JPH1197747A - Lighting circuit for ac light emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized power source circuit for lightening an LED with an AC source in which circuit heat generation is little, at a low cost. SOLUTION: Instead of a current limiting resistor of an AC power source 1, capacitive reactance of a capacitor 12 or inductive reactance of a coil 18 is used. A current-limited AC is rectified with a rectifier circuit 11, and lightens an LED 2. A constant voltage element 13 is connected in parallel with the LED 2. A rush current into the capacitor 12 generated at a phase when a power source is closed is bypassed, or a high voltage generated from the coil 18 is limited, thereby protecting the LED 2 from an excessive current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC light emitting diode lighting circuit for lighting a light emitting diode using a commercial power supply.

[0002]

2. Description of the Related Art Generally, a light emitting diode (hereinafter referred to as LE)
D) is driven by a DC voltage, which is less than a few volts. Further, when the temperature rises, the voltage between the anode and the cathode of the LED decreases, and thermal runaway tends to occur when the voltage is driven. Therefore, a current limiting resistor is connected in series.

When such an LED is turned on by a commercial power supply,
A method in which a resistor is connected in series to limit the current, then rectify and apply a voltage to the LED, a method of applying a voltage to the LED through a resistor and a rectifier after stepping down a commercial power supply with a transformer, After converting the voltage to a low voltage, a method of applying a voltage to the LED or a method of applying a voltage to the LED only for a period equal to or less than a certain level of the AC voltage to reduce power consumption and reduce the size (Japanese Patent Laid-Open No. Hei. 24776), and the like.

[0004]

However, the method of dropping the voltage of the commercial power supply with a resistor has a problem that the voltage of the commercial power supply is higher than the voltage of the LED, so that the resistor generates more heat.

Further, the method of stepping down a commercial power supply by a transformer has a problem that the transformer is large and heavy, which hinders downsizing and weight reduction of equipment.

Further, the method using a switching power supply circuit and the method described in JP-A-3-24776 have a problem that the circuit configuration is complicated and the cost of the product is increased.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a small-sized, inexpensive, AC light emitting diode lighting circuit that emits light from a light emitting diode using a commercial power supply.

[0008]

Therefore, an AC light emitting diode lighting circuit according to the present invention is a lighting circuit for lighting a light emitting diode using an AC power supply, comprising: an input terminal to be connected to an AC power supply; A rectifier circuit connected to the input terminal, for rectifying the AC input, an output terminal for applying the rectified output of the rectifier circuit to the light emitting diode to be lit, and connected in series between the input terminal and the rectifier circuit; And a current limiting reactance comprising a capacitor or a coil.

One of the features of the present invention is that a capacitor or a coil having a reactance corresponding to a resistance value is connected to a power supply as a current limiting reactance instead of a series resistor, the current is rectified, and a direct current is applied to an LED. It is in the point which did.
As a result, an inexpensive light-emitting diode lighting circuit that is small, generates no heat, and is obtained.

When the current limiting reactance is a capacitor, when the AC power is turned on and the power is turned on when the AC voltage waveform is other than 0 V, a current for charging the capacitor flows through the LED as an inrush current. If the current value exceeds the maximum rated current of the LED, the LED is destroyed.

When the current-limiting reactance is a coil, a high voltage is generated across the coil when the AC voltage waveform is other than 0 V when the AC power supply is cut off, and the voltage becomes LE.
If the current applied to D exceeds the maximum rated current of the LED, the LED is destroyed.

Therefore, it is preferable to connect a constant voltage element for preventing an overvoltage that destroys the light emitting diode in parallel with the light emitting diode, and to limit the voltage applied to the LED to limit the current flowing through the LED.

When the current limiting reactance is a capacitor, a resistor for limiting an inrush current to the capacitor when power is turned on is connected in series between the capacitor and the input terminal in addition to the constant voltage element described above. The inrush current may be limited to the maximum rated current or less of the rectifier circuit, or a resistor for discharging the charge of the capacitor when the power is turned off may be connected in parallel to the capacitor.

When the current limiting reactance is a coil, in addition to or instead of the above-described constant voltage element,
A constant voltage element or a surge absorbing circuit for limiting a high voltage generated at both ends of the coil when the power is turned off may be connected to the coil in parallel.

Here, a Zener diode, a varistor, an arrester, and other semiconductor surge voltage absorbing elements can be used for the constant voltage element.
C. shown in FIG. The R surge absorber 20 and other circuits having similar functions can be used.

[0016]

The capacitor acts as a capacitive reactance with respect to alternating current. The smaller the capacitance, the larger the reactance, and the greater the current limiting effect. In addition, since the phase of the current flowing through the capacitor is ahead of the voltage by 90 °, the power consumption is theoretically zero. Thus, a small-sized and heat-free circuit can be realized.

In addition, the coil acts as an inductive reactance with respect to AC, and the current flowing through the coil has a phase delayed by 90 ° from the voltage, so that the power consumption is theoretically zero. Thereby, a circuit without heat generation can be realized.

The voltage of the commercial power supply is considerably higher than the LED forward voltage, and the current flowing through the LED is small.
The reactance of the capacitor or coil becomes sufficiently large with respect to the equivalent resistance value calculated from the forward voltage and the forward current. As a result, even if the change in the LED forward voltage, that is, the number of LEDs is changed from one to a plurality connected in series, the change in the flowing current is small, and it can be practically used as a constant current circuit.

