JP2526560B2 - Constant voltage generator - Google Patents

Description

TECHNICAL FIELD The present invention relates to a constant voltage generating circuit having a small temperature characteristic with a simple configuration and capable of obtaining an arbitrary voltage.

[Conventional technology]

As a conventional constant voltage generating circuit, for example, there is one shown in FIG. The constant voltage generating circuit and the transistor Q _1, Q ₃ which emitter is grounded directly, and the transistor Q ₂ to which emitter is grounded through a resistor R _2, the emitter through a resistor R ₃ to the collector of the transistor Q ₂ Connected transistor Q ₄ , transistors Q ₅ and Q ₆ with emitters connected to each other, transistors Q ₇ and Q ₈ with bases connected to each other, and transistor Q ₉ with base connected to collector of transistor Q ₈ The transistor Q ₁ has a resistor R ₁ between the collector and the reference voltage output terminal V _REF , and the base and collector are directly connected, and the transistor Q ₃ has a resistor R ₅ between the input terminal V _IN and And a capacitor C ₁ between the base and collector, the transistors Q ₅ and Q ₆ have their emitters grounded through a resistor R ₆ , and transistor Q ₉ has their emitter connected to the output terminal V _{0 and} has a resistor R 1. Through ₇ Then transistor Q ₆
The connected to the base, the base of the transistor Q ₆ is grounded through a resistor R _8, transistor Q ₇ is connected between the base and the collector directly. Here, the circuit A having the reference voltage output terminal V _REF is a reference voltage generating circuit that generates a bandgap voltage, and is widely known as described in, for example, "Semiconductor Handbook" issued by Ohm Co., Ltd. Circuit.

Briefly explaining the circuit operation, a potential difference ΔV _BE having a positive temperature coefficient is generated across the resistor R ₂ , and the voltage V _BE3 between the base and emitter of the transistor Q ₃ is generated.
Has a negative temperature coefficient (about −2 mV / ° C.), and is added according to the following equation to obtain the zero temperature coefficient reference voltage V _REF .

Vg ₀ is a bandgap voltage of 1.205V, and based on this, a voltage V ₀ satisfying the following equation is obtained at the output terminal V ₀ .

(Problems to be solved by the invention) However, according to the conventional constant voltage generating circuit, in order to reduce the temperature characteristic of the output voltage, the output voltage is 1.
Since it is determined to be around 025V, in order to generate a voltage higher than this, as shown in FIG. 5, a circuit having a differential amplifier and resistors R ₇ and R ₈ for voltage division in the reference voltage generation circuit A Must be connected, which complicates the configuration and is not preferable in terms of current consumption.

[Means for solving problems]

The present invention has been made in view of the above, and a diode is inserted between the collector of the transistor Q ₂ and the constant current source in order to obtain a small temperature characteristic with a simple configuration and to obtain an arbitrary voltage of 1.2 V or more. And a constant voltage generating circuit.

 Hereinafter, the constant voltage generating circuit of the present invention will be described in detail.

〔Example〕

FIG. 1 shows a first embodiment of the present invention, and the portions common to those of FIG. 5 are designated by the common reference numerals, and thus the duplicate description will be omitted, but the emitter of the transistor Q ₂ is directly grounded, and the collector is A diode D ₁ is inserted in series with a resistor R ₃ between the transistor Q _{4 and} the emitter of the transistor Q ₄ , and resistors R ₁ and R ₂ are connected in series between the collector of the transistor Q ₁ and the output terminal V _0. The base continues at the connection point.

Further, in FIG. 2, the resistor R ₂ is inserted between the emitter of the transistor Q ₂ and the ground.

In the configuration shown in FIGS. 1 and 2, However, V _BE1 is the base-emitter voltage of the transistor Q ₁ , and V _BE2 is the base-emitter voltage of the transistor Q ₂ .

Here, if ΔV _BE = V _BE1 −V _BE2 , the temperature characteristic of the formula is δV ₀ / δT = δV _BE1 / δT + R ₁ / R ₂ · δΔV _BE / δT In order to make the output voltage temperature characteristic zero, , ΔV ₀ / δT = 0 must be satisfied.

Here, since δV _BE1 / δT≈− ₂ mV / ° C., it is necessary from the formula that R ₂ / R ₁ · δΔV _BE / δT≈− ₂ mV / ° C.

On the other hand, it is well known that the temperature characteristic of the output voltage becomes almost zero in the conventional reference voltage generating circuit A shown in FIG. 5 in which the output voltage V ₀ is V _REF ≈1.2V.

Therefore, in the embodiment of the present invention, the temperature characteristic of the difference ΔV _BE between the base-emitter voltage V _BE of the transistors Q ₁ and Q ₂ can be made smaller than that of the conventional circuit by the amount that the resistance ratio R ₁ / R ₂ is increased. It can be said that the formula holds. This will be explained below.

