JPH0587840A - Voltage detecting circuit - Google Patents

Abstract

PURPOSE:To detect the variation of the electric power source voltage in stable manner for the variation of the environmental temperature, as for a voltage detecting circuit fir detecting the variation of the electric power source voltage. CONSTITUTION:An electric power source voltage Vcc is divided by resistors R1, R2 and R3 and a transistor Q1. A pair of differential transistors Q4 and Q5 connected in common with an emitter are constituted so that the base.emitter normal direction voltage has an offset voltage. The divided voltage on the under side of the resistor R2 is inputted into the base of the transistor Q5. The divided voltage on the upper side of the resistor R2 is supplied into the base of the transistor Q4 through a resistor R4. A resistor R5 is connected between the base and emitter of the transistor Q4. The temperature coefficient of the threshold value voltage of the electric power source voltage Vcc for the reversal of the outputs of the transistors Q4 and Q5 is the sum of the negative value corresponding to the energy in the prohibited band width of a semiconductor which constitutes the transistors Q4 and Q5, positive value corresponding to the base.emitter normal direction voltage of the transistors Q4 and Q5 and the value which is positive or negative according to the offset voltage, and can be set zero by the values of the resistors R1, R2, R3, R4, and R5 and the offset voltage value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage detection circuit, and more particularly to a voltage detection circuit for detecting fluctuations in power supply voltage.

[0002]

2. Description of the Related Art Conventionally, CPU (Central Processing)
Unit: Central processing unit) A voltage detection circuit is known for detecting fluctuations in power supply voltage in a system or the like, and for initial resetting the CPU when the power is turned on, or for resetting the CPU when the power supply voltage drops momentarily. ..

FIG. 4 is a circuit diagram of a reset circuit to which an example of a conventional voltage detection circuit is applied. In the figure, V _CC is a power supply voltage, which is used as a power supply for a CPU, for example. The voltage detection circuit 1 includes a differential amplifier composed of a transistor Q ₁ , transistors Q ₂ ... Q ₆ , and resistors R ₁ , ... R ₃ , R.
_6, is composed of ... R _8. In the voltage detection circuit 1,
The power supply voltage V _CC (input DC voltage) is supplied from the input terminal 5 through the resistor R ₁₂ .

The drive circuit 2 includes transistors Q _7, ... Q ₁₁ ,
And resistors R ₉ and R ₁₀ . Output circuit 3
Is composed of an output transistor Q ₁₂ and a resistor R ₁₁ . The load resistor R _L is connected to the collector of the output transistor Q ₁₂ via the output terminal 4. The drive circuit 2 drives the output transistor Q ₁₂ of the output circuit 3 according to the output of the voltage detection circuit 1. CPU for output terminal 4
Etc. reset signal input terminals are connected.

In the voltage detection circuit 1, the power supply voltage V _CC supplied from the input terminal 5 via the resistor R ₁₂ is connected to the resistors R _1, R _2, R _3, R _7, R ₈ (minutes) connected in series. It is divided by the pressure means). The connection point between the resistors R _{1 and} R ₂ is the transistor Q ₄ (second
(Transistor) is connected to the base.

The connection point between the resistors R _{2 and} R ₃ is a transistor Q.
₅ is connected to the (first transistor) total over scan, the voltage of the first divided a voltage resistors R _2, R ₃ of the connection point is inputted to the transistor Q ₅ total over scan. Transistor Q _4, Q
Reference numeral ₅ is a differential pair transistor whose emitters are commonly connected. The emitter current densities of the transistors Q _{4 and} Q ₅ are set to be nonuniform, and the base-emitter voltage has an offset voltage ΔV _BE .

The transistor Q ₆ has a collector as a common emitter of the transistors Q _4, Q _{5 and} a base as resistors R _7, R _8.
The emitter is connected to the ground through a resistor R ₆ at the connection point of. The transistor Q ₁ is the transistor Q ₆
The collector current I _{C6 of} is the constant current.

