JPS61285871A - Driving device for light emitting diode - Google Patents

Abstract

PURPOSE:To obtain the light emitting diode driving device which is small-sized and has a small quantity of the power consumption by opening and closing the first switch element at the prescribed period by the control circuit which receives the feeding of a DC-DC converter and operates, and closing the second switch element only while the opening and closing action is executed. CONSTITUTION:A DC-DC converter 106 receives the electric power of a battery 101 through an electric power source switch (the third switch element) 107 having an always opening contact, and boosts to attain, for example, the electric power source voltage Vcc of 5V. By a control circuit 108 fed by the DC-DC converter 106, the coil electric current is controlled, light emitting diodes 104 and 105 are made to put on/out lights by the self-electromotive force of the coil, except the time of putting on/out lights, the second switch element 105 is opened and the forward current is made not to flow at the light emitting diodes 104 and 105.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention uses a battery as a power source and a light emitting diode (hereinafter referred to as L
E D (light emitting diode)
This invention relates to a light emitting diode drive device for lighting up a light emitting diode (referred to as e).

[Conventional technology]

FIG. 9 shows a conventional light emitting diode driving bag Re, which is for illustration purposes only, and shows a transmitting device of an infrared remote control device as an example. In this FIG. 9, la,
lb is a dry battery with an electromotive force of 1.5V, 2 is a control circuit, and 21 is an IC (Integrated C1rc).
22a and 22b are switches, 23 is a vibrator, 24a and 24b are capacitors, 3 is an infrared LED 14 is an NPN transistor, and 25 and 5 are resistors. Series-connected batteries 1a, ll), resistors 5. The infrared LED 3 and the transistor 4 constitute a series circuit, and the IC 21 is connected to the switch 22 to be operated.
&.

A code corresponding to 22b is created, and a carrier wave obtained by frequency division from an oscillation circuit consisting of a vibrator 23 and capacitors 24a and 24b is modulated by the above code, and the resulting output signal is sent to a transistor via a renostar 25. 4, the base is opened and closed, and the infrared LED 3t blinks. Therefore, this device has switches 22a and 22b.
The switches 22a and 22b perform operations corresponding to the switches 22a and 22b by transmitting a code corresponding to the switch 22a and 22b as infrared rays, receiving the infrared rays by a light receiving device (not shown), and decoding the code.

[Problem that the invention seeks to solve]

The forward voltage of infrared LEDs and visible LEDs is generally high when the forward current of actual use is applied, and infrared LEDs for remote control
Maximum 1.5 V for ED (when DC forward current is 100 mA), maximum 2.8 V for visible LED (when DC forward current is 2
0 mA). Further, a pulse forward current of several hundred mA is normally applied to the infrared LED. Therefore, the LED
It is not possible to obtain the necessary forward current simply by connecting in series a single battery with an electromotive force of 1.5V. Further, the electromotive force of a small battery suitable for carrying is generally 1.2 to 1.5V. Therefore, in the past, the electromotive force was 1.5 as in the above device.
Two V batteries are connected in series and the total electromotive force is 3 V, causing the infrared LED 3' to emit light. However, the volume of the battery is generally large, which poses an obstacle to downsizing the device. Additionally, it is possible to obtain a power supply voltage that is even higher than the forward voltage of an LED by boosting the voltage from a single battery using a DC-DC converter, etc., but in order to flow a large forward current, a large transformer is required. There was a problem.

This invention was made to solve the above problems, and uses a battery that has a lower forward voltage and electromotive force than the forward current required to light the LED used, and lights the LED with its forward current. The object of the present invention is to obtain a light emitting diode driving device that is small in size and has low power consumption.

[Means for solving problems]

In the light emitting diode drive device according to the present invention, the battery, the coil, and the first switch element constitute a first series port wr, and when the first switch element is opened, the battery, the coil, and the light emitting diode are connected. and the second switch element constitute a second series circuit, and the third switch element Kanakura is provided with a DC-DC converter supplied with power from a battery, and is operated by receiving the supply tV of this DC-DC converter. The control circuit opens and closes the first switch element at a predetermined cycle, and closes the second switch element only during this opening and closing operation.

[For production]

In the light emitting diode driving device of the present invention, a battery having a lower electromotive force than the forward voltage required to light the light emitting diode with a predetermined forward current is used as a power source, and a DC-
A DC converter generates a predetermined power supply voltage from this battery, and a control circuit supplied with power from this DC-DC converter controls the coil current, and the self-electromotive force of this coil turns on and off the light emitting diode. At the same time, when the light is turned on or off, a second switch element is opened outside the plate to prevent forward current from flowing through the light emitting diode.

[Fruitful example]

FIG. 1 is a block circuit diagram showing a light emitting diode driving device according to an embodiment of the present invention. In the figure, 101
, 102 and 103 are a battery (electromotive force is 1.5V), a coil, and a transistor (
104 and 105 are the battery 101 and the coil 102, respectively, when the transistor 103 is off.
The infrared LED, the transistor (second switch element), and 106 which together constitute a second series circuit receive the power of the battery 101 through the power switch (third switch element) 107 having a normally open contact and boost the voltage. For example, a DC-DC converter 108 constitutes a 5V power supply voltage Vcc.
This microcomputer 108 is a control circuit that operates by receiving power from the C-DC converter 106. -j: Input/output circuit 1081.108
2. Memory 1083, CP01084'! ? The terminal It-In of the input circuit 1081 is set to the power supply voltage Vc in advance.
c t or ground, and the output terminals MI M2 are connected to respective other ends of resistors 109, 110, each of which has one end connected to a transistor 103, 105, respectively.

Next, write a memo of the microcomputer 108 about the operation of the light emitting diode drive device configured in this way. 7-1083
The explanation will be based on the 70-chart (FIG. 2) and the time chart (FIG. 3) of the program stored in the program.

First, at time t1 in FIG.
When input, the DC-DC converter 106 operates,
Outputs a source voltage VCe of 5V. Receiving this power,
The microcomputer 108 starts operating by a power-on reset circuit (not shown).

That is, in FIG. 2, starting from a starting point, initialization is performed in step 201, and output terminals Ml and Mz' are both set to low level L in step 202. Next, in step 203, the input terminal is checked.

~In f) Condition 7E [(High Level or Lowe Percha)
t-read and store this. Next step 204
The variable i is set to 1 in step 205, and the state of the input terminal Ii is determined, and if the p level is L, step 2
At step 06, a constant To is set in the variable TR, and if it is at a high level H, a constant TuTh is similarly set at step 207. Next, in step 208, the output terminal M2' is set to a high level H (tz in FIG. 3), the h-land duster 105 is closed, and in step 209, a high level and a low level are set from the Ta output terminal M1 for a predetermined period of time at a period T. The signal is repeatedly output to open and close the transistor 103'6. As a result, the infrared LED 104 turns on and off at a period T, and this operation will be described in detail later.

Next, in step 210, the output terminal M2tl is set to a low level LK, and the transistor 105 is opened (time ts in FIG. 3). Next, in step 211, the variable t for time measurement is cleared to zero, and in step 212, it is determined whether the variable i is the number of the last input terminal In, and if so, the execution of the program is stopped. If not, the variable i is incremented in step 213. Next step 2
At step 14, the CPU waits until the time TR elapses (time 14) in FIG. 3, and then repeats the execution from step 205. In this way, input end check! A signal (hereinafter referred to as a code signal) in which a carrier wave (period T) is modulated in accordance with the state of ~In
is output from the output terminal M1, and in response to this, the infrared LED
104 converts it into an optical signal and outputs it, and the transmission of the optical signal ends at time ts in FIG.

Next, the operating principle of turning on and off the infrared LED 104 will be explained. When the transistor 103 is at time 1=0,
When switched from off to on, the other circuit becomes the first series circuit as shown in FIG. 4(a). In the figure, L is the self-inductance of the coil 102, RL is its resistance valve,
E is the electromotive force of the battery 101, RB is its internal resistance, and i is the circuit current.

The circuit equation for this series circuit is shown below, and the circuit current i is given by a well-known formula. The opening/closing period of the transistor 103 by the microcomputer 108 is T (duty is 50%).
Then, the circuit current l flows for a time j, and the time t =
The value at T/2 is I T/2.

Next, at time t = T/2, the transistor 103
is turned off, the current i that had been flowing through the coil 102 is transferred to the battery 101, the coil 102, and the infrared LED 104.
and a transistor 105. The equivalent circuit of this circuit is shown in the fourth @ mountain). This fourth
In figure (b), RD z vD are each infrared LE
When the forward characteristics of D104 are approximated by a broken line as shown in FIG. 5, this is an equivalent forward resistance expressed by an approximation formula and an equivalent power supply representing a forward voltage drop.

Also, the circuit equation of this circuit is di.

LH+1(RB+RL+RD)+Vp-E=0, so the circuit current i is given by. Subsequently, as the transistor 103 opens and closes, the waveforms of the current iL flowing through the coil 102 and the current ip flowing through the infrared LED 104 become as shown in FIG.

Note that the peak current I T/2 of the LED current iD is the coil 1
The self-inductance Lt of 02 can be freely set by selecting an appropriate value or by setting the ON time of the transistor 103 to an appropriate value.

By the way, in FIG. 4(b), the circuit current l after an infinite time has elapsed is determined by the characteristics of the infrared LED 104 shown in FIG. 5, the electromotive force E of the battery 101, the internal resistance RB, and the resistance RL of the coil. For example, when looking at RB and RL'em, as mentioned above, there are some that are 100 mA.

Therefore, when the user continues to press the power switch 107 during a period when the infrared LED 104 is not turning on or off, or even after all code signals have been output, a steady current flows through the VC and the infrared LED 104. This will speed up the consumption of the battery 101. The transistor 105 is provided to prevent this.

Furthermore, the microcomputer 108 has a CMOS structure.
By employing a converter such as C, the power consumption can be made very small, and therefore the DC-DC converter 106
Since it is sufficient to supply electricity commensurate with that amount,
It can be configured compactly and requires little power loss during operation.

In this way, the infrared LED 104'e can be turned on with a single battery, and low power consumption and miniaturization can be achieved.

FIG. 7 is a diagram showing a light emitting diode drive device according to another embodiment of the present invention. In this other embodiment, a transistor 111 serving as a second switching element is provided between the battery 101 and the coil 102, and the transistor 111 is provided between the battery 101 and the coil 102. 112, and 113 and 114 are registers.

Since the other configurations are the same as those in the above embodiment, corresponding parts are given the same reference numerals and explanations thereof will be omitted. Further, the operation is similar to that of the above embodiment.

FIG. 8 shows still another embodiment of the present invention. In this embodiment, the first switching element is a transistor 115, and the second switching element is a transistor 116.
The transistor 115 is driven by the transistor 117. And register 1
The configurations other than 18, 119 and 120 are the same as in the above embodiment, and the operation thereof is also the same.

In each of the above embodiments, an infrared transmitting device has been described as an example, but it goes without saying that the present invention is not limited to this and can be applied to various uses including various information display devices using visible LEDs.

〔Effect of the invention〕

As explained above, the light emitting diode driving device of the present invention uses a battery as a power source, which has a lower electromotive force than the forward voltage required to light a light emitting diode with a predetermined forward current, and converts the battery using a DC-DC converter. A control circuit supplied with power from this DC-DC converter controls the first switch element and controls the coil current, so that the self-electromotive force of this coil causes the light emitting diode to have a predetermined voltage. Since the structure is configured such that forward current flows and the second switching element is controlled to cut off the steady current of the light emitting diode, the device can be made smaller and the power consumption can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing the configuration of a light emitting diode drive device according to an embodiment of the present invention, and FIGS. Time chart, Figures 4(a) and 4(b) are circuit diagrams showing the circuits of the same light-emitting diode drive device, Figure 5 is a characteristic diagram of the light-emitting diode, and Figure 6 explains the lighting/extinguishing operation of the light-emitting diode. 7 and 8 are block circuit diagrams showing a light emitting diode driving device according to another embodiment of the present invention and still another embodiment, respectively, and FIG. 9 shows a conventional light emitting diode driving device. FIG. 101... Battery, 102... Coil, 103, 11
5... Transistor (first switch element), 104
...Infrared LED, 105,111,116...Transistor (second switch element), 106...DC-
DC converter, 107...power switch (third switch element), 108...iku stomach computer (control circuit). In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A light-emitting diode, a battery whose electromotive force is smaller than the forward voltage required to light the light-emitting diode with a predetermined forward current,
A first switch including this battery, a coil, and a first switch element.
a second series circuit in which, when the first switch element is opened, the second switch element, the light emitting diode, the battery and the coil are connected in a direction in which a forward current flows through the light emitting diode; a series circuit, a DC-DC converter that receives power from the battery via a third switch element and boosts it to form a predetermined power supply voltage;
The control circuit is actuated by the output of the C-DC converter to open and close the first switch element at a predetermined period, and closes the second switch element only during the opening and closing operation. Characteristic light emitting diode drive device.