JPS62100130A - Constant current circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a constant current source, and more particularly to a constant current circuit equipped with a starting circuit.

[Conventional technology]

FIG. 2 shows a constant current circuit that does not depend on fluctuations in the t-source and is equipped with a conventional starting circuit. transistor. The collectors and emitters of 1°Q are connected in common, and their emitters are grounded through a resistor R1, connected to the base of the transistor Q and the anode side of the diode D, and connected to the base of the transistor Q and the anode side of the diode D. The cathode side is grounded, and the collectors of transistors Q and Q2 are transistors. ,
ko L/, 17 j' g l): base and transistor. 4 # QH north<-, the other end of the constant current source is connected to the positive power supply terminal along with the emitters of transistors Qs, Q+, and Q5, and the collector of transistor Q4 is connected to transistor Q! The base of the diode D2 is connected to the anode side of the diode D, the cathode side of the diode D2 is connected to the anode side of the diode D, and the cathode side of the diode Ds is grounded.

When the power is turned on, a constant current flows through the diode DI, and the forward voltage VD of the diode DI is applied to the base of the transistor Q1.
A voltage of , is generated. Therefore, transistor Q becomes conductive, and transistor Qs4 becomes conductive. Transistor Q4, which forms a current mirror circuit with transistor Q, becomes conductive.
Current also flows through the

Since this current flows through the diodes Dt, Ds, the base of the transistor Q has diodes D,,D.

A voltage VD, +VD, which is the sum of the forward voltages of , is generated, and the transistor Qt becomes conductive. VD here.

<VD, +V,, so transistor Q becomes non-conductive, (VD, +VD Vlm) / R1
An output current of (VBz, . . . base-emitter voltage of plane transistor Q2) is obtained at the collector of transistor Q1.

[Problem that the invention seeks to solve]

In the conventional constant current circuit described above, when the resistor R8 changes and the collector current of the transistor Q changes, the current flowing through the diodes DI, D, and t changes by the current mirror circuit formed by the transistors Qs and Q4.

The forward current-voltage rise characteristic of the diode is not very steep, so when the current flowing through the diode changes, the forward voltage also changes. Therefore, the base voltage of transistor Q, VD, 10vD, changes,
The collector current of transistor Q further changes, and the collector current of transistor Q, which is the output current, has the disadvantage that it is affected not only by the fluctuation of resistor R3 but also by the change in VD. Also, diode D
t, DtIf the constant current for total bias is small, the diode D
, , D becomes thicker, and as a result, if the output resistance of transistor Q4 is low, the second drawback is that the power supply noise rejection ratio becomes large. In addition, the diodes D and -Ds of the device each require separate insulation regions, and the I
There is also a third drawback that the chip area increases when converted to C. The emitters of the first transistor and the second transistor are grounded via a resistor,
A base of the first transistor is connected to a connection point between a constant current source and a cathode side of a Zener diode of Ml, and an anode side of the first Zener diode is grounded;
The collectors of the first transistor and the second transistor are connected to the base and collector of the third transistor of the second conductivity type and the base of the fourth transistor of the second conductivity type, and the other end of the constant current source and the The emitter of the third transistor and the emitter of the fourth transistor are connected in common, the collector of the fourth transistor is connected to the base of the second transistor and the cathode side of the second Zener diode, and the collector of the fourth transistor is connected to the base of the second transistor and the cathode side of the second Zener diode. The anode side of the second Zener diode is grounded, and the reverse withstand voltage of the second Zener diode is larger than the reverse withstand voltage of the first Zener diode.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows a circuit diagram of an embodiment of the present invention. In this embodiment, the first conductivity type is NPN, and the second conductivity type is PNP. Parts equivalent to those in Figure 1 are indicated with the same symbols. 1st
The difference from the diagram is that the diode D□ is a Zener diode Zl, and the diodes D and ID are Zener diodes Z. In this circuit, when the power is turned on, a constant current flows through the Zener diode z1 and the transistor Q.

A voltage called Zener voltage vz1 is generated at the base of .

Therefore, transistor Q becomes conductive, and transistor Qs
When the transistor Qs is not conductive, a current also flows through the transistor Q4 forming a current mirror circuit with the transistor Qs. Since this current flows through the Zener diode z2, a voltage called Zener voltage Vzffi is generated at the base of the transistor Q, and the transistor Q1 becomes conductive. here,
Zener diode Z1. Zt k selection.

When transistor Q is non-conducting, a constant current is obtained at the collector of transistor Q. For example, Zener diode 2. EB Zener, Zener diode 2. When using a bulk zener, each zener voltage is v2
．． Medium 6.6 V I Vz becomes medium 7.2V. The voltage-current characteristic of a Zener diode has a steeper rise characteristic than that of an ordinary diode, so the resistance Rt
changes, the collector current of transistor Q changes,
Even if the current flowing through the Zener diode Z changes, the Zener voltage vz! remains almost constant. In other words, Q! The base potential of the transistor Q is kept almost constant, and the influence W on the collector current of the transistor Q, which is the output current, is only the variation of the resistor R.

〔Effect of the invention〕

As explained above, in the present invention, the resistor R1 changes and the collector current of the transistor Q4 changes, and the Zener diode 2! Even if the current flowing through the transistor Q changes, the base potential of the transistor Q remains almost constant, so that the only effect on the output current is the variation in the resistor R, and a stable output current can be obtained. Furthermore, since the internal impedance of the Zener diode Z is lower than that of a conventional PN grounding diode, the power supply noise rejection ratio due to the collector output resistance of the transistor Q can be improved.

Also, Zener diode Z, and Z! can be formed in the same insulating region, and the number of elements can be reduced compared to the conventional example, which has the effect of increasing the integration density.

[Brief explanation of drawings]

FIG. 1 is a circuit connection diagram of an embodiment of the present invention, and FIG. 2 is a circuit connection diagram of a conventional example. Q+-Qs...Transistor% R8...
...Resistance, Z1eZ2 ...Zener diode, D, ~D. ...Diode, ■...Constant 1FL flow source. Agent Patent Attorney Uchihara fl, 1”B
. <!

Claims (1)

[Claims] The emitters of a first transistor and a second transistor of a first conductivity type, each having a collector and an emitter commonly connected, are grounded via a resistor, and a base of the first transistor is connected to a constant current source and a first Zener diode. The anode side of the first Zener diode is grounded, and the collectors of the first transistor and the second transistor are connected to the base, collector and collector of a third transistor of the second conductivity type. the other end of the constant current source, the emitter of the third transistor, and the emitter of the fourth transistor are connected in common, and the collector of the fourth transistor is connected to the base of the second transistor and the cathode side of the second Zener diode, the anode side of the second Zener diode is grounded, and the reverse withstand voltage of the second Zener diode is equal to that of the first Zener diode. A constant current circuit characterized by a reverse withstand voltage greater than that of a diode.