From the equation, δΔV _BE / δT = δV _BE1 / δT−δV _BE2 / δT Here, it can be considered that δV _BE1 / δT in the first term is the same as that of the conventional circuit.

Therefore, δV _BE / δT <0.

On the other hand, since δV _BE2 / δT <0 and δΔV _BE / δT> 0, it can be understood that the value of | δV _BE2 / δT | should be smaller than that of the conventional circuit example shown in FIG.

On the other hand, in FIGS. 1 and 2, VF ₁ a forward voltage of the voltage VR ₃ applied to both ends of the resistor R ₃ is diode D _1,
If the base-emitter voltage of the transistor Q ₃ is V _BE3 , VR ₃ = V ₀ − (VF ₁ + V _BE3 ) The voltage I ₂ flowing through the resistor R ₃ is I ₂ = VR ₃ / R ₃ = (V ₀ − the _{VF-V BE3) / R 3} .

Therefore, the temperature characteristics of the voltage I ₂ is _{δVF 1 / δT, δV BE3 /} δ
Since both T are negative, δI ₂ / δT> 0.

Now, ignoring the base current of transistor Q ₃ ,
I ₂ can be thought of as the collector current of transistor Q ₂ . That is, according to the equation, since the collector current I ₂ of the transistor Q ₂ has a positive temperature characteristic, the temperature characteristic | ΔT _BE2 / ΔT | of the base-emitter voltage V _BE2 of the transistor Q ₂ is offset and becomes small.

Thus, by choosing the value of _{R 1 / R 2, (R} 1 / R 2) (δ
ΔV _BE / δT) ≈ 2mV / ° C can be set. At this time, since the equation is established, the temperature characteristic of the output voltage in FIGS. 1 and 2 becomes almost zero.

FIG. 3 shows another embodiment, in which the transistors Q ₁ , Q ₂ ,
The collector of Q _3, Q ₄ is connected to the base of the transistor _{Q 2, Q 3, Q 4} , Q 5, emitter size of the transistor Q ₂ is compared to the transistor Q ₁ 1: it has a 4 ratio, the collector A resistor R ₃ and a diode D ₁ are inserted in series between the transistor and the transistor Q ₅ .

In the above configuration, when the resistance ratio R ₀ is 5.3 KΩ,
_{R 1 = 4R 0, R 2} = R 0/4, and _{R 3 = 5.5R 0, R 4} = 50KΩ, the transistors _{Q 1, Q 2, Q 3} , a saturation current I ₃ of Q ₄ I ₃ = 1.24 × Ten
^If the temperature characteristics of ^-16 A and resistors R ₁ , R ₂ , R ₃ , and R ₄ are 2000 ppm / ° C, a reference voltage generating circuit with an output voltage V ₀ of 1.9 V and a temperature characteristic of almost zero is realized.

FIG. 4 (a) shows still another embodiment of the present invention,
In the illustrated embodiment, in place of the diode D _1, a diode _{D 1, D 2, D 3} ...... D n is inserted, the emitter size of the transistor Q ₂ is compared to the transistor Q _{1 1:} m (m>
Based on the ratio of 1), the base / emitter voltages V _BE1 , V
_BE2 is different.

FIG. 4 (b) embodies the embodiment of FIG. 4 (a) in which the emitter size ratio is m = 7, the diodes D ₁ , D ₂ , D ₃ and D ₄ are inserted, and , when the resistor _{R 0 = 8.6KΩ, R 1 =} 10R 0, R 2 = R 0/10, R 3 = 2R 0, is obtained by R ₄ = 100KΩ.

With this circuit configuration, the output voltage V ₀ = 5V was obtained.

〔The invention's effect〕

As described above, according to the constant voltage generating circuit of the present invention, since the diode is inserted between the collector of the transistor Q ₂ and the constant current source, the temperature characteristic is small with a simple configuration, and any voltage of 1.2 V or more is used. The voltage can be obtained.

[Brief description of drawings]

1 to 4 are circuit diagrams showing a plurality of embodiments of the present invention.
FIG. 5 is a circuit diagram showing a conventional constant voltage generating circuit. REFERENCE SIGNS _{R 1, R 2, R 3} , R 4, R 5, R 6, R 7, R 8, R 9 ...... resistor _{Q 1, Q 2, Q 3} , Q 4, Q 5 ...... transistor D ₁ , D ₂ …… D _n …… Diode C ₁ …… Capacitor A …… Reference voltage generation circuit

Claims (1)

(57) [Claims] 1. A first transistor having a base connected to a constant current source through a resistor, a grounded emitter, and a collector connected to the base; and a grounded emitter of the first transistor. A second transistor having a base connected to the collector and a collector connected to the constant current source through a diode and another resistor, the diode forming the current mirror circuit; A constant voltage generating circuit having a configuration for changing a ratio of a mirror current flowing through a second transistor according to temperature.