When the power source is turned on and the power source voltage V _CC gradually rises from 0 volt to 1.2 V, for example,
I _C1 and I _C6 flow to turn on the transistors Q ₁ and Q ₆ , and the differential amplifier starts operating. As a result, the transistors Q _7, ... Q ₁₁ of the drive circuit 2 and the output transistor Q ₁₂ of the output circuit 3 are turned on, the output voltage V ₀ of the output terminal 4 becomes 0 V from the power supply voltage V _CC , and the initial reset of the CPU is performed. Done.

When the power supply voltage V _CC continues to rise, the difference between the base input voltages of the transistors Q _{4 and} Q ₅ approaches ΔV _BE, and the output current I _C12 of the output transistor Q ₁₂ increases. When V _CC rises until the difference between the base input voltages of the transistors Q _{4 and} Q ₅ reaches ΔV _BE , the output of the transistor Q ₅ which is the output of the differential amplifier is inverted and the transistor Q ₇ is turned off. output transistor Q ₁₂ of the transistor Q _9, Q _10, Q ₁₁ and the output circuit 3 is turned off. Therefore, the output voltage V _O rises from 0 volt to the power supply voltage V _CC . The power supply voltage V _CC rises further and the normal power supply voltage, for example, 5
V.

On the other hand, the power supply voltage V _CC is a regular power supply voltage of 5V.
When it gradually decreases and the difference between the base input voltages of the transistors Q _{4 and} Q ₅ becomes ΔV _BE , the output of the transistor Q ₅ is inverted. As a result, the transistor Q ₇ is turned on, the transistors Q _9, Q ₁₀ , Q ₁₁ and the output transistor Q ₁₂ are turned on, the output voltage V ₀ becomes 0 V from the power supply voltage V _CC , and a low level reset signal is output to the output terminal 4. Is output to.

As described above, the voltage detection circuit 1 detects a decrease in the power supply voltage from the normal power supply voltage and outputs a reset signal to the output terminal 4 to reset the CPU and the like.

[0012]

However, the conventional voltage detection circuit has a problem that when the environmental temperature changes, the V _{BE of the} differential pair transistor changes, and the detection voltage from which the reset signal is output becomes unstable. ..

In recent years, an electronic device equipped with a CPU or the like has been increasingly used in a portable manner such as a battery-operated notebook computer. For this reason, the change in environmental temperature is also large, and stable operation is required for this.

In view of the above points, it is an object of the present invention to provide a voltage detection circuit capable of stably detecting the fluctuation of the power supply voltage even if the environmental temperature changes.

[0015]

In order to solve the above problems, according to the present invention, a voltage dividing means for dividing an input DC voltage into a predetermined voltage dividing ratio and a first divided voltage from the voltage dividing means are provided. Input to the first transistor, the first transistor and the emitter are commonly connected, and the first transistor and the base are connected together.
A second transistor having a different emitter-to-emitter voltage, and the second divided voltage from the voltage dividing means is input to the base of the second transistor, and when the input DC voltage reaches a predetermined value, It is detected that the difference between the base input voltages of the first and second transistors becomes the difference between the base-emitter voltages of the first and second transistors and the input DC voltage reaches a predetermined value. In the voltage detection circuit, the second divided voltage is applied to one end and the other end is connected between the first resistor connected to the base of the second transistor and the base / emitter of the second transistor. And a second resistor that is
The voltage division ratio, the base-emitter voltage of each of the first and second transistors, and the resistance value of each of the first and second resistors are set so that the temperature coefficient of the predetermined value of the input DC voltage becomes zero. Set.

[0016]

According to the above construction, the difference between the base input voltages of the first and second transistors becomes the difference between the base-emitter voltages of the first and second transistors. It is detected that the input DC voltage has reached a predetermined value, but the temperature coefficient of this predetermined value is at least the first and second values.
A negative value according to the energy of the forbidden band width of the semiconductor composing the transistor of FIG. 3, a positive value according to the base-emitter voltage of the first and second transistors, and a value of the first and second transistors. It acts as a sum of positive and negative values depending on the difference between the source-emitter voltage, and each value is a voltage division ratio and the base-emitter of each of the first and second transistors. It is set to an arbitrary value by the inter-voltage and the resistance value of each of the first and second resistors, and of course acts to be set to zero.

[0017]

1 is a circuit diagram of a first embodiment of the present invention.

The voltage detection circuit 6 shown in the same figure is similar to the conventional voltage detection circuit 1 shown in FIG. 4 in that the base of the transistor Q ₄ is connected to the connection points of the resistors R ₁ and R ₂ via the resistor R _4. And a resistor R ₅ between the base and emitter of the transistor Q _4.
Configured by connecting.

The basic operation of the voltage detection circuit 6 having the above construction is similar to that of the conventional voltage detection circuit 1. That is, when the power supply voltage V _CC decreases and reaches the predetermined threshold voltage Vsh, the outputs of the transistors Q ₅ and Q ₆ are inverted. The detection output of the voltage detection circuit 6 is amplified by the differential amplifier 7, drives the output transistor Q ₁₂ , and outputs the reset signal to the output terminal 4.

By the way, the differential pair transistors Q _{4 and} Q ₅ have their emitter current densities set nonuniformly by differentiating the emitter junction areas, and the base-emitter voltage is offset voltage ΔV _BE. Is configured to have.

Then, the power supply voltage V coming into the input terminal 5
_CC is such that each base over scan voltage of the transistor Q _4, Q ₅ becomes the threshold voltage Vsh is [Delta] V _BE, resistors R _1, ... by R ₅ and diode-connected transistor to Q ₁ transistor Q _4, Q ₅ Each base is divided. As a result, when V _CC = Vsh, the output of the differential amplifier formed by the transistors Q _{4 and} Q ₅ is inverted, and the drop in the power supply voltage V _CC is detected.

The emitter junction area ratio of the transistors _{Q 4, Q 5 1: n} , the transistors Q _4, Q ₅ Nobesu-emitter voltage and V _BE4, V _BE5. The base input offset voltage ΔV _BE of the transistors Q _{4 and} Q ₅ is ΔV _BE = V _BE4 −V _BE5 (1).

The voltage and current of each part of the circuit are determined as shown in the figure. If I _C5 >> I _Ai , the balance condition of the differential amplifier formed by the transistors Q _{4 and} Q ₅ is I _C4 = I _c5 (2).

Further, when the i _B4 << I _5, since the voltage across V ₄ of the resistor R ₄ is _{V 4 = R 4 I 5 =} V BE4 R 4 / R 5 (3), both ends of the resistor R ₂ The voltage V ₂ is V ₂ = V ₄ + ΔV _BE (4)

Therefore, from equations (3) and (4), the resistance R
Across the voltage V ₂ of the ₂ becomes _{V 2 = V BE4 R 4 /} R 5 + ΔV BE (5).

[0026] By the way, the transistor Q ₄ input offset voltage ΔV _BE is _{V BE4 = Vgo (1-T} / T 0) of Nobesu-emitter voltage V _BE4 and the transistor _{Q 4, Q 5 + V BE04} (T / T ₀ ) (6) ΔV _BE = (kT / q) ln (n) (7)

However, Vgo is the energy (1.12 to 1.1) of the forbidden band width of the silicon constituting the transistors Q _{4 and} Q _5.
7 [eV]), T is the operating temperature [° K], T ₀ is the reference operating temperature [° K], V _BE04 is the base-emitter voltage of the transistor Q ₄ when T = T ₀ [ V] and k are Boltzmann's constant 1.380662 × 10 ⁻²³ [JK ⁻¹ ] and q is the amount of electron charge 1.6021892 × 10 ⁻¹⁹ [C].

Therefore, from the equation (5), V ₂ = (R ₄ / R ₅ ) {Vgo (1−T / T ₀ ) + V _BE04 (T / T ₀ )} + (kT / q) ln (n) ( 8). Next, if the threshold voltage Vsh of the power supply voltage V _CC coming into the input terminal 5 is i _B4 << I ₅ <I ₁ , then Vsh = V _BE1 + V ₂ (R ₁ + R ₂ + R ₃ ) / R ₂ + R ₁ It is represented by I ₅ (9).

