JP5857252B2 - Lighting circuit and lamp provided with the same - Google Patents

Description

  The present invention relates to a lighting circuit for lighting a light source, and more particularly to a technique for regulating use in a state where fluctuations in the amount of light of a light source have increased.

Conventionally, a power supply circuit including a DC-DC converter including a coil and a switching element has been proposed (see Patent Document 1). This power supply circuit can be used as a lighting circuit for supplying power to the light source.
The power supply circuit described in Patent Document 1 includes a rectifying / smoothing circuit that rectifies and smoothes an AC output from an AC power supply, and a voltage conversion circuit connected between output terminals of the rectifying and smoothing circuit. Here, the rectifying / smoothing circuit includes a diode bridge connected to the output end of the AC power supply and an electrolytic capacitor connected to the output end of the diode bridge for smoothing the pulsating flow.

  By the way, the smoothing action of the rectifying / smoothing circuit is not perfect and includes a pulsating flow component. This pulsating flow component depends on the capacitance of the electrolytic capacitor included in the rectifying and smoothing circuit, and the pulsating flow component increases as the capacitance of the electrolytic capacitor decreases. When the pulsating current component becomes a predetermined magnitude or more, the fluctuation of the output voltage of the voltage conversion circuit becomes remarkable. When this power supply circuit is used as a lighting circuit for lighting a light source using an LED or the like, when the output voltage of the voltage conversion circuit varies significantly, the variation of the light amount of the light source becomes significant.

  Therefore, when this power supply circuit is used as a lighting circuit, it is necessary to select the capacitance of the electrolytic capacitor so that the magnitude of the pulsating current component is not more than a predetermined magnitude.

JP 2011-171231 A

  By the way, when an electrolytic capacitor is used for a long time, for example, for smoothing a rectifying / smoothing circuit, the capacitance is reduced due to the diffusion of the internal electrolyte solution to the outside. When the capacitance of the electrolytic capacitor decreases, the magnitude of the pulsating component included in the output voltage of the rectifying and smoothing circuit increases accordingly. In particular, when this power supply circuit is used as a lighting circuit for a light source using an LED, since the LED has a long life, the pulsating flow is caused by the decrease in the capacitance of the electrolytic capacitor before the life of the LED. There is a risk of an increase in components. When the magnitude of the pulsating flow component is increased in this way, the variation in the light amount of the light source becomes remarkable, and the flickering of the light amount becomes conspicuous.

  The present invention has been made in view of the above-described reasons, and it is an object of the present invention to provide a lighting circuit that can be used in a state in which fluctuations in the amount of light of a light source become significant.

A lighting circuit according to the present invention is a lighting circuit for lighting a light source by receiving power supply from an AC power source, a rectifying circuit for rectifying AC, an electrolytic capacitor connected between output terminals of the rectifying circuit, and an electrolytic circuit When the voltage generated across the capacitor is stepped up and down and output to the light source and the average voltage across the electrolytic capacitor is greater than the voltage threshold, the voltage output to the light source is continued and the voltage across the electrolytic capacitor is A voltage conversion circuit that stops outputting the voltage to the light source when the average value is equal to or lower than the voltage threshold, the voltage threshold changing according to the voltage output to the light source, and the voltage output to the light source However, when the voltage is smaller than the minimum value of the voltage generated across the electrolytic capacitor, the voltage threshold is set larger than the voltage output to the light source .

  According to this configuration, the voltage conversion circuit stops operating when the voltage average value across the electrolytic capacitor becomes equal to or lower than the voltage threshold value. Therefore, by setting the voltage average value when the magnitude of the pulsating current component included in the voltage generated between the two ends of the electrolytic capacitor is at the upper limit of the allowable range, the magnitude of the pulsating current component is within the allowable range. It is possible to prevent the lighting circuit from continuing to operate in a state exceeding the above. As a result, when the voltage conversion circuit is used with a light source connected, it can be prevented from being used in a state in which the light amount of the light source varies significantly.

2 is a circuit diagram of a lighting circuit according to Embodiment 1. FIG. 2 is a circuit diagram of a drive circuit according to Embodiment 1. FIG. 3 is a diagram illustrating a time waveform of a voltage across the electrolytic capacitor according to Embodiment 1. FIG. (A) is a figure which shows the time-dependent change of the electrostatic capacitance of an electrolytic capacitor about the lighting circuit which concerns on Embodiment 1, (b) is a figure which shows the time-dependent change of the average value of the voltage between the both ends of an electrolytic capacitor. (C) is a figure which shows operation | movement of a switching element. 6 is a sectional view of a lamp according to Embodiment 2. FIG. It is a circuit diagram of the lighting circuit which concerns on a modification. It is a circuit diagram of the drive circuit concerning a modification. It is a figure which shows the relationship between the waveform of the voltage between the both ends of an electrolytic capacitor, and the voltage applied to an LED module about the lighting circuit which concerns on a modification. It is a circuit diagram of the lighting circuit which concerns on a modification. (A) is a figure which shows the waveform of the voltage between the both ends of an electrolytic capacitor about the lighting circuit which concerns on a modification, (b) shows the waveform of the drain current of the switching element in the period T1 represented to (a). It is a figure, (c) is a figure which shows the waveform of the drain current of the switching element in the period T2 represented to (a). It is a circuit diagram of the lighting circuit which concerns on a modification. It is a circuit diagram of the drive circuit concerning a modification. In the lighting circuit according to the modification, (a-1) and (b-1) are diagrams showing the waveform of the drain current of the switching element, and (a-1) and (b-2) are the operations of the thyristor. FIG.

<Embodiment 1>
<1> Configuration FIG. 1 shows a circuit diagram of a lighting circuit according to the present embodiment.
The lighting circuit 1 includes a rectifier circuit 2, an electrolytic capacitor C2, and a voltage conversion circuit 3. Here, the rectifier circuit 2 is connected to an AC power supply AC, and the voltage conversion circuit 3 is connected to an LED module 5.

The AC power supply AC is, for example, a commercial power supply, and is usually a power supply with an output voltage of 100 V in Japan (hereinafter referred to as “AC 100 V power supply”). This AC power supply AC is connected to the rectifier circuit 2 via a fuse F1.
The LED module 5 has a plurality of LEDs connected in series. Each LED is turned on when a voltage is supplied from the lighting circuit 1. In addition, the LED module 5 is not limited to what connected several LED in series. For example, a plurality of series connection bodies formed by connecting a plurality of LEDs in series may be connected in parallel.

<1-1> Rectifier Circuit The rectifier circuit 2 includes a diode bridge DB including four diodes. Connected between the output terminals of the rectifier circuit 2 is a low-pass filter including a capacitor C1 and an inductor NF connected to the output terminal on the high potential side of the diode bridge DB. This low-pass filter is for preventing high-frequency noise generated on the voltage conversion circuit 3 side from leaking to the diode bridge DB side. Note that this low-pass filter may be omitted.

<1-2> Electrolytic Capacitor The electrolytic capacitor C2 is connected between the output terminals of the rectifier circuit 2, and smoothes the pulsating current output from the rectifier circuit 2. The electrolytic capacitor C2 is composed of an aluminum electrolytic capacitor. The electrolytic capacitor C2 is not limited to an aluminum electrolytic capacitor, and may be, for example, a tantalum electrolytic capacitor. And the rectification smoothing circuit is comprised from the above-mentioned rectifier circuit 2 and this electrolytic capacitor C2.

