JP2015070108A - Light source drive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow for operation of a light source stable with respect to environment, with a simple circuit.SOLUTION: A light source drive device 1 comprises: parallel connection of a light source 20 and a smoothing capacitor C1; a transformer T1 comprising a first coil L1 and a second coil L2 magnetically coupled with each other; a first switching element Q1 for opening/closing connection between the first coil L1 and light source 20; a diode D1 for regenerating energy stored in the first coil L1; a feedback circuit 2 for feeding back positive voltage induced in the second coil L2 to a control terminal of the first switching element Q1; a current detection resistor Rs for detecting current flowing in the first coil L1 as a voltage value; and a switch circuit 3 for making an ON temperature characteristic uniform by turning OFF the first switching element Q1 when the detected voltage value is higher than a predetermined value and turning ON the first switching element Q1 when the detected voltage value is equal to or lower than the predetermined value.

Description

  The present invention relates to a light source driving device that controls lighting of a light source.

  In recent years, LED lighting fixtures using LEDs (Light Emitting Diodes) as light sources instead of conventional incandescent bulbs and fluorescent lamps have begun to spread. This is because the LED has a long lifetime and low power consumption, does not use environmental pollutants like mercury in fluorescent lamps, and has impact resistance and high-speed response. This LED lighting apparatus includes a plurality of LED light emitting elements, and emits light by applying a DC voltage to each LED light emitting element and flowing a predetermined constant current. As described above, the LED lighting apparatus requires an LED drive circuit for supplying a predetermined constant current to each LED light emitting element.

  The problem of Patent Document 1 is that “the control IC is not used, it is suitable for cost reduction, and it is possible to drive the LED stably and efficiently while adapting to an unstabilized DC input power source with large voltage fluctuation. A self-excited LED driving circuit is provided. "The solution means" an oscillation transformer T1 having a first coil L1 and a second coil L2 magnetically coupled to each other, and an oscillation circuit formed by the oscillation transformer The LED 21 is connected to the LED 21 by the first transistor Q1, the second transistor Q2 interposed in parallel with the control signal input circuit of the first transistor Q1, and the current detection resistor R2 interposed in series between the first transistor and the common ground line. Is controlled to a constant current.

JP 2011-1000083 A

  In the technique described in Patent Document 1, a change in the voltage between the base and the emitter of the second transistor is large with respect to a change in temperature. As a result, the current flowing through the LED may change due to temperature fluctuations. That is, in the technique described in Patent Document 1, the light source may not stably operate with respect to the environment.

  Accordingly, an object of the present invention is to provide a light source driving device that enables a stable light source operation with respect to the environment while being a simple circuit.

In order to solve the above-described problems, a light source driving device of the present invention includes a direct current power source, a light source that is connected to the direct current power source and emits light according to a flowing current, a smoothing capacitor that is connected in parallel to the light source, A transformer that includes a first coil and a second coil that are magnetically coupled, and that is excited by a current supplied from the DC power source, and a first switching that switches whether or not a current flows through the first coil. An element, a diode that regenerates energy stored in the first coil when the first switching element is off, and a positive voltage induced in the second coil. A feedback circuit that feeds back to the control terminal, a current detection resistor that detects a current flowing through the first coil as a voltage value, and the voltage value detected by the current detection resistor exceeds a predetermined value Off the mule said first switching element comprises a switching circuit to equalize the temperature characteristics on.
Other means will be described in the embodiment for carrying out the invention.

  ADVANTAGE OF THE INVENTION According to this invention, although it is a simple circuit, the light source drive device which enables the operation | movement of the light source stable with respect to an environment can be provided.

It is a block diagram which shows the circuit structure of the light source drive device in 1st Embodiment. It is a block diagram which shows the circuit structure of the light source drive device in the 1st application example of 1st Embodiment. It is a time chart explaining the slow start operation | movement of the light source drive device in the 1st application example of 1st Embodiment. It is a block diagram which shows the circuit structure of the light source drive device in the 2nd application example of 1st Embodiment. It is a block diagram which shows the circuit structure of the light source drive device in the 3rd application example of 1st Embodiment. It is a block diagram which shows the circuit structure of the light source drive device in 2nd Embodiment. It is a block diagram which shows the circuit structure of the light source drive device in the 1st application example of 2nd Embodiment. It is a block diagram which shows the circuit structure of the light source drive device in the 2nd application example of 2nd Embodiment. It is a block diagram which shows the circuit structure of the light source drive device in the 3rd application example of 2nd Embodiment. It is a block diagram which shows the circuit structure of the light source drive device in 3rd Embodiment. It is a block diagram which shows the circuit structure of the light source drive device in 4th Embodiment.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
(Basic configuration of the first embodiment)
FIG. 1 is a block diagram illustrating a configuration of a light source driving device 1 according to the first embodiment.
As shown in FIG. 1, the light source driving device 1 includes a DC power source Vdc, an electrolytic capacitor C0, a light source 20, a smoothing capacitor C1 connected in parallel to the light source 20, and a first coil magnetically coupled to each other. A transformer T1 including L1 and a second coil L2, a first switching element Q1, a diode D1, and a current detection resistor Rs are included. The first coil L1 and the second coil L2 are wound in opposite directions. The light source driving device 1 further includes a feedback circuit 2, a Zener diode ZD 1, and a switch circuit 3. The light source driving device 1 is a buck converter system and generates an average output voltage lower than the input voltage.

Electrolytic capacitor C0 is connected between the positive electrode and the negative electrode of DC power supply Vdc. The electrolytic capacitor C0 reduces the switching noise of the DC power supply Vdc and stabilizes the voltage.
The light source 20 and the smoothing capacitor C1 are connected in parallel, one end of which is connected to the positive electrode of the DC power supply Vdc, and the other end is connected to the first coil L1 of the transformer T1. The light source 20 is an LED that is connected to the positive electrode of the DC power supply Vdc and emits light when a predetermined constant current is passed in the direction of the first coil L1 from the positive electrode side of the DC power supply Vdc. The smoothing capacitor C1 smoothes the voltage across the light source 20.

The transformer T1 is excited by the current supplied from the DC power source Vdc to the first coil L1. One end of the first coil L1 is connected to the other end of the parallel connection of the light source 20 and the smoothing capacitor C1, and the other end is connected to the drain of the first switching element Q1.
The first switching element Q1 is, for example, an FET (Field Effect Transistor), the source is connected to the ground via the current detection resistor Rs, and the gate (control terminal) is connected to one end of the second coil L2 of the transformer T1. Is done. The first switching element Q1 switches whether or not to pass a current through the first coil L1 of the transformer T1. The current detection resistor Rs detects the current flowing through the light source 20 and the first coil L1 as a voltage value.
The diode D1 is forward-connected in the direction from the connection node between the first coil L1 of the transformer T1 and the drain of the first switching element Q1 to the positive electrode of the DC power supply Vdc. The diode D1 flows a regenerative current that regenerates energy accumulated in the first coil L1 of the transformer T1 when the first switching element Q1 is off.

The feedback circuit 2 includes a bias setting circuit in which a resistance element R1 and a capacitor C2 are connected in series, and a second coil L2 of the transformer T1. The feedback circuit 2 is configured so that the first switching element Q1 is turned on and the current flows from the DC power source Vdc through the path of the light source 20, the first coil L1, the first switching element Q1, and the current detection resistor Rs. The positive voltage induced in the second coil L2 is fed back to the gate (control terminal) of the first switching element Q1, and the ON operation of the first switching element Q1 is continued.
A bias setting circuit, which is a series connection of the resistor element R1 and the capacitor C2, is connected between the positive electrode and the negative electrode of the DC power supply Vdc. The other end of the second coil L2 is connected to a connection node between the resistor element R1 and the capacitor C2 constituting the bias setting circuit, and further, the cathode of the Zener diode ZD1 is connected.
The Zener diode ZD1 is connected between the other end of the second coil L2 and the ground. The Zener diode ZD1 clamps the gate voltage of the first switching element Q1 so as not to exceed the gate-source voltage when the DC power supply Vdc is turned off. In a normal operation state, no current flows through the Zener diode ZD1. When the power supply voltage is lower than the gate source voltage, the Zener diode ZD1 is not necessary.

  One end of the second coil L2 is connected to the gate (control terminal) of the first switching element Q1 and the switch circuit 3. Thus, a positive feedback loop that causes self-excited oscillation is formed by the first switching element Q1 and the first coil L1.

  The switch circuit 3 includes a reference voltage generation circuit 4 and a comparator 5. The switch circuit 3 turns off the first switching element Q1 when the voltage value detected by the current detection resistor Rs exceeds a predetermined value determined by the reference voltage generation circuit 4.

The reference voltage generation circuit 4 generates the reference voltage Vref based on the voltage supplied from the voltage source Vcc. The voltage source Vcc is configured as a power supply circuit in the light source driving device 1 or an external voltage source, and the configuration of the supply source is not particularly limited.
The comparator 5 has an inverting input terminal connected to the current detection resistor Rs, a non-inverting input terminal connected to the reference voltage generation circuit 4, and an output terminal connected to the gate (control terminal) of the first switching element Q1. The comparator 5 generates a comparison signal that compares the reference voltage Vref output from the reference voltage generation circuit 4 with the voltage value based on the current detected by the current detection resistor Rs. The comparator 5 outputs this comparison signal to the gate (control terminal) of the first switching element Q1, and controls the ON operation of the first switching element Q1. Therefore, the light source driving device 1 can flow a stable predetermined constant current that is not affected by the ambient temperature to the light source 20.

By using the comparator 5, when the voltage detected by the current detection resistor Rs exceeds the reference voltage Vref, a comparison signal for quickly setting the gate voltage of the first switching element Q1 to the Low level is output. Therefore, the light source driving device 1 can obtain good line regulation (regulation of output current with respect to input voltage).
That is, the switch circuit 3 can stably turn on the first switching element Q1 with respect to the environment (temperature, voltage fluctuation, etc.) by the comparator 5 having good response and the reference voltage generation circuit 4. it can. Thereby, the light source driving device 1 can flow a predetermined constant current that is stable against the environment resistance to the light source 20.

  The comparator 5 may be a Darlington connection in which a PNP transistor for current amplification is added on the output side. Thus, when the first switching element Q1 is turned off, the energy accumulated in the second coil L2 is released, and a sink current for maintaining the control terminal of the first switching element Q1 at the low level is further increased. Can be bigger. In other words, the comparator 5 can stably control the off operation of the first switching element Q1 by increasing the discharge capability of the energy accumulated in the second coil L2 of the transformer T1.

Hereinafter, the operation of the light source driving device 1 will be described. When the DC power supply Vdc is turned on, the light source driving device 1 starts operation.
In the initial state of operation, the bias voltage is applied to the gate (control terminal) of the first switching element Q1 by the bias setting circuit via the resistance element R1 and the second coil L2. At this time, since no current flows through the light source 20, the first coil L1 of the transformer T1, and the current detection resistor Rs, the voltage at the inverting input terminal of the comparator 5 is equal to or lower than the reference voltage Vref. As a result, the first switching element Q1 is turned on, and an on-current flows through the light source 20 and the first coil L1.

  The on-current that flows through the light source 20 and the first coil L1 of the transformer T1 flows through the current detection resistor Rs via the drain and source of the first switching element Q1. Due to the current flowing through the first coil L1, a positive voltage is generated in the second coil L2 of the transformer T1. This positive voltage is fed back to the gate (control terminal) of the first switching element Q1. As a result, the first switching element Q1 is kept on. A voltage corresponding to the on-current is generated in the current detection resistor Rs.

  The comparator 5 of the switch circuit 3 compares the voltage detected by the current detection resistor Rs with the reference voltage Vref of the reference voltage generation circuit 4. When the voltage detected by the current detection resistor Rs exceeds the reference voltage Vref, the comparator 5 sets the gate of the first switching element Q1 to the low level. Thereby, the first switching element Q1 is turned off. When the first switching element Q1 is turned off, the regenerative current of the first coil L1 of the transformer T1 flows to the light source 20 via the diode D1.

  While the regenerative current of the first coil L1 of the transformer T1 flows through the light source 20, a negative voltage is generated in the second coil L2 of the transformer T1. This negative voltage is fed back to the gate (control terminal) of the first switching element Q1, and the first switching element Q1 remains off.

When the regenerative current of the first coil L1 of the transformer T1 becomes zero, the negative voltage generated in the second coil L2 of the transformer T1 decreases to zero. Thereby, the starting voltage by the bias setting circuit is applied to the gate (control terminal) of the first switching element Q1, and the first switching element Q1 is turned on again.
By repeating ON / OFF of the first switching element Q1 as described above, the light source driving device 1 can cause a predetermined constant current to flow through the light source 20 and perform a self-resonant (oscillation) operation. The light source driving device 1 is a resonance type (critical operation) driving circuit, and when the regenerative current of the first coil L1 of the transformer T1 becomes zero, the first switching element Q1 is turned on from off.

  The light source driving device 1 of the first embodiment can realize a resonance current self-oscillation type driving device of a zero current switch with a circuit configuration with few parts. Here, the zero current switch is to turn on the first switching element Q1 with the zero current of the transformer T1. Therefore, the light source driving device 1 can obtain high efficiency by reducing the switching loss of the first switching element Q1. As a result, the light source driving device 1 does not require a heat sink for heat dissipation, and the cost can be reduced and the circuit can be downsized.

(First application example of the first embodiment)
FIG. 2 is a block diagram showing a circuit configuration of the light source driving device 1a in the first application example.
As shown in FIG. 2, the light source driving device 1a of the first application example is different from the light source driving device 1 having the basic configuration in that a slow start circuit including a differentiation circuit 6 and a dimming setting circuit 7 is provided. It has been added. This slow start circuit gradually increases the amount of light from the light source 20 by gradually increasing the current flowing through the light source 20 when the DC power source Vdc of the light source driving device 1a is turned on. Thereby, it is possible to prevent a sudden change in the amount of light of the light source 20 and prevent human beings from being dazzled.

  The differentiation circuit 6 is a series circuit of a capacitor C3 and a resistance element R2, and is connected between the positive electrode and the negative electrode of the DC power supply Vdc. One end of the capacitor C3 is connected to the positive electrode of the DC power supply Vdc, and the other end of the capacitor C3 is connected to the negative electrode of the DC power supply Vdc via the resistance element R2. A connection node between the other end of the capacitor C3 and the resistance element R2 is connected to a dimming setting circuit 7 described later. The differentiating circuit 6 outputs a differentiated voltage Va obtained by differentiating the input voltage applied by the DC power supply Vdc.

  The dimming setting circuit 7 includes resistance elements R3 and R4. The resistor element R4 is connected between the current detection resistor Rs and the inverting input terminal of the comparator 5. The resistance element R3 is connected between the other end of the capacitor C3 of the differentiation circuit 6 and the inverting input terminal of the comparator 5. The dimming setting circuit 7 superimposes the differential voltage Va output from the differentiation circuit 6 on the voltage detected by the current detection resistor Rs.

3A to 3E are time charts illustrating a slow start operation of the light source driving device 1a in the first application example of the first embodiment. The horizontal axis of each figure shows the common time, and the reference numerals in FIG. 2 are referred to as appropriate.
FIG. 3A is a time chart of the input voltage Vi (power supply voltage) applied by the DC power supply Vdc. FIG. 3B is a time chart of the differential voltage Va output from the differentiating circuit 6. FIG. 3C is a time chart of the dimming voltage Vb applied to the inverting input terminal of the comparator 5.
FIG. 3D is a time chart of the output current Io flowing through the light source 20.
FIG. 3E is a partially enlarged view of part A of the time chart of the dimming voltage Vb shown in FIG.

At time t0, the DC power supply Vdc is turned on, and the input voltage Vi shown in FIG. 3A is applied to each part of the light source driving device 1a. At this time, the start-up voltage is applied to the gate (control terminal) of the first switching element Q1 by the series connection of the resistor element R1 and the capacitor C2, which is a bias setting circuit, so that the first switching element Q1 can be turned on. It becomes a state.
The differential voltage Va is applied as a dimming voltage Vb to the inverting input terminal of the comparator 5 via the resistance elements R3 and R4 of the dimming setting circuit 7.
The differential voltage Va shown in FIG. 3B is a voltage generated at the connection node between the capacitor C3 and the resistance element R2, and immediately after the DC power supply Vdc is turned on, it becomes equal to the applied voltage of the DC power supply Vdc. Gradually descend. The differential voltage Va is output from the differentiating circuit 6 and applied as a dimming voltage Vb to the inverting input terminal of the comparator 5 through the resistance element R3 of the dimming setting circuit 7.
In the dimming voltage Vb shown in FIG. 3C, the differential voltage Va output from the differentiation circuit 6 and the voltage detected by the current detection resistor Rs are superimposed. From time t0 to time t1, the dimming voltage Vb is higher than the reference voltage Vref.
After time t1, when the dimming voltage Vb becomes lower than the reference voltage Vref, the output voltage of the comparator 5 becomes a high level, and the first switching element Q1 starts to turn on. As the differential voltage Va decreases, the contribution of the detection voltage of the current detection resistor Rs increases. As a result, the output current Io gradually increases as shown in FIG.
FIG.3 (e) is an enlarged view of the A section of FIG.3 (c). When the dimming voltage Vb becomes lower than the reference voltage Vref, a triangular wave having a peak at the reference voltage Vref is generated by turning on and off the first switching element Q1. The dimming voltage Vb gradually decreases, the amplitude of the triangular wave gradually increases, and the magnitude of the output current Io shown in FIG. 3D gradually increases.
With the above operation, the slow start can be activated when the input voltage Vi is applied.
Thus, since the light source drive device 1a of the first application example can realize a slow start with a small number of components, a fade-in lighting function in the lighting device can be realized at low cost.

(Second application example of the first embodiment)
FIG. 4 is a block diagram showing a circuit configuration of the light source driving device 1b in the second application example.
As shown in FIG. 4, the light source driving device 1 b of the second application example further includes a dimming setting circuit 7 with respect to the light source driving device 1 of the basic configuration.
The dimming setting circuit 7 includes resistance elements R3 and R4. The resistor element R4 is connected between the current detection resistor Rs and the inverting input terminal of the comparator 5. The resistance element R3 is connected between the inverting input terminal of the comparator 5 and the input terminal of the DC dimming signal Sdc. The dimming setting circuit 7 performs DC dimming control of the light source 20 in accordance with the DC dimming signal Sdc by superimposing a DC dimming signal Sdc input from the outside on the voltage detected by the current detection resistor Rs. is there.
In the second application example, the current detection resistor Rs is grounded. Therefore, DC dimming is possible with an inexpensive configuration.

(Third application example of the first embodiment)
FIG. 5 is a block diagram showing a circuit configuration of the light source driving device 1c in the third application example.
As shown in FIG. 5, the light source drive device 1c of the third application example further includes a second switching element Q2 with respect to the light source drive device 1 having the basic configuration.
The second switching element Q2 is, for example, an NPN transistor, the emitter is connected to the ground, the collector is connected to the connection node between the output terminal of the comparator 5 and the gate of the first switching element Q1, and the signal Sp is applied to the base. Have been entered. The second switching element Q2 controls PWM (Pulse Width Modulation) dimming or on / off operation of the light source 20 according to a signal Sp input from the outside.
For example, when the signal Sp input from the outside is a PWM signal, the light source 20 can be dimmed and controlled according to the duty of the PWM signal. Further, when the signal Sp is an on / off signal (low level / high level signal), the light source 20 can be controlled to be turned on / off.
Since the light source driving device 1c is a low-side switch type, PWM dimming or on / off control can be performed with an inexpensive circuit configuration.

(Basic configuration of the second embodiment)
FIG. 6 is a block diagram illustrating a configuration of the light source driving device 1d according to the second embodiment.
As shown in FIG. 6, the light source driving device 1d of the second embodiment is different from the light source driving device 1 of the first embodiment in the configuration of the switch circuit 3a.
The switch circuit 3a of the second embodiment includes two switching elements Q3 and Q4 that are Darlington-connected and a thermistor TH. The switching element Q3 is, for example, an NPN transistor. The switching element Q4 is, for example, a PNP transistor.
The base of the switching element Q3 is connected to the current detection resistor Rs and further connected to the ground via the thermistor TH. That is, the base of the switching element Q3 is connected to one end of the parallel connection of the current detection resistor Rs and the thermistor TH.