Further, the constant voltage element connected in parallel to the LED can protect the LED from the rush current of the capacitor caused by the AC power-on phase. When a coil is used as the current limiting reactance, the LED can be protected from a high voltage generated at both ends of the coil due to the AC power supply phase when the AC power supply is cut off.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to specific examples shown in the drawings. FIG. 1 shows a preferred embodiment of an AC LED lighting circuit according to the present invention. In the figure, 1 is an AC power supply, 10 is an LED lighting circuit, 14, 14
Is an input terminal to be connected to the AC power supply 1, and 11 is a bridge circuit using four diodes.
A rectifier circuit connected to 4, 14 for rectifying the AC input;
5 and 15 are output terminals for applying the rectified output of the rectifier circuit 11 to the LED 2 to be turned on, 12 is a capacitor connected in series between the input terminal 14 and the rectifier circuit 11 and functioning as a current limiting reactance; 13 is a Zener diode as a constant voltage element connected between the output terminals 15 and 15 so as to be in parallel with the LED, and 16 is a capacitor 1
2 is connected in series between the input terminal 2 and the input terminal 14, and a resistor for limiting an inrush current to the capacitor 12 when the power is turned on;
A resistor 17 is connected in parallel with the capacitor 12 and discharges the charge of the capacitor 12 when the power is turned off.

The AC power supply 1 is, for example, 100 V AC or AC
200V, 60Hz or 50Hz commercial power supply. Capacitor 2 functions as a current-limiting capacitive reactance. More specifically, an example of selecting the capacitor capacity is as follows. The capacitor capacity used at the power supply voltage of 100 V AC and 60 Hz is 0.33 μF, and the rated voltage AC
A 125 VAC alternating current metallized plastic film capacitor is used. The current flowing at this time is about 0.01
2A RMS.

The rectifier circuit 11 performs full-wave rectification on the alternating current,
2 works to turn on. In this example, there is one LED 2, but there may be a plurality of LEDs connected in series. The maximum number of LEDs that can be connected is determined by the minimum current flowing through the LEDs.

The zener diode 13 limits the voltage applied to the LED 2, and bypasses the rush current flowing into the capacitor 12 generated by the commercial power-on phase to the zener diode 13, thereby preventing the LED from being destroyed due to an excessive current. Work to protect The voltage of the Zener diode 13 is set to a value higher than the forward voltage in the use state of the LED 2 and lower than the forward voltage at the maximum forward current.

FIG. 2 shows a second embodiment of the present invention. The same reference numerals as those in FIG. 1 denote the same or corresponding parts. In this embodiment, a coil 18 is used instead of a capacitor, and an overvoltage absorbing varistor 19 is connected to the coil 18 in parallel. In this example, the same operation and effect as those of the first embodiment can be obtained, but since it can be easily understood, a detailed description thereof will be omitted.

FIG. 3 shows a second embodiment using the coil 18 as a surge absorbing circuit for absorbing a high voltage generated at both ends of the coil 18 when the power is turned off. 1 shows a configuration example of an R surge absorber 20.

FIGS. 4 to 7 show another embodiment of the present invention using a capacitor as a current limiting reactance. The same reference numerals as those in FIG. 1 denote the same or corresponding parts. However, in the figure, the inrush current limiting resistor and the capacitor charge / discharge resistor are not shown. Here, FIG. 4 shows a third embodiment in which single-phase half-wave rectification is performed, FIG. 5 shows a fourth embodiment in which single-phase three-wire full-wave rectification is performed, and FIG. 6 shows three-phase three-wire full-wave rectification. FIG. 7 shows a fifth embodiment in which three-phase four-wire full-wave rectification is performed. In the case of a single-phase three-wire system, a three-phase three-wire system, and a three-phase four-wire system, it is practically sufficient to use only two of the three or four wires. The same circuit can be applied to other polyphase alternating current. When a capacitor is connected in parallel with the LED, a current with little pulsation can be applied.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of an AC LED lighting circuit according to the present invention.

FIG. 2 is a circuit diagram showing a second embodiment.

FIG. 3 is a circuit diagram showing a configuration example of a surge absorbing circuit employed in place of a varistor in the second embodiment.

FIG. 4 is a circuit diagram showing a third embodiment.

FIG. 5 is a circuit diagram showing a fourth embodiment.

FIG. 6 is a circuit diagram showing a fifth embodiment.

FIG. 7 is a circuit diagram showing a sixth embodiment.

[Explanation of symbols]

 Reference Signs List 1 AC power supply 2 LED 10 LED lighting circuit 11 Rectifier circuit 12 Capacitor (reactance for current limitation) 13 Zener diode (constant voltage element) 14 Input terminal 15 Output terminal 16, 17 Resistance 18 Coil (reactance for current limitation) 19 Overvoltage absorption Varistor 20 C.I. R surge absorber (surge absorption circuit)

Claims (4)

[Claims] 1. A lighting circuit for lighting a light emitting diode using an AC power supply, an input terminal to be connected to the AC power source, a rectifier circuit connected to the input terminal for rectifying an AC input, and a light emitting device to be lit. An output terminal for applying a rectified output of the rectifier circuit to the diode, and a current limiting reactance that is connected in series between the input terminal and the rectifier circuit and includes a capacitor or a coil. LED lighting circuit for AC. 2. The light emitting diode for AC according to claim 1, wherein a constant voltage element for preventing an overvoltage that destroys the light emitting diode is connected between the output terminals in parallel with the light emitting diode. circuit. 3. The current limiting reactance is a capacitor, a resistor for limiting an inrush current to the capacitor when power is turned on is connected in series between the capacitor and an input terminal, and the power is turned off to the capacitor. 2. An AC light emitting diode lighting circuit according to claim 1, wherein a resistor for discharging a charge of the capacitor is sometimes connected in parallel. 4. The current limiting reactance is a coil, and a constant voltage element or a surge absorbing circuit for limiting a high voltage generated at both ends of the coil when power is turned off is connected to the coil in parallel. LED lighting circuit for AC.