JPS6215834Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a display power supply circuit, and particularly to a display device power supply circuit using a plurality of light emitting diodes.

When displaying output data from a microcomputer or the like, a display device consisting of a shift register connected to its display output port and a light emitting diode directly connected to each digit of the shift register is sometimes used. In such a display device, the light emitting diodes must be turned off when output data is transferred from a microcomputer or the like to a shift register. This is because the shift register and the light emitting diode are directly connected, and if the light emitting diode is energized while output data is being transferred, the noise during the transfer will be displayed, causing smearing and making it difficult to see. Put it away. Conventionally, therefore, the power source of the light emitting diode is configured to be controllable, and the light emitting diode is turned off by a command from a microcomputer, the display data is transferred to the shift register, and after that, the light emitting diode is turned on. I am taking a method.

However, according to such conventional methods, it is necessary to provide a large current transistor to control the light emitting diode, a blanking output port, an accompanying blanking program, a display timer to determine the display transfer frequency, etc., and the device is complicated. Moreover, it is difficult to avoid being large and expensive.

Therefore, in consideration of this reason, a display element, such as a light emitting diode, is energized by a pulsating current obtained by rectifying a normal commercial power supply, and the pulsating current drops below the operating voltage (forward drop V) of the light emitting diode. A display device shown in FIG. 1 has been proposed in which the period during which the display disappears is used as a blanking period for data transfer. In FIG. 1, 1 is a microcomputer, 2 is a shift register, 3 is a waveform shaping circuit, 4 is a commercial power supply, 5 is a rectifier diode, and 6 is a light emitting diode.

The alternating current voltage from the commercial power source 4 is only rectified by the diode 5 and is not smoothed, but is applied to the light emitting diode 6 and the waveform shaping circuit 3 as a pulsating voltage e ₁ shown in FIG. The waveform shaping circuit 3 creates an interrupt signal e ₂ shown in FIG. 2C from the pulsating voltage e ₁ and supplies it to the microcomputer 1.

The light emitting diode 6 is energized and ready for display when the pulsating voltage e ₁ is applied, but is deenergized when e ₁ decreases below its forward drop V. Therefore, the light emitting diode 6 has a deactivation period t ₁ and an activation period t ₂ as shown in FIG. 2B. In order to transfer data using this deactivation period t ₁ , the interrupt signal e ₂ becomes high level during the deactivation period t ₁ and interrupts the microcomputer 1 to temporarily cause a display operation. , shift register 2
The data _S1 to be displayed on the clock pulse _S2 is transferred within the period _t3 shown in FIG. 2D in synchronization with the clock pulse S2. The light emitting diode 6 thus displays this transferred data in the next energization period _t2 .

In the display device as described above, a smoothing capacitor is not used in the power supply circuit as described above, and a pulsating current flows through the light emitting diode 6.

However, since the power supply circuit described above is not stabilized, it is a practical problem if left as it is. Furthermore, if a stabilized power supply using a conventional smoothing capacitor is used, the above-mentioned blanking method effect of the display device cannot be obtained, and the efficiency is also not good.

It is an object of the present invention to further improve upon these problems and provide a display power supply circuit that is efficient and stable, and that can easily perform blanking operations at the same time as necessary. The present invention will be described below with reference to embodiments shown in the drawings.

FIG. 3 shows an embodiment of the display power supply circuit according to the present invention, in which the output of the diode 5 is connected to the transistors 7 and 8.
Light emitting diode 6 through a stabilizing circuit consisting of etc.
It is now being applied to transistor 7
The base includes a regulated power supply 9 and an unregulated power supply 1.
0 are connected to each other via a diode 11 and a resistor 12, and a transistor 13 for blanking operation is connected to ground as necessary.

The voltage actually applied to the light emitting diode 6 has a trapezoidal wave as shown in FIG. 4a. Although the light emitting diode is deenergized at the cutoff portion e of the trapezoidal wave voltage, since the ratio is small and the cycle is fast, there is no problem in practical use, even if it becomes slightly dark.

When the AC voltage of the commercial power source 4 decreases, the pulsating voltage naturally decreases from the dotted line waveform to the solid line waveform as shown in Figure 5, so the lighting section of the light emitting diode changes slightly from the trapezoidal wave part in Figure 5. Although it decreases, the average current energizing the light emitting diode is not significantly affected, and the same is true if the alternating current voltage is increased.

In the embodiment described above, transistors 7, 8
The loss is proportional to the area of the part b in Figure 4, but in a conventional power supply circuit using a smoothing capacitor, the area of the part d in Figure 6 causes a loss, so the circuit of the present invention is proportional to the area of the part b in Figure 4. but the losses will be much less. Moreover, since the stabilized power supply 9 is connected to the transistor 7 via the diode 11 inserted in the reverse direction, no load is taken from the stabilized power supply.
The stabilizing effect is not reduced, and there is almost no heat generation associated with increased power consumption.

As described above, according to the power supply circuit of the present invention, not only can stabilization characteristics be efficiently obtained, but also blanking operation can be easily performed by simply adding the transistor 13, and the load of the power transformer 14 is a pure resistance. Since it is close to , it has the effect of reducing the amount of heat generated by the transformer, and furthermore, the circuit configuration is extremely simple.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a display device, FIGS. 2A to 2D are waveform diagrams for explaining its operation, FIG. 5
The figures are waveform diagrams for explaining their operations, and FIG. 6 is an output waveform diagram of a conventional power supply circuit. 4: commercial power supply, 5: diode, 6: light emitting diode, 7, 8: stabilizing transistor, 9: stabilizing power supply, 13: blanking diode.

Claims (1)

[Scope of utility model registration request] A pulsating voltage obtained by rectifying the AC voltage from an AC power source is applied to the display element, and a deactivation period during which the pulsating voltage drops below the operating voltage of the display element is used as a blanking period for data transfer. In the display device configured, a stabilizing transistor is connected between the AC power supply and the display element, and the pulsating current voltage is applied to the display element via the stabilizing transistor, and the above-mentioned A display power supply circuit characterized in that the base of a stabilizing transistor is connected to a stabilized power supply.