JPH01238074A - Led driving circuit - Google Patents

Abstract

PURPOSE:To give an appearance of two indication LED's lighting ON on one drive terminal, by making two mode indications available on one terminal simultaneously in a driving circuit made by a combination of LED's, a PNP transistor and an NPN transistor. CONSTITUTION:A PNP transistor Q1 and an NPN transistor Q2 are turned into cutoff and conduction states alternately by a gate circuit consisting of AND circuits G1 and G2. The output of the AND circuit G1 is reversed by an inversion circuit G3 to switch incoming current of a LED1 and a LED2 so that both LED's appear to light ON. The conditions for the NPN transistor Q2 to conduct is that two inputs to the AND circuit G2, a mode input from a mode input terminal IN2 (second voice program) and a switch pulse signal, are in a first logical state (H) and the conditions for the PNP transistor Q1 to conduct is that two inputs to the AND circuit G1, a mode input from a mode input terminal IN1 (stereo) and the switch pulse signal, are in a first logical state (H).

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a drive circuit for a display device using LEDs.

(Prior Art) FIG. 3 shows a conventional LED drive circuit. Third
In the figure, 1 is an LED drive terminal, Ql is a PNP transistor, Q2 is an NPN transistor, R3 is a current limiting resistor, LEDl and LED are mode display LEDs, R□
, R2 is a bias resistor.

IN, IN is a mode input terminal, and VCC is a power supply.

Next, the operation of the conventional example of the L-synthetic acid will be explained.

In FIG. 3, for example, the mode input terminal IN is connected to the second
When the logic state (L) is reached, the PNP transistor Q becomes conductive, and the PNP transistor Q, j &
, anti-R,, LED drive terminal 1. LED...

Current flows through resistor R1 and the LED lights up.

On the other hand, when the mode input terminal IN becomes the first logic state (H) and the NPN transistor Q2 becomes conductive, the power supply ■Cc
From resistor R, , LED, , LED drive terminal 1. Resistance R,
, a current flows through the NPN transistor Q2 and the LED,
lights up. Here, if resistor R1 = resistor R2, the potential at the connection point of resistor R□ and resistor R2 becomes Vcc/2, and LE
If the current flowing through LED 1 when D1 is lit is , then the current flowing through LED 2 when LED 2 is lit is . □, it is necessary to select a small value for R2.

(Problem to be Solved by the Invention) However, in the above conventional configuration, two display LEs
There was a problem in that D (LEDl, LED2) could not be turned on at the same time.

The present invention solves these conventional problems,
The purpose of this is to pseudo-light two display LEDs using one drive terminal.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an LED drive circuit that includes conventional LEDs, PNP transistors, and NPN transistors, as well as a gate circuit and an inverting circuit configured as an AND circuit. It is equipped with the following.

(Function) With the above configuration, the present invention can time-share two L
The ED can be lit alternately, giving the appearance of two L lights.
This has the effect that two LED displays can be performed at the same time using the ED drive terminal.

(Example) Before explaining the embodiments, the main points of the background of the present invention will be described.

In recent years, with the increase in the degree of integration of semiconductor integrated circuits, it has become possible to accommodate many functions within one chip. On the other hand, there are restrictions on the size of the package and the number of terminals, and the trend is to integrate as many circuits as possible while minimizing the number of terminals, and the present invention also contributes in this direction.

- For example, specifically regarding integrated circuits for TV audio multiplexing and demodulation, multiplex broadcasting in two languages and stereo is currently carried out in one country, but both broadcasts are not carried out at the same time, and therefore the TV set When displaying the broadcast status of each mode using LEDs, the LEDs of both modes at the same time.
There was no need to turn it on. On the other hand, Zenith system (hereinafter referred to as USA system) audio multiplex broadcasting is being implemented in the United States, and demodulation integrated circuits are being developed in accordance with this system. The USA system is stereo broadcasting and
It consists of an audio program, and both programs are often broadcast at the same time. In this case, the viewer needs to know whether only one broadcast or both broadcasts are currently being broadcast, and therefore LED displays for both modes are required. In order to meet the above requirements and reduce the number of terminals in an integrated circuit, it is desirable to be able to display two modes with one drive terminal.

FIG. 1 shows a basic circuit of an embodiment of the present invention. In FIG. 1, 1 is an LED drive terminal.

Q is a PNP transistor, G2 is an NPN transistor, R3 is a current limiting resistor, R,, R2 is a bias resistor, LED is a display LED, G1. G2 is an AND circuit, G is an inversion circuit, Q and Q are switching pulse signals, and IN, , IN are mode input terminals.

Next, the operation shown in FIG. 1 will be explained. In Fig. 1 above, the PNP transistor QU and the NPN transistor Q2 are alternately connected and disconnected by a gate circuit composed of an AND circuit Gt*a*, and the output of the AND circuit G is inverted by an inverter circuit G3. By switching the inflow currents of LEDl and LED, both LEDs appear to be lit.

The condition for conduction of the NPN transistor Q2 is when both the mode input (second audio program) from the mode input terminal IN of the AND circuit G2 and the switching pulse signal are in the first logic state (H). can be.

The condition for conducting the PNP transistor Q1 is when the two inputs of the AND circuit G1, that is, the mode input (stereo) from the mode input terminal IN and the switching pulse signal are both in the first logic state (H). Note that the switching pulse signal Q, which is an input to the AND circuit Gi, and the switching pulse signal Q, which is an input to the AND circuit G, are logically inverted pulses.

FIG. 2 shows a specific circuit of one embodiment of the present invention. In Figure 2, G31 Q4t QljQ,,Q
,,Q are NPN transistors, Q is a PNP transistor, A is a frequency dividing circuit, and B is a switching oscillation source.

To show the relationship between FIG. 1 and FIG. 2, the PNP transistor Q in FIG. 1 corresponds to the NPN transistor Q in FIG.
The NPN transistor Q2 in the figure corresponds to the NPN transistor Q4 in Figure 2.6 Also, the NPN transistor Q in Figure 2 corresponds to the inverting circuit G and the AND circuit G in Figure 1. Q, and resistors R,,R,, and what corresponds to the AND circuit G2 in FIG. 1 are the NPN transistors Q,,Q, and resistors R,,R4 in FIG.

Pulses (Q, Q) of opposite polarity are required as switching pulse signals for the AND circuits G, , G, and various methods can be considered as the source of the pulses. Here, as an example, a method is shown in which a signal obtained by waveform shaping or frequency division of oscillation from one oscillator is used.

In the description of the above embodiment, the mode input to the mode input terminal IN1 is stereo, and the mode input to the mode input terminal IN is the second audio program, but the mode input terminal IN□
Of course, it is also possible to set the mode input terminal IN to the second audio program and the mode input terminal IN to stereo, in which case the LED1+
The contents of the mode display of the LED should naturally be reversed.

(Effects of the Invention) As is clear from the embodiments described above, the present invention has the effect that two mode LEDs can be simultaneously lit and displayed without increasing the number of terminals.

[Brief explanation of the drawing]

FIG. 1 is a basic circuit diagram of an embodiment of the present invention, FIG. 2 is a specific circuit diagram of the embodiment, and FIG. 3 is a conventional LED drive circuit diagram. Q,, Q,...PNP transformer, Q2゜Q,,
Q,, Q,, Q,, Q,, Q,...NPN
Transistor, R engineering ~ R1...resistance, LEDl, LE
D,... LED, G□, G2... AND circuit, G
3... Inversion circuit, INl. IN2...mode input terminal, A...divider circuit, B...
...Switching oscillation source, Q, Q...Switching pulse signal (Q and Q are inverted pulses), VCC...Power supply. Patent Applicant Matsushita Electric Industrial Co., Ltd. Figure 1 Gt, GrS Association Pt dwarf! l bribe G5″ inversion 1
Takashi Q, 6 Rosbatheskugo (oho+-anti'λshir Niparejin) + LEo! t111屝3 匡D+
, LED2/Kaindai-V Light Ho) Figure 2

Claims (2)

[Claims] (1) Constructed by combining LED, PNP transistor, and NPN transistor, and can display two modes at the same time.
An LED drive circuit characterized in that it can be driven by a terminal. (2) The LED drive circuit according to claim (1), wherein the mode display LEDs are connected in antiparallel.