JP5327251B2 - LED lighting device - Google Patents

Abstract

The invention provides an LED lighting device, which can stably light the LED without using an electrolytic capacitor as a smoothing capacitor connected to the output end of a rectification circuit. The LED lighting device (10) comprises a rectification circuit (13) which conducts a full-wave rectification on an AC power supply, a voltage-reducing chopper circuit (14) which has a winding (Np) and a switch element (Q1) and reduces voltage of the full-wave rectification output from the rectification circuit (13), an LED module (15) connected to the output end of the voltage-reducing chopper circuit (14), and a self-excitation drive signal generating circuit (17) which has a winding (Nd) in a magnetic coupling with the winding (Np) and drives the voltage-reducing chopper circuit (14). The self-excitation drive signal generating circuit (17) has a turn-on time correcting circuit (22), which regulates the turn-on time of the switch element (Q1). When the output voltage of the voltage-reducing chopper circuit (14) is relatively high, the turn-on time is shortened, and when the output voltage is relatively low, the turn-on time is prolonged.

Description

  The present invention relates to an LED lighting device using an LED (light emitting diode) as a light source, and more particularly to an improvement of an LED lighting device that stably lights an LED lamp.

  2. Description of the Related Art In recent years, lighting devices using LEDs have been widely spread because of their low power consumption and long life. Since an LED is a DC drive element, it is common to drive a pulsating voltage source obtained by full-wave rectification of a commercial AC power source using a smoothing capacitor and drive using the DC voltage from the smoothing capacitor as a power source ( (See Patent Documents 1 and 2). At that time, a large-capacity electrolytic capacitor is often used as the smoothing capacitor.

  Further, the luminance of the LED element can be controlled by the amount of current, but it is not always easy to accurately control the amount of direct current. Therefore, a method of controlling the luminance of the LED element by supplying a high-frequency switching pulse to the LED element and controlling the duty ratio is preferably employed.

Japanese Patent Laid-Open No. 10-321914 JP 2009-302017 A

  LED elements are highly heat-generating parts, but electrolytic capacitors are vulnerable to heat, so that there is a problem that their characteristics deteriorate due to long-term use at high temperatures and their life is shortened. Although one of the features of LED elements is long life as described above, if the life of an electrolytic capacitor, which is one of the components that drive LED elements, becomes short, the advantages of LED elements can be utilized. I can't. Therefore, the LED drive circuit is required to have a long life together with the LED element without using an electrolytic capacitor.

  When other existing capacitors are used instead of electrolytic capacitors, the capacity is not sufficient to rectify the pulsating flow of the full-wave rectified wave, and only a capacity that can smooth high-frequency components due to switching can be secured. For this reason, a full-wave rectified wave is applied to the input terminal of the LED drive circuit. Since the full-wave rectified wave falls to around 0V every cycle, it cannot operate in the valley period around 0V. Therefore, it is necessary to supply an LED current that is as stable as possible outside the valley period, and it is necessary to make the luminance constant during the lighting period of the LED.

  The present invention has been made to solve the above problems, and an object of the present invention is to stably light an LED without using an electrolytic capacitor as a smoothing capacitor connected to the output terminal of the rectifier circuit. The object is to provide a possible LED lighting device.

  In order to solve the above problems, an LED lighting device according to the present invention includes a rectifier circuit that rectifies an AC power source, a chopper circuit that includes a first winding and a switching element, and transforms a rectified waveform output from the rectifier circuit; An LED element connected to an output terminal of the chopper circuit; and a self-excited drive signal generation circuit that includes a second winding that is magnetically coupled to the first winding and drives the chopper circuit. The drive signal generation circuit defines the on-time of the switching element, and the on-time is shortened when the output voltage of the rectifier circuit is relatively large, and the on-time when the output voltage is relatively small. And an on-time correction circuit that controls the length to be longer.

  According to the present invention, the current level during the on-time of the LED can be stabilized. Therefore, the luminance during the lighting period of the LED can be made constant without using an electrolytic capacitor as a smoothing capacitor, and the LED can be lit stably.

