JP2010245421A - Control circuit for light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the power factor of a control circuit controlling light emission of a light-emitting element. <P>SOLUTION: The control circuit includes: a rectification part 30 for full-wave rectifying an AC power source; a switching element 36 for switching current flowing through the light-emitting element for receiving a voltage which has been rectified by the rectification part 30; a voltage divider circuit 42 for dividing the voltage which has been full-wave rectified by the rectification part 30 to obtain a reference voltage V<SB>ref</SB>; a comparator 40 comparing a comparative voltage V<SB>cmp</SB>according to a current flowing through the light-emitting element with the reference voltage V<SB>ref</SB>; and a control part 38 controlling switching of the switching element 36 according to a result of comparison by the comparator 40. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a control circuit that controls a light emitting element.

  An illumination system using a light emitting diode (LED) as a light emitting element for illumination has been developed.

  FIG. 5 shows a control circuit 100 of a conventional lighting system. The control circuit 100 includes a rectifying unit 10, a rectifying capacitor 12, a choke coil 14, a regenerative diode 16, a switching element 18, a control unit 20, and a comparator 22.

  When AC power is supplied to the rectifier 10, the AC power is full-wave rectified. The full-wave rectified voltage is smoothed by the rectifying capacitor 12 and supplied as a drive voltage to the power supply voltage of the control unit 20 and the anode terminal of the LED 102. The cathode of the LED 102 is grounded via a series connection of the choke coil 14, the switching element 18, and the resistance element R1. By performing switching control of the switching element 18 by the control unit 20, current is supplied to the LED 102 via the choke coil 14, the switching element 18, and the resistance element R <b> 1, thereby causing the LED 102 to emit light. Further, when the switching element 18 is turned off, a regenerative diode 16 that regenerates energy stored in the choke coil 14 to the LED 102 is provided in parallel with the LED 102 and the choke coil 14.

  The comparator 22 has a constant reference voltage Vref obtained by resistance-dividing the comparison voltage Vcmp generated at both ends of the resistance element R1 by the current flowing through the LED 102 and the voltage Vreg generated by the control unit 20 receiving the smoothed power source. And are input. The control unit 20 controls switching of the switching element 18 based on the comparison result between the reference voltage Vref and the comparison voltage Vcmp by the comparator 22. When the comparison voltage Vcmp is smaller than the reference voltage Vref, the control unit 20 turns on the switching element 18 to flow current to the LED 102, and when the comparison voltage Vcmp becomes larger than the reference voltage Vref, the control unit 20 turns off the switching element 18. To interrupt the current to the LED 102.

  In this manner, the current flowing through the LED 102 can be controlled, and the average light emission intensity of the LED 102 can be controlled.

  However, in the control circuit 100 of the above prior art, since the reference voltage Vref is a constant voltage, as shown in FIG. 6, the phase of the input AC voltage and the current flowing through the LED 102 do not match and the power factor is large. There was a problem that I could not.

  One aspect of the present invention includes a rectifier that full-wave rectifies an AC power supply, a switching element that switches a current flowing in a light-emitting element that receives light rectified by the rectifier, and a full-wave in the rectifier. A voltage dividing circuit that divides the rectified voltage to obtain a reference voltage, a comparator that compares the reference voltage according to the current flowing through the light emitting element, and the reference voltage, and according to a comparison result by the comparator And a control unit for controlling switching of the switching element.

  Here, it is preferable that the voltage dividing circuit includes a Zener diode that limits the reference voltage to be a predetermined value or more.

  Further, the control unit controls the switching element such that a current flows through the light emitting element when the comparison voltage is larger than the reference voltage, and a current flows through the light emitting element when the comparison voltage is smaller than the reference voltage. It is preferable to control the switching element so as not to flow.

  According to the present invention, the power factor can be improved. In addition, the stable operation of the system can be improved.

It is a figure which shows the structure of the control circuit of the light emitting element in embodiment of this invention. It is a figure which shows the effect | action of the control circuit of the light emitting element in embodiment of this invention. It is a figure which shows the structure of another example of the control circuit of the light emitting element in embodiment of this invention. It is a figure which shows the effect | action of the other example of the control circuit of the light emitting element in embodiment of this invention. It is a figure which shows the structure of the control circuit of the conventional light emitting element. It is a figure which shows the effect | action of the control circuit of the conventional light emitting element.

