JPH07261861A - Power source stabilizing circuit - Google Patents

Abstract

PURPOSE:To provide a backup power source stabilizing circuit which is low in current consumption. CONSTITUTION:A control current is supplied to the base terminal of a 2nd transistor(TR) Q2 through a resistance means R1. The 2nd TR Q2 generates a driving current corresponding to a control current and a driving part Q1 generates a load current I2 with the driving current and supplies it to a load RL. As the load current IL rises, an output voltage Vo begins to rise and a detecting means ZD1 generates a detection voltage corresponding to the output voltage Vo. A 1st TR Q3 which inputs the detection voltage at its base terminal has transition from the cutoff state to the conduction state once the detection voltage reaches the base terminal-emitter terminal voltage VBE3. Then the 1st TR Q3 is connected to the base terminal of the 2nd TR Q2, so the current supply by the resistance means R1 is suppressed to suppress the driving current and further the load current IL. This feedback loop holds the constant output voltage Vo at all times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called power supply stabilizing circuit, and more particularly to a power supply stabilizing circuit for generating a constant voltage power supply from a battery of an automobile.

[0002]

2. Description of the Related Art Electronic equipment mounted on an automobile uses a microcomputer, including a drive control circuit of the automobile itself, and important data for operating these microcomputers is stored in a ROM, a RAM or the like. . In particular, the RAM and the like can hold data on condition that the voltage is applied at a constant level, so that the memory content is lost and the operation of the microcomputer cannot be guaranteed when the voltage drops below the reference level even for a moment. Therefore, in the control electronic circuit related to the system control of the automobile itself,
Power source stability is especially important.

Usually, a lead-acid battery or the like is used for this power supply source.
A so-called car battery is charged. The microcomputer obtains electric power from this, and the voltage required for the microcomputer or the like to operate normally, for example, 5
It is necessary to obtain [V].

However, for a car battery, when the engine is driven or stopped, or when a load such as a starter motor that requires an excessive current is operated, the load condition is not constant and the power supply voltage fluctuates greatly. Therefore, it is usual to use a power supply stabilizing circuit to obtain an optimum voltage for an electronic circuit.

A conventional power supply stabilizing circuit is shown in FIG. The car battery has the lowest voltage when the starter motor is driven. The power supply voltage at this time is 8 [V]
It will be about. On the other hand, the Zener diode ZD ₂ that provides the reference voltage requires a current of about 0.5 mA or more in consideration of the change in the voltage of the power supply source.
The value of the resistor R is _{R = (V min -V o)} / I ZDmin = (8-5) /0.5
= 6 [kΩ].

The operating characteristic of this circuit becomes a characteristic curve as shown in FIG.

[0007]

However, in the above-mentioned conventional power source stabilizing circuit, when the vehicle engine is stopped and the electronic circuit is being backed up, the backup current flows too much and the car battery is discharged. Therefore, there is a problem that the deterioration of the battery is accelerated. Originally SR
Although the backup current itself required for backup of memory elements such as AM (Static-RAM) is sufficiently small, the current consumption of the power supply stabilization circuit itself is too large,
The situation occurs that the total current consumption increases.

Under the above conditions, the bias current I flowing through the resistor R is generated when the engine with the highest power supply voltage is stopped.
Is I _max = (V _max −V _o ) /R=1.3 [mA]. This current reaches more than twice the required Zener diode current.

The circuit of FIG. 3A also has a problem that the output voltage fluctuates under the influence of the temperature characteristic of the transistor. To compensate for this drawback, the circuit of FIG. 3B in which a transistor is directly connected is also proposed, but this circuit is also affected by the temperature characteristic of the transistor, and the characteristic fluctuates as in the circuit of FIG. 3A. The problem remains. Furthermore, in this circuit, the influence of the saturation voltage (V _CEsat ) between the collector terminal and the emitter terminal of the transistor is great, and V _{CE
If sat} = 0.6 [V], 0.6 × in the two-stage configuration
Since there is a voltage drop of 2 = 1.2 [V], there is a drawback that the allowable range of operation compensation for the power supply voltage is narrowed (characteristic curve as shown in FIG. 2A).

Therefore, an object of the present invention is to provide a power supply stabilizing circuit capable of supplying an optimal backup current regardless of the voltage of the power supply source.

[0011]

In order to achieve the above object, a power supply stabilizing circuit according to a first aspect of the present invention is such that power is supplied from a power supply source, an output terminal is connected to a load, and a constant drive current is controlled. In a power supply stabilizing circuit having a drive section for holding the output voltage of the detection means, a detection means connected to the output terminal for detecting a detection voltage corresponding to the output voltage, and a switching means that becomes conductive when the detection voltage is higher than the reference voltage. And a current control means for supplying a drive current corresponding to the control current from the power supply source to the drive terminal of the drive section through the resistance means, and one end connected to the power supply source and the other end for current control. Means and a resistance means connected to the switch means.

