JPS635650A - Led lighting circuit for telephone set - Google Patents

Abstract

PURPOSE:To reduce a chip area in an integrated circuit by connecting the 1st and 2nd PNP transistor connected to a constant current circuit to a current mirror circuit formed with specific NPN transistors and driving a state display LED in a current mirror circuit connected to the 2nd PNP transistor. CONSTITUTION:If a lock switch 7 is turned on, a fixed voltage is given as the base bias voltage of the PNP transistor 42 from an earth current side. The current mirror circuit configured with the NPN transistors 45 and 46 brings an LED 5 to light up. However the PNP transistor 41 is off. If its base voltage is lower than that of the PNP transistor 42, said transistor 42 becomes off, and the LED 5 goes out. Again the base voltage of the PNP transistor 41 is restored to become higher than the base voltage of the PNP transistor 42, the PNP transistor 42 becomes on, leads in the current of a constant current circuit 61 to cause the LED 5 to light up, and the PNP transistor 41 attains an off state.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an LED lighting circuit for a telephone.

[Conventional technology]

Conventionally, an LED lighting circuit for a telephone includes a line terminal 1.2, a resistor 11.12 connected in series between the line terminals 1.2, and a capacitor connected in parallel to the resistor 11, as shown in FIG. 4, and a constant current circuit 7 whose one end is connected to the line terminal 1.
1, a PNP transistor 51 whose base is connected to the connection point of the resistor 11 and 12, whose emitter is connected to the other end of the constant current circuit 71, and whose cover is connected to the line terminal 2, and whose emitter is connected to the emitter of the PNP transistor 51. Connected PNP
A transistor 52, an LED 5 whose anode is connected to the collector of the PNP transistor 52, and a cathode connected to the line terminal 2, and a resistor 13 whose one end is connected to the line terminal 1 and the other end is connected to the base of the PNP transistor 52. , a diode 31 whose anode is connected to the base of the PNP transistor 52, and a diode 32 whose anode is connected to the cathode of the diode 31.
One end is the cathode of the diode 32, and the other end is the line terminal 2.
It consisted of a lock switch 7 connected to the line terminal 1, and a communication circuit 3 connected to the line terminal 1 at one end and the line terminal 2 at the other end.

Next, the operation of this circuit will be explained.

When the lock switch 7 for LED control is in the off state, P
The NP transistor 52 is turned off and the LED 5 is turned off. On the other hand, the PNP transistor 51, to which a constant voltage is applied as a base bias voltage from the power supply side through the resistors 11 and 12 and the capacitor 4, is turned on and draws current from the constant current circuit 71. In this state, even when an AC signal is overlapped by a low voltage power supply such as when a subscriber line is connected to a long distance, the emitter of the transistor 51 can drop to almost the ground potential, which is the saturation region, and the constant current circuit 71 Enables low voltage operation without saturation.

When the lock switch 7 is turned on, a constant voltage is applied from the ground potential side by the resistor 13 and the diodes 31 and 32 as the base bias voltage of the PNP transistor 52, and this base bias voltage is more than the base bias voltage of the PNP transistor 51. The PNP transistor 52 is turned on and draws current from the constant current circuit 71, and the ED 5 is turned on, but the transistor 51 is turned off. However, when an AC signal is superimposed on a low-voltage power supply when connected to a subscriber line long path M, etc., the amplitude of the AC signal causes the base voltage of the PNP transistor 510, which is set at a constant potential from the power supply side, to be lower than the base voltage of the PNP transistor 52. When it becomes low, the PNP transistor 52 is turned off and the L
The ED 5 goes out and the constant current circuit 71 tries to stop operating. Kono Shun 1'5'1PNP) - Ranjisuku 51
A constant bias voltage applied to the base of the PNP
The transistor 51 turns on and draws the current from the constant current circuit 71. When the base voltage of the PNP transistor 51 recovers again and becomes equal to or higher than the base voltage of the PNP transistor 52, the PNP transistor 52 turns on and draws the current from the constant current circuit 71. The pull-in LED 5 is turned on and the PNP transistor 51 is turned off. At this time, the LED 5 is turned off for a short time, and to the human eye, it appears to be on.

In this way, the PNP transistors 51 and 52 constitute a current switch circuit in which switching is performed while comparing their base voltages, and the low voltage of the constant current circuit 71 is maintained while the LED S lighting and non-lighting states are the same. It was possible to operate.

[Problem that the invention seeks to solve]

The conventional telephone LED lighting circuit described above has a configuration in which a status display LED is connected in series to the collector of a PNP transistor constituting a current switch circuit. However, in integrated circuits such as LSIs, the current capacity of PNP transistors is small, and when trying to flow sufficient current to an LED, the two transistors that make up the current switch circuit and the constant current circuit occupy a very large amount of space. There is a drawback that it can be damaged.