The thermistor TH is an NTC (negative temperature coefficient) thermistor whose resistance decreases with increasing temperature. The thermistor TH is connected in parallel with the current detection resistor Rs. The parallel connection of the current detection resistor Rs and the thermistor TH reduces its own impedance when the environmental temperature rises.
The base-emitter voltage of the switching element Q3 has a temperature characteristic of about −2 [mV / ° C.]. The parallel connection of the current detection resistor Rs and the thermistor TH reduces its own impedance as the base-emitter voltage decreases as the environmental temperature increases. In other words, the thermistor TH compensates for the temperature characteristic of the switching element Q3, and makes the on-temperature characteristic of the switch circuit 3a uniform.
Thereby, the switch circuit 3a can control stably the electric current which flows into the light source 20 without being influenced by ambient temperature. Thus, since the light source driving device 1d includes the switch circuit 3a having a good temperature characteristic, the light amount of the light source 20 can be stably controlled with respect to the environment.

The emitter of the switching element Q3 is grounded. The collector of the switching element Q3 is connected to the base of the switching element Q4. The collector of the switching element Q4 is grounded, and the emitter of the switching element Q4 is connected to the gate (control terminal) of the first switching element Q1. Thereby, switching elements Q3 and Q4 can have a large current amplification factor hfe.
In this way, by using the switch circuit 3a of the Darlington circuit having a large current amplification factor hfe, when the first switching element Q1 is turned off, the energy accumulated in the second coil L2 is released and the first switching is performed. The sink current for maintaining the control terminal of the element Q1 at the low level can be sufficiently increased. In other words, since the ability to discharge the energy stored in the second coil L2 of the transformer T1 is high, the off operation of the first switching element Q1 can be stably controlled.

Hereinafter, the operation of the light source driving device 1d will be described. When the DC power supply Vdc is turned on, the light source driving device 1d starts operation.
In the initial state of operation, the bias voltage is applied to the gate (control terminal) of the first switching element Q1 by the bias setting circuit via the resistance element R1 and the second coil L2. At this time, since no current flows through the light source 20 and the current detection resistor Rs, the voltage applied to the base (control terminal) of the switching element Q3 of the switch circuit 3a is the base-emitter voltage (for example, 0.6 V). Is less than. Accordingly, the Darlington-connected switching elements Q3 and Q4 are turned off. That is, the switch circuit 3a is turned off. As a result, the first switching element Q1 is turned on, and an on-current flows through the light source 20.

  The on-current that flows through the light source 20 flows from the first coil L1 of the transformer T1 to the current detection resistor Rs via the drain and source of the first switching element Q1. Due to the current flowing in the first coil L1 of the transformer T1, a positive voltage is generated in the second coil L2 of the transformer T1. This positive voltage is fed back to the gate (control terminal) of the first switching element Q1. As a result, the first switching element Q1 is kept on. A voltage corresponding to the on-current is generated in the current detection resistor Rs.

The switching element Q3 of the switch circuit 3a is turned on when the voltage detected by the current detection resistor Rs exceeds the base-emitter voltage, and the switching element Q4 is also turned on. As a result, the switch circuit 3a is turned on to set the gate (control terminal) of the first switching element Q1 to the Low level. Thereby, the first switching element Q1 is turned off.
When the first switching element Q1 is turned off, the regenerative current of the first coil L1 of the transformer T1 flows to the light source 20 via the diode D1.

  While the regenerative current of the first coil L1 of the transformer T1 flows through the light source 20, a negative voltage is generated in the second coil L2 of the transformer T1. This negative voltage is fed back to the gate (control terminal) of the first switching element Q1, and the first switching element Q1 remains off.

When the regenerative current of the first coil L1 of the transformer T1 becomes zero, the negative feedback voltage of the second coil L2 of the transformer T1 decreases to zero. As a result, the bias setting circuit applies a starting voltage to the gate (control terminal) of the first switching element Q1 via the resistance element R1 and the second coil L2, and the first switching element Q1 is turned on.
By repeating the on / off of the first switching element Q1 as described above, the light source driving device 1d can cause a predetermined constant current to flow through the light source 20 and perform a self-resonant (oscillation) operation.

Similarly to the first embodiment, the light source drive device 1d of the second embodiment is a resonance type (critical operation) drive circuit, and when the regenerative current on the first coil L1 side of the transformer T1 becomes zero, The first switching element Q1 is turned on from off.
In addition, it has the same effect as the first embodiment.

(Each application example of the second embodiment)
FIG. 7 is a block diagram showing a circuit configuration of the light source driving device 1e in the first application example of the second embodiment.
As shown in FIG. 7, the light source driving device 1e of the first application example of the second embodiment is similar to the light source driving device 1a (see FIG. 2) of the first application example of the first embodiment. A slow start circuit including a dimming setting circuit 7 is provided, and the same effect as that of the first application example of the first embodiment is obtained.

FIG. 8 is a block diagram showing a circuit configuration of the light source driving device 1f in the second application example of the second embodiment.
As shown in FIG. 8, the light source driving device 1f of the second application example of the second embodiment is similar to the light source driving device 1b (see FIG. 4) of the second application example of the first embodiment. 7 and has the same effect as the second application example of the first embodiment.

FIG. 9 is a block diagram showing a circuit configuration of the light source driving device 1g in the third application example of the second embodiment.
As shown in FIG. 9, the light source driving device 1g of the third application example of the second embodiment is similar to the light source driving device 1c (see FIG. 5) of the third application example of the first embodiment. The element Q2 is provided and has the same effect as the third application example of the first embodiment.

(Basic configuration of the third embodiment)
FIG. 10 is a block diagram illustrating a configuration of a light source driving device 1h according to the third embodiment.
As shown in FIG. 10, the light source driving device 1 h according to the third embodiment is a buck-boost converter system, and generates a negative output voltage from a positive input voltage.
The light source 20 and the smoothing capacitor C1 are connected in parallel, one end of which is connected to the positive electrode of the DC power supply Vdc, and the other end is connected to the cathode of the diode D2. The anode of the diode D2 is connected to the first coil L1 of the transformer T1. The light source 20 emits light by the regenerative current that the diode D2 flows. The light source 20 emits light by applying a predetermined constant current in the direction from the cathode of the diode D2 to the positive electrode of the DC power supply Vdc.
Other than that, it is comprised similarly to the light source drive device 1 (refer FIG. 1) of 1st Embodiment, and has the same effect as the light source drive device 1 of 1st Embodiment.

(Basic configuration of the fourth embodiment)
FIG. 11 is a block diagram illustrating a configuration of a light source driving device 1i according to the fourth embodiment.
As shown in FIG. 11, the light source driving device 1 i of the fourth embodiment is a flyback converter system (insulation type), and actively uses magnetic energy accumulated in the excitation inductor of the transformer.
The light source driving device 1i of the fourth embodiment includes a transformer T2 instead of the transformer T1, and further includes diodes D3 and D4.

  The transformer T2 includes a first coil L1, a second coil L2, and a third coil L3 that are magnetically coupled. The first coil L1 and the second coil L2 are wound in opposite directions. The first coil L1 and the third coil L3 are wound in the same direction. The transformer T2 is excited by the current supplied to the first coil L1 from the DC power supply Vdc. The first coil L1 has one end connected to the DC power supply Vdc and the cathode of the diode D3, and the other end connected to the drain of the first switching element Q1 and the anode of the diode D3. The diode D3 flows the energy stored in the first coil L1 as a regenerative current, like the diode D1 of the first embodiment.

The second coil L2 is connected similarly to the first embodiment. The third coil L3 has one end connected to the anode of the diode D4 and the other end connected to one end of the parallel connection of the light source 20 and the smoothing capacitor C1. The cathode of the diode D4 is connected to the other end of the parallel connection of the light source 20 and the smoothing capacitor C1. Thereby, the transformer T2 can insulate between the DC power supply Vdc and the light source 20.
Other than that, it is comprised similarly to the light source drive device 1 (refer FIG. 1) of 1st Embodiment, and has the same effect as the light source drive device 1 of 1st Embodiment.

