JP3218641B2 - Voltage detection circuit - Google Patents

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 a fluctuation in a power supply voltage.

[0002]

2. Description of the Related Art Conventionally, a CPU (Central Processing)
There is known a voltage detection circuit for detecting fluctuations in the power supply voltage in a system or the like and resetting the CPU initially when the power is turned on, or resetting the CPU when the power supply voltage drops instantaneously. .

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, for example, a CPU. Voltage detecting circuit 1, the transistor Q _1, a differential amplifier, and a resistor R ₁ consists of transistors _{Q 2 ... Q 6, ... R} 3, R
₆ ,... R ₈ . The voltage detection circuit 1 includes:
Supply voltage from the input terminal 5 via a resistor R ₁₂ V _CC (the input DC voltage) is supplied.

[0004] The driving circuit 2, transistor Q _7, ... Q _11,
And resistors R ₉ and R ₁₀ . Output circuit 3
It is constituted by the output transistors Q ₁₂ and resistors R _11,. The collector of the output transistor Q _12, the load resistor R _L through the output terminal 4 is connected. Driving circuit 2 in accordance with the output of the voltage detecting circuit 1 for driving an output transistor Q ₁₂ of the output circuit 3. The output terminal 4 has a CPU
Reset signal input terminals are connected.

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

[0006] The connection point of the resistors R _2, 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. Transistors Q4 _and Q
Reference numeral ₅ denotes a differential pair transistor whose emitter is commonly connected. Transistors Q _4, Q ₅ is an emitter current density of each have been unevenly set, to database emitter voltage is configured to have an offset voltage [Delta] V _BE.

[0007] The transistor Q ₆ is, the collector to the common emitter of the transistor Q _4, Q _5, the resistance of the base over the scan R _7, R ₈
The connection point is connected to ground the emitter via a resistor R _6. The transistor Q ₁ is connected to the transistor Q _6
Is a constant current.

When power is turned on and the power supply voltage V _CC gradually increases from 0 volts to, for example, 1.2 V,
I _C1 and I _C6 flow, transistors Q ₁ and Q ₆ turn on, and the differential amplifier starts operating. Thus, the transistor Q ₇ of the driver circuit _2, ... becomes Q ₁₁ and the output circuit 3 of the output transistor Q ₁₂ is turned on the output voltage V ₀ which output terminal 4 when the power supply voltage V _CC from 0 volts, the initial reset the CPU Done.

As the power supply voltage V _CC further increases, 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 the transistor Q _4, V _CC until the difference of the respective base over scan input voltage is [Delta] V _BE of Q ₅ is increased, the transistor Q ₇ is turned off the output of the transistor Q ₅ is the output of the differential amplifier is inverted, 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 volts to the power supply voltage V _CC . The power supply voltage V _CC further rises, and the normal power supply voltage, for example, 5
V.

On the other hand, if the power supply voltage V _CC is
Difference gradually decreased transistors Q _{4 and,} Q ₅ Nobesu input voltage from the becomes a [Delta] V _BE, the output of the transistor Q ₅ is inverted. Thus the transistor Q ₇ is turned on and the transistor Q _9, Q _10, Q ₁₁ and the output transistor Q ₁₂ is the output voltage V ₀ is turned on becomes the power supply voltage V _CC from 0 volts, the output reset signal of a low level terminals 4 Is output to

As described above, a drop in the power supply voltage from the normal power supply voltage is detected by the voltage detection circuit 1, and a reset signal is output 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 ambient temperature changes, the V _{BE of the} differential pair transistor changes, and the detection voltage for outputting the reset signal becomes unstable. .

In recent years, electronic devices equipped with a CPU and the like have been increasingly used in portable devices such as notebook computers operated by batteries. For this reason, the change in the environmental temperature is increasing, and it is required to operate stably.

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

[0015]

In order to solve the above-mentioned 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. A first transistor input to the base; and a second transistor having the emitter and the emitter commonly connected and having a different base-emitter voltage from the first transistor. Of the second divided voltage of the second
When the input DC voltage reaches a predetermined value, the voltage of the difference between the base input voltages of the first and second transistors is changed to 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 set to the voltage of the difference between the respective base-emitter voltages. comprising a first resistor connected base over the scan of the second transistor and a second resistor connected between to database emitter of said second transistor, said
The division ratio and the base of each of the first and second transistors
And the emitter-to-emitter voltage and the resistance of each of the first and second resistors.
Set to the predetermined value by setting a resistance value
At the same time, the temperature coefficient of the predetermined value is set to zero.
Was.

[0016]

According to the above arrangement, when the voltage of the difference between the base input voltages of the first and second transistors becomes the voltage of the difference between the base-emitter voltages of the first and second transistors, respectively. It is detected that the input DC voltage has reached a predetermined value, and the temperature coefficient of this predetermined value is at least the first and second values.
A negative value corresponding to the energy of the forbidden bandwidth of the semiconductor constituting the transistor, a positive value corresponding to the base-emitter voltage of the first and second transistors, and a positive value corresponding to the energy of the first and second transistors. And a positive / negative value depending on the difference between the source-emitter voltage. Each value is determined by the voltage dividing 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 so as to be set to zero.

[0017]

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

The voltage detection circuit 6 shown in FIG. 1 is different from the conventional voltage detection circuit 1 shown in FIG. 4 in that the base of the transistor Q ₄ is connected to the connection point between the resistors R ₁ and R ₂ via the resistor R _4. Connect a resistor R ₅ between the base and emitter of transistor Q _4.
Was connected.

The basic operation of the voltage detecting circuit 6 having the above configuration is the same as that of the conventional voltage detecting circuit 1. That is, when the power supply voltage V _CC decreases to reach the predetermined threshold voltage Vsh, the outputs of the transistors Q ₅ and Q ₆ are inverted. Then, the detection output of the voltage detection circuit 6 is amplified by the differential amplifier 7, to drive the output transistor Q _12, a reset signal is output to the output terminal 4.

The differential pair transistors Q _{4 and} Q ₅ have different emitter current densities by differentiating the emitter junction area, so that the base-emitter voltage has an offset voltage ΔV _BE It is configured to have.

The power supply voltage V input to the input terminal 5
_The resistors R ₁ ,... R ₅ and the diode-connected transistor Q ₁ connect the transistors Q _4, Q ₅ so that the voltage between the bases of the transistors Q _4, Q ₅ becomes ΔV _BE when _CC becomes the threshold voltage Vsh. Each base is divided. Thus, in the V _CC = Vsh, the output of the differential amplifier constituting at transistor Q _4, Q ₅ is reversed, 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 as follows: ΔV _BE = V _BE4 −V _BE5 (1)

The voltage and current of each part of the circuit are determined as shown. When I _C5 >> I _Ai, equilibrium conditions of the differential amplifier constituted by transistors Q _4, 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 becomes V ₂ = V ₄ + ΔV _BE (4).

Therefore, according to 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)

[0027] However, Vgo the transistor Q _4, the forbidden band width of silicon constituting the Q ₅ of the energy (from 1.12 to 1.1
7 [eV]), T is the operating temperature [° K], T ₀ the operating temperature as a reference is [° K], V _BE04 is the transistor Q ₄ Nobesu-emitter voltage when T = T ₀ [ V], k is the Boltzmann constant 1.380662 × 10 ⁻²³ [JK ⁻¹ ], and q is the electron charge amount 1.6021892 × 10 ⁻¹⁹ [C].

Therefore, from equation (5), V ₂ = (R ₄ / R ₅ ) ｛Vgo (1−T / T ₀ ) + V _BE04 (T / T ₀ )｝ + (kT / q) ln (n) ( 8) Next, the threshold voltage Vsh of the power supply voltage V _CC incoming to the input terminal 5, i _B4 << I ₅ <When _{I 1 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
Since 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) (where V _BE01 is T = T ₀ , base-emitter voltage of transistor Q ₁ ), and I ₅ << I ₁

[0030]

(Equation 1)

## EQU1 ##

In the equation (14), R ₄ (R ₁ + R ₂ + R ₃ )
/ R ₂ R ₅ = r ₁ , (R ₁ + R ₂ + R ₃ ) / R ₂ = r ₂

[0033]

(Equation 2)

## EQU1 ##

The equation (15) shows the temperature coefficient of the threshold voltage Vsh (shV
sh / ∂T), and can take 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 not to have a 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 following condition, and the emitter junction area ratio of the transistors Q _{4 and} Q ₅ is selected. By setting n, the temperature coefficient of the threshold voltage Vsh (∂
Vsh / ΔT) = 0.

By the way, when T = T ₀ , the threshold voltage Vsh
₀ is represented by Vsh ₀ = V _BE01 + r ₁ V _BE04 + (r ₂ kT ₀ / q) ln (n) (18) by _setting T = T _{0 in} 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 be considered. But R_Three
> R ₁It does not matter much if it is designed as

As described above, according to the present embodiment, the power supply voltage V
_CCChanges when the transistor Q _Four,Q_FiveOutput is inverted
The temperature coefficient of the threshold voltage Vsh at which₁, R_Two, R_Three, R_Four,
R_FiveAnd transistor Q_Four,Q_FiveEmitter area ratio
can be set to any positive or negative value by selecting n.
Can be. Of course, as mentioned above,
It is possible.

[0040] Thus, without varying the threshold voltage Vsh even when the environmental temperature changes, it is possible to stably detected by the power supply voltage V _CC voltage detecting circuit 6 the lowering of. The detection output of the voltage detection circuit 6 is amplified to drive the output transistor Q ₁₂ by a differential amplifier 7, a 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 supply voltage V
_CC may be divided.

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 denoted by the same reference numerals. 2, a drive circuit 8 is connected to the output of the voltage detection circuit 6, and drives the output circuit 3.

The drive circuit 8 is composed of transistors Q ₈ and Q ₉ , a resistor R ₁₀ , and multi-collector transistors Q _{13 and} Q ₁₄ whose collectors are partially fed back.
Multi-collector transistor Q ₁₃ Nobesu is connected to the collector of the transistor Q ₅ of the voltage detection circuit 6.

According to the above configuration, when the power supply voltage V _CC input to 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 to a 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 can stably reset the CPU or the like at a constant threshold voltage Vsh without fluctuation of the threshold voltage Vsh with respect to a temperature change. .

[0046] Further, in FIG. 2, the transistor Q ₃ Nobesu-separating transistor Q ₂ Nobesu collector
And collectors connected in common, the multi-collector transistor Q ₁₃ Nobesu drive circuit 8, when 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 And can be reversed.

FIG. 3 is a circuit diagram of a main part of a second embodiment of the present invention. The circuit configuration in the figure is the same as the voltage detection circuit shown in FIG. Voltage detection circuit 9 shown in FIG. 3, the current ratio of the transistor Q _4, Q ₅ 1: and at the same time as n _1, the current ratio of the transistor Q _2, Q ₃ to a constant-current load transistor Q _4, Q ₅ Were also weighted with n ₂ : 1.

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

[0049] The input offset voltage of the transistor Q _4, Q ₅ is _{ΔV BE = (kT / q)} ln (n 1 n 2) (21) becomes, compared with the case of the first embodiment ln (n ₁ n ₂ / n) times. Therefore, the first term (V
_BE4 R ₄ / R ₅ ) can be reduced, so that a large amount of current can be caused to flow through the transistor Q ₄ by the resistor R ₅ .

[0050]

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

[Brief description of the 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 and 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 supply voltage Vsh Threshold voltage

Claims (1)

(57) [Claims] 1. A voltage dividing means 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 means is inputted to a base, and a first transistor And a second transistor having an emitter commonly connected and having a first transistor and a second transistor having a different base-emitter voltage, wherein a second divided voltage from the voltage dividing means is applied to a base of the second transistor. When the input DC voltage reaches a predetermined value, the voltage of the difference between the base input voltages of the first and second transistors is changed to the base voltage of each of the first and second transistors. A voltage detection circuit that detects that the input DC voltage has reached a predetermined value, the second divided voltage being applied to one end, and the other end of the second transistor being connected to the second transistor; A first resistor connected to the base, It said second second; and a resistor connected between to database emitter of the transistor, and the voltage dividing ratio, the people said first and second transistors respectively
A base-emitter voltage and the first and second resistors
Set to the predetermined value by setting various resistance values
So that the temperature coefficient of the predetermined value becomes zero.
A voltage detection circuit.