  As shown in FIG. 1, the light emitting element control circuit 200 according to the embodiment of the present invention includes a rectifying unit 30, a choke coil 32, a regeneration diode 34, a switching element 36, a control unit 38, a comparator 40, and a voltage dividing circuit. 42 is comprised. In addition, FIG. 2 shows voltages and currents of respective portions in the control circuit 200 in the present embodiment.

  The control circuit 200 controls light emission of the light emitting element. For example, it is connected to a light emitting diode (LED) 102 for illumination, and controls the current to the LED 102.

  The rectifying unit 30 includes a rectifying bridge circuit 30a. The rectifier 30 receives the AC voltage Sin, performs full-wave rectification on the AC voltage Sin, and outputs the full-wave rectified voltage Srec. As shown in FIG. 1, the rectifying unit 30 may be provided with a protective fuse 30b and a filter 30c for removing noise.

  In this embodiment, the anode terminal of the LED 102 is not provided by providing the large-capacity rectifying capacitor 12 after the rectifying unit 30 or by providing only a small-capacity film capacitor that does not function as the rectifying capacitor 12. The drive voltage to and the power supply voltage to the control unit 38 become a full wave rectified voltage Srec which is not smoothed.

  A full-wave rectified voltage Srec is supplied to the anode terminal of the LED 102. The cathode terminal of the LED 102 is grounded via the choke coil 32, the switching element 36, and the voltage detection resistor R1.

  The choke coil 32 is provided to make the current flowing through the LED 102 and the switching element 36 intermittent. As shown in FIG. 1, the choke coil 32 may be provided with a forward winding so that the power supply voltage to the control unit 38 can also be supplied.

  The switching element 36 is provided to supply / cut off the current to the LED 102. The switching element 36 is an element having a capacity corresponding to the power consumption of the LED 102, and for example, a high power power field effect transistor (MOSFET) or the like is used. Switching of the switching element 36 is controlled by the control unit 38.

  The regenerative diode 34 is a flywheel diode, and is connected to the LED 102 and the choke coil 32 in parallel. The regenerative diode 34 regenerates the energy stored in the choke coil 32 to the LED 102 when the switching element 36 is cut off.

  The voltage dividing circuit 42 divides the full-wave rectified voltage Srec obtained by the rectifying unit 30 to generate a reference voltage Vref and outputs it to the comparator 40. The voltage dividing circuit 42 can be, for example, a series connection of resistors R2 and R3. The full-wave rectified voltage Srec is divided by the resistors R2 and R3, and the terminal voltage of the resistor R3 is input to the non-inverting input terminal of the comparator 40 as the reference voltage Vref.

  As shown in FIG. 2, the reference voltage Vref shows a change proportional to the change of the full-wave rectified voltage Srec by the voltage dividing circuit 42.

  The comparator 40 receives the comparison voltage Vcmp generated at both ends of the voltage detection resistor R1 by the current flowing through the LED 102 at the inverting input terminal. The comparator 40 receives a reference voltage Vref obtained by dividing the full-wave rectified voltage Vrec that has not been smoothed by the voltage dividing circuit 42 at a non-inverting input terminal. The comparator 40 compares the comparison voltage Vcmp with the reference voltage Vref and outputs the comparison result to the control unit 38.

  The control unit 38 controls switching of the switching element 36 based on a comparison result between the reference voltage Vref and the comparison voltage Vcmp by the comparator 40. The control unit 38 is configured as a semiconductor integrated circuit. When the comparison voltage Vcmp is smaller than the reference voltage Vref, the control unit 38 turns on the switching element 36 to flow current to the LED 102, and when the comparison voltage Vcmp becomes larger than the reference voltage Vref, the control unit 38 turns off the switching element 36. To interrupt the current to the LED 102.