  The on-time correction circuit includes a capacitor, a first resistor circuit including a first resistor, and a second resistor circuit including a series circuit of a second resistor and a first Zener diode, And one end of the second resistor circuit is connected to the capacitor, the first Zener diode has a first Zener voltage, and an input current is less than the first Zener voltage. Flows through the first resistor circuit to the capacitor, and when the input voltage is greater than or equal to the first Zener voltage, the input current flows through both the first resistor circuit and the second resistor circuit. Preferably, it flows through the capacitor. According to this configuration, the on-time correction circuit can be realized with a simple configuration.

  The on-time correction circuit includes a third resistor circuit including a series circuit of a third resistor and a second Zener diode, and one end of the third resistor circuit is combined with the first and second resistor circuits. The second Zener diode is connected to the capacitor, the second Zener diode has a second Zener voltage higher than the first Zener voltage, and the input voltage is equal to or higher than the first Zener voltage and the second Zener voltage. The input current flows through the first resistor circuit and the second resistor circuit to the capacitor when the input voltage is greater than or equal to the second Zener voltage. More preferably, the current flows through all of the first to third resistance circuits to the capacitor. According to this configuration, the correction accuracy by the on-time correction circuit can be further increased.

  The LED lighting device according to the present invention preferably further includes a zero-cross stop circuit that forcibly stops the operation of the chopper circuit during a period in which the rectified waveform output from the rectifier circuit is lower than a predetermined threshold level. If the rectified wave from the rectifier circuit is not smoothed using a large-capacity smoothing capacitor, a large pulsating rectified wave is input to the chopper circuit, the chopper circuit operates randomly, and the light emission of the LED becomes unstable. . However, by forcibly stopping the operation of the chopper circuit, the luminance during the lighting period of the LED can be made constant.

  The LED lighting device according to the present invention preferably further includes an open protection circuit that forcibly stops the operation of the chopper circuit when the output terminal of the chopper circuit is opened. When the output end of the chopper circuit is opened due to breakage of the LED element, the voltage between the terminals of the chopper circuit rises and the elements and circuits in the LED lighting device may be damaged, but an open protection circuit is provided. In some cases, such damage can be prevented.

  In the LED lighting device according to the present invention, the self-excited drive signal generation circuit further includes a slicer for limiting a peak value of the output voltage of the second winding, and the output voltage of the second winding causes the slicer to It is preferable to be supplied to the switching element. After the output voltage of the second winding is limited by the slicer and then supplied to the switching element, the gate breakdown voltage of the switching element can be secured and the voltage of the second winding can be made as high as possible. Thus, the chopper circuit can be operated for a long time.

  ADVANTAGE OF THE INVENTION According to this invention, the LED lighting device which can light LED stably can be provided, without using an electrolytic capacitor as a smoothing capacitor.

It is a block diagram showing a configuration of an LED lighting device according to a preferred embodiment of the present invention, It is a circuit diagram of the LED lighting device shown in FIG. It is operation | movement explanatory drawing of the pressure | voltage fall chopper circuit 14, Comprising: (a) has shown the operation | movement of the switching element Q1 being an ON state, (b) has each shown the operation | movement of the switching element Q1 being an OFF state. 3 is a circuit diagram for explaining the configuration and operation of an on-time correction circuit 22. FIG. It is a graph which shows the voltage / current waveform between terminals of capacitor C5 by simulation, (a) shows a current waveform and (b) shows a voltage waveform, respectively. It is a graph which shows the power supply voltage waveform and LED current waveform of the rectifier circuit by simulation, Comprising: (a) is a power supply voltage waveform when not using an ON time correction circuit, (b) is LED when not using an ON time correction circuit. The current waveform, (c) shows the power supply voltage waveform when the on-time correction circuit is used, and (d) shows the LED current waveform when the on-time correction circuit is used. It is a graph which shows the power supply voltage waveform and LED current waveform of the rectifier circuit by an actual circuit, Comprising: (a) is a power supply voltage waveform when not using an ON time correction circuit, (b) is the case where an ON time correction circuit is not used (C) shows the power supply voltage waveform when the on-time correction circuit is used, and (d) shows the LED current waveform when the on-time correction circuit is used. It is a circuit diagram which shows the structure of a zero cross stop circuit. It is an input / output signal waveform diagram of a zero cross stop circuit. It is a circuit diagram which shows the structure of an open protection circuit.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing a configuration of an LED lighting device according to a preferred embodiment of the present invention. FIG. 2 is a circuit diagram of the LED lighting device shown in FIG.

