JPH0642908A - Adjuster of amount of light of led in photosensor - Google Patents

Abstract

PURPOSE:To correct the variation of an optical sensor for detecting a shielding object by the automatic adjustment of the amount of light of an LED. CONSTITUTION:Comparators 12-14 are provided to compare the output voltage of a phototransistor 11 with a set voltage. This adjuster is also provided with a counter 15 which is controlled with respect to the UP/DOWN by the outputs of the comparators 12, 13. Moreover, an A/D converter 16 is provided to A/D convert the output of the counter 15. The gate of a FET 18 for controlling the current of an LED 17 is connected to the output of the A/D converter 16. When clocks are input to the counter 15, the value of the counter is suitably changed, so that the current of the LED 17 is adjusted.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an LED in an optical sensor.
Regarding the light quantity adjuster.

[0002]

2. Description of the Related Art In an optical sensor using an LED and a phototransistor, there are large variations in the light amount of the LED and in the photocurrent of the phototransistor, and the output voltage greatly differs for each combination. Further, when the shield to be detected partially transmits light, if the output voltage is set higher than necessary, there is a possibility that even if the shield is present, it will be detected that there is no shield due to the transmitted light. Therefore, it is necessary to appropriately adjust the output voltage according to each combination.

Conventionally, as shown in FIG. 2, a method has been used in which the current of the LED 21 is manually adjusted by the variable resistor 22 to make the output voltage of the phototransistor 23 constant.
Further, as shown in FIG. 3, the gate voltage of the FET 35 is controlled by the output voltage of the phototransistor 31, and the LED 3 is controlled.
A method of controlling the current of 4 was used.

[0004]

In the prior art, in the circuit of FIG. 2, adjustment is time consuming when a large number of detectors are provided because adjustment is performed manually. Further, in the circuit of FIG. 3, the current of the LED 34 does not fluctuate in response to a sudden output voltage drop due to the shield due to the resistor 32 and the capacitor 33, but when the shield is stagnant, the current gradually increases and the shield permeates. There is a drawback that light causes a malfunction.

[0005]

The LED light quantity adjuster in the photosensor of the present invention comprises a first and a second reference voltages, which are reference values of the output voltage of the phototransistor, and a first comparison device for comparing the output of the phototransistor. A second comparator, an up / down counter whose count-up and count-down are controlled by the output of the comparator, an A / D converter for A / D converting the counter output, and a current controlled by the A / D converter output voltage. And a controller.

[0006]

The present invention will be described below with reference to the drawings.
FIG. 1 is a circuit diagram showing an embodiment of the present invention. As shown in FIG. 1, the LED 17 serving as a light source, the FET 18 for controlling the current thereof, the phototransistor 11 of the light receiving element, the comparators 12 to 14 for detecting the level of the input voltage of the phototransistor, the comparator 12, and the comparator 13 are included. It is constituted by a 4-bit A / D converter 16 for A / D converting the output of the 4-bit counter 15 and the 4-bit counter 15 which are controlled to count up / down by the output.
The presence or absence of the shield is obtained from the output of the comparator 14.

The upper limit setting voltage of the output voltage of the phototransistor when there is no shield is applied to the negative input terminal of the comparator 12. The lower limit setting voltage of the output voltage of the phototransistor when there is no shield is applied to the positive input terminal of the comparator 13. A threshold voltage for detecting the presence or absence of a shield is applied to the negative input terminal of the comparator 14.

Each reference voltage is made by resistance division.
In addition, the upper limit set voltage is set so that the output threshold voltage of the phototransistor is not exceeded by the transmitted light and dark current of the shield even when the light amount changes due to temperature change, etc.
Similarly, the lower limit set voltage is set so that the output of the phototransistor does not become lower than the threshold voltage even when there is no shield even when there is a change. If the difference between the upper limit setting voltage and the lower limit setting voltage is small, the up / down counter, A
The BIT number of the / D converter is increased to precisely control the LED current.

The automatic adjustment of the light amount is performed by inputting a clock when there is no shield. The pulse width of the input clock needs to be larger than the total value of the delays of the LED 17, the phototransistor 11, and the A / D converter 16. The operation when a clock is input will be described below. When the output voltage of the phototransistor is higher than the upper limit set value, the output of the comparator 12 is “H”, the comparator 1
The output of 4 outputs'L '. This output gives 4 BIT
The up / down counter 15 is controlled to count down. When the clock is input in this state, the counter value decreases and the output voltage of the A / D converter 16 decreases. As a result, the gate voltage of the FET 18 drops and the LED 17
Current is reduced and the output of the phototransistor is reduced.

When the output voltage of the phototransistor is lower than the upper limit set value and higher than the lower limit set value, the comparator 12,
Both outputs of the comparator 13 output'L '. This output controls the 4BIT up / down counter 15 to hold. This state does not change even if a clock is input.

When the output voltage of the phototransistor is lower than the lower limit set value, the output of the comparator 12 is'L ', the comparator 1
The output of 4 outputs'H '. This output gives 4 BIT
The up / down counter 15 is controlled to count up. When the clock is input in this state, the counter value increases and the output voltage of the A / D converter 16 increases. As a result, the gate voltage of the FET 18 rises, the current of the LED 17 increases, and the output of the phototransistor increases.

When the clock is input by the above control, the output voltage of the phototransistor fluctuates so as to be a voltage between the upper limit setting value and the lower limit setting value. The maximum value of the 4BIT counter is 1 until the automatic adjustment is completed.
You only need 6 clocks. Further, as a method of confirming that the automatic adjustment is completed, it can be confirmed by checking that the outputs of the comparator 12 and the comparator 13 are both “L”. Further, when the clock is not input, the current of the LED 17 does not change, so that even if there is stagnation of the shield, it is possible to detect the shield stably without fluctuation of the light amount.

[0013]

As described above, according to the present invention, the reference voltage 1 and the reference voltage 2 which are the reference values of the output voltage of the phototransistor, the comparator for comparing each reference voltage with the output of the phototransistor, and the output of the comparator are used. Input a clock by having an up / down counter that controls counting up and counting down, an A / D converter that A / D converts the counter output, and a current controller that is controlled by the A / D converted already output voltage. As a result, the amount of light is automatically adjusted, and the amount of light is fixed when there is no clock input, so even if there is stagnation in the shielding, it is possible to detect the shielding stably without fluctuation in the amount of light. Have an effect.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a first conventional example.

FIG. 3 is a circuit diagram showing a second conventional example.

[Explanation of symbols]

 11 LED 12-14 Comparator 15 4BIT Up / Down Counter 16 A / D Converter 17 LED 18 FET 21 LED 22 Variable Resistor 23 Phototransistor 31 Phototransistor 32 Resistor 33 Capacitor 34 LED 35 FET

Claims (1)

[Claims] 1. A first and second comparator for comparing the output voltage of the phototransistor with first and second reference voltages for determining the upper limit value and the lower limit value of the output voltage of the phototransistor when there is no shield. An up / down count whose count up and count down are controlled by the output of the comparator, an A / D converter for A / D converting the counter output, and a current controller controlled by the output voltage of the A / D converter are provided. An automatic light amount adjustment circuit characterized by.