<1-3> Voltage Conversion Circuit The voltage conversion circuit 3 is connected between both ends of the electrolytic capacitor C2, and steps up and down the voltage generated between both ends of the electrolytic capacitor C2 and outputs it to the LED module 5. The voltage conversion circuit 3 includes a drive circuit U1, a step-up / step-down circuit 31, and an instruction circuit 4.
<Buck-boost circuit>
The step-up / down circuit 31 includes an inductor L2, a diode D1, a resistor R6, and capacitors C8 and C11. The step-up / down circuit 31 outputs a voltage to the LED module 5 by alternately selecting a first current path and a second current path, which will be described later.

The inductor L2 has one end connected to the high potential side of the electrolytic capacitor C2 and the other end connected to the drain terminal D of the drive circuit U1. In addition, one end side of the inductor L2 is connected to the cathode of the LED constituting a part of the LED module 5.
The diode D <b> 1 has an anode connected to the other end of the inductor L <b> 2 and a cathode connected to the anode of the LED constituting a part of the LED module 5.

The resistor R6 and the capacitor C8 are connected in parallel between one end of the inductor L2 and the cathode of the diode D1.
Here, the first current path is a current path in which energy is accumulated in the inductor L2, and the current flowing from the rectifier circuit 2 to the voltage conversion circuit 3 side is the high potential side of the electrolytic capacitor C2, the inductor L2, and the switching. This is a path that returns to the low potential side of the electrolytic capacitor C2 through the element Q101 and the resistor R101 (see FIG. 2) in this order. The second current path is a current path for transmitting the energy accumulated in the inductor L2 to the LED module 5, and the current flowing out from the other end of the inductor L2 passes through the diode D1 and the LED module 5 in this order. And return to the inductor L2.

<Drive circuit>
The drive circuit U1 is incorporated in one semiconductor package, and the power supply terminal VCC connected to the high potential side of the electrolytic capacitor C2, the drain terminal D, the source terminal S, and a constant voltage that outputs a constant voltage. It has a terminal VDD and input terminals EX and CL. The drive circuit U1 includes a determination circuit 121 connected to the output terminal of the instruction circuit 4 inside.

Here, the other end side of the inductor L2 and the anode of the diode D1 are commonly connected to the drain terminal D.
The source terminal S is connected to the low potential side of the electrolytic capacitor C2.
A resistor R1 and a variable resistor R2 are connected in series between the constant voltage terminal VDD and the low potential side of the electrolytic capacitor C2. A capacitor C6 is connected in parallel with the variable resistor R2. A resistor R8 is connected between the constant voltage terminal VDD and the high potential side of the electrolytic capacitor C2, and a capacitor C5 is connected between the constant voltage terminal VDD and the low potential side of the electrolytic capacitor C2. Yes.

  The input terminal EX is connected to a connection point between the resistor R1 and the variable resistor R2 via a resistor R7. By changing the voltage of the input terminal EX, the value of the current flowing through the inductor L2 can be changed. Therefore, in order to change the value of the current flowing through the inductor L2, the voltage of the input terminal EX may be changed by changing the resistance value of the variable resistor R2.

The input terminal CL is connected to the instruction circuit 4. When the voltage at the input terminal CL becomes lower than a later-described determination reference voltage, the current flowing through the inductor L2 stops.
The details of the internal configuration of the drive circuit U1 will be described later.
The capacitor C11 is connected between the cathode of the diode D1 and the source terminal S of the drive circuit U1. The capacitor C11 can stabilize the cathode potential of the diode D1.

<Indication circuit>
The instruction circuit 4 is connected to the input terminal CL of the drive circuit U1, and when the voltage average value between both ends of the electrolytic capacitor C2 becomes equal to or lower than the voltage threshold, the voltage input to the input terminal CL is reduced, thereby causing the drive circuit U1 to It is a circuit that instructs to stop the operation. The instruction circuit 4 includes a switching element Tr made of a PNP bipolar transistor, resistors R3, R4, R11, R12, R13, R14, and capacitors C7, C12. The instruction circuit 4 may be configured without the resistor R13.

  The resistors R11 and R12 are connected in series between both ends of the electrolytic capacitor C2. The capacitor C12 is connected between the connection point of the two resistors R11 and R12 and the low potential side of the electrolytic capacitor C2. The resistors R3 and R4 are connected in series between the constant voltage terminal VDD of the drive circuit U1 and the low potential side of the electrolytic capacitor C2, and the capacitor C7 is connected in parallel with the resistor R4. The switching element Tr has an emitter connected to the connection point of the resistors R3 and R4 via the pull-up resistor R14, a collector connected to the low potential side of the electrolytic capacitor C2, and a base connected to the resistor R13. It is connected to the connection point of R11 and R12. A connection point between the emitter of the switching element Tr and the resistor R14 is connected to the input terminal CL of the drive circuit U1.

  Here, the resistance values of the resistors R11 and R12 and the capacitance of the capacitor C12 are such that the decay time constant of the voltage across the resistor R12 is less than the decay time constant of the pulsating voltage generated between the output ends of the rectifier circuit 2. It is set to be large. This is because an average value of a voltage including a pulsating current component generated between both ends of the resistor R12 is input to the base of the switching element Tr. For example, if the period of the pulsating voltage is 0.1 s, the voltage decay time constant across the resistor R12 is set to be greater than 0.1 s.

  When the voltage between the emitter and base is smaller than the turn-on voltage of the switching element Tr, the indicating circuit 4 maintains the switching element Tr in the off state, and the voltage between the emitter and base is equal to or higher than the turn-on voltage of the switching element Tr. The switching element Tr is turned on. Here, the turn-on voltage of the switching element Tr corresponds to a voltage generated at the connection point of the resistors R3 and R4 when the voltage across the electrolytic capacitor C2 is at a predetermined voltage threshold.

  Here, when the average voltage value across the electrolytic capacitor C2 is lowered, the voltage at the connection point of the resistors R11 and R12 is also lowered, and the base voltage of the switching element Tr is also lowered. When the voltage average value across the electrolytic capacitor C2 reaches the voltage threshold value or less, the voltage between the emitter and base of the switching element Tr reaches the turn-on voltage of the switching element Tr, and the switching element Tr is turned on.

  Incidentally, when the switching element Tr is in an OFF state, the relational expression (1) is established between the input voltage VCL from the instruction circuit 4 to the input terminal CL and the voltage VDD of the constant voltage terminal of the drive circuit U1.

Here, R3 and R4 represent resistance values of the resistors R3 and R4.
On the other hand, when the switching element Tr is in the ON state, the relational expression (2) is established between the input voltage VCL from the instruction circuit 4 to the input terminal CL and the voltage VDD of the constant voltage terminal of the drive circuit U1.

Here, R14 represents the resistance value of the resistor R14.
The resistors R3, R4, and R14 are selected so that the relational expression (3) is established.

That is, in the instruction circuit 4, when the average voltage value across the electrolytic capacitor C2 is equal to or lower than the voltage threshold value, the switching element Tr is turned on, and the input voltage to the input terminal CL decreases.
<2> Drive Circuit Next, the configuration of the drive circuit U1 will be described in detail. In the following description, the “High” level corresponds to a predetermined voltage of 0 V or higher, and the “Low” level corresponds to a voltage of approximately 0 V.

A circuit diagram of the drive circuit U1 is shown in FIG.
The drive circuit U1 includes a switching element Q101, a regulator 110 connected to the power supply terminal VCC, and a start / stop circuit 113 connected to the regulator 110. The drive circuit U1 includes an oscillator 101 that outputs two types of rectangular wave signals, an AND circuit 102, an RS flip-flop circuit 103, a NAND circuit 105, and a gate driver 106 connected to the gate of the switching element Q101. Is provided. The drive circuit U1 further includes a resistor R101 connected to the switching element Q101, a turn-off control circuit 122 that controls the timing at which the switching element Q101 is turned off, a blanking pulse generation circuit 112, and an input terminal of the AND circuit 102. And a determination circuit 121 connected to the.