[Means for solving problems]

The LED lighting circuit for a telephone according to the present invention includes first and second line terminals, a first resistor whose one end is connected to the line terminal of the vine 1, one end of which is connected to the other end of the resistor of the bamboo 1, and the other end of the resistor. A second resistor whose ends are respectively connected to the line terminals of the vine 2, a capacitor whose one end is connected to the first line terminal, and whose other end is connected to the connection point of the first and second resistors; a constant current circuit connected to the first line terminal; a first PNP transistor whose emitter is connected to the other end of the constant current circuit; and whose base is connected to the connection point of the first and second resistors; A PNP whose collector is connected to the collector of the t-transistor and an NPN whose emitter is connected to the second line terminal.)
- a predetermined current mirror in cooperation with a first NPN transistor whose base is connected to the base of the first NPN transistor, whose collector is connected to the first line terminal and whose emitter is connected to the second line terminal; a second NPN transistor forming a current mirror circuit having a ratio of
and a third resistor having one end connected to the first line terminal;
The base is the other end of the third resistor and the emitter is the first PNP
a second PNP transistor connected to the emitter of the transistor, and a second PNP transistor whose base and collector are connected to each other;
a third NPN transistor whose collector is connected to the collector of the NP transistor, the emitter is connected to the second line terminal, and the base is connected to the base of the third ONPN transistor, whose collector is connected to the cathode of the LED, and whose emitter is connected to the second line terminal, respectively. a fourth NPN transistor connected and cooperating with a third NPN transistor to form a current mirror circuit having a predetermined current mirror ratio; and a locking switch connected at one end to the second line terminal;
one or more series-connected diodes with an anode connected to the base of a second PNP transistor and a cathode connected to the other end of the lock switch; one end connected to a first line terminal and the other end connected to a second line terminal; and communication circuits respectively connected to the terminals.

Therefore, only the second and fourth NPN transistors need to have a large current capacity, and the other transistors and the constant current circuit need only have a small capacity. Also, an NPN transistor has a smaller chip area on an integrated circuit than a PNP transistor. Since it is small, the overall chip area is also reduced.

〔Example〕

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

Figure 1 is a configuration diagram showing an embodiment of the LED lighting circuit for a telephone according to the present invention.

In this embodiment, the line terminal 1.2 and the line terminal 1゜21Wl
A capacitor 4 is connected in parallel to the resistor 11, a constant current circuit 61 whose one end is connected to the line terminal 1, and an emitter is connected to the connection point between the resistors 11 and 12 whose bases are connected to the line terminal 1. A PNP transistor 41 is connected to the other end of the constant current circuit 61, an NPN transistor 4 whose base and collector are connected to the collector of the PNP transistor 41, and whose emitter is connected to the line terminal 2.
3 and the base of the NPN transistor 43,
An NPN transistor 44 has a collector connected to the line terminal 1 and an emitter connected to the line terminal 2, and cooperates with the NPN transistor 43 to form a current mirror circuit having a predetermined current mirror ratio. a resistor 13 whose one end is connected to the line terminal 1; a PNP transistor 42 whose base is connected to the other end of the resistor 13 and whose emitter is connected to the emitter of a PNP transistor 41; and a PNP transistor whose base and collector are connected to the emitter of a PNP transistor 41. 42, an NPN transistor 45 whose emitter is connected to the line terminal 2;
An NPN transistor whose base is connected to the base of the NPN transistor 45, whose collector is connected to the cathode of the LED 5, and whose emitter is connected to the line terminal 2, and which cooperates with the NPN transistor 45 to form a current mirror circuit having a predetermined current mirror ratio. 46 and the anode is N
A diode 31 connected to the base of the PN transistor 42, a diode 32 whose anode is connected to the cathode of the diode 31, and a lock switch 7 whose one end is connected to the cathode of the diode 32 and the other end is connected to the line terminal 2. It is comprised of a communication circuit 3, one end of which is connected to a line terminal 1, and the other end of which is connected to a line terminal 2.

Therefore, when the lock switch 7 for controlling εD is in the OFF state, the PNP transistor 42 is in the OFF state, and the NPN transistor 45 cannot draw current;
The transistor 46 is turned off and the LED 5 is turned off. - side, resistor I+, 12 and capacitor 4
As a result, the PNP transistor 41, which is supplied with a constant voltage from the power supply side, turns on, draws in the current from the constant current circuit 61, and flows to the LED when the LED is turned on by the current mirror circuit composed of the NPN transistors 43 and 44. The expected current value is changed to the NPN transistor 44.
This makes the conditions when the LED is on and off the same. - In this state, even if the AC signal is interrupted by a low voltage power supply, such as when the subscriber line is connected to a long distance, PNP will not be activated.
The emitter of the transistor 41 can drop almost to the ground potential, which is the saturation region, and the constant current circuit 61 can operate at a low voltage without becoming saturated. lock switch 7
When turned on, resistor 13 and diode 3L32
Therefore, a constant voltage is applied from the ground potential side as the base bias voltage of the PNP transistor 42, and this base bias voltage is set sufficiently lower than the base bias voltage of the PNP transistor 41, and the PNP transistor 42 is turned on and a constant current is generated. The current of the circuit 61 is drawn in, and the LED 5 is turned on by the current mirror circuit constituted by the NPN transistors 45 and 46, but the PNP transistor 41 is in the off state. However, when an AC signal is generated by a low-voltage power supply such as when a subscriber line is connected to a long distance, the base voltage of the PNP transistor 41, which is set at a constant potential from the power supply side depending on the amplitude, becomes the base voltage of the PNP transistor 42. When the voltage becomes lower, the PNP transistor 42 turns off, E05 turns off, and the constant current circuit 61 stops operating.
A constant bias voltage applied to the base of PN
P transistor 41 is turned on, and constant current circuit 6
Since the current of 1 is not drawn, the current mirror circuit composed of NPN transistors 43 and 44 operates, and the
The current tNPIl that should flow through D5 is drawn as the collector current of the laser resistor 44.The base voltage of the PNP transistor 41 is restored again, and the PNP transistor 4
If the base voltage exceeds the base voltage of PNP transistor 42
turns on, draws current from the constant current circuit 61, and
The ED5i is turned on and the PNP transistor 41 is turned off. At this time, when the LED 5 is turned off, it is slightly open, and to the uninitiated eye, it looks like it is still on.

In this way, this embodiment uses PNP transistors 41 and 42.
constitutes a current switch circuit that performs switching while comparing each other's hemi-sumi pressure, so that the state is the same when the 5 LEDs are lit and when the LEDs are not lit, and enables low voltage operation of the constant current circuit 61. Transistors 43, 44 and 4
By adding a current mirror circuit according to 5.46, the current for lighting the LED S, which was flowing through the PNP transistor (1FrNPN) - is made to flow through the transistor 46.0 In this embodiment, the diode 31.32
Although two LEDs are used, the number may be changed depending on the characteristics of the LED 5.

In this way, in the conventional circuit, the maximum current that can flow through the collector of the PNP transistor is 100 μA, so L
To send a current of 2 mA to ED 5, connect 2 to constant current circuit 71.
0 pieces, 40 pieces in each switch circuit, 20 pieces on the left and right, 60 pieces in total
PNP transistors were required. However, in the circuit of this embodiment, the constant current circuit 61 has one PNP transistor, the current switch circuit has three PNP transistors, one on each side, and the current mirror circuit has a current mirror ratio of 1:20, resulting in 42 transistors on the left and right sides. An NPN transistor is required. However, the required chip area per emic of an NPN transistor is about 0.6 times that of a PNP transistor, and 42 transistors is equivalent to 42 x 0.6 = 25, or 25 PNP transistors. Therefore, the number of transistors is now 28, compared to 60 in the conventional circuit, and the chip area has been halved.

〔Effect of the invention〕

As explained above, the present invention connects the first and second PNP transistors connected to a constant current circuit to a current mirror circuit formed of NPN transistors each having a predetermined current mirror ratio, and ) - By driving a status display LED using a current mirror circuit connected to a transistor, it is possible to significantly reduce the chip area of an integrated circuit constituting an LED lighting circuit for a telephone.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of an LED lighting circuit for a telephone according to the present invention, and FIG. 2 is a block diagram showing a conventional example. 1.2......Line terminal, 3...
・・・Telephone circuit, 4 ・−・−・・・・・・・・・Capacitor, 5・・・・−−−−L E D, 7−−−
・−・−・・Lock switch, +1.12.
13-... Resistor, 31.32... Diode 41.42-----PNP Transistor, 43.44, 45.46... NPN
Transistor, 51.52-...PNP
Transistor, 61.71-... Constant current circuit.

Claims (1)

[Claims] First and second line terminals, a first resistor whose one end is connected to the first line terminal, whose one end is connected to the other end of the first resistor, and whose other end is connected to the second line terminal. a second resistor connected to each of the line terminals; a capacitor having one end connected to the first line terminal and the other end connected to the connection point of the first and second resistors; and one end connected to the first line terminal. a first PNP transistor whose emitter is connected to the other end of the constant current circuit and whose base is connected to the connection point of the first and second resistors; a first NPN transistor having a collector connected to the PNP transistor, an emitter connected to the second line terminal, a base to the base of the first NPN transistor, and a collector connected to the first line terminal;
second NPN transistors each having an emitter connected to the second line terminal and cooperating with the first NPN transistor to form a current mirror circuit having a predetermined current mirror ratio; a third resistor with one end connected to the first line terminal; a PNP whose base is connected to the other end of the third resistor and whose emitter is connected to the first line terminal;
a second P connected respectively to the emitters of the transistors;
an NP transistor, a third NPN transistor whose base and collector are respectively connected to the collector of the second PNP transistor and whose emitter is connected to the second line terminal; and whose base is connected to the base of the third NPN transistor and whose collector is connected to the LED. , the emitters are respectively connected to the second line terminal, and the third line terminal is connected to the cathode of the
a fourth NPN that cooperates with the NPN transistor to form a current mirror circuit having a predetermined current mirror ratio;
a transistor; a locking switch having one end connected to a second line terminal; and one or more series-connected diodes having an anode connected to the base of the second PNP transistor and a cathode connected to the other end of the locking switch. An LED lighting circuit for a telephone, comprising a communication circuit having one end connected to a first line terminal and the other end connected to a second line terminal.