(Modification)
The present invention is not limited to the above-described embodiment, and can be modified without departing from the spirit of the present invention. For example, there are the following (a) to (e).
(A) The light source 20 may be an element that is connected to the DC power supply Vdc and emits light in response to a flowing current. For example, the light source 20 is an organic EL (Organic Electro-Luminescence) element or an inorganic EL (Inorganic Electro-Luminescence) element. Also good.
(B) The light source drive device 1h of the third embodiment may include any one of the configurations of the first to third application examples of the first embodiment. Similarly, the light source driving device 1i of the fourth embodiment may include any one of the configurations of the first application example to the third application example of the first embodiment.
(C) The light source driving device 1d (see FIG. 6) of the second embodiment may have a configuration of a buck-boost converter system or a flyback converter system.
(C) The number of switching elements provided in the switch circuit 3a of the second embodiment is not limited to two, and may be more than that.
(D) The first switching element Q1 is not limited to the FET, and may be a bipolar transistor or the like.

1, 1a to 1i Light source driving device 2 Feedback circuit 3, 3a Switch circuit 4 Reference voltage generation circuit 5 Comparator 6 Differentiation circuit 7 Dimming setting circuit 20 Light source C0 Electrolytic capacitor C1 Smoothing capacitor C2, C3 Capacitor D1 to D4 Diode Io Output Current L1 First coil L2 Second coil L3 Third coil Q1 First switching element Q2 Second switching elements Q3 and Q4 Switching elements R1 to R4 Resistance element Rs Current detection resistance Sdc DC dimming signal Sp signal T1 , T2 transformer TH thermistor ZD1 Zener diode Vdc DC power supply Vcc voltage source Vref reference voltage Vi input voltage (power supply voltage)
Va differential voltage Vb dimming voltage

Claims (6)

DC power supply,
A light source connected to the DC power source and emitting light according to a flowing current;
A smoothing capacitor connected in parallel to the light source;
A transformer including a first coil and a second coil that are magnetically coupled and excited by a current supplied from the DC power supply;
A first switching element for switching whether or not to pass a current through the first coil;
A diode for regenerating energy stored in the first coil when the first switching element is off;
A feedback circuit that feeds back a positive voltage induced in the second coil to a control terminal of the first switching element;
A current detection resistor for detecting a current flowing through the first coil as a voltage value;
A switch circuit that turns off the first switching element if the voltage value detected by the current detection resistor exceeds a predetermined value, and makes the temperature characteristics of the switch uniform;
A light source driving device comprising: The switch circuit is
A reference voltage generation circuit for generating a reference voltage;
A comparison signal is generated by comparing the reference voltage output from the reference voltage generation circuit with the voltage value detected by the current detection resistor, and the comparison signal is output to the control terminal of the first switching element. A comparator,
The light source driving device according to claim 1, comprising: The switch circuit is
The voltage value detected by the current detection resistor is input, and a signal for controlling the ON operation of the first switching element according to the magnitude of the voltage value is output to the control terminal of the first switching element. A plurality of Darlington-connected switching elements;
A thermistor connected between the input terminal of the current detected by the current detection resistor and the ground;
The light source driving device according to claim 1, comprising: A differential circuit connected between a positive electrode and a negative electrode of the DC power supply;
A dimming setting circuit connected to the differential circuit, the input terminal of the switch circuit, and the current detection resistor, and applying a differential voltage output from the differentiation circuit to the current detection resistor;
Further comprising a slow start circuit including
The slow start circuit gradually increases the current flowing through the light source immediately after the DC power supply starts supplying power.
The light source driving device according to claim 1, wherein the light source driving device is a light source driving device. A dimming setting circuit that is connected to the input terminals of the current detection resistor and the switch circuit and that performs DC dimming control of the light source according to a signal input from the outside;
The light source driving device according to claim 1, wherein the light source driving device is a light source driving device. A second switching element connected between the control terminal of the first switching element and GND, and performing PWM dimming control or on / off control of the light source in accordance with an externally input signal; ,
The light source driving device according to claim 1, wherein the light source driving device is a light source driving device.

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