  As shown in FIG. 1, the LED lighting device 10 includes a filter circuit 12, a rectifier circuit 13, a step-down chopper circuit 14, an LED module 15, and a filter circuit 12 that removes high-frequency noise from a commercial power supply (AC 100V, 50/60 Hz) 11. An overcurrent protection circuit 16, a self-excited drive signal generation circuit 17, a zero cross stop circuit 18, and an open protection circuit 19 are provided.

  The filter circuit 12 is an LC filter including a capacitor C1, an inductor L1, and a resistor R1 connected to the commercial power supply 11. The output terminal of the filter circuit 12 is connected to the input terminal of the rectifier circuit 13.

  The rectifier circuit 13 is a bridge-type full-wave rectifier circuit composed of four diodes, and a diode D1 and a smoothing capacitor C2 are connected to an output end thereof. Since the smoothing capacitor C2 is not an electrolytic capacitor, it has high heat resistance, but does not have a capacity capable of smoothing the full-wave rectified waveform and can smooth switching noise.

  The step-down chopper circuit 14 includes a voltage-controlled switching element Q1, a winding Np, a flywheel diode D2, and a capacitor C3. The switching element Q1 according to the present embodiment is an N-type MOSFET. Winding Np, flywheel diode D2 and capacitor C3 constitute a loop circuit, one end of capacitor C3 is connected to one end of winding Np, and the cathode of diode D2 is connected to the other end of capacitor C3. The other end of the winding Np is connected to the anode of the diode D2.

  Further, the positive side output terminal of the rectifier circuit 13 is connected to one end of the winding Np via a diode D1, and the drain of the switching element Q1 is connected to the other end of the winding Np. The source of the switching element Q1 is connected to the negative output terminal (ground) of the rectifier circuit 13 via the current detection resistor R2 of the overcurrent protection circuit 16.

  Both ends of the capacitor C3 constitute a pair of output terminals of the step-down chopper circuit 14, and an LED module 15 composed of a series circuit of LED elements is connected to the output terminals. The cathode side of the LED module 15 is connected to one end of the capacitor C3, and the anode side is connected to the other end of the capacitor C3.

  3A and 3B are diagrams for explaining the operation of the step-down chopper circuit 14. FIG. 3A shows the switching element Q1 in the on state, and FIG. 3B shows the switching element Q1 in the off state.

  As shown in FIG. 3A, when the switching element Q1 is on, the current from the power supply VCC (rectifier circuit 13) flows through a loop circuit composed of the winding Np and the switching element Q1, and the winding Np has excitation energy. Is accumulated.

  3B, when the switching element Q1 is turned off, the excitation energy of the winding Np is supplied to the LED module 15, so that the LED module can be lit even when the switching element Q1 is turned off. it can. At this time, electrostatic energy is accumulated in the capacitor C3.

  When the switching element Q1 is turned on again, as shown in FIG. 3A, the current from the power supply VCC flows again through the loop circuit composed of the winding Np and the switching element Q1, but the electrostatic energy of the capacitor C3 is changed to the LED module. 15, the LED module 15 can be lit even when the switching element Q1 is on.

  In the step-down chopper circuit 14 according to the present embodiment, since only the excitation energy is supplied to the LED module 15, it is only necessary to limit only the peak and cycle of the excitation current, and the constant current operation is relatively easy. Since the step-down chopper circuit 14 automatically operates in the critical mode, a certain amount of core volume is required. However, it is only necessary to limit the on-time of the switching element Q1, and the brightness of the LED module 15 can be easily controlled. It is.

  As shown in FIGS. 1 and 2, the step-down chopper circuit 14 is connected to a starting resistor Rst. The starting resistor Rst is provided between the plus side output terminal of the rectifier circuit 13 and the gate of the switching element Q1. Further, a resistor R3 is provided between the gate of the switching element Q1 and the negative output terminal of the rectifier circuit 13. Since the starting resistor Rst applies a voltage on the rectifier circuit 13 side to the gate of the switching element Q1 to provide a forward bias that allows the switching element Q1 to operate, the switching element Q1 can be turned on.

