JPS60194814A - Constant current generating circuit - Google Patents

Abstract

PURPOSE:To supply a current depending on a base-emitter voltage with high accuracy to a load and to attain the operation of the titled circuit at a low power voltage by controlling a collector current of a transistor (TR) constituting a current mirror circuit with a negative feedback loop. CONSTITUTION:A stable output is obtained by feeding back an output of the current mirror circuit comprising a current supply TRQ3 and load current supply TRs QL1-QLn to a feedback TRQ2 via a TRQ1. Then the collector potential of the TRQ1 is brought nearly to 1VBE by connecting a base of the TRQ2 to the collector of the TRQ1 and the emitter to a common so as to constitute the circuit to be activated even with one dry battery (1.5V) thereby attaining low voltage operation of the circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a constant current generation circuit configured to generate a constant current depending on the temperature characteristics of the base-emitter voltage of a transistor.

[Prior art]

Conventional general constant current generation circuits stabilize the current value against fluctuations in power supply voltage, and are also temperature compensated so that the current value remains constant even against changes in ambient temperature. It's normal. And in such a constant current generation circuit,
The extrapolated voltage value of the silicon energy bandgap is applied to create a constant voltage or current that is independent of temperature, but in order to create such a voltage or current, the voltage between the base and emitter of the transistor must be Current and voltage depending on temperature coefficient are required.

Conventionally, there was a circuit shown in FIG. 1 that attempted to generate such a current. In other words, this circuit stabilizes against fluctuations in power supply voltage, and stabilizes against fluctuations in ambient temperature.
The base-to-emitter voltage of a transistor, that is, VB
This is an attempt to accurately generate a current having a negative temperature coefficient that depends on the temperature coefficient of H.

In FIG. 1, transistors Ql and Q2 are NPN type transistors, and transistors Q3゜QLI, Q
l2.・=, QLn is composed of a PNP type transistor. The base of transistor Q1 and the emitter of transistor Q2 are connected to one terminal of resistor R1, and the collector of transistor Q1 is connected to the base of transistor Q2 and one terminal of resistor R2. Furthermore, the collector of transistor Q2 is connected to the collector and base of transistor Q3, and to the collector and base of transistor QLI, Ql2. ...,
Connect to the base of QLn. The emitter of the transistor Q1 is connected to the other terminal of the resistor R1, and this connection point is set as a ground terminal GND. The other terminal of the resistor R2 is connected to the emitter of the transistor Q3 and the transistor QL1.
Ql2. . . , are interconnected to the emitters of QLn, and this connection point is defined as a power supply terminal Vcc. A power source for operating this circuit is connected between the power terminal Vcc and the ground terminal GND. and transistors QLI, Ql
2. ...+ Each collector of QLn is output terminal 01,0
2. ..., is turned on. And each of the above output terminals 01
,02. ..., load RL between Qn and ground terminal GND
1. RL2. ..., RLn, and connect these loads RLI, RL2 . . . . attempts to supply current to RLn.

Next, the operation will be explained. When the power is first turned on,
A current flows from the base of the transistor Q2 to the emitter through the resistor R2, and further current flows through the resistor R1 and the base of the transistor Q1, and connects to the ground terminal GND through each of them.
When the current is removed, the circuit starts operating. Then, negative feedback is applied by the transistors Ql and Q2, and as a result, a current obtained by dividing the voltage between the base and emitter of the transistor Q1 by the resistor R1 is obtained as the collector current of the transistor Q2. A current depending on the base-emitter voltage of transistor Ql is supplied to transistor Q3.

Here, since the base and collector of the transistor Q3 are connected to each other, the transistor QL1. Ql2.
. . . constitute a current mirror circuit for transistors QLn, and therefore transistors QL1 . Ql2. ...+
A load RL1 .QLn connected to each collector. RL2
．． -, RLn is supplied with a current that depends on the base-emitter voltage.

I c (Q2) −VBE (Ql) /R1=・(
1) Here, Ic(Q2) represents the collector current of transistor Q2, and Ic(Q2) represents the collector current of transistor Q1 to Q3 . QL1~QL
The base current of each transistor was ignored, assuming that the DC current amplification factor hFE of n was sufficiently high.

The collector current of this transistor Q2 is the same as that of the transistor Q3. Transistor QLI is supplied to a current mirror circuit composed of QLI to QLn.

QL2+ ・l Each collector current I c (Q
LI).

I c (Ql2), -, I c (QLn), each output terminal 01.02. ..., a current whose characteristics are determined by the voltage between the base and emitter of the transistor Q1 is obtained when the transistor Q1 is turned on. That is, Ic (QLI) = Ic (Ql2) =・==
Ic (QLn) = Ic (mouth 2) ... (2) VBE (Ql) /R1 = Ic (QLI) = I
c (Ql2) = ・-=Ic (QLn) = (
3).

Since the conventional constant current generating circuit is configured as described above, the collector potential of transistor Q1 is determined by the sum of the base-emitter voltages of transistors Q1 and Q2, and the voltage between both terminals Vcc and GND is determined by the sum of the base-emitter voltages of transistors Q1 and Q2. The power supply voltage is 2
A voltage higher than twice VBE is required. Therefore, when operating with a single dry battery, the operating conditions are severe.

Further, when the circuit shown in FIG. 1 is configured as an integrated circuit, transistors Q 3 , QLI, Ql2 . -, QLn are manufactured using lateral PNP) transistors, so there is a drawback that the DC current amplification factor hFE cannot be large and the error in the current supplied to each load becomes large.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and it connects the emitter of the second transistor, which forms a negative feedback circuit together with the first transistor for constant voltage generation, either directly or through a resistor. and connect it to the ground terminal.
Furthermore, by controlling the collector current of the third transistor that constitutes a current mirror circuit for the load current supply transistor using a negative feedback loop, it is possible to operate with a low power supply voltage, and the DC current amplification ratio of the load current supply transistor is An object of the present invention is to provide a constant current generating circuit that can reduce errors in current supplied to a load even when the current is low.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows an embodiment of the first invention of the present application,
The same reference numerals as in FIG. 1 indicate the same or corresponding parts. In this embodiment, the emitter of the transistor Q2 is directly connected to the ground terminal GND, and the collector of the transistor Q3 is connected directly to the ground terminal GND. QLI, Ql2゜..., connected to the base of QLn. Further, a transistor Q3 for supplying power supply current to the resistor R1 has its collector connected to the connection point between the base of the transistor Q1 and the resistor R1, and the transistor Q3 is connected to the transistor Q1. Together with Q2, it constitutes a negative feedback circuit.

Next, the operation will be explained.

When the power is turned on, current flows through the resistor R2 and the base and emitter of the transistor Q2, and the circuit starts operating. Then, current is supplied from the transistor Q3 to the resistor R1 and the base of the transistor Q1, and this resistor R1
The voltage drop at is detected by transistor Q1. The collector potential of the transistor Q1, which is this detection output, is transmitted to the base of the transistor Q2, and the transistor Q
2 amplifies the signal, thereby controlling the base voltage and thus the collector current of transistor Q3.

In this way, transistors Ql, Q2 . Q3 constitutes a negative feedback loop, and a current obtained by dividing the base-emitter voltage VBE (Ql) of transistor Q1 by resistor R1 is obtained as the collector current of transistor Q3.

Here, the base and emitter of transistor Q3 are respectively connected to transistors QL1. Ql2. .
．． - constitutes a current mirror circuit for QLn. For this reason, transistors QLI, Ql2. ..., Q
A load RLI connected to each collector of Ln, RL2.
..., RLn has the above-mentioned base-emitter voltage V
A current dependent on BE(Ql) will be supplied.

In this example circuit, the emitter of transistor Q2 is directly connected to the ground terminal GND, so that
The collector potential of the transistor Q1 is approximately IVBE, and the transistor Q1 can be operated satisfactorily even with a single dry battery (1.5V). In addition, since the transistor Q3 is provided in the negative feedback loop so that the collector current of the transistor Q3 is constant, even when the current mirror circuit is configured with a lateral PNP transistor with a relatively low DC current amplification factor hFE, The influence of the base current can be eliminated, making it possible to supply a highly accurate constant current to each load.

FIG. 3 shows another embodiment of the first invention of the present application, in which the resistor R2 in the circuit shown in FIG. 2 is replaced by a constant current source IB.
That is. The other configurations are the same, and the operations and effects are also exactly the same as in the above embodiment.

