JPH0575166A - Led drive circuit - Google Patents

Abstract

PURPOSE:To eliminate the adverse effect due to cansumed current fluctuation to other circuit when an LED is driven by high frequency pluses with a large electric current, relating to the LED drive current used far auto-focusing of a compact camera, etc. CONSTITUTION:A constant-current source 5 is connected to an LED 1 and a switch 2 which bypasses the current applied to the LED 1 is also connected in paralleled with the LED 1. By changing over the switch 2, the LED 1 is operated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED driving circuit used for autofocusing a compact camera.

[0002]

2. Description of the Related Art FIG. 10 is a connection diagram showing a conventional LED drive circuit. In the figure, reference numeral 1 is an LED that emits infrared rays of high brightness when a current flows, and reference numeral 2 is this LED
A switch 3 which is connected in series to control lighting and extinction of the switch 3 is a pulse control circuit which generates a driving pulse which repeats "H" level for a certain period and "L" level for a certain period, and is at "H" level. When switch 2 is turned on,
When it is at L "level, the switch 2 is turned off. 4 is LE
A resistor that limits the current flowing through D1, and is connected between the power supply (Vcc) and the anode of LED1. Also, L
The cathode of ED1 is connected to the reference potential (GN
D).

Next, the operation will be described. When the pulse control circuit 3 generates an output of "H" level, the switch 2 is turned on, and during this period, Vcc changes to the resistor 4, the LED 1,
A current flows through the switch 2 to GND, and the LED 1 lights up. Further, when the pulse control circuit 3 generates an output of "L" level, the switch 2 is turned off, and during this period, LE
Since no current flows through D1, LED1 is turned off.

[0004]

DISCLOSURE OF THE INVENTION The conventional LED described above
In the drive circuit, the flowing current fluctuates as the LED 1 blinks, and when such a circuit is used for autofocus of a compact camera, the high-brightness infrared LED consumes a large current of several hundred mA to several A, Also, several tens KHz
In some cases, pulse driving is performed at the frequency of 1. Therefore, noise or the like is superposed on Vcc due to induction due to current fluctuation, and there is a problem that other circuits connected to the same Vcc are adversely affected.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain an LED drive circuit that prevents noise generation due to fluctuations in current consumption.

[0006]

An LED according to the present invention
The drive circuit connects a constant current source to the LED and also LE
The switch for bypassing the current supplied to D is the LE
It is characterized in that the LED is connected in parallel and the blinking of the LED is controlled by switching this switch.

In the second invention, a constant current source is connected to a plurality of LEDs connected in series, and a plurality of switches for bypassing the current supplied to each LED are connected in parallel with each LED. In addition, a selection circuit for selecting a specific switch from these switches and causing a specific LED to blink is provided.

Further, in the third invention, a constant current source is connected in parallel to a plurality of LEDs connected in parallel, and
A switch that bypasses the current supplied to the multiple LEDs is connected in parallel with the multiple LEDs, and
There is provided a selection circuit for selecting a specific LED to blink the LED.

[0009]

In the LED drive circuit according to the present invention, the use of the constant current source makes it possible to prevent the fluctuation of the current consumption when the LED blinks.

Further, it is possible to select the switch of the LED to be blinked from a plurality of LEDs by the selection circuit.

Further, the selection circuit can select an LED to be blinked from a plurality of LEDs.

[0012]

EXAMPLES Example 1. An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, reference numeral 2 denotes a switch that is connected in parallel to the LED 1 and bypasses the current supplied to the LED 1. The switch 2 is on / off controlled by a pulse control circuit 3. Reference numeral 5 is a constant current source inserted between the parallel connection body of the LED 1 and the switch 2 and Vcc. The connection point between LED1 and switch 2 is GN.
Connected to D.

Next, the operation will be described. The pulse control circuit 3 turns on the switch 2 when it is at "H" level and turns it off when it is at "L" level as in the conventional example. While the switch 2 is off, the current of the constant current source 5 is supplied only to the LED 1, and the LED 1 is in a lighting state. On the other hand, switch 2
During the ON period, the current of the constant current source 5 flows to GND through the switch 2. At this time, the internal resistance of the switch 2 is Ron, the current of the constant current source 5 is I, LED
The voltage between the anode and the cathode at which the current starts to flow at 1 is V
If Vt> Ron · I, then LED
1 is turned off. Therefore, the switch 2 is turned on,
The LED 1 can be made to blink by controlling the turning off by the repeated pulse which is the output of the pulse control circuit 3. Further, according to this embodiment, since the constant current source 5 is connected to the LED 1 and the switch 2 for bypassing the current supplied to the LED 1 is provided, the switch 2 is provided.
There is no change in the current consumption due to the switching of, and it is possible to eliminate the adverse effect on the other circuits due to induction.

Example 2. FIG. 2 is a connection diagram showing a second embodiment of the present invention, in which the switch 2 is composed of an NPN transistor 6 and bias resistors 7 and 8. In the figure, 6 is an NPN transistor connected so as to bypass the current supplied to the LED 1, and its base is connected to the pulse control circuit 3 via a resistor 7. With such a configuration, the switch can be switched even when the pulse control circuit 3 is pulse-driven at a frequency of several tens of KHz, so that the LED 1 can be blinked at a high frequency. Further, since the internal resistance when the NPN transistor 6 is in the ON state is low and the collector-emitter voltage (saturation voltage) can be generally lowered to several tens mV to several hundreds mV, ideal switching is performed. Can be done.

Example 3. Next, FIG. 3 is a connection diagram of a third embodiment of the present invention, in which the NPN transistor 6 in FIG. 2 is replaced with an N-channel MOS-FET 9.

According to this structure, the switches can be switched even when the pulse control circuit 3 is pulse-driven at a frequency of several tens of KHz, as in the second embodiment, so that the LED 1 can blink at a high frequency. It will be possible.
Further, since the N-channel MOS-FET 9 has a high input impedance, and the current flowing into the gate terminal is extremely small, the pulse control circuit 3 has the N-channel MOS-F.
The power for switching the ET9 can be reduced.

Example 4. FIG. 4 is a connection diagram showing an embodiment of the second invention, and in this example, a drive circuit of an LED used for auto focus of a compact camera is assumed. In the figure, 1a, 1b, and 1c are LE
LED is connected in series in order from the high potential side at D.
The anode of 1a is connected to Vcc via constant current source 5 and LED
The cathodes of 1c are respectively connected to GND. 2a, 2b, and 2c are between the anode and cathode of the LED 1a, between the anode and cathode of the LED 1b, and L, respectively.
It is a switch connected between the anode and the cathode of ED1c. Reference numeral 10 is a selection circuit for selecting and connecting each switch to the pulse control circuit 3. In autofocus of a compact camera, when focusing on a subject, the distance to the subject is measured by emitting high-intensity infrared light from LED1, but when there is one LED, for example, two When the subjects are lined up, the light emission of the LED may be directed between the subjects, so that the distance to the object behind the subject is measured and the focus is lost. The hollow phenomenon can occur. For this reason,
High-intensity infrared rays are sequentially emitted at the three positions of left, middle, and right to prevent the occurrence of the hollow defect and focus is taken. It is necessary to operate three LEDs sequentially. Become.

Next, the operation will be described. As shown in FIG. 4, when only the switch 2a is connected to the pulse control circuit 3 by the selection circuit 10, the switches 2b and 2c are always kept in the ON state. Therefore, when the pulse control circuit 3 outputs an "L" level pulse, the switch 2a is turned off, and during this period, the current of the constant current source 5 flows to GND through the LED 1a, the switch 2b, and the switch 2c, and the LED 1a is turned on. Turn on the light. When the switch 2a is turned on, the current is
The current flows to GND via a, the switch 2b, and the switch 2c, and the LED 1a is turned off. Also, switch 2
The same applies when b and the switch 2c are selected by the selection circuit 10. Therefore, LEs connected in series
Since D1a, 1b, 1c can be selectively turned on and off, and the current supplied to the LED can be bypassed by the switch as in the first embodiment, the consumption current does not change.

Example 5. Next, FIG. 5 is a connection diagram showing a second embodiment of the second invention. The switch 2a in FIG.
The switch 2b and the switch 2c are composed of an NPN transistor 6a, bias resistors 7a and 8a, an NPN transistor 6b, bias resistors 7b and 8b, an NPN transistor 6c, and bias resistors 7c and 8c, respectively. In this case, the switches 2b and 2c which are not selected in the selection circuit 10 are turned on by connecting the input terminals to Vcc so as to bring the input terminals to the "H" level, and keep the LEDs 1b and 1c off.

Example 6. FIG. 6 is a connection diagram showing a third embodiment of the second invention, in which the NPN transistors in FIG. 5 are replaced with N-channel MOS-FETs 9a, 9b and 9c, respectively.