  The overcurrent protection circuit 16 is a circuit that turns off the switching element Q1 when the current flowing through the switching element Q1 of the step-down chopper circuit 14 becomes excessive, and includes a transistor Q2 and a current detection resistor R2. The collector of the transistor Q2 is connected to the gate of the switching element Q1, and the emitter of the transistor Q2 is connected to the source of the switching element Q1 (the negative output terminal of the rectifier circuit 13). When a predetermined peak current flows through the current detection resistor R2, the transistor Q2 is turned on, the gate and source of the switching element Q1 are short-circuited, and the switching element Q1 is turned off. Therefore, overcurrent of the step-down chopper circuit 14 can be prevented.

  The self-excited drive signal generation circuit 17 includes an inductor (drive winding) Nd, a slicer 20, a gate drive circuit 21, and an on-time correction circuit 22. The winding Nd is magnetically coupled to the winding Np of the step-down chopper circuit 14. Yes. That is, the winding Np and the winding Nd constitute a primary winding and a secondary winding of the transformer T1, respectively. When the switching element Q1 is turned on, a current flows through the winding Np of the step-down chopper circuit 14, and an induced voltage is also generated in the winding Nd.

  The slicer 20 includes a transistor Q3, a resistor R4 connected between the base and collector of the transistor Q3, a series circuit of a Zener diode DZ1 and a diode D3 connected to the base of the transistor Q3, and between the collector and emitter of the transistor Q3. The output voltage of the winding Nd is limited to about 10 V by the slicer 20 including the connected diode D4, and then input to the gate of the switching element Q1 through the gate drive circuit 21 including the diode D5, the capacitor C4, and the resistor R5. As a result, the ON state of the switching element Q1 is maintained. In order to operate the step-down chopper circuit 14 for as long a period as possible, it is necessary to increase the voltage of the winding Nd as much as possible. However, since the gate breakdown voltage of the switching element Q1 is exceeded as it is, the voltage applied to the gate of the switching element Q1 is The slicer 20 is used for that purpose.

When the transistor Q2 of the overcurrent protection circuit 16 is turned on by the overcurrent and the gate and the source of the switching element Q1 are short-circuited, the forward bias is lost, so the switching element Q1 is turned off. When the switching element Q1 is turned off, the excitation energy accumulated in the winding Np is released by the back electromotive force as shown in FIG . At this time, since the polarity of the voltage between the terminals of the winding Nd is reversed, the gate voltage of the switching element Q1 is drawn and immediately turned off. This polarity inversion continues until the winding Np finishes releasing the excitation energy, and the capacitor C4 is charged during this period. When the winding Np finishes releasing the excitation energy, the electrostatic energy discharged from the capacitor C4 applies a forward bias to the gate of the switching element Q1, so that the switching element Q1 is rapidly turned on. Thereafter, the above-described circuit operation is repeated, so that the LED module is always lit by the charging current and the discharging current.

When the switching element Q1 is on, an induced current flows through the winding Nd electromagnetically coupled to the winding Np, and this current charges the capacitor C5 of the on-time correction circuit 22. When the capacitor C5 is charged and the voltage across its terminals exceeds the base voltage of the transistor Q4, the transistor Q4 is turned on, the gate and source of the switching element Q1 are short-circuited, and the switching element Q1 is turned off.

  Next, the on-time correction circuit 22 will be described.

  FIG. 4 is a circuit diagram for explaining the configuration and operation of the on-time correction circuit 22.

  As shown in FIG. 4, the on-time correction circuit 22 includes a transistor Q4, a capacitor C5 connected between the base and emitter of the transistor Q4, a first resistor circuit including a resistor R6, a Zener diode DZ2 and a second resistor. A second resistor circuit formed of a series connection of resistors R7, a third resistor circuit formed of a Zener diode DZ3 and a resistor R8 connected in series, and a resistor R9 connected in parallel to the capacitor C5. One end of each of the first to third resistance circuits is connected to one end of the winding Nd, and the other ends of the first to third resistance circuits are all connected to one end of the capacitor C5. The other end of the capacitor C5 is connected to the negative output terminal of the rectifier circuit 13.

