JPH0564420A - Led intensity correcting circuit - Google Patents

Abstract

PURPOSE:To make constant the intensity of an LED, representing a power supply condition, regardless of the on-off condition of a load. CONSTITUTION:A series circuit of a first current decreasing resistor R1 and an LED is connected between DC output terminals (a), (b) of a power supply circuit, and a resistor R4, which is a second current decreasing resistor, is connected between the output side of a voltage regulator circuit, comprising a resistor R2, a transistor Q1 and a Zener diode ZD1, and the LED. A drive current flows into the LED through the resistor R1, when a load is turned off, and through the resistor R1 and the resistor R4 when the load is turned on.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load such as a motor for driving a printer, which is turned on and off intermittently, a voltage regulator circuit, and an LED which is turned on and off according to the turning on and off of the load.
The invention relates to an LED brightness correction circuit that prevents the brightness of an LED from becoming unstable in a device including.

[0002]

2. Description of the Related Art FIG. 2 shows a circuit diagram of a power supply circuit having a conventional LED brightness correction circuit.

A motor M that is turned on and off intermittently is used as a load, and a three-terminal voltage regulator circuit composed of a transistor Q1, a resistor R2 and a zener diode ZD1 supplies current to the motor M. A voltage regulator control circuit including a transistor Q2 and a resistor R3 is connected to the three-terminal voltage regulator circuit, and when a signal of "L" is given to the terminal k, the voltage regulator circuit is turned on and a current is supplied to the motor M. Supplied. Further, when the terminal k is set to "H", the Zener diode ZD1 is short-circuited, so that the voltage regulator circuit is turned off and the motor M
Current is no longer supplied to. The power supply circuit steps down a commercial AC power supply voltage by a transformer PT and converts it into a DC voltage of a predetermined voltage by a diode bridge. The output voltage of this power supply circuit is V1. In addition, a series circuit of a resistor R1 for current reduction and an LED is connected between the DC output terminals of the power supply circuit, and the LED is driven by the current directly supplied from the power supply circuit to display the power supply state. ing.

In the above structure, the voltage V1 varies in magnitude depending on whether the three-terminal voltage regulator is on or off. That is, the voltage V1 is high when the voltage regulator circuit is off. The resistor R1 is set to a value such that a prescribed current flows through the LED when the voltage V1 is applied. Therefore, when the voltage regulator circuit is off, that is, when the motor M is stopped, LE
D emits light normally.

[0005]

However, in the above circuit configuration, when the motor M is on, that is, when the voltage regulator circuit is on, the voltage V1
Will decrease (the degree of this decrease depends on the capacity of the power supply circuit, etc.). As a result, L passes through the resistor R1.
The current flowing through the ED also decreases, so LE may be applied in some cases.
In some cases, the current of D becomes insufficient and the light emission state becomes insufficient. That is, the LED indicating the power supply state
There is a disadvantage that the lighting state of is very difficult because the brightness changes depending on the on / off state of the intermittent load.

An object of the present invention is to provide an LED brightness correction circuit in which the brightness of the LED is stable regardless of the on / off state of the load.

[0007]

According to the present invention, there is provided a power supply circuit having a DC output terminal, a series circuit of a first current reducing resistor and an LED connected between the DC output terminals, and the DC output terminal. A voltage regulator circuit connected between a load that is turned on and off intermittently; a voltage regulator control circuit that turns off the voltage regulator circuit when the load is off; and a voltage regulator control circuit that turns on the voltage regulator circuit when the load is on; It is characterized by comprising a second current reducing resistor connected between a connection terminal with the first current reducing resistor and the output side of the voltage regulator circuit.

[0008]

When the voltage regulator circuit is in the off state, the voltage of the DC output terminal of the power supply circuit rises, so that a sufficiently large voltage is applied to the series circuit of the first current reducing resistor and the LED. Emits light with sufficient brightness. On the other hand, when the voltage regulator circuit is turned on, a large current flows to the load, causing a voltage drop at the DC output terminal of the power supply circuit. Therefore, the first current reduction resistor and L
There is a possibility that a sufficient LED drive current will not flow in the series circuit of the ED, but at this time, the output side of the voltage regulator circuit outputs L to the LED via the second resistor for current reduction.
ED drive current is supplied. Therefore, since the current is supplied to the LED from both the first current-decreasing resistor and the second current-decreasing resistor, it is possible to prevent the brightness of the LED from decreasing.

[0009]

1 is a circuit diagram of a power supply circuit including an LED brightness correction circuit according to an embodiment of the present invention.

In the configuration, the difference from the power supply circuit shown in FIG. 2 is that in the present embodiment, the output side (emitter side) terminal of the transistor Q1 of the voltage regulator circuit, the connection terminal of the resistor R1 and the LED (the anode of the LED). That is, a resistor R4 is connected as a second current-decreasing resistor to the side terminal).

According to the above circuit configuration, when the input terminal k of the voltage regulator control circuit is "H", the transistor Q2 is turned on and the voltage regulator circuit is turned off.

That is, no current is supplied to the motor M. At this time, since the load current does not flow and the voltage V1 between the DC output terminals a and b of the power supply circuit becomes high, a sufficient drive current is supplied to the LED via the resistor R1 which is the first current-decreasing resistor. Flowing.

On the other hand, when the input terminal k of the voltage regulator control circuit becomes "L", the transistor Q2 is turned off, so that the voltage regulator circuit is turned on. At this time, since a large drive current flows to the motor M, the voltage V1 at the DC output terminals a and b decreases. Therefore, the LED drive current passing through the resistor R1 also becomes small. However, at this time, the current is supplied from the output side of the transistor Q1 of the voltage regulator circuit to the LED via the resistor R4 which is the second current reducing resistor.

As a result, a sufficient drive current still flows to the LED.

As described above, regardless of the on / off state of the motor M, a sufficient drive current flows to the LED, so that the light emitting state of the LED indicating the power supply state always maintains sufficient brightness.

By appropriately selecting the values of the resistors R4 and R1, it is possible to keep the magnitude of the current flowing through the LED constant.

[0017]

The output side of the voltage regulator circuit and the LED
By simply connecting one second current reducing resistor between the terminals, the lighting state of the LED indicating the power supply state can be made to have a constant luminance regardless of the on / off state of the load.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a power supply circuit including an LED brightness correction circuit according to an embodiment of the present invention.

FIG. 2 shows a circuit diagram of a conventional power supply circuit.

[Explanation of symbols]

 a, b-DC output terminal of power supply circuit R1-first current reducing resistor R4-second current reducing resistor M-motor (load) Q1, R2, ZD1- voltage regulator circuit Q2, R3- voltage regulator control circuit

Claims (1)

[Claims] 1. A power supply circuit having a DC output terminal, a series circuit of a first current reducing resistor and an LED connected between the DC output terminals, and the DC output terminal and a load that is intermittently turned on and off. A voltage regulator circuit connected thereto; a voltage regulator control circuit that turns off the voltage regulator circuit when the load is off; and a voltage regulator control circuit that turns on the voltage regulator circuit when the load is on; the LED and the first current reducing resistor; A second terminal connected between the connection terminal and the output side of the voltage regulator circuit
An LED brightness correction circuit comprising: