JPS6022222A - Voltage stabilizing circuit having low voltage information display circuit - Google Patents

Abstract

PURPOSE:To stabilize the voltage and to detect a low level of voltage by flowing the base current of a pnp transistor of a voltage stabilizing circuit via an LED and switching on the LED when the power supply voltage which is supplied to an emitter has a drop. CONSTITUTION:When a unit of LED is added to a voltage stabilizing circuit, the collector-emitter saturation voltage of a pnp transistor TRQ1 is set at VCE (SAT) with the output voltage set at VOUT. Thus the detection voltage V1 of low level is shown as V1=VOUT+VCE(SAT). Then the voltage V1 can be uniquely decided only by the voltage VCE(SAT) as long as the voltage VOUT is set at a fixed level.

Description

[Detailed Description of the Invention] The present invention relates to a voltage stabilizing circuit with a low voltage information display circuit,
More specifically, the base current of the PNP output transistor of the voltage stabilizing circuit is passed through the light emitting diode, and the base current of the PNP output transistor increases when the power supply voltage supplied to the emitter decreases. The present invention relates to a voltage stabilizing circuit with a low voltage information display circuit that lights up a light emitting diode to display a drop in the power supply voltage supplied to the emitter.

Traditionally, in devices that operate on batteries, the battery voltage fluctuates, so it is common for the power supply to have a voltage stabilization circuit to stabilize the operation of the device, and the battery capacity is limited. When the battery capacity decreases, the user must be informed and asked to replace the battery with one with a higher capacity, or have the battery recharged so that the battery capacity always matches the battery capacity required for the operation of the device. Therefore, in many cases, the power supply voltage stabilization circuit, low voltage detection circuit, and low voltage information display circuit are separately provided. There is an advantage in that all of the above functions can be realized with the smallest circuit scale and without an increase in circuit current. There are great advantages if

Embodiments of the present invention will be illustrated and described in detail below.

FIG. 1 shows a conventional voltage stabilizing circuit using an I'NP transistor in its output. The long voltage VB is supplied to the emitters and ri of the output PNP transistor, and at the same time starts up the star door pull circuit 5TART and operates the voltage stabilizing circuit shown in Fig. 1. Error voltage amplifier 1 is PNP) run,
The collector voltage VOUT of resistor Q1 is set by resistor 1 and resistor R.
Compare the voltages V&EF divided by 2, and control the heath current IB of the PNP) transistor Ql through the transistor Q2 so that they match, and change the voltage VcE between the emitter and collector of the PNP) transistor. ing.

However, the voltage Vn supplied to the emitter of PNP) transistor Q1 and the collector voltage VO of PNP) transistor Q1
As UT approaches, the value of VB-VOUT increases to the emitter-collector saturation voltage VCK (8 μT) of PNP transistor Q1.
), increase the base current In of the transistor Q1 -C and the value of Vn -VOUT, the value of VOUT will hardly change and the voltage stabilizing circuit will adjust the output voltage VOUT.
If you keep T constant, it will become exposed.

This situation is shown in FIG.

Now, the DC current amplification degree of PNP transistor Q1 is hFE
Then, about 1. Considering R2 as a sufficiently large resistance, the relationship between the Ib flowing to the load RL of the voltage stabilizing circuit and the base current IB of the transistor Q1 is In=IL/hpg.・・・
■It becomes. Now VB>V□, PNP) transistor. 1
DC current amplification degree hpE is PNP) Collector emitter of transistor Q1, threshold voltage VCE is PNP) transistor Q
Since the collector emitter of 1 is larger than the sibling sum voltage Vcg (sAT), it can be regarded as an almost constant value hFFil.

Therefore, the base current IBI of the PNP transistor Q1 at this time is l1st = IL/hrzt...
Song...■. When VB<Vl, the DC current amplification degree hFK of the transistor Q1 is PNP) The collector emitter of the transistor Q1, and the threshold voltage VCB is PNP) The collector emitter of the transistor Q1, the sum voltage VCE <
8AT), so as VB decreases, the PNI)) DC current amplification degree hPE of transistor Q1
decreases, and therefore the voltage stabilizing circuit load RI
Since L is constant, IB increases rapidly. This state is shown in FIG. 2, and the output voltage votrt
The relationship between and power supply voltage is shown by a dotted line.

The present invention is to insert a light emitting diode D1 between the base of the PNP transistor Q1 and the collector of the transistor Q2, and to turn on the light when the power supply voltage VB is lower than V to notify the user of the decrease in the power supply voltage.

FIG. 3 shows an embodiment of the present invention, and FIG. 1 shows a light emitting diode D.
1 is added and shown. Here, the light emission start threshold current Ifh of the light emitting diode is generally required to have a certain finite value, but as shown in FIG. 2, it is selected to satisfy Ifh>IQI.

Therefore, according to the present invention, by simply adding one light emitting diode to the voltage stabilization circuit as described above, in addition to the voltage stabilization circuit function, the low voltage detection circuit function and the low voltage information display circuit function can be added. The above functions can be realized without increasing the circuit current, and low voltage detection voltage ■1 is PNP
) Collector emitter of transistor Q1, sum voltage VO
If R (SAT), then V, = VOUT + VOE (SAT) ・−−−・・−
・If we assume that the output voltage VOUT of the voltage stabilization circuit is constant (expressed as (i)), a low voltage detection voltage can be set since it is uniquely determined only by the collector-emitter saturation voltage VOR (SAT>) of the PNP transistor Ql. This has a great advantage in that it eliminates the need for adjustment and reduces adjustment man-hours.

[Brief explanation of the drawing]

Figure 1 shows a conventional constant voltage circuit, and Figure 2 shows a PNP transistor Q for the input power supply voltage of the voltage stabilization circuit in Figure 1.
FIG. 3 is a diagram showing the relationship between the base current (solid line) of No. 1 and the output voltage VOUT (dotted line), and FIG. 3 is a diagram showing an embodiment of the present invention. In the figure, Ql...PNP) transistor, Q2...NPN) transistor, R1, R,
2...Resistance, RL...Load resistance, C.
... Capacitor, 1 ... Error voltage amplifier, VB ... Input power supply voltage, VOUT ...
・Output voltage, IL...Load current, In...
...Base current of Ql, 'R, EF...Reference voltage generator, STA, R'l'...Start-up circuit, Dl...Light-emitting diode, fh-・
. . . is the light emission start threshold current of the light emitting diode. Second eye

Claims (1)

[Claims] Power supply voltage is supplied to the emitters of the transistor (PNP),
In the voltage stabilizing circuit configured to control the emitter-collector voltage by controlling the base current so that the collector voltage is kept constant, the PN
P) A voltage stabilizing circuit with a low voltage information display circuit, characterized in that a light emitting diode is connected to the base of a transistor.