<Switching element>
The switching element Q101 is composed of a power MOSFET, and the drain is connected to the drain terminal D. Further, a resistor R101 for detecting a drain current flowing through the switching element Q101 is connected between the source of the switching element Q101 and the source terminal S.

<Regulator>
The regulator 110 receives power supply from the power supply terminal VCC, outputs a constant voltage to the start / stop circuit 113, and outputs a constant voltage to the constant voltage terminal VDD. Here, the voltage output from the regulator 110 to the start / stop circuit 113 is equal to the voltage output from the regulator 110 to the constant voltage terminal VDD.

<Start / stop circuit>
The start / stop circuit 113 is a circuit for limiting the on / off operation of the switching element Q101 during a period when the output voltage of the regulator 110 does not rise to the rated voltage when the drive circuit U1 is started. The start / stop circuit 113 outputs voltages having different levels according to the magnitude of the input voltage from the regulator 110. Specifically, the start / stop circuit 113 holds a predetermined reference voltage, and “high” is input to the OR circuit 104 in a period in which the input voltage from the regulator 110 is smaller than the reference voltage after the drive circuit U1 is started. Enter the level voltage. On the other hand, when the input voltage from the regulator 110 to the start / stop circuit 113 reaches a reference voltage or higher, the start / stop circuit 113 inputs a “Low” level voltage to the OR circuit 104.

<Oscillator>
The oscillator 101 includes a clock terminal te101a that outputs a clock signal having a constant period, and a signal terminal te101b that outputs a rectangular wave signal synchronized with the clock signal. Each of the clock signal and the rectangular wave signal is a voltage signal having a rectangular pulse train-like time waveform composed of a “High” level and a “Low” level. Here, the signal output from the clock terminal te101a is a signal for determining the timing at which the switching element Q101 is turned on, and the rectangular wave signal output from the signal terminal te101b is the maximum on-duty value of the switching element Q101. It is a signal for setting. For example, when the on-duty of the rectangular wave signal is set to 80%, the maximum on-duty value of the switching element Q101 is 80%.

<AND circuit>
When the input voltage from the clock terminal te101a of the oscillator 101 is at “High” level and the input voltage from the determination circuit 121 is at “High” level, the AND circuit 102 applies “ A “High” level voltage is input.

On the other hand, the AND circuit 102 inputs a “Low” level voltage to the set terminal S when at least one of the input voltage from the clock terminal te101a of the oscillator 101 and the input voltage from the determination circuit 121 is “Low” level.
<Determination circuit>
The determination circuit 121 includes resistors R102 and R103 connected in series between the constant voltage terminal VDD and the source terminal S, and a comparator 108. The comparator 108 has a positive input terminal connected to the input terminal CL and a negative input terminal connected to the connection point of the resistors R102 and R103. The comparator 108 outputs a “High” level voltage if the voltage at the input terminal CL is equal to or higher than the voltage at the connection point of the resistors R102 and R103 (hereinafter referred to as “determination reference voltage”). When the voltage of CL becomes smaller than the determination reference voltage, a “Low” level voltage is output. Accordingly, when the voltage at the input terminal CL becomes smaller than the determination reference voltage, the input voltage from the determination circuit 121 to the AND circuit 102 is maintained at the “Low” level, and the clock signal is supplied to the set terminal S of the RS flip-flop circuit 103. Regardless of the signal voltage, a “Low” level voltage is always input. As a result, the switching element Q101 is maintained in the OFF state, and the drive circuit U1 is stopped.

  By the way, when the resistance values of the resistors R102 and R103 constituting a part of the determination circuit 121 of the drive circuit U1 are expressed as R102 and R103, respectively, the input voltage (VCL = R4 × VDD / (R3 + R4) (expression) (See (1)), or the relational expression (4) is established between VCL = R4 * R14 * VDD / [R3 * (R4 + R14) + R4 * R14] (see expression (2))). The resistance values of the resistors R102 and R103 are selected.

That is, the input voltage from the instruction circuit 4 when the switching element Tr is in the off state is larger than the determination reference voltage, while the input voltage from the instruction circuit 4 when the switching element Tr is in the on state is It is smaller than the reference voltage.
When the switching element Tr is in the OFF state, the comparator 108 determines the determination reference voltage (= R103 × VDD / (R102 + R103) of the negative input terminal rather than the voltage (= R4 × VDD / (R3 + R4)) of the positive input terminal. )) Is small, so a “High” level voltage is output.

On the other hand, when the switching element Tr is in the ON state, the comparator 108 determines the criterion of the negative input terminal with respect to the voltage of the positive input terminal (= R4 × R14 × VDD / [R3 × (R4 + R14) + R4 × R14]). Since the voltage (= R103 × VDD / (R102 + R103)) is large, a “Low” level voltage is output.
<Turn-off control circuit>
The turn-off control circuit 122 includes a comparator 107, an AND circuit 111, and an OR circuit 104. Comparator 107 has a positive input terminal connected to a connection point between switching element Q101 and resistor R101, and a negative input terminal connected to input terminal EX. The AND circuit 111 has two input terminals connected to the output terminal of the comparator 107 and the output terminal of the blanking pulse generation circuit 112, respectively. The AND circuit 111 receives a “High” level voltage from the blanking pulse generation circuit 112 and also inputs a “High” level voltage from the comparator 107 to the reset terminal R of the RS flip-flop circuit 103. Input a “High” level voltage. The OR circuit 104 has two input terminals connected to the output terminals of the start / stop circuit 113 and the AND circuit 111, and one inverting input terminal connected to the signal terminal te101b of the oscillator 101. The output terminal of the OR circuit 104 is connected to the reset terminal R of the RS flip-flop circuit 103. Here, when the input voltage from the signal terminal te101b to the inverting input terminal of the OR circuit 104 becomes the “Low” level, the reset terminal R of the RS flip-flop circuit 103 does not depend on the level of the input voltage from the AND circuit 111. The voltage is set to the “High” level.

<Blanking pulse generator>
The blanking pulse generation circuit 112 inputs a “High” level voltage to the AND circuit 111 after a predetermined blanking time has elapsed after the turn-on signal is output from the gate driver 106 to the switching element Q101. As a result, the voltage at the reset terminal R of the RS flip-flop circuit 103 is maintained at the “Low” level until at least the blanking time elapses after the switching element Q101 is turned on. Therefore, immediately after the switching element Q101 is turned on, a spike current flowing through the switching element Q101 is detected to prevent the reset terminal R of the RS flip-flop circuit 103 from being set to the “High” level.

<RS flip-flop circuit>
When the input voltage from the AND circuit 102 to the set terminal S becomes “High” level, the RS flip-flop circuit 103 sets the input voltage from the output terminal Q to the NAND circuit 105 to “High” level. At this time, the switching element Q101 is turned on.

On the other hand, when the voltage generated between both ends of the resistor R101 reaches the voltage generated at the input terminal EX and the input voltage from the OR circuit 104 to the reset terminal R becomes “High” level, the RS flip-flop circuit 103 becomes the AND circuit 102. If the input voltage to the set terminal S is “Low” level, the output voltage from the output terminal Q is set to “Low” level.
<NAND circuit>
In the NAND circuit 105, when the input voltage from the RS flip-flop circuit 103 is “High” level and the input voltage from the signal terminal te101b of the oscillator 101 is “High” level, the output voltage is “Low” level. become. Further, when the input voltage from the RS flip-flop circuit 103 is at the “Low” level and the input voltage from the signal terminal te101b of the oscillator 101 is at the “High” level, the output voltage is at the “High” level.

<Gate driver>
The gate driver 106 controls the gate voltage of the switching element Q101 according to the magnitude of the input voltage from the NAND circuit 105. Specifically, when the input voltage from the NAND circuit 105 is “Low” level, the gate driver 106 sets the gate voltage of the switching element Q101 to “High” level, and the input voltage from the NAND circuit 105 is “High”. If it is level, the gate voltage of switching element Q101 is set to “Low” level. Then, when the gate voltage of the switching element Q101 becomes “High” level, the switching element Q101 is turned on, and when the gate voltage of the switching element Q101 becomes “Low” level, the switching element Q101 is turned off.

<2> Operation <2-1> Basic Operation Next, a basic operation of the lighting circuit according to the present embodiment will be described with reference to FIGS.
When the lighting circuit 1 is activated and a DC voltage Vin is input across the electrolytic capacitor C2, a current flows from the high potential side of the electrolytic capacitor C2 to the inductor L2, the capacitor C5, and the power supply terminal VCC of the drive circuit U1 (FIG. 1). At this time, in the drive circuit U1, the current flowing into the power supply terminal VCC flows to the constant voltage terminal VDD via the regulator 110 (see FIG. 2). The capacitor C5 is charged when current flows from the high potential side of the electrolytic capacitor C2 via the resistor R8 and current also flows from the constant voltage terminal VDD of the drive circuit U1 (see FIG. 1). Here, during the period when the capacitor C5 is not charged, the voltage input from the regulator 110 to the start / stop circuit 113 is smaller than the start voltage, while during the period when the capacitor C5 is charged, the start / stop is performed from the regulator 110. The voltage input to the circuit 113 becomes a voltage higher than the starting voltage (see FIG. 2). At this time, the current flowing out from the constant voltage terminal VDD of the drive circuit U1 flows into the capacitor C7 via the resistor R3, and the capacitor C7 is also charged (see FIG. 1).

  Here, during a period in which the voltage input from the regulator 110 to the start / stop circuit 113 is smaller than the start voltage, a “High” level voltage is input from the start / stop circuit 113 to the input terminal of the OR circuit 104 (FIG. 2). reference). Then, a “High” level voltage is input from the OR circuit 104 to the reset terminal R of the RS flip-flop circuit 103, and the input voltage from the output terminal Q to the NAND circuit 105 is maintained at the “Low” level.

On the other hand, when the voltage input from the regulator 110 to the start / stop circuit 113 reaches a voltage equal to or higher than the start voltage, a “Low” level voltage is input from the start / stop circuit 113 to the input terminal of the OR circuit 104. Then, a “Low” level voltage is input from the OR circuit 104 to the reset terminal R of the RS flip-flop circuit 103.
The voltage output from the instruction circuit 4 is input to the input terminal CL of the drive circuit U1, and the voltage obtained by dividing the voltage of the constant voltage terminal VDD by the resistors R1 and R2 is input to the input terminal EX. (See FIG. 1).

Here, in the drive circuit U1, when the voltage of the input terminal CL is higher than the voltage obtained by dividing the voltage of the constant voltage terminal VDD by the resistors R102 and R103 (hereinafter referred to as “determination reference voltage”), the comparison is made. The input voltage from the device 108 to the AND circuit 102 becomes “High” level (see FIG. 2). On the other hand, when the voltage at the input terminal CL is equal to or lower than the determination reference voltage, the input voltage from the comparator 108 to the AND circuit 102 is “Low” level. The input voltage from the comparator 108 to the AND circuit 102 is “High” level. In this case, when the voltage level of the clock signal input from the oscillator 101 to the AND circuit 102 becomes “High” level, the input voltage to the set terminal S of the RS flip-flop circuit 103 becomes “High” level. Then, the input voltage from the RS flip-flop circuit 103 to the NAND circuit 105 becomes “High” level. Here, when the voltage level of the rectangular wave signal input from the signal terminal te101b of the oscillator 101 to the NAND circuit 105 is “High” level, the input voltage to the gate driver 106 becomes “Low” level. Then, the gate voltage of the switching element Q101 connected to the gate driver 106 becomes “High” level, the switching element Q101 is turned on, and the drain current starts to flow through the switching element Q101.

  At this time, the current flowing from the rectifier circuit 2 to the drive circuit U1 side returns to the low potential side of the electrolytic capacitor C2 through the high potential side of the electrolytic capacitor C2, the inductor L2, the switching element Q101, and the resistor R101 in this order (first step). At the same time, the energy is stored in the inductor L2 (see FIG. 1). In addition, when a drain current flows through the switching element Q101, a voltage generated between both ends of the resistor R101 is input to the plus side input terminal of the comparator 107 of the turn-off control circuit 122 (see FIG. 2).

  Then, when the drain current increases after the drain current starts to flow through the switching element Q101, and the voltage generated across the resistor R101 becomes equal to the voltage at the negative input terminal of the comparator 107, it is initially at the “Low” level. Further, the input voltage from the comparator 107 to the AND circuit 111 becomes the “High” level. Further, when the blanking period has elapsed since the drain current began to flow through the switching element Q101, the input voltage from the blanking pulse generation circuit 112 to the AND circuit 111 is also at the “High” level. Then, the input voltage from the AND circuit 111 to the OR circuit 104 becomes “High” level. Then, the input voltage from the OR circuit 104 to the reset terminal R of the RS flip-flop circuit 103 becomes “High” level, and the switching element Q101 is turned off. That is, the turn-off control circuit 122 turns off the switching element Q101 so that the peak value of the drain current of the switching element Q101, that is, the peak value of the voltage generated across the resistor R101 does not exceed the voltage of the input terminal EX. ing.

  When the switching element Q101 is turned off, the current flowing from the rectifier circuit 2 to the drive circuit U1 is cut off (see FIG. 1). The current flowing out from the other end side (the drive circuit U1 side) of the inductor L2 follows a path (second current path) that returns to the inductor L2 through the diode D1 and the LED module 5 in this order. Here, the energy accumulated in the inductor L2 is supplied to the LED module 5, and the LED module 5 is turned on.

  After that, when the input voltage from the clock terminal te101a of the oscillator 101 to the AND circuit 102 becomes “High” level again, if the input voltage from the determination circuit 121 to the AND circuit 102 is “High” level, the RS flip-flop circuit 103 The input voltage to the set terminal S becomes “High” level (see FIG. 2). Then, the switching element Q101 is turned on again.

<2-2> Operation of Instruction Circuit Next, the operation of the instruction circuit 4 according to the present embodiment will be described.
A time waveform of the voltage Vin across the electrolytic capacitor C2 is shown in FIG. Here, FIG. 3A shows a time waveform of the voltage Vin when the electrolytic capacitor C2 is normal, and FIG. 3B shows that the electrolytic capacitor C2 loses its capacitance and the capacitance of the electrolytic capacitor C2 decreases. The time waveform of the voltage Vin at the time of doing is shown. 3A and 3B, the average value of the voltage Vin when the electrolytic capacitor C2 is normal is the voltage VC0.