  A series circuit of diodes D6 and D7 as an overvoltage protection circuit is inserted between the base and emitter of the transistor Q4. Further, the base of the transistor Q4 is connected to one end of the capacitor C5.

  Like the transistor Q2 of the overcurrent protection circuit 16, the collector of the transistor Q4 is connected to the gate of the switching element Q1, and the emitter of the transistor Q4 is connected to the source of the switching element Q1 (the negative output terminal of the rectifier circuit 13). ing. Therefore, when the transistor Q4 is turned on, the gate and source of the switching element Q1 are short-circuited, and the switching element Q1 is turned off.

In the present embodiment, the Zener diode DZ2 of the second resistor circuit is turned on at 10V, and the Zener diode DZ3 of the third resistor circuit is turned on at 20V. Therefore, when the voltage between the terminals of the winding Nd is in the range of 0 to 10 V, no current flows through the second and third resistance circuits, and a current flows only through the first resistance circuit. Therefore, the current input to the capacitor C5 is only the current _IR6 passing through _R6 , and the capacitor C5 is slowly charged.

When the voltage between the terminals of the winding Nd is in the range of 10 to 20 V, no current flows through the third resistor circuit, and current flows only through the first and second resistor circuits. Therefore, the current input to the capacitor C5 is I _R6 + I _R7 , and the amount of current is larger than when it is 0 to 10 V, and the capacitor C5 is charged quickly.

When the voltage between terminals of the winding Nd is in the range of 20 to 30 V, current flows through all of the first to third resistance circuits. Therefore, the current input to the capacitor C5 is I _R6 + I _R7 + I _R8 , and the amount of current is further increased than when it is 10 to 20 V, and the capacitor C5 is charged more quickly.

  As described above, the charging speed of the capacitor C5 is slow when the voltage between the terminals of the winding Nd is low and is fast when the voltage between the terminals of the winding Nd is high. Therefore, the operation of the switching element Q1 is as follows. Become.

  That is, when the voltage between the terminals of the winding Nd is high, the capacitor C5 is rapidly charged. As a result, the transistor Q4 is immediately turned on and the switching element Q1 is immediately turned off. Therefore, the ON time of the switching element Q1 is shortened, and the current supplied to the LED module 15 is reduced.

  On the other hand, when the voltage between the terminals of the winding Nd is low, the capacitor C5 is slowly charged. As a result, the transistor Q4 is turned on later and the switching element Q1 is turned off later. Therefore, the ON time of the switching element Q1 becomes longer, and the supply current to the LED module 15 increases.

  FIG. 5 is a graph showing a voltage / current waveform between terminals of the capacitor C5 by simulation, where (a) shows the current waveform and (b) shows the voltage waveform.

  As shown in FIGS. 5A and 5B, when the switching element Q1 is on, a positive current flows through the capacitor C5, whereby the capacitor C5 is charged, and the voltage across the terminals of the capacitor C5 during the charging period. Gradually increases. When the terminal voltage of the capacitor C5 reaches 0.65V, the transistor Q4 is turned on and the switching element Q1 is turned off. Then, from the moment when the switching element Q1 is turned off, the capacitor C5 is reversed to a discharge state and is discharged with a time constant determined by the resistor R9.

  In this way, the amount of current supplied to the LED module 15 is corrected to be small when the voltage between the terminals of the winding Nd is high and large when the voltage is low, so that a current waveform with a flat high level period can be obtained. Can do.

  FIG. 6 is a graph showing the power supply voltage waveform and the LED current waveform of the rectifier circuit by simulation. (A) and (b) show the case where the on time correction circuit is not used, and (c) and (d) show the on time A case where a correction circuit is used is shown. Further, (a) and (c) show the power supply voltage waveform, and (b) and (d) show the LED current waveform, respectively.

  As shown in FIGS. 6A and 6B, when the on-time correction circuit is not used, that is, when only the first resistor circuit (only resistor R6) is connected to the capacitor C5, the LED module 15 is connected to the LED module 15. The supply current has a waveform with a dull rise and fall. On the other hand, as shown in FIGS. 6C and 6D, a second resistor circuit composed of a resistor R7 and a Zener diode DZ2 and a third resistor circuit composed of a resistor R8 and a Zener diode DZ3 are added. When the time correction circuit is used, the high level period has a flat waveform.

