JPS60142711A - Constant current generating circuit - Google Patents

Abstract

PURPOSE:To make surely an output current stable against a change in a power supply voltage by converting a base-emitter voltage of a transistor (TR) into a current with high accuracy and using the current as a source. CONSTITUTION:A collector current of a TRQ2 is a value obtained by dividing the base-emitter voltage of a TRQ1. Since a current mirror circuit where bases and emitters of TRs Q3, Q4 and Q5 are connected mutually and the collector current of the TRQ3 is used as a reference current, the collector current of the TRs Q4, Q5 flows depending on the collector current of the TR3. Thus, since the collector current of the TRQ4 is supplied because of the collector constituted as an output terminal and the collector current of the TRQ1 is supplied as the collector current of the TRQ5, the collector current of the TRQ1 is immune against the fluctuation of the power supply voltage.

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 in response to fluctuations in power supply voltage.

[Prior art]

Conventional general constant current generation circuits stabilize the current value against fluctuations in power supply voltage, and are usually temperature compensated so that the current value remains constant even against changes in ambient temperature. It is. In such a constant current generation circuit, the extrapolated voltage value of the energy band gap of silicon is applied to create a constant voltage or constant current that is independent of temperature. requires a current that depends on the temperature coefficient of the transistor's base-emitter voltage.

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.
Transistor base-emitter voltage, or VBH
This is an attempt to accurately generate a current with a negative temperature coefficient that depends on the temperature coefficient of .

In the figure, first and second transistors Ql.

Q2 is composed of an NPN type transistor, and the third and fourth transistors Q3. Q4 is composed of a PNP type transistor. The base of the first transistor Q1 and the emitter of the second transistor Q2 are connected to one terminal of the first resistor R1, and the collector of the first transistor Q1 is connected to the base of the second transistor Q2 and one terminal of the second resistor R2. Connect to. Furthermore, the collector of the second transistor Q2 is connected to the collector and base of the third transistor Q3 and to the base of the fourth transistor Q4. The emitter of the first transistor Q1 is connected to the other terminal of the first resistor R1, and this connection point is set as a ground terminal GND. Further, the other terminal of the second resistor R2 is interconnected to the emitter of the third transistor Q3 and the emitter of the fourth transistor Q4, and this connection point is defined as the power supply terminal Vcc. And the power supply terminal V
A power source for operating the circuit of the present invention is connected between cc and the ground terminal GND. Then, the collector of the fourth transistor Q4 is set as the output terminal 0UTPUT. and the output terminal 0UTPUT and the ground terminal GN.
A load is connected between terminals D and current is supplied to this load.

Next, the operation will be explained.

First, when the power is turned on, a current flows to the base of the second transistor Q2 via the second resistor R2, a current flows to the emitter of the second transistor Q2, and further flows between the first resistor R1 and the first transistor Q1. A current flows through the base and follows a route to the ground terminal GND via each base, and the circuit of the present invention starts operating. Then, the first and second transistors Q1. Negative feedback is applied by Q2 and the first resistor R1, and as a result, the collector current of the second transistor Q2 is the value obtained by dividing the voltage VBE (Ql) between the base and emitter of the first transistor Q1 by the value R1 of the first resistor R1. is obtained.

Here, Ic(Q2) indicates the collector current of the second transistor Q2, and Ic(Q2) indicates the collector current of the second transistor Q2, and
The base current of each transistor was ignored, assuming that the DC current amplification factor hFE was sufficiently high.

The collector current of the second transistor Q2 is then applied to the third and fourth transistors Q3. A current whose characteristics are determined by the voltage between the base and emitter of the first transistor Q1 is obtained at the output terminal 0UTPUT as the collector current rc (Q4) of the fourth transistor Q4. That is, T c (Q4) −1c (Q2) ・・・・・・(
2) The conventional constant current generating circuit is configured as described above, and the base-emitter voltage of the first transistor and the second
Since the collector voltage of the first transistor is determined as the sum of the base-emitter voltages of the transistors, the voltage applied between both terminals of the second resistor varies depending on fluctuations in the power supply voltage. As the current flowing through the resistor changes and the collector current of the first transistor also changes, the voltage between the base and emitter of the first transistor also changes, and as a result, the current flowing through the first resistor and eventually the load increases as the power supply voltage fluctuates. The drawback was that it fluctuated.

[Summary of the invention]

This invention was made to eliminate the drawbacks of the conventional devices as described above, and by accurately converting the voltage between the base and emitter of a transistor into a current, and using this current as a source, it is possible to reduce the power supply voltage. It is an object of the present invention to provide a constant current generating circuit that can reliably stabilize the output current against changes and also has faithfully the characteristic temperature characteristics of the voltage between the base and emitter of a transistor as the output current characteristics.

[Embodiments of the invention]

FIG. 2 shows an embodiment of the invention.