[0012]

According to the invention described in claim 1, when the power is turned on,
Since the load voltage is zero, the detection voltage is below the reference voltage. A control current is supplied to the current control means from the power supply source via the resistance means. Then, the current control means generates a drive current corresponding to the control current and supplies the drive current to the drive unit, so that the current is supplied to the load.

The output voltage starts to increase as the load current increases, and when the detecting means of the detecting means exceeds the reference voltage, the switch means shifts from the cutoff state to the conductive state. Then,
The current supply that has been supplied to the current control unit via the resistance unit is suppressed, and the drive current supplied to the drive unit decreases.

When the load current decreases as the driving current decreases, the detection voltage also decreases, and the switch means shifts to the cutoff state again. After that, when the load becomes heavier and the output voltage tries to decrease, the drive current is supplied in a form that compensates for it, and the load current also increases. Further, when the load becomes lighter and the output voltage tries to increase, the drive current decreases and the load current also decreases.

Since the control current is connected to the power supply source, it is possible to generate the drive current corresponding to the detection voltage detected by the detection means without being affected by the fluctuation of the output voltage.

With the above operation, a constant output voltage can always be obtained.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of a power supply stabilizing circuit of the present invention will be described with reference to the drawings. In this embodiment, particularly, a power supply stabilizing circuit for an electronic device mounted on an automobile will be described.

FIG. 1 shows the configuration of an embodiment of the present invention. Figure 1
As shown in, the power supply stabilizing circuit of the present invention inputs the power supply voltage B _in from the power supply source such as a car battery to the emitter terminal and supplies the output voltage V _o from the collector terminal to the load such as the electronic circuit. The base terminal is connected to the transistor Q ₁ , the Zener diode ZD ₁ connected to the output terminal for detecting the voltage, the resistor R _2, and the Zener diode ZD ₁ , the emitter terminal is grounded, and the collector terminal is connected to the resistor R ₁ . Transistor Q connected to power supply voltage Bin via
_3, the emitter terminal is connected to the base terminal to the collector terminal of the transistor Q ₃ is grounded, the transistor Q having its collector terminal connected to the base terminal of the transistor Q _1
2 and a capacitor C _G that bypasses surges, noises, etc. of the output voltage and protects the circuit against momentary interruption of the power supply voltage B _in
And, and are configured.

It is assumed that the load is connected to an electronic circuit which requires a voltage of 5 [V]. Next, the operation will be described. First, when the car battery is connected to the power input terminal of the entire system, the output voltage of the car battery, for example, 1
3.5 [V] is applied to the power input terminal B _in of the power stabilizing circuit.

At this time, the voltage between the base terminal and the emitter terminal of the transistor Q ₃ (hereinafter referred to as V _{BE 3} ) is zero, so the transistor Q ₃ is in the cutoff state.

From the power source B _in via resistor R ₁ .
A base current (hereinafter referred to as I _B2 ) flows into the transistor Q ₂ . Then, the transistor Q _2
Flows a collector current (hereinafter expressed as I _C2 ) defined by an internal current amplification factor (expressed as h _fe2 ).

This I _C2 is the transistor Q ₁
Of the base current I _B1 , the transistor Q ₁ increases the collector current I _C1 according to the current amplification factor defined by the internal current amplification factor h _fe1 . This is namely because the load current I _L, the current will be supplied to initiate the load R _L.

As a result, the load voltage (output voltage = V _o ) starts to rise due to the load resistance R _L. Furthermore, the output voltage V _o
There continues to rise, the Zener voltage V _{ZD 1} of the Zener diode ZD _1, the base terminal of the transistor Q ₃ - emitter terminal voltage between the (. The following, expressed as referred V _BE3), V _o 〓V _ZD1 When the relationship of + V _BE3 is established, the transistor Q ₃ becomes conductive and the collector current I _C3 of the transistor Q ₃ starts to flow. This is the power source B via resistor R _1.
Base current I of transistor Q ₂ supplied from _{in
Since B2} is bypassed, the collector current I _C2 also decreases. Further, this change also affects the collector current I _C1 of the transistor Q ₁ , that is, the load current I _L , and the current supplied to the load is limited.

Accordingly, the rate of increase of the output voltage V _o also decreases, and finally, the feedback loop formed by the Zener diode ZD ₁ , the transistor Q ₃ , the transistor Q ₂ and the transistor Q ₁ becomes stable and becomes a constant voltage. Reach

The output voltage V _{o at} this time has a relationship of V _o = V _ZD1 + V _BE3 .

Therefore, the V _BE of the transistor is 0.7
When V, Zener voltage V _ZD1 of Zener diode ZD _{1 is, V ZD1 = V o -V BE3} = 5-0.7 = 4.3 may be set so as that [V].

The capacitor C _G removes noise from the power supply source B _in , and when the voltage B _in of the power supply source instantaneously falls outside the allowable range due to an accident such as a short circuit (instantaneous interruption). Etc.) and is responsible for supplying power to the load for a short time.