  FIG. 7 is a graph showing the power supply voltage waveform and the LED current waveform of the rectifier circuit by an actual circuit, in which (a) and (b) do not use the on-time correction circuit, (c) and (d) A case where an on-time correction circuit is used is shown. Further, (a) and (c) show the power supply voltage waveform, and (b) and (d) show the LED current waveform, respectively.

  As shown in FIGS. 7A to 7D, it can be seen that the same result as the simulation can be obtained even in an actual circuit. That is, as shown in FIGS. 7A and 7B, when the on-time correction circuit is not used, the current supplied to the LED module 15 has a waveform with a dull rise and fall, but FIG. ) And (d), when the on-time correction circuit is used, the high level period has a flat waveform.

  Next, the zero cross stop circuit 18 will be described.

  FIG. 8 is a circuit diagram showing a configuration of the zero-cross stop circuit 18.

  As shown in FIG. 8, the zero cross stop circuit 18 is a circuit that forcibly stops the oscillation operation near the zero cross of the full-wave rectified waveform output from the rectifier circuit 13. When the step-down chopper circuit 14 operates at random, the light emission luminance of the LED is not stable. Therefore, the operation of the step-down chopper circuit 14 is forcibly stopped to prevent instability of the luminance of the LED.

  The zero-cross stop circuit 18 includes a transistor Q5, a parallel circuit of a capacitor C6 and a resistor R10 connected between the base and emitter of the transistor Q5, and a stop pulse generation circuit 23 that generates a stop pulse.

  Similar to the transistor Q2 of the overcurrent protection circuit 16, the collector of the transistor Q5 is connected to the gate of the switching element Q1, and the emitter of the transistor Q5 is connected to the source of the switching element Q1 (the negative output terminal of the rectifier circuit 13). . Therefore, when the transistor Q5 is turned on, the gate and source of the switching element Q1 are short-circuited, and the switching element Q1 is turned off.

  The stop pulse generation circuit 23 monitors the full-wave rectified waveform of the rectifier circuit 13 and generates a stop pulse when the full-wave rectified waveform is equal to or lower than a predetermined threshold voltage. When the capacitor C6 is charged by the stop pulse, the transistor Q5 is turned on, and the operation is stopped by short-circuiting the gate and the source of the switching element Q1. When the supply of the stop pulse ends, the capacitor C6 is discharged through the resistor R10, and the transistor Q5 is turned off.

  The stop pulse generation circuit 23 according to the present embodiment includes a pair of PNP transistors Q6 and Q7 constituting a differential amplifier circuit, and a series circuit of a resistor R11, a diode D8, and a resistor R14 connected to the emitters of the transistors Q6 and Q7. And a capacitor C7 connected to the emitters of the transistors Q6 and Q7 via a resistor R14. One end of the capacitor C7 is connected to the emitters of the transistors Q6 and Q7 via the resistor R14, and the other end is connected to the negative output terminal of the rectifier circuit 13.

  The stop pulse generation circuit 23 includes a Zener diode DZ4 connected between the base and collector of the transistor Q6, a resistor R15 connected between the base and emitter of the transistor Q6, and a resistor R12 connected to the base of the transistor Q7. And a parallel circuit of a resistor R13, a capacitor C8 and a Zener diode DZ5 connected between the base of the transistor Q7 and the collector of the transistor Q6. The collector of the transistor Q7 is connected to the base of the transistor Q5, and the output signal of the transistor Q7 is supplied to the transistor Q5 as a stop pulse.

The inter-terminal voltage of the winding Nd is supplied to the emitters of the transistors Q6 and Q7 via the resistor R11, the diode D8, and the resistor R14. On the other hand, the output voltage of the rectifier circuit 13 is divided by the resistors R12 and R13 and then supplied to the base of the transistor Q7. Whereas the maximum voltage between terminals of the winding Nd is 30 to 40V, the maximum value of the output voltage of the rectifier circuit 13 is about 140V, so that a large reverse bias voltage is applied between the emitter and base of the transistor Q7. Although the reverse bias withstand voltage between the emitter and base of the transistor Q7 is only a few volts, the cathode of the Zener diode DZ5 is connected to the base of the transistor Q7 to protect against the reverse bias voltage. .

  Further, the inter-terminal voltage of the winding Nd is also supplied to the base of the transistor Q6 via the resistor R11, the diode D8, and the resistor R15. The base voltage of the transistor Q6 is held constant by the Zener diode DZ4. Since the inter-terminal voltage of the winding Nd is a full-wave rectified waveform, and the stop pulse generating circuit 23 needs to operate stably even near the zero cross, the operation of the transistors Q6 and Q7 is performed using a capacitor C7 having a capacity as large as possible. It is necessary to hold the voltage. The capacitor C7 is charged when the switching element Q1 is on. That is, when a voltage is applied to the winding Np, a voltage is generated in the winding Nd to charge the capacitor C7. Capacitor C7 is charged during the period when the winding voltage is rising, and discharged during other periods. Due to the presence of the diode D8, the discharge current of the capacitor C7 is always supplied to the emitters of the transistors Q6 and Q7 via the resistor R14.

  FIG. 9 is a waveform diagram of input / output signals of the zero cross stop circuit 18.

  As shown in FIG. 9, the comparator by the differential amplifier circuit of the transistors Q6 and Q7 compares the constant reference voltage defined by the Zener diode DZ4 with the reference voltage that is the full-wave rectified waveform from the rectifier circuit 13. . A stop pulse is not generated in a period when the reference voltage is higher than the reference voltage, a stop pulse is generated in a period lower than the reference voltage, the stop pulse is supplied to the capacitor C6, and the capacitor C6 is charged. Thereby, the transistor Q5 is turned on and the switching element Q1 is turned off, so that the operation near the zero cross can be stopped.

  Next, the open protection circuit 19 will be described.

  FIG. 10 is a circuit diagram showing a configuration of the open protection circuit 19.

  As shown in FIG. 10, in the open protection circuit 19, for example, when at least one LED element in the LED module 15 is damaged, the output terminal of the step-down chopper circuit 14 is opened, and the voltage between the terminals of the step-down chopper circuit 14 is reduced. This is a circuit for preventing a part of the elements in the LED lighting device 10 from being damaged.

The open protection circuit 19 includes a capacitor C9, a Zener diode DZ6, and a diode D9. The cathode of the diode D9 is connected to one end of the winding Nd via the resistor R11, and the anode of the diode D9 is connected to the negative side output terminal of the rectifier circuit 13 via the capacitor C9. The cathode of the Zener diode DZ6 is connected to the base of the transistor Q7, and the anode of the Zener diode DZ6 is connected to the anode of the diode D9.

Of the voltage across the winding Nd, only the negative voltage is taken out by the diode D9, smoothed by the capacitor C9, and connected to the reference voltage input terminal of the comparator, that is, the base of the transistor Q7 via the Zener diode DZ6.

  When the output terminal of the step-down chopper circuit 14 is opened and the voltage between the terminals of the step-down chopper circuit 14 rises, and the voltage applied to the Zener diode DZ6 becomes equal to or higher than the Zener voltage, the transistor Q7 is turned on, and a stop pulse is generated. The voltage is supplied to the capacitor C6, and the capacitor C6 is charged. Thereby, the transistor Q5 is turned on, the gate and the source of the switching element Q1 are short-circuited, and the switching element Q1 is turned off.

  When the output terminal of the step-down chopper circuit 14 is open, the exciting energy of the winding Nd is excessive, so that much energy is charged in the capacitor C4 of the gate drive circuit 21, and the gate drive voltage rises. For this reason, a Zener diode DZ7 as a clamper for connecting the gate and source of the switching element Q1 is necessary. It is possible to intermittently operate by consuming excess excitation energy with the Zener diode DZ7, thereby preventing destruction of each element. This threshold value must be set higher than the clamper voltage so that it does not conduct during normal operation.