Here, the base of the transistor Q ₁
The emitter-to-emitter voltage V _BE1 is V _BE1 = Vgo (1-T / T ₀ ) + V _BE01 (T / T ₀ ) (10) I ₅ = V _BE4 / R ₅ (11) (However, V _BE01 is T = T _0, the base-emitter voltage of the transistor Q ₁ ), and I ₅ << I ₁ ,

[0030]

[Equation 1]

It becomes

In the formula (14), R ₄ (R ₁ + R ₂ + R ₃ )
/ R ₂ R ₅ = r ₁ and (R ₁ + R ₂ + R ₃ ) / R ₂ = r ₂ and partial differentiation of each side with the temperature T,

[0033]

[Equation 2]

It becomes

Equation (15) is the temperature coefficient of the threshold voltage Vsh (∂V
sh / ∂T), which can be any positive or negative value depending on the values of r ₁ , r ₂ and n. Therefore, (∂Vsh
By setting the values of r ₁ , r ₂ and n so that / ∂T) becomes zero, the threshold voltage Vsh can be configured to have no temperature characteristic.

[0036] That _{is, Vgo (1 + r 1)} = V BE01 + r 1 V BE04 + (r 2 kT 0 / q) ln (n) (16) ∴V BE01 + r 1 V BE04 = Vgo (1 + r 1) - (r 2 kT ₀ / q) ln (n) (17) The values of the resistors R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are selected so as to satisfy the condition, and the emitter junction area ratios of the transistors Q _{4 and} Q ₅ are selected. By setting n, the temperature coefficient of the threshold voltage Vsh (∂
Vsh / ∂T) = 0.

By the way, the threshold voltage Vsh when T = T _0
0 is expressed as Vsh ₀ = V _BE01 + r ₁ V _BE04 + (r ₂ kT ₀ / q) ln (n) (18) by _setting T = T _{0 in the} equation (14).

However, in the circuit of the above embodiment, I_FiveIs large
Kikute I₁If it cannot be ignored compared to,
And the third term R₁I_FiveNeed to consider. But R₃
> R ₁If you design as, it will not be a problem.

As described above, according to this embodiment, the power supply voltage V
_CCQ changes when the transistor Q _Four,Q_FiveOutput is inverted
The temperature coefficient of the threshold voltage Vsh₁, R₂, R₃, R_Four,
R_FiveAnd transistor Q_Four,Q_FiveEmitter junction area ratio
It can be set to any positive or negative value by selecting n.
You can Of course, you can set this to zero as described above.
It is possible.

As a result, even if the environmental temperature changes, the threshold voltage Vsh does not fluctuate, and the decrease in the power supply voltage V _CC can be stably detected by the voltage detection circuit 6. The detection output of the voltage detection circuit 6 is amplified by the differential amplifier 7 to drive the output transistor Q ₁₂ , and the reset signal is output to the output terminal 4.

[0041] Incidentally, if the voltage drop R ₁ I ₁ by the resistance R ₁ is set to the value of the voltage drop R ₄ I ₅ only increases as the resistance R ₁ by the resistance R ₄ in the above embodiment, the resistor R ₄ It can be short-circuited and omitted.

Further, the resistor R ₁ is omitted without omitting the resistor R ₄ , and the resistor R ₂ is directly connected to the input terminal 5 so that the power source voltage V
You may divide _CC .

Next, FIG. 2 is a circuit diagram of an example of a reset circuit to which the first embodiment of the present invention is applied. In the figure, the same components as those in FIGS. 1 and 4 are designated by the same reference numerals. In FIG. 2, a drive circuit 8 is connected to the output of the voltage detection circuit 6 to drive the output circuit 3.

