JPH026640Y2 - - Google Patents

Description

[Detailed explanation of the invention] This invention is an ECL circuit (emitter coupled logic circuit)
This invention relates to a light emitting diode control circuit using an ECL circuit output to control lighting and dimming of a light emitting diode using the output of the ECL circuit.

The conventional light emitting diode control circuit of this type is
As shown in the figure, a logic output from, for example, a positive logic output terminal 13 of an OR gate 12 in the ECL circuit 11 is applied to the base of a transistor 14. The emitter of the transistor 14 is connected to the emitter of the transistor 15 and connected to one end of the current source 16, and the collector of the transistor 14 is connected to the emitter of the transistor 15.
The collector of the other transistor 15 is connected to the power supply terminal 18 through a light emitting diode 19 . The light emitting diode 19 and the transistor 15 are polarized in the forward direction. transistor 15
The base of is connected to the power supply terminal 18 through a resistor 21 and to the other power supply terminal 24 through resistors 22 and 23. transistor 14
The base of is connected to the power supply terminal 24 through the resistive element 25.

When the output of the ECL circuit 11, that is, the output of the terminal 13, is at a high level, the transistor 14 is conductive and the transistor 15 is non-conductive, so that the light emitting diode 19 is off. When the output of the output terminal 13 is at a low level, the transistor 14 is non-conductive and the transistor 15 is conductive, causing current to flow through the light emitting diode 19 and lighting it up. In this way, the state of the output of the ECL circuit 11 is displayed by the on/off state of the light emitting diode 19, or this information is displayed together with the light receiving element coupled to the light emitting diode, a so-called light emitting diode, forming a photocoupler. The information is transmitted to others through the light receiving element.

This configuration is based on the following reasons: the amplitude of the output terminal 13 of the ECL circuit 11;
In other words, the difference between the high level and low level of the logic output is approximately
0.8V, and on the other hand, the conduction voltage of the light emitting diode 19 is about 2V, so the output of the ECL circuit 11 cannot directly control whether the light emitting diode 19 is turned on or off. Therefore, as shown in Fig. 1, a differential amplifier circuit is used, and the ECL circuit 1
The light emitting diode 19 was controlled depending on the state of the light emitting diode 19. Instead of such a configuration, there is also a device that converts the output of the ECL circuit into a so-called TTL circuit to control the lighting of the light emitting diode.
In any case, the conventional light emitting diode control circuit is
It cannot be directly controlled by the output of the ECL circuit,
Since it uses the amplifier and TTL circuit shown in Figure 1, it is expensive and has the disadvantage of increasing the number of parts.

This idea allows the light-emitting diode to be directly turned on and off using the output of the ECL circuit, and can be constructed at low cost with a small number of elements.
An object of the present invention is to provide a light emitting diode control circuit using ECL circuit output.

FIG. 2 shows an example of a light emitting diode control circuit according to this invention, and parts corresponding to those in FIG. 1 are given the same reference numerals. The ECL circuit 11 has a positive logic output terminal 13a and a negative logic output terminal 13b, that is, it outputs complementary outputs. The positive logic output terminal 13a and the negative logic output terminal 13b are connected to each other through the light emitting diode 19 and the diode 27. These diodes 19 and 27 have the same polarity and are in the forward direction with respect to the terminals 13a and 13b, respectively. Further, in this example, the diode 27 includes two diode elements 27a, 2
7b are connected in series. diode 2
A connection point 28 between 7 and 19 is connected to a power supply terminal 24 through a resistance element 29.

The output of the ECL circuit 11 is at a high level, for example -
0.8V, -1.6V at low level, power supply terminal 24
The voltage V _EE of the light emitting diode 19 is -5.2V, the conduction voltage Vf ₁ of the light emitting diode 19 is 2.0V, the conduction voltage Vf ₂ of each of the diodes 27a and 27b is 0.7V, and the resistance element 2
The resistance value of 9 determines the current value required for lighting the light emitting diode.

The output of the positive logic output terminal 13a of the ECL circuit 11 is, for example, a low level of -1.6V, and the negative logic terminal 1
When the output of 3b is high level -0.8V, the negative logic output terminal 13 is output through the diodes 27a and 27b.
A current flows from the connection point 28 to the power supply terminal 24 through the resistance element 29. At this time, connection point 28
The potential of diode 2 is from -0.8V of terminal 13b.
The potential becomes -2.3V, which is twice the conduction voltage of 7a and 27b, which is 0.7V. Therefore, the positive logic output terminal 13a is -1.6V, and the potential of the connection point 28 is -
2.3V, and the potential difference between them is 0.7V, which is sufficiently smaller than the conduction voltage of the light emitting diode 19, 2.0V, and the light emitting diode 19 does not light up.

Conversely, the output of the positive logic output terminal 13a is at a high level,
When the output of the negative logic output terminal 13b becomes low level, the output from the terminal 13a passes through the light emitting diode 19,
Further, current flows through the resistive element 29 to the power supply terminal 24 . At this time, the potential of the connection point 28 becomes -2.8V, which is the value obtained by subtracting the conduction voltage Vf ₁ =2.0V of the light emitting diode 19 from -0.8V, and the potential of the diodes 27a, 27
-1.6V of terminal 13b and connection point 2 are connected between both ends of b.
A voltage of 1.2V, which is the difference from -2.8V of 8, is applied. Since this value of 1.2V is smaller than the sum of the conduction voltages of the diodes 27a and 27b, 1.4V, no current flows through these diodes.

In this manner, the light emitting diode 19 is controlled to be turned on or off depending on the state of the ECL circuit 11.

Assuming that the high level of the output of the ECL circuit 11 is Vh, the low level is Vl, the conduction voltage of the diode 19 is Vf ₁ , and the conduction voltages of the diodes 27a and 27b are Vf ₂ , the following conditions are satisfied from the above conditions. There is a need to.

Vl−(Vh−2Vf ₂ )<Vf ₁ Vl−(Vh−Vf ₁ )<2Vf ₂ In the above, the light emitting diode lights up when the positive logic output terminal 13a of the ECL circuit 11 is at a low level, and turns off when it is at a high level. In the above example, the light is turned on when the level is high, and it may be turned off when the level is low. For this purpose, diode 2 is connected to the terminal 13a side.
7 may be connected to the light emitting diode 19 on the terminal 13b side. Further, the diode 27 may be constructed of a single element instead of using a plurality of elements as described above. Furthermore, both the diodes 19 and 27 may be light emitting diodes, and one of them may be shielded so that it is not displayed externally, or may be used to transmit the output of the ECL circuit 11 as an optical signal to the outside, or both may be used. The light outputs of the light emitting diodes may be output as logical outputs that are opposite to each other.

As described above, according to the light emitting diode control circuit of this invention, it is possible to directly control the light emitting diode by the output of the ECL circuit 11, and there is no need for an amplifier circuit using transistors as in the conventional case. , or there is no need to convert the logic output using a TTL circuit, and it can be easily configured with a small number of elements and can be manufactured at low cost.

As the diode 27, for example, the conduction voltage is
1.4 to 2V junction diode or Zener voltage 1.4
~2V Zener diodes can also be used.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing a conventional light emitting diode control circuit, and FIG. 2 is a connection diagram showing an example of a light emitting diode control circuit according to this invention. 11: ECL circuit, 13a: Positive logic output terminal,
13b: Negative logic output terminal, 19: Light emitting diode, 29: Resistance element that determines the current value necessary for lighting the light emitting diode.

Claims (1)

[Scope of utility model registration request] A positive logic output terminal and a negative logic output terminal of the ECL circuit are connected to each other through first and second diodes in the forward direction, and the connection point of these first and second diodes is connected to a power supply terminal through a resistive element. The threshold values of the first and second diodes are selected so that the diode connected to the output terminal that provides a high-level output is conductive and the other diode is non-conductive. At least one of the two diodes is a light emitting diode.The light emitting diode control circuit uses the ECL circuit output.