First, if we look at Figure 2 in comparison with Figure 1, we will see that the second resistor R2 in Figure 1 has been removed and a PNP type 5 resistor has been replaced instead.
A transistor Q5 is inserted, the base of the fifth transistor Q5 is connected to the base of the third transistor Q3,
It can be seen that this circuit is configured such that the collector of the fifth transistor Q5 is connected to the base of the second transistor Q2, and the emitter of the fifth transistor Q5 is connected to the power supply terminal Vcc.

Assuming that this circuit is already in operation, the base-emitter voltage VBE (Q
The collector current Ic (Q2) of the second transistor Q2 is determined by dividing the value R1 of the first resistor R1 by the value R1 of the first resistor R1.

(Same as equation (1) above) Here, the third, fourth, and fifth transistors Q3°Q4.
Since the bases of each transistor Q5 and the vines of each transistor are connected to each other to form a current mirror circuit that uses the collector current of the third transistor Q3 as a reference current, the collector current Ic of the fourth transistor Q4 (Q4 ) and the collector current re(Q5) of the fifth transistor Q5 flows depending on the collector current 1c(Q3) of the third transistor Q3, and can be expressed by the following equation.

I c (Q3) = I c (Q2) ...
・(511c (Q4) =1 c (Q3)...
...(6) I c (Q5) = I c (Q3)
-... (71 Therefore, the collector current 1c (Q4) of the fourth transistor Q4 is connected to the output terminal 0UT.
Since it is configured as a PUT, [4), (51,
+61 formula can be expressed as the following formula.

(Same as equation (3) above) Furthermore, the collector current of the first transistor Q1 c(Ql
) is the collector current Ic (Q5) of the fifth transistor Q5
Since it is supplied as 14>, +5>.

From equation (7), it can be expressed as the following equation.

That is, in the conventional circuit shown in FIG. 1, the collector current of the first transistor Q1 fluctuates due to fluctuations in the power supply voltage, so the voltage between the base and emitter of the first transistor Q1 also fluctuates accordingly. On the other hand, in the circuit of this embodiment shown in Fig. 2,
Since the collector current of the first transistor Q1 is not affected by fluctuations in the power supply voltage, as can be seen from equation (9) above, the characteristics are improved.

Next, FIG. 3 shows a second embodiment of the present invention.

First, if we look at Figure 3 in comparison with Figure 2, we will see that this is the circuit of Figure 2 with an NPN type sixth transistor Q6 and a third resistor R3.
It can be seen that has been added.

Here, the base of the sixth transistor Q6 is connected to the base of the fifth transistor Q5, and the base of the sixth transistor Q6 is connected to the base of the fifth transistor Q5.
The collector of No. 6 is connected to the power supply terminal Vcc, and the collector of No. 6
The emitter of the transistor Q6 is connected to one terminal of the third resistor R3, and the other terminal of the third resistor R3 is connected to the ground terminal GND.

The circuit S composed of the sixth transistor Q6 and the third resistor R3 is added as a starting circuit for the constant current generating circuit of the present invention, and is a circuit S for starting the circuit of the present invention. This is just an example.

First, when the power is turned on to the circuit shown in FIG.
Each fifth transistor Q3. Q4. Current flows from the emitter of Q5 to the base.

Then, current is supplied to the base of the sixth transistor Q6, passes through the emitter, flows, and further flows to the ground terminal GND via the third resistor R3.

Therefore, the third. 4th. Each fifth transistor Q3,Q
4. As the base current of Q5 flows, each transistor Q3. Q4. Collector current flows through Q5, especially the fifth
The collector current of the transistor Q5 flows from the base to the emitter of the second transistor Q2, whereby the circuit of the present invention starts operating.

Next, FIG. 4 shows a third embodiment of the present invention.

First, if we look at Figure 4 in comparison with Figure 3, we can see that this
．． 4th. Fifth transistor Q3. A fifth. 4th. It can be seen that the accuracy of the current mirror circuit constituted by these elements is improved by inserting the sixth resistors R5, R4, and R26 to cause a voltage drop across each resistor.

Furthermore, in this circuit, a PNP type seventh transistor Q7 is added, and the emitter and base of the transistor Q7 are connected to the base and collector of the transistor Q3, and the collector of the transistor Q7 is grounded, thereby implementing the current mirror circuit described above. It can be seen that the error in the output current value due to the base current of each constituent transistor can be reduced, and improvements have been made to further improve accuracy.