As shown in FIG. 3A, when the electrolytic capacitor C2 is normal, the half-life of the voltage Vin between both ends of the electrolytic capacitor C2 is sufficiently larger than the cycle of the pulsating voltage output from the rectifier circuit 2. There is little variation in the voltage Vin across the capacitor C2.
On the other hand, as shown in FIG. 3B, when the capacitance of the electrolytic capacitor C2 is lower than the normal capacitance, the half-life of the voltage Vin across the electrolytic capacitor C2 is output from the rectifier circuit 2. As the cycle of the flowing voltage approaches, the fluctuation of the voltage Vin across the electrolytic capacitor C2 increases, and the average value of the voltage Vin decreases to a voltage VC1 lower than the voltage VC0.

FIG. 4 (a) shows the change over time of the capacitance of the electrolytic capacitor C2, FIG. 4 (b) shows the change over time of the average value Vave of the voltage Vin across the electrolytic capacitor C2, and the operation of the switching element Tr. As shown in FIG.
As shown in FIG. 4A, in the electrolytic capacitor C2, the internal electrolytic solution diffuses to the outside as the usage time elapses, and the capacitance decreases. Along with this, as shown in the electrolytic capacitor C2 and (b), the average value Vave of the voltage Vin across the electrolytic capacitor C2 in the lighting circuit 1 also decreases.

Then, as shown in FIG. 4C, when the average value Vave of the voltage Vin across the electrolytic capacitor C2 decreases to the voltage threshold Vth, the emitter-base between the switching elements Tr constituting a part of the indicating circuit 4 Becomes equal to the turn-on voltage of the switching element Tr, and the switching element Tr is turned on.
By the way, if the magnitude of the pulsating flow component included in the voltage Vin generated between both ends of the electrolytic capacitor C2 is within a predetermined allowable range, the fluctuation of the output voltage from the voltage conversion circuit 3 is not significant, and the LED The fluctuation of the light quantity of the module 5 does not become remarkable.

  Therefore, in the lighting circuit 1 according to the present embodiment, the voltage threshold value Vth is the voltage average value when the magnitude of the pulsating current component included in the voltage Vin generated across the electrolytic capacitor C2 is at the upper limit of the allowable range. Vave is set. Thereby, the indication circuit 4 can stop the power conversion circuit 2 when the magnitude of the pulsating flow component included in the voltage Vin exceeds the allowable range.

  When the switching element Tr is turned on and the voltage of the input terminal CL of the drive circuit U1 becomes equal to or lower than the determination reference voltage, the input voltage from the determination circuit 121 to the AND circuit 102 becomes “Low” level (see FIG. 2). Then, the input voltage to the set terminal S of the RS flip-flop circuit 103 of the drive circuit U1 is always “Low” level regardless of the voltage level of the clock signal, and the switching element Q101 is maintained in the off state, and the drive circuit U1. Stops voltage output.

  Eventually, in the lighting circuit 1 according to the present embodiment, when the voltage across the electrolytic capacitor C2 that smoothes the pulsating current output from the rectifier circuit 2 becomes less than or equal to the voltage threshold Vth, the indicating circuit 4 3 stops operation. Therefore, by setting the voltage average value Vave when the magnitude of the pulsating current component included in the voltage Vin generated across the electrolytic capacitor C2 is at the upper limit of the allowable range to the voltage threshold Vth, the magnitude of the pulsating current component Thus, it is possible to prevent the lighting circuit 1 from continuing to output a voltage in a state where the value exceeds the allowable range. As a result, when the LED module 5 is connected to the voltage conversion circuit 3 and used, it is possible to prevent the LED module 5 from being used in a state in which the variation in the light amount becomes significant.

  Further, when the magnitude of the pulsating component included in the voltage Vin across the electrolytic capacitor C2 increases, the current flowing in the lighting circuit 1 cannot be removed by the noise filter including the inductor NF and the capacitor C1. The frequency component will increase. If it carries out like this, the noise which leaks outside from the lighting circuit 1 may increase, and there exists a possibility of affecting a peripheral device. In particular, when a signal transmission wire is wired in the vicinity of the lighting circuit 1, there is a possibility that noise is given to a signal transmitted through the wire.

On the other hand, in the lighting circuit 1 according to the present embodiment, the voltage conversion circuit 3 stops before the magnitude of the pulsating current component included in the voltage Vin across the electrolytic capacitor C2 exceeds the allowable range. Thus, it is possible to prevent the lighting circuit 1 from being continuously used in a state where high-frequency noise has leaked from the lighting circuit 1 to the outside.
Moreover, in the lighting circuit according to the present embodiment, the instruction circuit 4 can be configured from a relatively inexpensive discrete component. Accordingly, there is an advantage that the manufacturing cost of the lighting circuit can be reduced by reducing the component cost.

<Embodiment 2>
FIG. 5 shows a cross-sectional view of the lamp 1000 according to the present embodiment.
As shown in FIG. 5, the lamp 1000 is a light bulb-shaped LED lamp, and includes the lighting circuit 1 according to the first embodiment, the LED module 5, a globe 1101, a housing 1102, and a base 1103.

The lighting circuit 1 is housed in the housing 1102, and the power received by the base 1103 from the AC power supply is supplied via the lead wires 1104a and 1104b. The lighting circuit 1 rectifies and smoothes the power supplied from the AC power supply, and then boosts and lowers the power and supplies it to the LED module 5.
In the present embodiment, an example of a current-type LED lamp has been described. However, the present invention is not limited to this example. For example, a straight-tube LED lamp on which the lighting circuit 1 is mounted may be used.

<Modification>
(1) In Embodiment 1, the example of the lighting circuit 1 in which the indicating circuit 4 includes a PNP bipolar transistor has been described. However, the present invention is not limited to a circuit including a bipolar transistor.
For example, the instruction circuit 4 may include a switching element made of a P-channel MOSFET instead of the switching element Tr made of a PNP bipolar transistor. In this case, the switching element has a drain commonly connected to the input terminal CL of the drive circuit U1, a source connected to the low potential side of the electrolytic capacitor C2, and a gate connected to the resistors R11 and R12 via the resistor R13. Connected to. According to this modification, since the path of the large current on the electrolytic capacitor C2 side and the path of the small current on the input terminal CL side of the drive circuit U1 are separated from the switching element, the input terminal of the drive circuit U1 Noise input to CL can be reduced.

  (2) In the first embodiment, when the average value Vave of the voltage Vin across the electrolytic capacitor C2 becomes smaller than the voltage threshold Vth, the voltage input from the instruction circuit 4 to the input terminal CL of the drive circuit U1 decreases. Although the example has been described, the present invention is not limited to this as long as the output voltage changes according to the magnitude relationship between the average value Vave of the voltage Vin across the electrolytic capacitor C2 and the voltage threshold Vth. For example, contrary to the first embodiment, when the average value Vave of the voltage Vin across the electrolytic capacitor C2 becomes smaller than the voltage threshold Vth, the voltage input from the indicating circuit 4 to the input terminal CL of the drive circuit U1 is changed. It may rise.

A circuit diagram of the lighting circuit 1001 according to this modification is shown in FIG. 6, and a circuit diagram of the drive circuit U2 according to this modification is shown in FIG.
As shown in FIG. 6, the lighting circuit 1001 is different from the first embodiment in the configuration of the instruction circuit 24 included in the voltage conversion circuit 23. Further, as shown in FIG. 7, the drive circuit U2 is different from the drive circuit U1 according to the first embodiment in that the drive circuit U2 includes a determination circuit 221 having a configuration different from that of the determination circuit 121. In addition, about the structure similar to Embodiment 1, the same code | symbol is attached | subjected and description is abbreviate | omitted suitably.

As shown in FIG. 6, the instruction circuit 24 includes a switching element Tr2 made of an NPN bipolar transistor, resistors R21, R22, R23, R24, and a capacitor C21.
The resistors R21 and R22 are connected in series between both ends of the electrolytic capacitor C2. The switching element Tr2 has an emitter connected to the low potential side of the electrolytic capacitor C2, a collector connected to the constant voltage terminal VDD of the drive circuit U2 via the pull-up resistor R24, and a base connected to the resistor R23. It is connected to the connection point of the resistors R21 and R22. A capacitor C21 is connected between the collector and emitter of the switching element Tr2. Here, a voltage across the resistor R22 is applied between the emitter and base of the switching element Tr2 of the indicating circuit 24. The turn-on voltage of the switching element Tr2 is equal to the voltage generated across the resistor R22 when the average value Vave of the voltage Vin across the electrolytic capacitor C2 reaches the voltage threshold Vth.

As shown in FIG. 7, in the determination circuit 221, the inverter 208 is connected to the output terminal of the comparator 108.
When the average value Vave of the voltage Vin across the electrolytic capacitor C2 is larger than the voltage threshold, a voltage equal to or higher than the turn-on voltage of the switching element Tr2 is applied between the emitter and base of the switching element Tr2. It will be in an ON state (refer FIG. 6). At this time, the voltage input to the input terminal CL of the drive circuit U2 is approximately 0V. Then, in the determination circuit 221, in the comparator 108, the voltage at the minus side input terminal is larger than the voltage at the plus side input terminal, so that the input voltage from the comparator 108 to the inverter 208 becomes the “Low” level ( (See FIG. 7). Then, the input voltage from the inverter 208 to the AND circuit 102 becomes “High” level. Here, when the voltage level of the clock signal input from the clock terminal te101a of the oscillator 101 to the AND circuit 102 becomes “High” level, the input voltage to the set terminal S of the RS flip-flop circuit 103 becomes “High” level. The switching element Q101 is turned on.

  On the other hand, when the average value Vave of the voltage Vin across the electrolytic capacitor C2 is equal to or lower than the voltage threshold Vth, the voltage applied between the emitter and base of the switching element Tr2 becomes smaller than the turn-on voltage of the switching element Tr2, and the switching element Tr2 is turned off (see FIG. 6). At this time, the voltage input to the input terminal CL of the drive circuit U2 is substantially equal to the voltage of the constant voltage terminal VDD. Then, in the determination circuit 221, in the comparator 108, the voltage at the minus side input terminal is smaller than the voltage at the plus side input terminal, so that the input voltage from the comparator 108 to the inverter 208 is at the “High” level. Then, the input voltage from the inverter 208 to the AND circuit 102 becomes “Low” level, and a voltage of “Low” level is always input to the set terminal S of the RS flip-flop circuit 103 regardless of the signal voltage of the clock signal. Is done. As a result, the switching element Q101 is maintained in the OFF state, and the drive circuit U2 stops outputting the voltage.

According to this modification, since the number of circuit elements of the instruction circuit 24 is smaller than the number of circuit elements of the instruction circuit 4 according to the first embodiment, the instruction circuit 24 can be reduced in size, and consequently the lighting circuit 1001 as a whole. Can be miniaturized.
In this modification, an example in which the switching element Tr2 made of an NPN bipolar transistor is provided has been described. However, the present invention is not limited to this. For example, instead of the switching element Tr2 made of an NPN bipolar transistor, an N-channel MOSFET is used. A switching element may be provided. In this case, the switching element has a source connected to the low potential side of the electrolytic capacitor C2, a drain connected to the constant voltage terminal VDD of the drive circuit U2 via the pull-up resistor R24, and a gate connected to the resistor R23. To the connection point of the resistors R21 and R22. According to this configuration, since the switching element can be reduced in size, the instruction circuit 24 can be further reduced in size.

(3) In the first embodiment, the example of the lighting circuit 1 in which the voltage threshold value Vth with respect to the average value Vave of the voltage Vin between the both ends of the electrolytic capacitor C2 has been described has been described. The voltage threshold Vth may be changed according to the magnitude of the voltage applied to the module 5.
The relationship between the waveform of the voltage Vin across the electrolytic capacitor C2 and the voltage VLED applied to the LED module 5 is shown in FIG.

As shown in FIG. 8, if the voltage VLED across the LED module 5 is smaller than the minimum value Vmin of the voltage Vin, the lighting circuit can be driven normally even if the voltage threshold value Vth is lowered accordingly.
FIG. 9 shows a circuit diagram of a lighting circuit 3001 according to this modification.
As shown in FIG. 9, the lighting circuit 3001 includes a voltage conversion circuit 33 including variable resistors R42 and R41 instead of the variable resistor R2 and the resistor R11 in the voltage conversion circuit 3 according to the first embodiment. Further, the second embodiment is different from the first embodiment in that a control circuit U41 that changes the resistance values of the variable resistors R42 and R41 in conjunction with each other is provided. In addition, about the structure similar to Embodiment 1, the same code | symbol is attached | subjected and description is abbreviate | omitted suitably.

  The voltage applied to the LED module 5 is determined by the peak value of the drain current flowing through the switching element Q101. As the peak value of the drain current becomes smaller, the voltage applied to the LED module 5 becomes smaller. The peak value of the drain current is determined by the voltage of the input terminal EX of the drive circuit U1 as described in the first embodiment. As the voltage at the input terminal EX is lower, the peak value of the drain current is smaller.

  Therefore, in the control circuit U41 according to this modification, when the resistance value of the variable resistor R42 decreases so that the voltage at the input terminal CL of the drive circuit U1 decreases, the variable resistor R41 that constitutes a part of the instruction circuit 44 accordingly. Reduce the resistance value. Thereby, the ratio of the voltage applied between the emitter and base of the switching element Tr to the voltage across the electrolytic capacitor C2 can be reduced, and the voltage threshold Vth of the indicating circuit 44 can be lowered.

  (4) In the first embodiment, an example of the lighting circuit 1 that detects a decrease in the average value Vave of the voltage Vin across the electrolytic capacitor C2 by the resistors R11 and R12 connected across the electrolytic capacitor C2 will be described. However, the present invention is not limited to this. For example, a decrease in the voltage Vin across the electrolytic capacitor C2 may be detected from a change in the ratio (on duty) of the time when the switching element Q101 is in the ON state.

  The waveform of the voltage Vin across the electrolytic capacitor C2 is shown in FIG. 10A, the waveform of the drain current of the switching element Q101 in the period T1 shown in FIG. 10A is shown in FIG. FIG. 10C shows the waveform of the drain current of the switching element Q101 in the period T2 represented by 10 (a). 10B and 10C, Ton indicates a period during which the switching element Q101 is in an on state (hereinafter referred to as “on period”), and Toff indicates that the switching element Q101 is in an off state. A period (hereinafter referred to as “off period”) is shown.

  As shown in FIGS. 10A and 10B, the drain current flowing through the switching element Q101 after the switching element Q101 is turned on has a peak value Id0 according to the magnitude of the voltage Vin across the electrolytic capacitor C2. The period until reaching (the period in which the switching element Q101 is in the ON state) is different. As the voltage Vin across the electrolytic capacitor C2 decreases, the period during which the switching element Q101 is in an on state, in other words, the on duty increases. Therefore, the lighting circuit 4001 according to the present modification indirectly detects a decrease in the voltage Vin between both ends of the electrolytic capacitor C2 from the magnitude of the on duty of the switching element Q101.

FIG. 11 shows a circuit diagram of a lighting circuit 4001 according to this modification, and FIG. 12 shows a circuit diagram of a drive unit U3 according to this modification.
As shown in FIG. 11, the voltage conversion circuit 43 that constitutes a part of the lighting circuit 4001 is different from the first embodiment in that it includes a drive unit U3. Further, as shown in FIG. 12, the drive unit U3 is different from the drive circuit U1 according to the first embodiment in that an instruction determination circuit 54 in which an instruction circuit and a determination circuit are integrated is provided. . In addition, about the structure similar to Embodiment 1, the same code | symbol is attached | subjected and description is abbreviate | omitted suitably.

  The instruction determination circuit 54 includes a constant current source 541, a switching element Q542 made of a P-channel MOSFET, a switching element Q543 made of an N-channel MOSFET, a capacitor C544, resistors R545, R547, R548, and a thyristor S546. Prepare. The constant current source 541 is connected to the regulator 110 and receives a power supply from the regulator 110 to output a constant current. The switching element Q542 has a source connected to the constant current source 541 and a gate connected to the output terminal of the NAND circuit 105. Switching element Q543 has a drain connected to the drain of switching element Q542, a gate connected to the output terminal of NAND circuit 105, and a source connected to source terminal S. Capacitor C544 is connected between the connection point of switching elements Q542 and Q543 and source terminal S. Resistors R547 and R548 are connected in series between both ends of the capacitor C544. The thyristor S546 has an anode connected to one end of the capacitor C544, a cathode connected to the other end of the capacitor C544, and a gate connected to a connection point between the resistors R547 and R548. The resistor R545 is connected between the regulator 110 and the anode of the thyristor S546.

Next, the operation of the instruction determination circuit 54 will be described.
With respect to the lighting circuit according to this modification, FIGS. 13 (a-1) and (b-1) are diagrams showing the waveform of the drain current of the switching element, and FIG. 13 (a-2) is a diagram showing the operation of the thyristor. And (b-2). Here, Ton indicates the ON time of the switching element Q101, and Ts indicates the time (hereinafter referred to as “stop reference time”) required for the thyristor S546 to be turned on after the switching element Q101 is turned on.

  When the output voltage from the NAND circuit 105 becomes “Low” level, the switching element Q101 is turned on, and the drain current Id flowing through the switching element Q101 increases (see FIG. 13A-1). At this time, the switching element Q542 is also turned on simultaneously. Then, when a current flows from the constant current source 541 into the capacitor C544, the voltage across the capacitor C544 increases. When the magnitude of the drain current Id flowing through the switching element Q101 reaches Id0 before the voltage across the capacitor C544 reaches the turn-on voltage of the thyristor S546, the output voltage of the NAND circuit 105 becomes “High” level. Thus, the switching element Q101 is turned off, and the drain current Id is cut off (see FIG. 13 (a-1)). At this time, switching element Q542 is turned off and switching element Q543 is turned on. Then, the charge charged in the capacitor C544 is discharged through the switching element Q543, and the voltage across the capacitor C544 decreases.

Therefore, if the output voltage of the NAND circuit 105 becomes “High” level before the voltage across the capacitor C544 rises to the turn-on voltage of the thyristor S546 after the switching element Q542 is turned on, the thyristor S546 is in the off state. It will be maintained (refer to FIG. 13 (a-2)).
On the other hand, when the rise of the drain current flowing through the switching element Q101 is gentle, the switching element Q542 is compared with the time until the magnitude of the drain current Id flowing through the switching element Q101 reaches Id0 after the switching element Q101 is turned on. After the turn-on, the time until the voltage across the capacitor C544 rises to the turn-on voltage of the thyristor S546 (that is, the time taken for the thyristor S546 to turn on after the switching element Q101 is turned on) is shorter ( (Refer FIG.13 (b-1) and (b-2)). Then, once the thyristor S546 is turned on, the thyristor S546 is kept on, and the voltage at the connection point between the resistor R545 and the thyristor S546 is maintained at the “Low” level (see FIG. 13B-2). Then, the input voltage from the instruction determination circuit 54 to the AND circuit 102 is maintained at the “Low” level, and the set terminal S of the RS flip-flop circuit 103 always has the “Low” level voltage regardless of the voltage level of the clock signal. Is entered. As a result, the switching element Q101 is maintained in the OFF state, and the drive circuit U1 is stopped.

  Here, when the turn-on voltage of the thyristor S546 is Vt, the capacitance value of the capacitor C544 is C, and the current value of the current flowing from the constant current source 541 to the capacitor C544 is I, the stop reference time Ts is expressed by the equation (5). .

As can be seen from Equation (5), in the instruction determination circuit 54 according to this modification, the stop reference time Ts can be freely set by adjusting the capacitance of the capacitor C544. Specifically, the stop reference time Ts can be set shorter as the capacitance of the capacitor C544 is reduced.
Further, according to the present modification, the instruction determination circuit 54 is incorporated in the drive unit U3, so that the lighting circuit 4001 can be further reduced in size.

(5) In the first embodiment, the example in which the voltage conversion circuit 3 configures the step-up / step-down circuit has been described. However, the present invention is not limited to this, and may be composed of, for example, a booster circuit or a step-down circuit. .
(6) In the first embodiment, the example in which the determination circuit 121 is incorporated in the semiconductor package constituting the drive circuit U1 and the instruction circuit 4 is provided outside the drive circuit U1 has been described. For example, the instruction circuit 4 may also be incorporated in a semiconductor package constituting the drive circuit U1.

(7) In Embodiments 1 and 2, the example in which the LED module 5 using LEDs is used has been described, but the present invention is not limited to this. For example, a light emitting module using an organic EL (electric luminescence element) element or other inorganic EL element may be used.
(8) In the second embodiment, the example of the lamp on which the lighting circuit 1 according to the first embodiment is mounted has been described. However, the present invention is not limited to this, and has been described in the modification examples (1) to (5). It may be a lamp equipped with a lighting circuit.

  (9) In the first embodiment, the example in which the voltage conversion circuit 3 stops the voltage output when the voltage across the electrolytic capacitor C2 becomes equal to or lower than the voltage threshold has been described. Further, the voltage across the electrolytic capacitor C2 There may be provided an informing means for informing the outside that the voltage is below the voltage threshold. As this notification means, for example, a detector that detects the voltage of the input terminal CL of the drive circuit U1, a speaker, and a buzzer sound when the voltage detected by the detector is below a predetermined reference voltage. And a control unit that controls the operation of the speaker so as to generate the noise. Alternatively, an alarm lamp provided outside the lighting device including the lighting circuit is provided, and the control unit is configured to turn on the alarm lamp when the voltage detected by the detector is equal to or lower than a predetermined reference voltage. In addition, the operation of the alarm lamp may be controlled.

  (10) In Embodiment 1, the example in which the indication circuit 4 changes the voltage of the input terminal CL of the drive circuit U1 based on the voltage across the electrolytic capacitor C2 has been described. However, the present invention is not limited to this. For example, when the capacitors C1 and C8 are constituted by electrolytic capacitors, the voltage at the input terminal CL of the drive circuit U1 may be changed based on the voltage between both ends of the capacitors C1 and C8.

  (11) In Embodiment 1, the example in which the instruction circuit 4 changes the voltage of the input terminal CL of the drive circuit U1 based on the average value of the voltage generated across the electrolytic capacitor C2 has been described. Is not to be done. For example, the voltage of the input terminal CL of the drive circuit U1 may be changed based on the maximum value or the minimum value of the voltage generated between both ends of the electrolytic capacitor C2.