Example 7. FIG. 7 is a wiring diagram showing an embodiment of the third invention. As shown in FIG.
The anodes of D1b and LED1c are connected in parallel to Vcc via a constant current source 5, and the respective LEDs 1a-1
The cathode of c is connected to GND via the selection circuit 10. The switch 2 is connected between the anodes of the LEDs 1a to 1c and the GND, and is controlled to be turned on and off by the pulse control circuit 3. In this example, as in the case of the fourth embodiment, by connecting the LEDs 1a to 1c to the selection circuit 10, only one LED 1a can be selected and the pulse control circuit 3 can control the blinking.

Next, the operation will be described. As shown in FIG. 7, only the cathode of the LED 1a is connected to the GND by the selection circuit 10, and the LED 1b and the LED 1c are connected.
The cathode is always open. While the switch 2 controlled by the pulse control circuit 3 is off, the current of the constant current source 5 is the LED 1a and the selection circuit 10.
Since it flows to GND via the LED 1, the LED 1a is turned on. On the other hand, while the switch 2 is on, the current of the constant current source 5 flows to GND via the switch 2, so that the LED 1
a is turned off. Therefore, a plurality of Ls connected in parallel
Since the EDs 1a to 1c can be selectively blinked and the current supplied to the LED 1a can be bypassed by the switch 2 as in the first embodiment, the consumption current does not change. Further, in many LED cells in which a plurality of LEDs 1a to 1c are integrated in the same package, the common anode type or the common cathode type are connected in parallel. Therefore, in this embodiment, the parts are easily available and the configuration is easy.

Example 8. FIG. 8 is a connection diagram showing a second embodiment of the third invention, in which the switch 2 of FIG. 7 is composed of an NPN transistor 6 and bias resistors 7 and 8.

Example 9. FIG. 9 is a connection diagram of the third embodiment of the third invention, in which the NPN transistor 6 of FIG. 8 is replaced with an N-channel MOS-FET 9.

[0025]

As described above, in the present invention, L
Equipped with a switch that connects a constant current source to the ED and bypasses the current supplied to the LED. The LED blinks when the switch is switched, so there is no fluctuation in current consumption and the adverse effect on other circuits due to induction is eliminated. can do.

By providing a switch or a selection circuit for selecting an LED, the LED can be made to blink selectively from a plurality of LEDs, and an LED drive circuit effective for autofocusing of a compact camera can be obtained. ..

[Brief description of drawings]

FIG. 1 is a connection diagram showing an LED drive circuit according to an embodiment of the present invention.

FIG. 2 is a connection diagram showing a second embodiment of an LED drive circuit according to the present invention.

FIG. 3 is a wiring diagram showing a third embodiment of an LED drive circuit according to the present invention.

FIG. 4 is a connection diagram showing an LED drive circuit according to an embodiment of the second invention.

FIG. 5 is a connection diagram showing a second embodiment of the second invention.

FIG. 6 is a connection diagram showing a third embodiment of the second invention.

FIG. 7 is a connection diagram showing an LED drive circuit according to an embodiment of the third invention.

FIG. 8 is a connection diagram showing a second embodiment of the third invention.

FIG. 9 is a connection diagram showing a third embodiment of the third invention.

FIG. 10 is a connection diagram showing a conventional LED drive circuit.

[Explanation of symbols]

 1, 1a, 1b, 1c LED 2, 2a, 2b, 2c switch 5 constant current source 10 selection circuit

Claims (3)

[Claims] 1. An LED that emits high-intensity infrared light, a constant current source that supplies a constant current to the LED, and a switch that is connected in parallel with the LED and that bypasses the current supplied to the LED. An LED drive circuit characterized in that the LED is turned on by switching a switch. 2. A plurality of LEDs which are connected in series and emit high-intensity infrared light, a constant current source for supplying a constant current to these LEDs, and a plurality of LEDs which are respectively connected in parallel to each other and supplied to the LEDs. LED drive circuit, comprising: a plurality of switches for bypassing a specified current; and a selection circuit for selecting a specific switch from these switches to light a specific LED. 3. A plurality of LEDs connected in parallel to emit high-intensity infrared light, a constant current source for supplying a constant current to the LEDs, and a plurality of LEDs connected in parallel to the LEDs to be supplied to the LEDs. A switch for bypassing a current flowing through the LED and a selection circuit connected in series to each of the plurality of LEDs and selecting a specific LED from the plurality of LEDs to flow the current of the constant current source. circuit.