  Due to the operation of the comparator 40 and the control unit 38, as shown in FIG. 2, the current I flowing through the LED 102 becomes a reference voltage Vref in which the comparison voltage Vcmp changes in proportion to the change in the full-wave rectified voltage Srec. It flows until it rises, and when it exceeds the reference voltage Vref, it is repeatedly shut off. The envelope of the current I changes in synchronization with the full-wave rectified voltage Srec. That is, the conduction angle of the current I flowing through the LED 102 can be widened, and the power factor of the lighting system can be improved on the assumption that it changes in substantially the same phase as the AC voltage Sin. Further, the reactive power can be reduced and the harmonic current can be reduced.

  Since the reference voltage Vref may become too high depending on the AC voltage Sin, as shown in FIG. 1, the voltage dividing circuit 42 has a Zener diode 42a for clamping the reference voltage Vref to a predetermined voltage Vmax or less. It may be provided.

  Further, when the full-wave rectified voltage Vrec applied to the LED 102 is small, the light emission may become unstable. For example, when the AC voltage Sin is a sine wave voltage having an effective value of 100 V, the light emission of the LED 102 becomes unstable in a voltage region where the full-wave rectified voltage Vref is 20 V or less (about 1/5 of the effective value). Sometimes.

  Therefore, as shown in FIG. 3, the voltage dividing circuit 42 may be provided with a Zener diode 42b that cuts off the voltage dividing circuit 42 when the full-wave rectified voltage Srec is equal to or lower than a predetermined voltage value Vmin. That is, a Zener diode 42b whose breakdown voltage is the voltage value Vmin is inserted into the series connection of the resistors R2 and R3 so as to be on the high voltage side of the non-inverting input terminal of the comparator 40. As shown in FIG. 4, when the full-wave rectified voltage Srec becomes larger than the voltage value Vmin, the reference voltage Vref becomes a value corresponding to the change of the full-wave rectified voltage Srec, and the full-wave rectified voltage Srec becomes less than the voltage value Vmin. In this case, the Zener diode 42b is cut off, and the reference voltage Vref becomes the ground potential.

  Accordingly, when the full-wave rectified voltage Srec is equal to or lower than the breakdown voltage value Vmin of the Zener diode 42b, the reference voltage Vref becomes the ground potential, so that the switching element 36 is turned off and the LED 102 does not emit light. On the other hand, when the full-wave rectified voltage Srec becomes larger than the breakdown voltage value Vmin of the Zener diode 42b, the reference voltage Vref becomes a value corresponding to the full-wave rectified voltage Srec, and therefore the switching element 36 until the comparison voltage Vcmp rises to the reference voltage Vref. Is turned on, and the switching element 36 is turned off when the reference voltage Vref is exceeded. The current I flowing through the LED 102 flows according to the switching control of the switching element 36, as shown in FIG.

  Thus, by providing the Zener diode 42b, light emission can be stopped at a low voltage when the light emission of the LED 102 becomes unstable.

  DESCRIPTION OF SYMBOLS 10 Rectification part, 12 Rectification capacitor, 14 Choke coil, 16 Regenerative diode, 18 Switching element, 20 Control part, 22 Comparator, 30 Rectification part, 30a Rectification bridge circuit, 30b Fuse, 30c Filter, 32 Choke coil, 34 Regenerative diode, 36 switching element, 38 control unit, 40 comparator, 42 voltage divider circuit, 42a zener diode, 42b zener diode, 100, 200 control circuit.

Claims (3)

A rectifying unit for full-wave rectification of the AC power supply;
A switching element that switches a current flowing in a light emitting element that emits light by receiving a voltage rectified by the rectifying unit;
A voltage dividing circuit that obtains a reference voltage by dividing the voltage that has been full-wave rectified by the rectifying unit;
A comparator for comparing a reference voltage according to a current flowing through the light emitting element and the reference voltage;
A control unit for controlling switching of the switching element according to a comparison result by the comparator;
A control circuit for a light-emitting element, comprising: The control circuit according to claim 1,
The voltage dividing circuit includes a Zener diode that cuts off the voltage dividing circuit when a voltage subjected to full-wave rectification in the rectifying unit becomes a predetermined value or less. The control circuit according to claim 1 or 2,
The controller controls the switching element such that a current flows through the light emitting element when the comparison voltage is greater than the reference voltage, and a current flows through the light emitting element when the comparison voltage is smaller than the reference voltage. A control circuit for controlling the switching element so as not to exist.

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