JPS5821569A - Battery checker circuit - Google Patents

Abstract

PURPOSE:To enable the detection of voltage in a wide range from a low power source voltage to about several volts by comparing collector current of transistors which are different in the emitter area while commonly connected in the base. CONSTITUTION:After a power source voltage to be detected is divided with a resistance R0, a voltage is applied in common to the bases of transistors (Tr) Q1 and Q2. The resistance R1 connected to the emitter of the TrQ1, the resistance R2 connected to the emitters of Trs Q1 and Q2 and the ratio of the emitter areas of the Trs are so designed that collector currents of the TrQ1 and TrQ2 coincide with each other at the state of the threshold voltage to be detected. Then, as the power source voltage rises, the collector current of the TrQ2 won't readily change because of the resistance R2 where as the collector current of the TrQ1 increases in a larger measure. This turns off the TrQ5 and turns on the TrQ7 which leads to a higher level of the output. On the contrary, when the power source voltage lowers, the TrQ5 is turned on and the TrQ7 turned off which leads to a lower level of the output.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a battery checker circuit for detecting voltage levels.

Battery-powered electronic devices usually include a battery checker circuit for detecting power supply voltage in order to prevent malfunctions due to a drop in power supply voltage. However, with this type of circuit that has been used in the past, it is difficult to detect low power supply voltages, and the voltage range that can be set for detection is very narrow, so the range of application is limited. I didn't get it.

The present invention has been made in view of the drawbacks of the above-mentioned conventional circuits.
The present invention provides a battery checker circuit that can set a low power supply voltage, for example, a voltage in a wide range from less than 1.5V to several volts as a detection voltage.

Next, the present invention will be explained in detail using the drawings.

The present invention is configured as a so-called pad gap type voltage detection circuit, and in summary, the power supply voltage to be detected is detected by a resistor R.
Apply it to Q to derive the partial pressure. This derived voltage is commonly applied to the bases of the first transistor Qle and the second transistor Q2. On the other hand, while a resistor R1 is connected to the emitter of the first transistor Ql,
A resistor R2 is also connected between the emitter of the first transistor Q2 and the emitter of the second transistor Q2. The ratio of the emitter areas of each of the resistors and transistors and the resistors R1 and R2 are designed so that the collector currents of the first transistor Q and the second transistor Q2 almost match each other in the state of the threshold voltage to be detected. In the circuit configured as described above, a comparison circuit is provided to compare the collector current of the first transistor Q1 and the collector current of the second transistor Q2, and the output thereof is used as the output of the battery checker circuit.

In the figure, a resistor RQ is connected between the power supply voltage vce to be detected and the ground GND, and the divided voltage of the power supply VCC divided by the intermediate stage of the resistor RQ is derived, and the first transistor Ql, which is made of NPN, and the second transistor It is commonly applied to the bases of the transistor Q2 and the sixth transistor Q6. Here, the first transistor Ql and the second transistor Q2
As will be described later, the circuit is designed so that the collector current almost matches the level of the power supply voltage to be detected. Therefore, first, the desired base-emitter voltage difference ΔVB
In order to obtain E, the emitter areas of both transistors are designed to have different shapes.

For example, EQI the emitter area of each transistor.

Assuming EQ2, Eol: E(12= 1: I
Designed to O.