The drive circuit 8 comprises transistors Q ₈ , Q ₉ , a resistor R ₁₀ , and multi-collector transistors Q _13, Q ₁₄ whose collectors are partially fed back to the base.
The base of the multi-collector transistor Q ₁₃ is connected to the collector of the transistor Q ₅ of the voltage detection circuit 6.

With the above configuration, when the power supply voltage V _CC that enters the input terminal 5 via the resistor R ₁₂ becomes the threshold voltage Vsh, the collector output voltage of the transistor Q ₅ of the voltage detection circuit 6 is inverted and becomes low level. A reset signal is output to the output terminal 4 via the drive circuit 8 and the output circuit 3. The voltage detection circuit 6 is configured to satisfy the expression (17), and the threshold voltage Vsh does not fluctuate with respect to temperature changes, and the CPU or the like can be reset stably at a constant threshold voltage Vsh. ..

In FIG. 2, the base and collector of the transistor Q ₂ are separated and the base and collector of the transistor Q ₃ are separated.
If the collectors are commonly connected and the base of the multi-collector transistor Q ₁₃ of the drive circuit 8 is connected to the collector output of the transistor Q ₄ of the voltage detection circuit 6, the polarity of the output reset signal to the output terminal 4 becomes the above. And can be reversed.

Next, FIG. 3 is a circuit diagram of an essential part of the second embodiment of the present invention. The circuit configuration of the figure is the same as that of the voltage detection circuit shown in FIG. The voltage detection circuit 9 shown in FIG. 3 sets the current ratio of the transistors Q _4, Q ₅ to 1: n ₁ and at the same time sets the current ratio of the transistors Q _2, Q ₃ which is the constant current load of the transistors Q _4, Q _5. Is also weighted with n ₂ : 1.

The balance condition of this differential amplifier is I _C4 = n ₂ I _c5 (20).

Further _, the input offset voltage of the transistors Q _{4 and} Q ₅ is ΔV _BE = (kT / q) ln (n ₁ n ₂ ) (21), which is ln (n ₁ n compared with the case of the first embodiment. ₂ / n) can be doubled. Therefore, the first term (V
_BE4 R ₄ / R ₅ ) can be made small, so that a large amount of current due to the resistor R ₅ can flow through the transistor Q ₄ .

[0050]

As described above, according to the present invention, it can be detected that the input DC voltage has reached a predetermined value which is an arbitrary temperature coefficient by the sum of the positive value and the negative value. It is possible to set the temperature coefficient of this predetermined value to zero, and it is possible to stably detect the fluctuation of the input DC voltage even if the environmental temperature changes.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 is a circuit diagram of an example of a reset circuit to which the first embodiment of the present invention is applied.

FIG. 3 is a circuit diagram of a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a reset circuit to which an example of a conventional voltage detection circuit is applied.

[Explanation of symbols]

1, 6, 9 Voltage detection circuit 2, 8 Drive circuit 3 Output circuit 4 Output terminal 5 Input terminal 7 Differential amplifier R ₁ , ... R ₅ Resistance Q _2, Q _3, Q _4, Q ₅ Transistor V _CC Power supply voltage Vsh Threshold voltage

Claims (1)

[Claims] 1. A voltage dividing device for dividing an input DC voltage into a predetermined voltage dividing ratio, a first transistor to which a first divided voltage from the voltage dividing device is input to a base, and the first transistor. And a second transistor having a base-emitter voltage different from each other, the second transistor having a second divided voltage which is different from that of the second transistor. When the input DC voltage is input to the base and the input DC voltage reaches a predetermined value, the difference between the base input voltages of the first and second transistors is the base voltage of the first and second transistors. In the voltage detection circuit for detecting that the input DC voltage has reached a predetermined value, the second divided voltage is applied to one end and the other end is connected to the second direct current voltage. A first resistor connected to the base of the transistor A second resistor connected between the base and the emitter of the second transistor, and the voltage division ratio and the first resistor so that the temperature coefficient of the predetermined value of the input DC voltage becomes zero. And a voltage between the base and the emitter of each of the second transistors and a resistance value of each of the first and second resistors.