Alternatively, the indication circuit 4 detects the frequency at which the voltage generated across the electrolytic capacitor C2 falls below the voltage threshold, and when the detected frequency exceeds a predetermined reference number, the voltage at the input terminal CL of the drive circuit U1 is reduced. You may make it make it.
The instruction circuit 4 holds a voltage value (predetermined reference voltage value) generated between both ends of the electrolytic capacitor C2 at the start of use of the lighting circuit 1, and the voltage between both ends of the electrolytic capacitor C2 is the reference voltage. When the voltage becomes lower than the value, the voltage of the input terminal CL of the drive circuit U1 may be lowered.

  The present invention can be used for illumination such as an LED lamp.

DESCRIPTION OF SYMBOLS 1,1001,2001,3001,4001 Lighting circuit 2 Rectifier circuit 3,23,33,43 Voltage conversion circuit 4,34,44 Instruction circuit 5 LED module 31 Buck-boost circuit 54 Instruction determination circuit 101 Oscillator 102, 111 AND circuit 103 RS flip-flop circuit 104 OR circuit 105 NAND circuit 106 Gate driver 107, 108 Comparator 110 Regulator 112 Blanking pulse generation circuit 113 Start / stop circuit 121, 221 Judgment circuit 122 Turn-off control circuit 208 Inverter 541 Constant current source 1000 Lamp 1101 Globe 1102 Case 1103 Base 1104a, 1104b Lead AC AC power supply C1, C5, C6, C7, C8, C11, C12, C21, C31, C544 Capacitor C2 Electrolytic capacitor Sensor D1 Diode F1 Fuse L2 Inductor Tr1, Tr3, Q1, Q101, Q542, Q543 Switching element R1, R3, R4, R6, R7, R8, R11, R12, R13, R14, R21, R22, R23, R24, R31, R32, R33, R101, R102, R103, R545, R547, R548 Resistance R2, R41, R42 Variable resistance S546 Thyristor te101a Clock terminal te101b Signal terminal U1, U2 Drive circuit U3 Drive unit U41 Control circuit

Claims (11)

A lighting circuit for lighting a light source by receiving power supply from an AC power source,
A rectifier circuit for rectifying alternating current;
An electrolytic capacitor connected between output terminals of the rectifier circuit;
When the voltage generated across the electrolytic capacitor is stepped up / down and output to the light source and the average voltage across the electrolytic capacitor is greater than a voltage threshold, the voltage output to the light source is continued, A voltage conversion circuit for stopping output of the voltage to the light source when the voltage average value between both ends of the capacitor is equal to or lower than a voltage threshold;
The voltage threshold changes according to the voltage output to the light source, and when the voltage output to the light source is smaller than the minimum value of the voltage generated across the electrolytic capacitor, the voltage threshold is A lighting circuit, wherein the lighting circuit is set to be larger than a voltage output to the light source . The voltage conversion circuit includes:
By alternately selecting a first current path that has an inductor and causes energy storage in the inductor and a second current path that releases the energy stored in the inductor to the light source, a buck-boost circuit by applying lifting the voltage across output to the light source,
A drive circuit for adjusting the step-up / step-down by controlling a ratio between a period during which the step-up / step-down circuit selects the first current path and a period during which the second current path is selected;
When the voltage average value between both ends of the electrolytic capacitor is larger than the voltage threshold value, voltage output is continued, and when the voltage average value between both ends of the electrolytic capacitor is equal to or less than the voltage threshold value, The lighting circuit according to claim 1, further comprising: an instruction circuit that instructs to stop outputting the voltage to the light source of the step-up / step-down circuit. The drive circuit includes a determination circuit that determines a magnitude relationship between an input voltage and a determination reference voltage. When the determination circuit determines that the input voltage is equal to or higher than the determination reference voltage, the drive circuit outputs a voltage output to the step-up / down circuit. If it is determined that the input voltage is smaller than the determination reference voltage, the voltage output to the step-up / down circuit is stopped,
The indicating circuit is connected to the determination circuit, and when an average value of voltages between both ends of the electrolytic capacitor is equal to or lower than the voltage threshold, by inputting a voltage smaller than the determination reference voltage to the determination circuit, The lighting circuit according to claim 2, wherein the driving circuit is instructed to stop outputting the voltage to the light source of the step-up / down circuit. The indicating circuit is
Two resistors connected in series between both ends of the electrolytic capacitor;
A voltage stabilizing capacitor connected between a connection point of the two resistors and a low potential side of the electrolytic capacitor;
A constant voltage source that outputs a constant voltage;
Comprising a PNP bipolar transistor, the emitter is connected to the constant voltage source via a pull-up resistor, the collector is connected to the low potential side of the electrolytic capacitor, and the base is connected to the connection point of the two resistors And a switching element formed,
The lighting circuit according to claim 3, wherein a voltage between the emitter of the switching element and a low potential side of the electrolytic capacitor is output to the determination circuit. The determination circuit includes:
A first voltage output constant voltage source for outputting a constant first voltage;
An output terminal of the instruction circuit is connected to the plus side input terminal, and the first voltage output constant voltage source is connected to the minus side input terminal, and the second voltage and the first voltage output from the instruction circuit are obtained. A comparator for comparison,
The lighting circuit according to claim 4, wherein a magnitude relationship between an input voltage from the instruction circuit and the determination reference voltage is determined based on an output voltage of the comparator. The drive circuit includes a determination circuit that determines a magnitude relationship between an input voltage and a determination reference voltage, and outputs a voltage to the step-up / down circuit when the determination circuit determines that the input voltage is equal to or lower than the determination reference voltage. And when the determination circuit determines that the input voltage is greater than the determination reference voltage, the voltage output to the step-up / down circuit is stopped,
The indicating circuit is connected to the determination circuit, and when an average value of the voltage across the electrolytic capacitor is equal to or lower than the voltage threshold, by inputting a voltage larger than the determination reference voltage to the determination circuit, The lighting circuit according to claim 2, wherein the driving circuit is instructed to stop outputting the voltage from the step-up / step-down circuit to the light source. The indicating circuit is
Two resistors connected in series between both ends of the electrolytic capacitor;
A voltage stabilizing capacitor connected between a connection point of the two resistors and a low potential side of the electrolytic capacitor;
A constant voltage source that outputs a constant voltage;
It consists of an NPN bipolar transistor, the emitter is connected to the low potential side of the electrolytic capacitor, the collector is connected to the constant voltage source via a pull-up resistor, and the base is connected to the connection point of the two resistors And a switching element formed,
The lighting circuit according to claim 6, wherein a voltage between the collector of the switching element and a low potential side of the electrolytic capacitor is output to the determination circuit. The determination circuit includes:
A first voltage output constant voltage source for outputting a constant first voltage;
An output terminal of the instruction circuit is connected to the plus side input terminal, and the first voltage output constant voltage source is connected to the minus side input terminal, and the second voltage and the first voltage output from the instruction circuit are obtained. A comparator to compare;
An inverter connected to an output terminal of the comparator and inverting and outputting a voltage input from the comparator;
The lighting circuit according to claim 7, wherein a magnitude relationship between an input voltage from the instruction circuit and the determination reference voltage is determined based on an output voltage of the comparator based on an output voltage of the inverter. . The lighting circuit according to any one of claims 3 to 8, wherein the driving circuit and the instruction circuit are incorporated in one semiconductor package.   A lamp comprising the lighting circuit according to any one of claims 1 to 9.   The voltage threshold is a voltage near the center of the minimum value of the voltage generated between both ends of the electrolytic capacitor and the voltage output to the light source.
  The lighting circuit according to claim 1.

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