A resistor R1 (IOKΩ) is connected between the emitter of the first transistor Q1Φ and the ground GND, and an emitter of the second transistor Q2 is connected to the emitter of the first transistor Q1 through a resistor R2 (Ω to 2).
Connected to the emitter of transistor Q1. Both transistors Q1. Q2 is further provided with a circuit for comparing the collector currents of both transistors and deriving an output. In other words, in order to add the collector current of the first transistor Q1 to the collector of the second transistor Q2 by changing the direction. , an eighth transistor Q8 consisting of a PNP transistor, and a fourth transistor Q4, which are connected in a current mirror manner. The commonly connected bases of the eighth and fourth transistors Q8*Q4 are connected to the collector of the first transistor Q. 4th transistor Q
The collector of the second transistor Q2 connected to the collector of the first transistor Q2 is connected to the base of a PNP fifth transistor Q5, and the collector of the fifth transistor Q5 is connected to the collector of the first transistor Q5. Second
The NP sharing a base with the transistor QIsQ2
connected to the collector of the Nth sixth transistor Q6;
Transistor Q6 is used as an active load. The resistor R1 and #1 are connected between the emitter of the sixth transistor Q6 and the ground GND.
A resistor R3 (IOKΩ) having the same resistance value is inserted. transistor. The comparison result of the collector current of I*Q2 is the fifth transistor. 5 and the sixth transistor Q6
The base is connected to the connection point of both collectors, and the power supply VCC
The collector terminal OU of the seventh PNP transistor Q7 is connected through a resistor R4 (100KΩ) between the
(derived from T) Next, the operation of the circuit having the above configuration will be explained.

First, the operation when the power supply voltage is the threshold voltage to be detected will be explained.

Now the first transistor. 1 and the second transistor Q2 have an emitter area of Ii:Ql:EQ2=I:I
The difference ΔvaB between OK setting resistor Q2 and VBE is vBE=
The formula of KT/q@1nIc/Io is ΔvBE=KT/q
111n1°. The value of ΔVBH is about 60 mV when operated in an atmosphere of about 20°C. That is, 2
When a current flows such that a voltage of 60 mV is applied across the resistor R2, which is designed to have a resistance of Ω, the values of the collector currents of the first transistor Q1 and the second transistor Q2 match. In this state, the resistor R1 is connected to the first transistor Ql.
In addition to the current from the second transistor Q2, the current from the second transistor Q2 flows, so twice as much current flows. Further, since the value of the resistor R1 is designed to be R1=5Rg with respect to the resistor R2, a voltage of 600 mV is generated at the resistor R1. On the other hand, since a collector current of 30 μA flows through the first transistor Ql, the pace-emitter voltage VBH of the first transistor Q1 is approximately β = 100 of a transistor that constitutes a normal integrated circuit in an atmosphere of 20°C. By applying the following conditions, it becomes approximately 650 mV. The pace potential of the first transistor Q+ and the second transistor Q2 that lead to such a behavior pattern is 1.25V.

That is, when the voltage is 1.25V divided by the resistor RQ, the collector currents of both transistors QItQ2 become equal, indicating that the power supply voltage is at the set value level. Note that by moving the voltage dividing point of the resistor RQ, the level of the power supply voltage vcc to be detected can be changed.

Next, consider the temperature characteristics of the pace potential. Since the difference ΔVBE between the base and emitter voltages of both transistors has a characteristic that is proportional to the absolute temperature, it exhibits a temperature characteristic of +(,'/263)/℃ for an operating temperature of 20℃, which is 600℃.
For mV, it is +2.04m sir.

On the other hand, the pace-emitter voltage VBE of an integrated transistor is expressed as KT/q-InIC/Io,
Although it is not a perfect straight line, the collector current Ic = 30μ
At around 8, it becomes -2.05 m'/c, and the temperature characteristic of the base-emitter voltage difference ΔVBH (+2.04 mV
/C), and in the end almost no temperature characteristics are found. That is, the collector currents of the first transistor Q1 and the second transistor Q2 are compared. Although the above operation has been explained with the first transistor Q1 and the second transistor Q2 being the same, the collector currents of the first transistor Q1 and the second transistor Q2 are the same. A case where the base potential of Q2 rises will be explained. The collector current of the second transistor Q2 does not change easily because of the resistor R2 connected to the emitter terminal, and the increase in the collector current of the first transistor Q is greater, and at this time the fifth transistor Q5 is turned off. The seventh transistor Q7 is turned on, and the output derived from the collector terminal of the seventh transistor Q7 is at a high level, that is, about (Wee-0.1V), indicating a high potential. Conversely, if the base potential drops, the fifth
The transistor Q5 is turned on, the seventh transistor Q7 is turned off, and the output level becomes a low level, and the voltage level is detected by the voltage division of the resistor RQ corresponding to the power supply voltage to form an output signal. The power supply voltage to be detected is detected at the boundary between the two power signals.

However, the problem with the battery checker circuit is that it must be prevented from inverting the output and deriving an erroneous output signal when the power supply voltage level drops further below the decision point. However, in the circuit shown in the above embodiment, there is no risk of malfunction as described above. That is, the circuit for comparing the collector currents of the first transistor Q1 and the second transistor Q2 uses a current mirror consisting of the third transistor Q8 and the fourth transistor Q4 to compare the collector currents of the first transistor Q1 and the second transistor Q2.
The structure is such that the directions of the currents are changed and added together. Here, the PNP transistor has a problem in that the collector current of the first transistor Q1 and the collector current of the fourth transistor Q4 are not equal because β is small, but in order to cancel this, the base current of the sixth transistor Q5 is changed to the third transistor. 4th TRAVEL/JIMETA Q3. Q4 is balanced by equalizing the sum of the base currents of the eighth and fourth transistors Q3. The collector current of Q4 is varied from the collector current of the first transistor Ql or the second transistor Q2 to the collector current of the third transistor Q1. Fourth transistor Q8. The collector current of the fifth transistor Q5 is the collector current of the sixth transistor Q6 minus the pace current of the seventh transistor Q4.
The collector current of the sixth transistor Q6 is the same as that of the first transistor Q6. The second collector current Ql can be made equal to the sum of the collector currents of Q2. Therefore, even if the current mirror is configured with low β transistors such as lateral PNP transistors created within the integrated circuit, the error in current comparison caused by the current mirror gain can be canceled out by the base current of the fifth transistor Q5. , accuracy can be improved, and a perfectly balanced state can be obtained by changing the value of the resistor R4 according to the set voltage, resulting in a check circuit with more stable characteristics.

As described above, according to the present invention, a wide range of power supply voltages can be detected by changing the resistance value that draws out the partial voltage.
In particular, it is possible to use a low voltage as the detection voltage, making it an optimal battery checker circuit for battery-powered equipment.In addition, a battery check circuit with high practical value such as excellent temperature characteristics and no variation in detection operation can be obtained.

[Brief explanation of drawings]

The figure is an electrical circuit diagram of an embodiment according to the present invention. Q+, Q2, Qs: NPN)' transistor,
Q3,04g5. Q7: PNP transistor,
RQ, R1, R2. R9, R4: Resistance 0 Agent Patent attorney Aihiko Fukushi

Claims (2)

[Claims] (1) A first transistor Q1 and a second transistor Q2 whose emitter areas are different from each other and whose bases are connected in common; a resistor R1 inserted between the emitter of the first transistor Ql whose emitter area is small and the ground; Both transistors Ql. Resistor R2 connected between the emitter of Q2 and the power supply vCC
a resistor RQ connected between and ground and for applying a divided voltage to the commonly connected bases of the transistors Ql and Q2, and a comparator circuit that compares the collector currents of both the transistors Q1 and Q2 and derives an output. A battery checker circuit equipped with (2) The comparison circuit includes third and fourth transistors Qa that supply the collector current of the first transistor Ql to the collector of the second transistor Q2. A current mirror consisting of Q4 and a second transistor Q2
A fifth transistor Q5 whose base is connected to the collector of
, the collector is connected to the collector of the fifth transistor Q5, and the base is connected to the collector of the first transistor Q5. Second transistor Q,,Q2
a sixth transistor Q6 commonly connected to the base of
The battery checker according to claim 1, further comprising a resistor R8 connected between the emitter of the sixth transistor Q6 and the ground and having substantially the same resistance value as the resistor R1. circuit 0