When backup power needs to be supplied to the RAM or the like of the electronic circuit, the power supply from the battery must not be cut off. At that time, the current consumption of the power stabilizing circuit 10 itself and the RAM or the like. The current required for backup will be consumed.

According to the above embodiment, since the loop gain is large, the base current flowing through each transistor may be weak, and therefore the resistance values of the resistors R ₁ and R ₂ can be set to sufficiently large values. This means that the operating current is low. The total operating current is I _ZD1 + I _C3 +
It is sufficient that I _B2 + I _B1 is 0.2 [mA] or less, and can be, for example, half or less of the operating current of the conventional example of FIG.

Further, the output voltage is stabilized even from a relatively low power supply voltage due to the magnitude of the loop gain (FIG. 2 (A)).
reference). Further, in the prior art, since the voltage fluctuation of the input power supply source is large, the supply current to the Zener diode is set in the range of 0.5 to 1.3 [mA] with a margin (FIG. 2 (B)). However, in the present embodiment, since the current is input from the output side where the voltage fluctuation is small and stable,
The supply current can be further reduced to the limit.

That is, as shown in the relational diagram of the operating current of the Zener diode of FIG. 2C, the voltage B of the power supply source is
Zener diode ZD _{1 of the} present embodiment with respect to variation of _in
The fluctuation of the operating current is sufficiently small that the Zener diode can maintain the Zener voltage, which is the minimum current that
The operating point can be set so as to come near the shoulder of the current characteristic (point s in FIG. 2B). The current flowing through the Zener diode at this time is about 100 [μA] (see the figure).
And significantly less than before.

However, the Zener voltage V _ZD1 when the voltage is set near the shoulder of the voltage-current characteristic is slightly smaller than the nominal value, so the nominal value of the Zener diode actually used is the theoretical value required. The value is 10 to 15% higher than the Zener voltage. Therefore, in this embodiment, a Zener voltage having a nominal value of 4.7 to 4.9 [V] is used.

Under the above conditions, the circuit constant is, for example, R ₁
= 220 [kΩ] and R ₂ = 6 [kΩ]. Other Modifications Various modifications are possible without being limited to the above embodiment of the present invention.

That is, in the above embodiment, the switching means is constituted by one transistor (Q ₃ ) and the transistor 1
Although the current driving means is composed of stages (Q ₂ ), the number of stages of transistors may be further overlapped to increase the loop gain.

Further, although the detecting means is composed of a Zener diode which is a constant voltage circuit, it may be a constant voltage circuit obtained by resistance-dividing a transistor, a constant voltage circuit which is formed by stacking diodes.

Further, in this embodiment, as the power supply stabilization circuit on the positive power supply side, the transistor Q ₁ is a PNP type transistor and the transistors Q ₂ and Q ₃ are NPN type transistors. , An NPN transistor is used as the transistor Q ₁ , and a transistor Q ₂ ,
A power stabilizing circuit on the negative power source side can be constructed by using a PNP transistor for Q ₃ .

Furthermore, not only transistors but also active elements such as FETs and switching elements can be applied instead of the transistors.

[0038]

According to the present invention, the power loss consumed by the detecting means can be reduced as much as possible, so that the current consumption can be reduced.

Further, by using a transistor or the like as the switch means, a large loop gain can be obtained, and since a simple switch operation having a reference voltage can be performed, the operating current required for the circuit operation can be weak. Power loss can be reduced.

Further, since the power consumption is low, deterioration due to excessive discharge of the battery can be suppressed as much as possible.

[Brief description of drawings]

FIG. 1 is a power supply stabilizing power supply circuit according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing output characteristics of the power supply stabilizing circuit of the present invention. (A) shows the input / output characteristics, and (B) shows the voltage-
It is an explanation of the operating region based on the current characteristics, and (C) is the operating current of the Zener diode.

FIG. 3 is a conventional power supply stabilizing power supply circuit. (A) is a conventional stabilized power supply circuit, and (B) is a stabilized power supply circuit obtained by improving the circuit of (A).

[Explanation of symbols]

Q ₁ to Q ₆ ... transistor R, R _1, R ₂ ... resistor ZD ₁ ~ZD ₃ ... Zener diode C _G ... capacitor B _in ... supply voltage V _o ... Output Voltage

Claims (1)

[Claims] 1. A power supply stabilization circuit having a drive unit that is supplied with power from a power supply source, has an output terminal connected to a load, and holds a constant output voltage by controlling a drive current, and connects the output terminal to the output terminal. A detection unit that detects a detection voltage corresponding to the output voltage, a switch unit that becomes conductive when the detection voltage is higher than a reference voltage, and a control current supplied from the power supply source via a resistance unit. Current control means for supplying the drive current corresponding to the current to the drive terminal of the drive part, and one end connected to the power supply source and the other end connected to the current control means and the switch means. A power supply stabilization circuit comprising: