JPS6239426Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved control device for sequentially blinking a cascade of light emitting display elements.

Generally, a blinking drive circuit for a light emitting element using an LED is used as a means of determining when a physical quantity such as temperature, voltage, sound, etc. has reached a certain level, but a typical example of conventional circuit configuration is as shown in Figure 1. Are known.

First, in Figure 1A, a light emitting element LED and a level shift diode D are connected between the collectors of the transistors whose emitters are grounded, with the emitter of the previous stage transistor Q2 connected to the base of the next stage transistor Q1.
As the number of cascaded stages increases, the number of components such as the level shift diode and resistor to equalize the potentials of the LED cathode and the transistor emitter increases. There are significant drawbacks. In addition, in a circuit as shown in Figure B, in which a transistor is connected in parallel to each of the LEDs connected in series in multiple series, and a control power source Bc is applied to each base from a common parallel-connected terminal via a resistor. Since the collector potential of the lowest stage transistor is level-shifted by the forward rising voltage of the dummy element L, which is kept energized at all times, there is no need to insert any extra circuit elements in addition to the components essential for the blinking display function. The disadvantage is that the control current changes significantly depending on the number of cascaded LEDs because the ignition signal must be supplied to each transistor base from a control power supply with a large current capacity.

In view of the above-mentioned conventional light-emitting element drive circuits, which required unstable and unclear blinking control of light-emitting display elements and unnecessary circuit elements, the present invention provides a constant current from the indicator lamp input power terminal to ground. A cascaded light emitting element body consisting of a plurality of light emitting elements connected in series to which power is supplied, an individual collector connected to the input side electrode of each of the above light emitting elements, one emitter connected to the base of the other, and the terminal emitter being grounded. A resistor sufficient to sufficiently control the shunt current based on the control power supply is connected between the transistor series and each base-emitter of the transistor series, and the terminal is grounded, and the base of the transistor having the highest potential is connected between the base and emitter of the transistor series. The present invention provides a blinking control device for a light emitting display element, characterized by comprising a cascaded resistor serving as a common terminal of the control power source.

An embodiment of the present invention will be described below with reference to FIG.

Figure 2A is an example of an m-stage cascade consisting of m light-emitting elements, m transistors, and m resistors.The light-emitting elements LED1, LED2...LEDm are connected in series from the indicator lamp input constant current source B _L to the ground. Lighting current I _CL
is powered. Then, the collector is connected to the input supply side terminal, that is, the anode, of each LED, and the emitter of one (upper stage) of the cascaded transistors above the lowest stage transistor Q1 with a common emitter is connected to the base of the other (lower stage). . Further, equal resistors R1 and R2 are connected between the bases of the above transistors.
...Connect each Rm and ground the terminal, and connect the base of the transistor Qm, which has the highest potential, to the control power supply Bc.
This is a common control terminal to which a control voltage e is applied from.

In such a configuration, the highest potential is applied to the base of the transistor Qm at the top stage, that is, the mth stage, so if Qm becomes conductive, the lighting current I _CL that has been flowing into the light emitting element LEDm will be lowered to the potential. The current is shunted to the collector of the decreased Qm, and I _CL flows through the emitter to the next stage transistor Qm-1.
The light-emitting element LEDm-1 is turned off by passing current through the base of the transistor to make it conductive, and the light-emitting element LEDm-1 is also turned off.In this order, the ignition signal generated by the amplification effect of the transistor is applied to the base of the next transistor, and the light-emitting element is turned off. go. Therefore, as shown in Figure B, when a base current I _B is applied to the transistor and a collector current Ic corresponding to the lighting current flows through the collector, the base-emitter voltage is V _BE1 , and the collector current equivalent to the lighting current is V BE1 . Assuming that the base-emitter voltage when conducting is V _BE2 , when all LEDs are currently lit, the input control voltage ec that should be applied to the base of the top transistor in order to turn off up to n stages is
When expressed by a general formula, e _c =(n-1)V _BE2 +(m-n+1)V _BE1 (1). Here m>n (both m and n are positive integers),
I _CL ≫ _{I B} , R1=~=Rn=Rm.

In a general silicon transistor, when collector current Ic = 20mA, V _BE1 ≒ 0.5V approximately V _BE
2 ≒0.8V, so if m=n in equation (1), the control voltage to turn off all the light emitting elements is e _n = (m-1)V _BE2 +V _BE1 ...(2) becomes. If the number of cascaded stages is m=10, e10=
7.88V, the control voltage for turning off the first stage, that is, the lowest stage LED1, is e ₁ =mV _BE1 =5V. Therefore, it can be seen that a control voltage range of 5V to 7.88V is sufficient to sequentially turn off the 10-stage light emitting element series.

In this way, the light emitting elements connected in cascade in multiple stages can be turned off by energizing the parallel transistors up to the corresponding stage by energizing the base of the next stage using the lighting current of the previous stage, and turning off the light one after another. The above description has been about turning off the light-emitting element that is in the lit state, but in the case of turning on the light-emitting element, the control voltage that has been applied so far may be removed to return the transistor to the cut-off state. The resistors R1, R2, . In addition, when all transistors in the cascade above the bottom stage of the cascade are in a conductive state,
The collector potential of the transistor becomes lower than the anode potential of the light emitting element, which is below the threshold voltage of the LED (approximately 1.7 to 2.2V), and the entire lighting current of the LED is shunted to the base of the next stage transistor. When the transistor is non-conducting, the lighting current to each collector shunt is cut off, so a common forward current flows through all the cascaded light emitting elements, so that they are lit with uniform brightness. Figure 2C is a graph showing the relationship between the number of cascaded stages and the change in control voltage, and it shows that for each stage, the distinction between lighting and extinguishing is clearly determined by the voltage difference of V _BE1 - V _BE2 , and changes in a linear relationship. I understand.

Thus, the device of the present invention sequentially turns off the light by utilizing the current amplification effect of the transistor whose collector is connected to the lighting input side and the emitter is connected to the base of the next stage for multiple light emitting elements connected in cascade. The lighting current flowing through the light emitting element is bypassed from the collector to the emitter to ignite the next stage base, so the light emitting element can be turned off quickly and reliably. , the light emitting element can be illuminated clearly as soon as the control voltage is reduced. Therefore, it is possible to obtain a control device in which all the component parts contribute to the blinking action, and also to control the base of one transistor by a low-voltage, weak-current control power source, even though it is a cascaded structure, so that the blinking classification can be clearly distinguished. This has great practical effects, such as being able to achieve accurate display control.

[Brief explanation of drawings]

Figures 1A and 1B are examples of different conventional light emitting element blinking circuits, Figure 2A is a circuit configuration diagram of an embodiment of the device of the present invention, and Figure 2B is a diagram showing the base current of the transistor and the connection to the light emitting element. FIG. 2C is a graph showing the relationship between the base-emitter voltage of the inflow current, and FIG. 2C is a graph showing the relationship between the number of cascaded stages of light emitting elements and the control voltage. LED1, LED2~LEDm...Light emitting element, Q
1, Q2~Qm...transistor, R1, R2~
Rm...Resistor, B _L ...Constant current source, _ICL ...Lighting current, Bc...Control power supply, e...Control voltage.

Claims (1)

[Scope of utility model registration request] In a device in which a lighting current flowing into a cascaded body in which a plurality of light emitting elements are connected in series between an input terminal of a constant current source and ground is intermittent by a switching action to cause the light emitting elements to blink, A cascade of transistors in which individual collectors are connected to the input side electrodes of each of the light emitting elements, emitters of the upper stage are connected to bases of the next stage, and the terminal emitter is grounded; and each base-emitter of the cascade of transistors. Grounded resistors were connected in series so that the shunt current based on the control power source applied from the base of the transistor with the highest potential applied between them was sufficiently larger than the value based on the base-emitter resistance value when the transistor was conductive. 1. A blinking control device for a light emitting display element, comprising: a cascade connection body;