JPS62252257A - Led lightening circuit for telephone set - Google Patents

Abstract

PURPOSE:To optionally constitute a call circuit, to secure the luminance of a LED, and to prevent the generation of a signal distortion. or clipping, by providing a constant current circuit, and a current switching circuit so as to keep the circuit at high impedance, and not to affect the call circuit, and using the constant current circuit as a LED lightening circuit. CONSTITUTION:Generally, the base bias voltage of a transistor 42 is set considerably below that of a transistor 41. As a result, the transistor 42 is turned on, and a current on the constant current circuit is pulled in, then the LED goes to a lightening state, on the other hand, the transistor 41 is turned off. However, when an AC signal is overlapped by a low voltage power source for a subscriber circuit long distance condition, etc., and the base voltage of the transistor 41 drops below the base voltage of the transistor 42 regulated at a regulated potential, the transistor goes to an offstate, and the LED 21 is lightened off, and a constant current circuit 61 tends to stop its operation. At the moment, the transistor 41 goes to an on-state by the base bias voltage supplied to the transistor 41, thereby the constant current circuit 61 is operated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to telephone circuits, and more particularly to LED lighting circuits.

[Prior Art] Conventionally, in this type of LED lighting circuit for a telephone, as shown in Fig. 2, an LED connected in series to a resistor is connected in parallel to a telephone call circuit by turning on and off a lock switch for controlling the LED state. It was added so that the lights could be turned on or off. That is, in FIG. 2, 1 and 2 are first and second line terminals, 3 is a communication circuit, 100 and 102 are resistors, 102 is an LED, and 103 is a lock switch for controlling the LED state.

When the LED state control lock switch 103 is in the OFF state, the common contact of the lock switch 103 is connected to the dummy resistor 10.
LED 101 is connected to the 2 side and does not light up. When the lock switch 103 is turned on, current is supplied to the LED 101 through the resistor 100 and the LED 101 is turned on.

The resistor 102 is a dummy resistor for not changing the impedance of the telephone when the LED 101 is on and off.

[Problems to be Solved] By the way, in the conventional circuit described above, the LED 101 connected in series with the resistor 100 is connected in parallel to the communication circuit 3, so that the subscriber line is in a long distance state. , the disadvantage is that branch connections cannot be made. In other words, when trying to increase the brightness of the LED 101,
The value of the resistor 100 connected in series with the LED l01 must be reduced.If the value of the resistor lOO is reduced, the communication circuit 3 must be designed with high impedance, but if the value of the resistor 100 is If it is too small, it will be impossible to design the communication circuit 3. Therefore, at present, the current flowing through the LED 101 is secured by increasing the power supply voltage, but this has the disadvantage that increasing the power supply voltage makes it impossible to perform branch connection operations over long distances between subscriber lines.

[Means for Solving Problems] The present invention has been made in view of the above circumstances, and includes a constant current circuit that maintains high impedance in the circuit and does not affect the communication circuit. It has a current switch circuit so that it can operate normally even when a low voltage AC signal is superimposed on it, such as under a distance condition.

To further explain, the present invention includes high voltage side and low voltage side line terminals to which one call signal is applied, and a light emitting diode that is inserted between these high voltage side and low voltage side line terminals and turns on when a lock switch is turned on. The LED lighting circuit for a telephone includes a constant current circuit whose one end is connected to the high-voltage line terminal and which outputs a current signal on which the call signal is superimposed, and the other end of which is connected to the constant current circuit. , a first transistor that supplies the current signal to the low-voltage line terminal via the light emitting diode; and a base bias voltage that is always constant for the first transistor regardless of the voltage of the call signal. a constant bias circuit that supplies the current signal; a second transistor that is connected to the other end of the constant current circuit and supplies the current signal directly to the low-voltage line terminal; and a variable bias circuit that supplies a base bias voltage according to the voltage of.

[Example] Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. LED as a whole
It consists of a constant current circuit that keeps the lighting circuit at high impedance and a current switch circuit that enables operation at low voltages.

l and 2 are the first and second line terminals, 3 is a communication circuit, 11.12.13 is a resistor, 21 is an LED, 31
．． 32 is a diode, 41° 42 is a PNP (PNP) transistor that constitutes a current switch circuit, 51 is a capacitor, 61
71 is a constant current circuit, and 71 is a lock switch for controlling the LED state.

the first line terminal 1 and one end of the capacitor 51;

One end of the first resistor 11, one end of the constant current circuit 61, and the third
One end of the resistor 13 and the positive power supply terminal of the communication circuit 3 are connected, and the other end of the capacitor 51 and the first resistor 1 are connected.
1, one end of the second resistor 12, and the first PNP
The other end of the constant current circuit 61 is connected to the emitter of the first PNP transistor 41 and the emitter of the second PNP transistor 42. The base, the other end of the third resistor 13, and the anode of the first diode 31 are connected, the cathode of the first diode 31 and the anode of the second diode 32 are connected, and the cathode of the second diode 32 is connected. and one end of the LED state control lock switch 71 are connected, the collector of the second PNP transistor 42 and the 7 node of the LED 21 are connected, and the second line terminal 2 and the second resistor 12 are connected. the other end and the first PNP) the collector of the transistor 41 and the L
The cathode of the ED 21, the other end of the lock switch 71 for controlling the LED state, and the negative power terminal of the communication circuit 3 are connected.

In the above configuration, when the lock switch for controlling the LED state is in the OFF state, the transistor 42 is in the OFF state and the LED 21 is not lit.

On the other hand, the speech signal applied to the first line terminal 1 is smoothed by the capacitor 51 and the resistor 11, and is smoothed by the resistor 12.
through to the second line terminal 2. As a result, the voltage drop across the resistor 12 is applied to the base of the transistor 41, turning on the transistor 41, and current flows from the constant current circuit 61 through the transistor 41.

In this state, even if an AC signal is superimposed on a low-voltage power supply such as in a long-distance subscriber line condition, the emitter of the transistor 41 can drop to almost the ground voltage, which is the saturation region, and the constant current circuit will not be saturated and the voltage will remain low. enable operation.

When the lock switch for controlling the LED state is in the ON state, a constant voltage is applied from the ground potential side as the base bias voltage of the transistor 42 by the resistor 13 and the diodes 31 and 32. This base bias voltage is a value uniquely determined by the forward drop voltage of the diodes 31 and 32, and is always constant regardless of the voltage of the communication signal applied between the first and second line terminals l and 2. Constant 0 Normally, the base bias voltage of this transistor 42 is set sufficiently lower than the base bias voltage of the transistor 41, and as a result, the transistor 42 is turned on, the current of the constant current circuit is drawn, and the LED is turned on. On the other hand, the transistor 41 is turned off. However, when an AC signal is superimposed on a low-voltage power supply such as under a long-distance subscriber line condition, and the base voltage of the transistor 41 becomes lower than the base voltage of the transistor 42, which is set to a constant potential, the transistor 42 turns off and the LE
D21 goes out and the constant current circuit 61 tries to stop operating. At this moment, the base bias voltage applied to the transistor 41 turns the transistor 41 on.
The constant current circuit 61 is operated.

The base voltage of the transistor 42 recovers again, and when the voltage becomes constant, the transistor 42 turns on, draws current from the constant current circuit, turns on the LED 21, and turns on the transistor 42.
1 is in the off state. At this time, the LED is turned off for a short period of time, and to the human eye, it appears to be on.

[Effects of the Invention] As explained above, the present invention can achieve high impedance by using a constant current circuit in an LED lighting circuit, and does not affect the communication circuit. Not only can a communication circuit be configured, but also any required current can be supplied to the LED, which has the effect of ensuring brightness.

Furthermore, by adopting a current switch circuit, LE
Even when an alternating current signal at low voltage is superimposed, such as when the subscriber line is far away when D is turned on, the constant current circuit can be operated normally, and there is an effect that signal distortion and clipping do not occur.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention. FIG. 2 is a block diagram showing a conventional circuit. 1, 2: First and second line terminals 3: Communication circuit 11.12.13 Two resistors 21: LED for status display 31.32: Diode 41.42: Transistor 51 constituting the comparison circuit: Capacitor 61: constant current circuit

Claims (1)

[Claims] high voltage side and resistance voltage side line terminals to which call signals are applied;
In a telephone LED lighting circuit comprising a light emitting diode inserted between the high voltage side and resistance voltage side line terminals and turned on by turning on a lock switch, one end is connected to the high voltage side line terminal. a constant current circuit that outputs a current signal on which the call signal is superimposed; and a first circuit that is connected to the other end of the constant current circuit and supplies the current signal to the resistance line terminal via the light emitting diode. a constant bias circuit that always supplies a constant base bias voltage to the first transistor regardless of the voltage of the call signal; and a constant bias circuit connected to the other end of the constant current circuit to It is characterized by comprising a second transistor that directly supplies a signal to the resistance line terminal, and a variable bias circuit that supplies a base bias voltage to the second transistor according to the voltage of the call signal. LED lighting circuit for telephones.