JPH10126238A - Drive circuit for infrared-ray emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the drive circuit which is suitable for an infrared-ray emitting element that generates infrared ray, used for a transmission means of a digital signal. SOLUTION: The circuit is made up of a MOS field effect transistor 6 that is conductive, when a pulse signal is received by its gate and provides a drive current to an infrared-ray emitting diode 5, when the transistor 6 is conductive and up of a MOS field effect transistor 9 that is inserted in a current supply path to the infrared-ray emitting diode 5 and changes from a low impedance into a high impedance when a pulse signal is received at its gate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for an infrared light emitting element for generating infrared light used as digital signal transmitting means.

[0002]

2. Description of the Related Art Remote control devices are widely used as devices for transmitting digital signals using infrared rays. Recently, signals from a keyboard or mouse used in a personal computer are transmitted to the computer by infrared rays. A device designed to do this has been commercialized.

[0003]

The circuit shown in FIG.
FIG. 1 shows a driving circuit of an infrared light emitting element generally used in the related art. In FIG. 1, reference numeral 1 denotes an infrared light emitting diode that emits infrared light when a driving current flows. Reference numeral 2 denotes a field-effect transistor that supplies a drive current to the infrared light emitting diode 1 when in a conductive state, and is in a conductive state when an H (high) level signal is applied to a gate that is a control electrode. In addition, a driving current is supplied to the infrared light emitting diode 1. Reference numeral 3 denotes a resistor connected in series to the infrared light emitting diode 1, and has a function of limiting the magnitude of a current flowing through the infrared light emitting diode 1.

In such a circuit, when an H-level pulse signal is applied to the input terminal 4 connected to the gate of the field effect transistor 2, the field effect transistor 2 is turned on while the pulse signal is applied. In the conduction state, a driving current is supplied to the infrared light emitting diode 1 during that time, so that the infrared light emitting diode 1 emits and emits infrared light.

Since each of the infrared light emitting diode, the transistor, the resistor, etc. has an internal impedance,
Even if a voltage is applied, the waveform of the current does not match the voltage waveform. FIG. 4 is a signal waveform diagram showing the relationship between the voltage applied to the control electrode of the field effect transistor 2 and the current flowing through the infrared light emitting diode 1 in the circuit shown in FIG. 3, where (A) is a voltage waveform. (B) is a corresponding current waveform.

As is apparent from FIG. 4, there is a transient characteristic that the rise of the current is delayed even when a voltage is applied, and when the pulse width of the applied voltage becomes narrow, that is, the driving operation speeds up. Then, there is a problem that no current flows and no infrared light is emitted from the infrared light emitting diode 1.

As a method of solving such a problem, there is a method of reducing the value of the resistor 3 to increase the voltage value applied to the infrared light emitting diode 1, but depending on the signal applied to the input terminal 4, there is no use. However, there is a problem that an excessive current, that is, an unnecessary current flows, and power consumption increases. Further, when the transfer speed of the signal is very low, a large current flows through the infrared light emitting diode 1 for a long time, and as a result, there is a problem that the infrared light emitting diode 1 is more likely to be destroyed. .

An object of the present invention is to provide a driving circuit for an infrared light emitting device which solves the above-mentioned problem.

[0009]

A driving circuit according to the present invention comprises a switching element which is turned on when a pulse signal is applied to a control electrode and which supplies a driving current to an infrared light emitting element when the pulse signal is applied. And an impedance element that is inserted and connected into a current supply path to the infrared light emitting element and changes from a low impedance state to a high impedance state during the operation of applying the pulse signal.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The circuit shown in FIG. 1 is an embodiment of the driving circuit of the present invention. In FIG. 1, reference numeral 5 denotes an infrared light emitting diode which emits infrared light while the driving current is flowing. It has the characteristic of generating infrared rays of a level corresponding to the level. Reference numeral 6 denotes an N-channel MOS for supplying a driving current to the infrared light emitting diode 5 when in a conductive state.
The gate, which is a type field effect transistor, is connected to an input terminal 7 to which a pulse signal is applied, and is configured to function as a switching element that performs a switching operation in accordance with the applied signal.

Reference numeral 8 denotes a resistor connected in series to the infrared light emitting diode 5; 9 denotes a P-channel MOS field effect transistor inserted and connected in a drive current supply path to the infrared light emitting diode 5; It is provided to operate as an impedance element. 10
Is a buffer amplifier circuit to which a signal applied to the input terminal 7 is input, and 11 is an integration circuit provided on the output side of the buffer amplifier circuit 10, and is constituted by a diode 12, a capacitor 13, and a resistor 14. I have. The time constant of the integrating circuit 11 is set so that an appropriate current flows at the lowest transfer rate of the maximum duty of the signal used for infrared communication, and the integrated output signal is output from the MOS type electric field. It is connected so as to be applied to the gate of the effect transistor 9.

The driving circuit of the present invention is configured as described above. Next, the operation of such a circuit will be described with reference to the signal waveform diagram shown in FIG. When a pulse signal having the voltage waveform shown in FIG. 2A is input to the input terminal 7, the signal is applied to the gate of the MOS field effect transistor 6
Immediately reverses to the conducting state.

The pulse signal input to the input terminal 7 is input to an integration circuit 11 through a buffer amplifier circuit 10 and integrated. The waveform diagram shown in FIG. 2B shows the waveform of the signal integrated by the integration circuit 11, and the signal having such a waveform is applied to the gate of the MOS field effect transistor 9.

The MOS type field effect transistor 9
Is a P-channel field-effect transistor, is in a conductive state when the voltage applied to the gate is low, and changes to a non-conductive state as the voltage applied to the gate increases. That is, the impedance between the drain and the source of the MOS field effect transistor 9 changes from a low impedance to a high impedance.

When the pulse signal shown in FIG. 2A is input to the input terminal 7, the voltage having the waveform shown in FIG.
As a result of being applied to the gate of the S-type field effect transistor 9, the drain
The impedance between the sources changes from low to high. When the impedance between the drain and the source of the MOS field effect transistor 9 changes from low to high, the magnitude of the driving current flowing through the infrared light emitting diode 5 becomes as shown in FIG.
It changes as shown by the solid line in (C). That is, when the pulse signal is applied to the input terminal 7, the drive current flowing through the infrared light emitting diode 5 is determined by the resistance of the resistor 8, and thereafter, the resistance of the resistor 8 and the resistance of the MOS field effect transistor 9 It is determined by the impedance between the drain and the source. The dashed line in FIG. 2C shows the waveform of the drive current when the MOS field effect transistor 9 is not inserted and connected, and the drive current of the present invention shown by the solid line is smaller. It can be easily understood.

In the present invention, a MOS is used as a switching element.
Although a field effect transistor is used, other field effect transistors and transistors can of course be used. Further, although a MOS type field effect transistor is used as the impedance element, another impedance variable element can be used.

[0017]

According to the driving circuit of the present invention, the magnitude of the driving current supplied to the light-emitting element that generates infrared rays can be minimized, so that the power consumption can be reduced.

Further, the impedance of the impedance element inserted and connected in the current supply path to control the drive current to the infrared light emitting element is set to a low impedance state when a pulse signal is applied, and then the impedance is increased. Therefore, the driving current supplied to the infrared light emitting element during the pulse signal applying operation can be increased, and as a result, the rising characteristics of the signal can be improved.

According to the present invention, an integrating circuit for integrating the input pulse signal is provided, and the control operation of the impedance element is performed by the signal integrated by the integrating circuit, that is, in accordance with the pulse signal. Since the impedance control operation is performed, the drive current control operation can be performed accurately.

[Brief description of the drawings]

FIG. 1 is an embodiment of a drive circuit according to the present invention.

FIG. 2 is a signal waveform diagram for explaining a drive circuit of the present invention.

FIG. 3 is an example of a conventional driving circuit.

FIG. 4 is a signal waveform diagram for explaining an operation of a conventional driving circuit.

[Explanation of symbols]

 Reference Signs List 5 infrared light emitting diode 6 MOS type field effect transistor 8 resistor 9 MOS type field effect transistor 11 integration circuit

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI H04B 10/04 10/06

Claims (5)

[Claims] A switching element that is turned on when a pulse signal is applied to a control electrode and that supplies a drive current to an infrared light emitting element when it is in a conductive state;
A driving circuit for an infrared light emitting element, comprising: an impedance element inserted and connected in a current supply path to the infrared light emitting element and changing from a low impedance state to a high impedance state when applying the pulse signal. 2. The drive circuit according to claim 1, wherein the operation of the impedance element is controlled by a pulse signal applied to a control electrode of the switching element. 3. The drive circuit according to claim 2, wherein an integration circuit for integrating the pulse signal is provided, and an operation of the impedance element is controlled by an output signal of the integration circuit. 4. The switching element according to claim 1, wherein a MOS field effect transistor is used.
4. The driving circuit according to 1. 5. The drive circuit according to claim 1, wherein a MOS field effect transistor is used as the impedance element.