FIG. 4 shows an embodiment of the second invention of the present application,
The circuit of this embodiment is similar to the circuit shown in FIG. 3 by connecting a resistor R5 between the emitter of the transistor Q2 and the ground terminal GND, connecting a capacitor C between the base and collector of the transistor Q2, and connecting the collector of the transistor Q2 and the power supply terminal. A transistor Q4 forming a current mirror circuit is connected between transistors Q3 and Vcc, and transistors Q3. Q4
゜Each of the emitters of Q LI NQ Ln and the power supply terminal V
cc, resistors R3, R4, RE1 to RE, respectively.
n are connected.

The basic operation of such an embodiment circuit is the same as that shown in FIGS. 2 and 3 above, and the same effects as the circuit shown in FIG. 2 above can be obtained.
Furthermore, the following effects can be obtained. That is, (i) Capacitor C2 Resistor R5 and Transistor Q4
Since this is provided, self-oscillation can be prevented and the negative feedback loop can be stabilized.

(ii) Since a resistor is connected to the emitter of each transistor, the offset of the base-emitter voltage of each transistor can be compensated for.

〔Effect of the invention〕

As described above, according to the constant current generation circuit according to the present invention,
The emitter of the second transistor that forms a negative feedback circuit together with the first transistor for constant voltage generation is connected to a ground terminal either directly or via a resistor, and further a current mirror circuit is formed for the load current supply transistor. Since the collector current of the third transistor is controlled by a negative feedback loop, it is possible to operate with a low power supply voltage, and there is an effect that a current dependent on a highly accurate base-emitter voltage can be supplied to the load.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional constant current generation circuit, FIG. 2 is a circuit diagram of a constant current generation circuit according to an embodiment of the first invention of the present application, and FIG. 3 is a circuit diagram of another constant current generation circuit of the first invention of the present application. A circuit diagram of a constant current generation circuit according to an embodiment. FIG. 4 is a circuit diagram of a constant current generation circuit according to an embodiment of the second invention of the present application. Ql...first transistor, Q2...second transistor, Q3...current supply transistor, QLI~Q
Ln...Load current supply transistor, RL1 to RL
n...Load, R1" R5, REI~REr+-resistance, C capacitor, IB...constant current source. In addition, the same symbol in the figure indicates the same - or equivalent part. Agent Masuo Oiwa Figure 1 Figure 2 Figure 3 Figure 4 Procedural amendment (voluntary) Commissioner of the Japan Patent Office 1, Indication of the case, Japanese Patent Application No. 59-51865 2, Name of the invention Constant current generation circuit 3, Drawing of the person making the amendment (No. 1) Figure, Figure 3) Figure 1 Figure 3

Claims (5)

[Claims] (1) A first resistor to which a power supply current is supplied through a current supply transistor, and a collector connected to a power supply terminal via a second resistor or a constant current source, and the first resistor is connected between the base and emitter. a first transistor connected to detect a voltage drop across the first resistor; an emitter connected to a ground terminal; a base connected to a collector of the first transistor; and a base voltage of the current supply transistor controlled in accordance with the collector voltage; 1. A constant current ordering circuit comprising: a second transistor having a load connected to its collector, and a load current supplying transistor forming a current mirror circuit with respect to the current supplying transistor. (2) A first resistor to which a power supply current is supplied through a current supply transistor, a collector of which is connected to a power supply terminal via a second resistor or a constant current source, and the first resistor is connected between the base and emitter. a first transistor that detects a voltage drop across the first resistor; an emitter connected to a ground terminal through the resistor; a base connected to the collector of the first transistor; and a base voltage of the current supply transistor controlled in accordance with the collector voltage; and a load current supply transistor having a collector connected to a load and forming a current mirror circuit with respect to the current supply transistor. (3) The constant current generating circuit according to claim 2, characterized in that a capacitor is connected between the base and collector of the second transistor. (4) A fourth transistor forming a current mirror circuit for the current supply transistor is connected between the collector of the second transistor and the power supply terminal. The constant current generating circuit described in Section 3. (5) Any one of claims 2 to 4, characterized in that a resistor is connected between the emitter and power supply terminal of each of the current supply transistor, load current supply transistor, and fourth transistor. A constant current generating circuit described in .