according to the LED drive device of Example 2, it operates similarly to the LED drive device of Example 1, and the same effect is obtained. Further, even if the load LD2 increases, the short-circuit detection unit only increases the number of diodes D5 and does not need to increase the number of transistors Tr and the like, so that the cost can be reduced.

 FIG. 3 is a configuration diagram of an LED drive device according to Embodiment 3 of the present invention. The LED drive device of Embodiment 3 shown in FIG. 3 is characterized in that a balance transformer T1 is further provided in the configuration of the LED drive device of Embodiment 2 shown in FIG. One end of the secondary winding Ns is connected to one end of the winding N1 of the transformer T1, and the other end of the winding N1 is connected to one end of the capacitor C11. One end of the secondary winding Ns is connected to one end of the winding S1 of the transformer T1, and the other end of the winding S1 is connected to one end of the capacitor C12.

 According to the above configuration, the primary winding N1 and the secondary winding S1 of the transformer T1 are magnetically coupled so that the currents flowing through them are balanced, so that the same current is supplied to the capacitors C1 and C2. Is charged. Accordingly, a balanced current flows through the load LD1 connected to the capacitor C1 and the load LD2 connected to the capacitor C2 even when the impedances are different. That is, it is possible to suppress variations in the current flowing through the loads LD1 and LD2.

 FIG. 4 is a configuration diagram of an LED drive device according to a fourth embodiment of the present invention. First, in order to reduce the cost of the LED driving device, it is desirable to reduce the capacitance of the capacitor C3. However, when the capacitance of the capacitor C3 is small, the time constant between the capacitor C3 and the resistor (not shown) is small, so that the rising of the voltage is higher at the point A than at the point B in FIG. There is a possibility that the operation will stop due to the protection circuit for load short-circuiting when the power is turned on.

 Therefore, the LED driving device of Example 4 shown in FIG. 4 is characterized in that a resistor R2 is provided between the cathode of the diode D3 and the point A. The resistor R2 increases the time constant between the resistor R2 and the capacitor C3, and the impedance on the protection circuit side increases. For this reason, the rising of the potential at the point A indicated by the dotted line in FIG. 5 is slower than the rising of the potential at the point B indicated by the solid line. As a result, it is possible to prevent the protection circuit for load short-circuiting from operating when the power supply is activated.

Here, when the resistor R2 is added, the impedance Zuv on the protection circuit side at the time of power activation is
Zuv = R2 + {(Ro / jωC3) / (Ro + 1 / jωC3)}
It is represented by Although not shown, Ro is a resistor connected in parallel to the capacitor C3.

On the other hand, the impedance Zled on the LED drive side is Zled = (1 / jωC1) + (1 / jωC11)
It is represented by

 In order to make the rise of the potential at the point A slower than the point B, a resistor R2 that satisfies Zuv> Zled may be added. For example, when the operating frequency is 100 kHz, C1 = C11 = 10 μF, C3 = 1 μF, and Ro = 1 MΩ, normal operation is achieved by adding a resistance of about 1Ω or more as R2.

 In the LED driving device of the fourth embodiment, the resistor R2 is provided between the cathode of the diode D3 and the point A. However, instead of providing the resistor R2, a constant current circuit may be provided.

 In the LED driving devices of Examples 1 to 4, the primary side of the transformer T is a resonance type power supply device, but the present invention is not limited to this, and is applicable to a flyback type, a forward type, an active clamp type, and the like. Is possible.

 Thus, as shown in FIG. 1, the LED driving device of the present invention has an input side of the rectifying / smoothing circuits C1, C11, D1, D11 for supplying a direct current to the loads LD1, LD2 (a cathode side of the diode D3). The point LD of the diode D3 may be the anode side of the diode D3) and the potential of the output side (point B) of the rectifying / smoothing circuits C1, C11, D1, and D11 (point B). Detects a short circuit. When a load short circuit occurs, the potential at point A is output via a delay circuit or hold circuit so that the potential at point A is higher than the potential at point B.

 In the LED driving circuits of Examples 1 to 4, the voltage doubler rectifier circuit is used on the secondary side of the transformer T. However, as shown in FIG. 6, the present invention provides a half-wave rectification on the secondary side of the transformer T2. A circuit may be used. In the configuration shown in FIG. 6, the secondary side of the transformer T2 is connected to the first series circuit of the secondary winding 1a having the same number of turns n1 and the secondary winding 1b. A series circuit of a diode D1 which is a wave rectifier circuit and a capacitor C1 is connected. A series circuit of a diode D3, a resistor R2, and a capacitor C3 is connected to both ends of the secondary winding 1b. By comparing the potential at the connection point A between the resistor R2 and the capacitor C3 with the potential at the connection point B between the diode D1 and the capacitor C1, a short circuit between the loads LD1 and LD2 is detected.

 Further, as shown in FIG. 7, a full-wave rectifier circuit may be used on the secondary side of the transformer T3. In the configuration shown in FIG. 7, on the secondary side of the transformer T3, a secondary winding 2a having 2 × n1 turns and a secondary winding 2b having a turn number n1 are provided, and all ends of the secondary winding 2a are provided at both ends. Diodes D11 to D14 constituting a wave rectifier circuit are connected, and a capacitor C1 is connected to both ends of the full wave rectifier circuit, and a load LD1 is connected. A series circuit of a diode D3, a resistor R2, and a capacitor C3 is connected to both ends of the secondary winding 2g. A short circuit of the load LD1 is detected by comparing the potential of the connection point A between the resistor R2 and the capacitor C3 with the potential of the capacitor C1.

 Also, instead of directly detecting the potential at point A, if the voltage is divided by, for example, a first resistor and a second resistor connected in series, and the divided voltage is detected, the detection level of the load short circuit can be set. Can be adjusted.

 Further, in the present invention, the resistor R2 in the LED driving device of the fourth embodiment may be provided in the LED driving device of the second embodiment, and the effects of the second and fourth embodiments are obtained. Further, the resistor R2 in the LED drive device of the fourth embodiment may be provided in the LED drive device of the third embodiment, and the effects of the second and third embodiments are obtained.

  The present invention is applicable to LED lighting devices and LED lighting for lighting LEDs.

DESCRIPTION OF SYMBOLS 1 PFM circuit 3 Cutoff circuit 10 Power supply means Vin DC power supply QL, QH Switching element D1, D2, D3, D4, D5, D11, D12, DL, DH Diode Cri Current resonance capacitor C1, C2, C3, C11, C12 Capacitor R1, R2 Resistance Tr Transistors T, T1, T2, T3 Transformers Np, N1 Primary winding Ns, S1 Secondary winding Lp Excitation inductance Lr1 Leakage inductance LD1, LD2 Load

Claims (5)

An LED driving device that rectifies and smoothes an alternating current and supplies the alternating current to the LED,
Resonance-type power supply means for outputting the alternating current;
A first rectifying / smoothing circuit connected to the output of the power supply means and having a first rectifying element and a first smoothing element;
A first LED group connected to the output side of the first rectifying and smoothing circuit and having a plurality of LEDs connected in series;
A short-circuit detector for detecting a short circuit of the first LED group by operating when a voltage on an input side of the first rectifying and smoothing circuit is larger than a voltage on an output side of the first rectifying and smoothing circuit;
An LED driving device comprising:   The short-circuit detection unit is provided between an input side of the first rectifying / smoothing circuit and an output side of the first rectifying / smoothing circuit, and includes a first diode and a transistor connected in series. The LED driving device according to claim 1.   The LED driving device according to claim 2, further comprising a cutoff circuit that stops the operation of the LED driving device when a current flows through the transistor. A second rectifying / smoothing circuit connected to the output of the power supply means and having a second rectifying element and a second smoothing element;
A second LED group connected to the output side of the second rectifying / smoothing circuit and having a plurality of LEDs connected in series;
A transformer having a first winding connected between the power supply means and the first rectifying and smoothing circuit, and a second winding connected between the power supply means and the second rectifying and smoothing circuit; Have
The second diode and the transistor are connected in series between the input side of the second rectifying and smoothing circuit and the output side of the second rectifying and smoothing circuit. 3. The LED driving device according to 3.   A third rectifying element, a resistor and a third smoothing element are connected in series to both ends of each rectifying and smoothing circuit, and a connection point between the resistor and the third smoothing element is connected to one end of the short-circuit detecting unit. The LED driving device according to claim 2, wherein the LED driving device is connected.

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