  As described above, since the LED lighting device 10 according to the present embodiment includes the on-time correction circuit 22, the rise and fall of the current supplied to the LED are steep and close to flat except for the zero cross period. be able to. Therefore, the luminance during the lighting period of the LED can be made constant without using an electrolytic capacitor as the smoothing capacitor.

  Further, the LED lighting device 10 according to the present embodiment includes the zero-cross stop circuit 18 that forcibly stops the oscillation operation of the step-down chopper circuit 14 in the zero-cross period of the full-wave rectified waveform output from the rectifier circuit 13. Instability of LED luminance can be further suppressed.

  Furthermore, since the LED lighting device 10 according to the present embodiment includes the open protection circuit 19 that detects that the output terminals of the step-down chopper circuit 14 are open due to destruction of the LED or the like, the switching element Q1 is forcibly set. Therefore, a safe circuit can be realized.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say, the invention is included in the invention.

  For example, in the above embodiment, the on-time correction circuit 22 is controlled by switching the parallel connection condition of three resistors with a Zener diode, but the current path is not limited to three, and two Or four or more. Also, the switching method is not particularly limited. In the present invention, other rectifier circuits such as a half-wave rectifier circuit may be used, and other transformer circuits such as a boost chopper circuit may be used.

10 LED lighting device 11 commercial power supply 12 filter circuit 13 rectifier circuit 14 step-down chopper circuit 15 module 16 overcurrent protection circuit 17 self-excited drive signal generation circuit 18 zero cross stop circuit 19 open protection circuit 20 slicer 21 gate drive circuit 22 on-time correction circuit 23 Stop pulse generation circuit C1 to C9 Capacitors D1 to D9 Diodes DZ1 to DZ7 Zener diode L1 Inductor Nd, Np Winding Q1 Voltage controlled switching elements Q2 to Q7 Transistors R1 to R15 Resistor Rst Start resistor T1 Transformer

Claims (5)

A rectifier circuit for rectifying an AC power supply;
A chopper circuit including a first winding and a switching element for transforming a rectified waveform output from the rectifier circuit;
An LED element connected to the output end of the chopper circuit;
A self-excited drive signal generating circuit that includes a second winding magnetically coupled to the first winding and drives the chopper circuit;
The self-excited drive signal generation circuit is
The on-time of the switching element is defined, and the on-time is shortened when the output voltage of the rectifier circuit is relatively large, and the on-time is controlled to be long when the output voltage is relatively small. Including an on-time correction circuit,
The on-time correction circuit includes:
A capacitor;
A first resistance circuit including a first resistance;
A second resistor circuit including a series circuit of a second resistor and a first Zener diode;
One end of each of the first and second resistance circuits is connected to the capacitor,
The first Zener diode has a first Zener voltage;
When the input voltage is less than the first Zener voltage, the input current flows through the first resistor circuit to the capacitor;
The LED lighting device according to claim 1, wherein when the input voltage is equal to or higher than the first Zener voltage, the input current flows to the capacitor through both the first resistance circuit and the second resistance circuit. The on-time correction circuit includes:
A third resistor circuit including a series circuit of a third resistor and a second Zener diode;
One end of the third resistor circuit is connected to the capacitor together with the first and second resistor circuits,
The second Zener diode has a second Zener voltage higher than the first Zener voltage;
When the input voltage is greater than or equal to the first Zener voltage and less than a second Zener voltage, the input current flows to the capacitor through both the first resistor circuit and the second resistor circuit;
2. The LED lighting according to claim 1 , wherein when the input voltage is equal to or higher than the second Zener voltage, the input current flows to the capacitor through all of the first to third resistance circuits. apparatus. 3. The LED according to claim 1 , further comprising a zero-cross stop circuit that forcibly stops the operation of the chopper circuit during a period in which a rectified waveform output from the rectifier circuit is lower than a predetermined threshold level. Lighting device. 4. The LED according to claim 1 , further comprising an open protection circuit that forcibly stops the operation of the chopper circuit when the output terminal of the chopper circuit is open. 5. Lighting device. The self-excited drive signal generation circuit further includes a slicer that limits a peak value of the output voltage of the second winding, and the output voltage of the second winding is supplied to the switching element via the slicer. The LED lighting device according to any one of claims 1 to 4 , wherein:

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