JPS6014233Y2 - voltage converter - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a voltage converter that drives a light emitting diode.

Some electronic watches display seconds by flashing light emitting diodes, but it is also possible to detect a drop in the power supply voltage when the light emitting diodes stop lighting up.

In this case, in an electronic watch that uses a 1.5V battery,
If the guaranteed voltage for the clock circuit is 1.2V, and the operating voltage of the light emitting diode is 1.5V, the light emitting diode cannot be lit within the guaranteed voltage range.

For this reason, a voltage converter described in Japanese Utility Model Application Publication No. 116014/1983 is known as a device that boosts the battery voltage and lights up a light emitting diode.

As an example of this conventional circuit, as shown in FIG. 1, a series circuit of a transistor Q and a resistor Ro, and a series circuit of a light emitting diode LED and a diode surface are connected in parallel between the output terminals of a power supply voltage E. A capacitor C is connected between both picture column circuits.

In this case, if the voltage of the power supply E is Vs and the forward voltage drop on the diode surface is Vdfo, the voltage Vc charged to the capacitor C is Vc = Vs - Vdf.

becomes.

When the transistor Q is turned on, the voltage Vdf applied to the light emitting diode is Vdf = VS + VC = 2VS - Vdf.

It is.

In the above equation, focusing on the temperature drift voltage of the diode, ΔVdf = −ΔVdf.

It is.

For example, when the temperature decreases and the operating voltage of the light emitting diode LED increases, the forward drop voltage of the diode Do also increases, so the charging voltage to the capacitor C decreases, and the boost effect can cause the light emitting diode to light up. Even within the guaranteed voltage range, the light emitting diode cannot be turned on, which has the disadvantage of being affected by the temperature characteristics of the diode Do.

The present invention provides a voltage converter with improved temperature characteristics by changing circuit connections.

Embodiments of the present invention will be described below based on the drawings.

First, in Fig. 2, the LED is a light emitting diode (li
ght emitting diode), R1 to R4
is a resistor, C is a capacitor, D□, D2 are diodes, Q
is a C-MOS) transistor, and P is a 1-second interval pulse given from a frequency dividing circuit of a clock device (the pulse width is, for example, 7.5 seconds).
8m5), E is the power battery.

When the transistor Q is off during the rest period of the pulse P, the diode D2 is forward biased by the resistor R2°R2, R3.

On the other hand, the capacitor C is charged by a current flowing through the resistor R4, the capacitor C, the resistor R3, and the diode D2.

However, since capacitor C is biased by diode D□, its charging voltage is
The forward voltage drop will not exceed 0.

Therefore, this charging voltage Vc is applied to the diode D1. It depends on the temperature characteristics of D2 and also on the voltage division ratio of resistors R2°R3.

After charging is completed, pulse P arrives and transistor Q
When the LED is turned on, the voltage applied to the light emitting diode LED is VS + VC, where the voltage of the power supply E is Vs. Depending on whether this value is above or below the operating voltage of the light emitting diode LED, However, the light may be lit while the transistor Q is on, or it may not be lit even when the transistor Q is on.

Therefore, the voltage vb at point b when the transistor Q is off is Vb=Vdf□+Vdf2 (Vdf□ and Vdf2 are the forward drop voltages of the diodes D1 and D2, respectively).

Also, the voltage V at point a when charging of capacitor C is completed is
a is.

Therefore, the charge BEVC of capacitor C at this time is Vc=Vb-Va (Vs - V city 2)) becomes.

Next, when transistor Q turns on, the light emitting diode LED
The voltage Vdf (Vdf = Vs + Vc).

In equation (1), if we focus only on the temperature drift voltage of the diode, we get:

That is, in this embodiment, as is clear from equation (2), for example, when the temperature decreases and the operating voltage of the light emitting diode LED increases, the voltage drop across the capacitor C increases due to the increase in the forward voltage drop of the diodes D1 and D2. The charging voltage increases, and the light emitting diode LED can be reliably lit within the guaranteed voltage range.

Moreover, the same effect is exhibited in the direction where the temperature increases.

indicates that the determination voltage can be set in accordance with the operating voltage of the light emitting diode LED.

The embodiment shown in FIG. 3 is a case where a light emitting diode LED is connected to the negative electrode side of the power source E, and its operation is the same as that shown in FIG. 2.

In addition, in each embodiment, when using a type of light emitting diode LED with a high operating voltage of 2V, for example,
A plurality of diodes may be connected in series to the diode D section.

As described above, the voltage converter of the present invention operates stably because the charging voltage to the capacitor due to the temperature characteristics of the diode is changed so as to offset the change in the operating voltage due to the temperature characteristics of the light emitting diode.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional example, and FIGS. 2 and 3 are circuit diagrams of an embodiment of the present invention. LED... Light emitting diode, R1-R4...
...Resistance, C...Capacitor, Dl, D2.
...Diode, Q... (knee MO3)
Ranjista.

Claims (2)

[Scope of utility model registration request] (1) A series circuit of a first resistor, a second resistor, and a first diode, and a series circuit of a third resistor and a switching element are connected in parallel between the output terminals of the DC power supply, and the third
A second diode is connected between a connection point between the resistor and the switching element and a connection point between the second resistor and the first diode, and a second diode is connected between the connection point between the first resistor and the second resistor. A capacitor is connected between a connection point between the third resistor and the switching element, a light emitting diode is connected in parallel with the first resistor, and the switching element is controlled to be turned on and off at a predetermined period. voltage converter. (2) The voltage converter according to claim (1), wherein the second diode is configured by connecting a plurality of diodes in series.