Next, FIG. 5 shows a circuit connected to the load section of the constant current generating circuit of the present invention, which is a feature of the present invention that generates a current that depends on the temperature characteristics of the voltage between the base and emitter of the transistor. The purpose is to cancel the temperature characteristics of the first resistor R1 that occurs when creating the resistor R1.
．． Ninth transistor Q8. Q9 is an NPN type transistor, and the seventh resistor R7 is the resistor R1 in FIGS. 1 to 4.
It has the same structure as . The collector of the eighth transistor Q8 is connected to the terminal A, the emitter is connected to the terminal B via the resistor R7, and the base and collector are connected by a diode. Also, the ninth transistor Q
The collector of transistor Q9 is connected to terminal C, the emitter is connected to terminal B, and the base is connected to the base of transistor Q8.

Here, referring to the above equation (8), the voltage drop due to the current flowing through the seventh resistor R7 can be expressed by the following equation.

VR7=I c (Q4) ·R7-...QOl Here, VH2 indicates the voltage drop at the seventh resistor R7, and R7 indicates the resistance value of the seventh resistor. Therefore, by substituting equation (8) into equation 00), we get the following.

Since this resistor R7 has the same structure as the resistor R1, it has the same temperature coefficient, and as shown in equation (11), the seventh
As a result of the temperature coefficient of the first resistor R1 being canceled by the resistor R7, the voltage VR7 is completely obtained as a voltage having a temperature coefficient of BE (Ql). Therefore, the terminal C in Fig. 5 is newly set as an output terminal. For example, a current (I c (Q9)) having temperature characteristics of an ideal transistor base-emitter voltage can be obtained.

〔Effect of the invention〕

As described above, according to the constant current generating circuit according to the present invention, the voltage between the base and emitter of the transistor is converted into a current with high precision, and this current is used as a source, so that it can withstand changes in the power supply voltage. This has the advantage that the output current can be reliably stabilized, and it can be used as a constant current source that can accurately generate a constant current having the same temperature characteristics as the temperature characteristics of the voltage between the base and emitter of a transistor.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional constant current generating circuit, and Fig. 2 is a circuit diagram showing an embodiment of the present invention, which is an improved version of the circuit shown in Fig. 1 so as not to be affected by the power supply voltage. 3 is a circuit diagram showing a second embodiment in which a starting circuit is added to the circuit in FIG. 2, and FIG. 4 is a circuit diagram showing the accuracy of the current mirror circuit in the circuit in FIG. Figure 5 is a circuit diagram of a third embodiment in which a resistor is inserted into the emitter of each transistor in order to improve the voltage and current conversion. FIG. 3 is a circuit diagram showing an additional circuit. In the figure, Ql to Q9 are first to ninth transistors, R1 to R7 are first to seventh resistors, Vcc is a power supply terminal, GND is a ground terminal, 0UTPUT and C are output terminals, L is a load, and S is a This is the starting circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Agent Masuo Oiwa 6 Figure 1 Figure 3 Figure 4 Figure 5

Claims (4)

[Claims] (1) The first transistor and the second transistor are transistors of the same conductivity type, the third transistor, the fourth transistor, and the fifth transistor are transistors of a conductivity type different from the first transistor, and the first transistor The base of the second transistor and the first
The emitter of the first transistor is connected to the other terminal of the first resistor, and this connection point is used as a ground terminal, and the collector of the first transistor is connected to the base of the second transistor and the second terminal. The collector of the second transistor is connected to the collector of the third transistor.
The base and collector of the third transistor are connected to each other, and further connected to the base of the fourth transistor and the base of the fifth transistor, and the emitter of the third transistor is connected to the emitter of the fourth transistor. is connected to the emitter and ivy of the fifth transistor, this connection point serves as a power supply terminal, the collector of the fourth transistor serves as an output terminal, and a power supply is connected between the power supply terminal and the ground terminal. Characteristic constant current generation circuit. (2) a sixth transistor whose collector is connected to the power supply terminal and whose base is connected to the base of the fifth transistor;
A starting circuit is provided, which includes a third resistor connected between the emitter of the sixth transistor and the ground terminal, and stably starts the constant current generating circuit when the power is turned on. A constant current generating circuit according to claim 1, characterized in that: (3) a fifth resistor is inserted between the emitter of the third transistor and the power supply terminal; a fourth resistor is inserted between the emitter of the fourth transistor and the power supply terminal; 3. The constant current generating circuit according to claim 2, further comprising a sixth resistor inserted between the emitter of the fifth transistor and the power supply terminal. (4) A load connected between the output terminal and the ground terminal includes eighth and ninth transistors having the same conductivity type as the first transistor, and a third transistor having the same structure as the first resistor. 7 resistors, the base and collector of the eighth transistor are connected, the base of the eighth transistor and the base of the ninth transistor are connected, and this connection point is connected to the output terminal. The emitter is connected to one terminal of the seventh resistor.
The other terminal of the resistor is connected to the emitter of the ninth transistor, this connection point is connected to the ground terminal, and the collector of the ninth transistor is used as a new output terminal. A constant current generating circuit according to any one of claims 1 to 3.