JPH03136111A - Constant-current circuit - Google Patents

Abstract

PURPOSE:To constitute the circuit so that an output current is not varied even in the case there is a temperature fluctuation by connecting a circuit for connecting in series a second PN junction element and a second resistance in parallel to a first resistance. CONSTITUTION:Between a positive voltage source V1 and a ground point, a series circuit of a resistance R1 and diodes D1, D2 is inserted, and to a connecting point (a) of the resistance R1 and the diode D1, a base of an NPN transistor Q1 is connected. Also, its collector is connected to a current output terminal T1, its emitter is grounded through a resistance R2, and also, between the emitter and a ground, a series circuit of a diode D3 and a resistance R3 is inserted. In such a way, to an output current, a current component having a positive temperature coefficient is added, in addition to a current component having a negative temperature coefficient. Accordingly, the circuit can be formed as a constant-current circuit which is not influenced by a variation of an ambient temperature even in a place in which a temperature is varied remarkably.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a constant current circuit that can output a constant current without being affected by power supply voltage fluctuations.

(Prior Art) The circuit shown in FIG. 3 or 4 has been commonly used as a circuit for obtaining a constant current that does not depend on the value of the power supply voltage. In Figures 3 and 4, ■1 is a positive voltage source, Q, and Q2 are N
PN) transistor, Dl and Dt are diodes, R8 and R
2 is a resistor, and T1 is a current output terminal.

(Problems to be Solved by the Invention) This conventional example is constructed using NPN transistors, and the direction of the output current (indicated by ■oLI7 in the figure) is the direction drawn from the outside. If you want the output current to flow out to the outside, use PNP.
) A circuit complementary to that shown in FIGS. 3 and 4 may be constructed using transistors. This also applies to the embodiments of the invention shown in FIGS. 1 and 2.

In FIGS. 3 and 4, if the current amplification factor of transistor Q is sufficiently large, the output current l. ul is approximately equal to the emitter current of transistor Q.

In this case, the emitter current of the transistor Q1 is given by the following equation.

2 R2 VIIl+ V112 ... Conduction voltage VBEl+VB of Dl and D2! □...Q,, base-emitter voltage of Q2 and V D l + V D 2 + V
B E l + V B E Z is the conduction voltage of the PN junction, and this voltage value is not affected by the current flowing through the PN junction and maintains an almost constant value (usually about 800 mV at room temperature). In other words, even if the current flowing through the resistor R1, the diodes D, , D, . ut to IE)
It is possible to maintain a vague value.

However, if the temperature changes here, 10LI
The disadvantage is that the number 7 fluctuates greatly.

As mentioned above, in both Figures 3 and 4, the output current is 10L.
IT is the voltage for one stage of PN junction divided by the value of resistor R2, but as is well known, the PN junction voltage ranges from -1 to -
Temperature coefficient of 3 mV/''C (the PN junction voltage decreases by about 1 to 3 mV every time the temperature rises by 1 degree) [The size of this temperature coefficient is determined by the current density of the PN junction (current value per unit junction area) ) is larger.], so as the temperature rises, I.LIT decreases. (For example, when the temperature rises by 50°C, I.LIT
The decrease in IT becomes 00mV. ) As described above, conventional constant current circuits have the disadvantage that the change in output current is small in response to power supply voltage fluctuations, but the change in output current is large in response to temperature changes.

The present invention was proposed in order to improve the above-mentioned drawbacks, and its purpose is to provide a constant current circuit whose output current does not change even when there is a temperature change.

(Means for Solving the Problems) To achieve the above object, the present invention detects the voltage present across a first PN junction element and converts the voltage into a current using a first resistor. In a constant radio wave circuit that creates a current through a transistor and outputs the current through a transistor, a second PN
The gist of the invention is a constant current circuit characterized in that a circuit in which a junction element and a second resistor are connected in series is connected in parallel to the first resistor.

(Function) The present invention is to add a current component having a positive temperature coefficient to the output current in addition to the conventional current component having a negative temperature coefficient. As a result, the circuit of the present invention can be a constant current circuit that is not affected by ambient temperature changes even in places where temperature changes are severe.

The present invention differs from the prior art in that a series connection of a PN junction and a resistor is additionally connected in parallel to the resistor (R2) that performs voltage to current conversion.

(Example) Next, an example of the present invention will be described. Note that the embodiments are merely illustrative, and it goes without saying that various changes and improvements can be made without departing from the spirit of the present invention.

FIG. 1 shows a first embodiment of the invention.

Insert a series circuit of resistor R1 and diodes D, Dz between positive voltage source ■1 and the ground point, and connect resistor R and diode D.
The base of the NPN transistor Q1 is connected to the connection point a with the current output terminal T1, and the collector is connected to the current output terminal T1.
The emitter is grounded through a resistor R2, and a diode D3. Insert a series circuit of resistor R3.

FIG. 2 shows a second embodiment of the present invention, and this embodiment differs from the first embodiment in that an NPN I-transistor is used instead of the diode D3 and resistor R3 of the first embodiment. Using Q3, connect the base of this transistor to the emitter of transistor Q, connect the collector of transistor Q3 to this emitter, and connect the collector of transistor Q
This is the point where the emitter of No. 3 is grounded via the resistor R3.

In the present invention, the output current is Q, as the emitter current).
In addition to the current 11 flowing through resistor R2, diode D3. There is an additional current I2 flowing through transistor Q3.

The present invention relates to the relationship between PN junction voltage and PN junction current, and the relationship between PN junction voltage and temperature. The following two well-known properties (1) and (2) are utilized.

■ The PN junction voltage is almost constant regardless of the PN junction current, but if we look at it in detail, we can see that the PN junction current (or
The larger the junction current density), the larger the PN junction voltage.

(2) The magnitude of the negative temperature coefficient of the PN junction voltage increases as the PN junction current density decreases.

In other words, there is a PNN junction, B, in which current of the same value flows.
If there is, and the junction area of A is larger than the junction area of B, then the junction voltage of A is ■.

is smaller than the junction voltage (1) of B, and the decrease in (2) due to temperature rise is greater than the decrease in (2).

This is a fact.

(First embodiment)...In the case of Fig. 1, assuming that the common emitter current amplification factor of transistor Q1 is sufficiently large,
Output current I. U, is approximately equal to the emitter current of transistor Q1. Furthermore, the emitter current is a current (1) flowing through the resistor R2, and a diode D3. It is the sum of the current I2 flowing through the resistor R3. These are respectively given by the following equations.

2 3 VO2...Conduction voltage of D3 Here, so that the above formula holds true, VDl+VDZ VIEI VI13>0, the junction area of diode D3 is larger than the junction area of transistor Q. Increase the bonding area.

Here, ■ゎ, ~VD3+ VQI is a PN junction voltage, and its value hardly depends on the current value flowing through the corresponding PN junction, and takes a nearly constant value.

That is, even if the voltage value of the power supply 1 fluctuates and the current flowing through the resistor R1° and the diodes DI and D2 changes, the current 1. and 12, and therefore the output type flow I which is their sum. UA maintains a nearly constant value.

On the other hand, when the temperature changes, the current 1. indicates a negative temperature coefficient as in the conventional example. (It decreases as the temperature rises.) Now, since the junction area of diode D3 is larger than the junction area of diode DI+D2+ transistor Q1, the magnitude of the temperature coefficient of VO2 is . It is larger than the temperature coefficient of 1lVD21VQl. That is, Vn++VnzV! II V D:
l has a positive temperature coefficient.

On the other hand, ■. Regarding I+VD2 VREI, it becomes a voltage equivalent to one stage of PN junction, and has a negative temperature coefficient. Therefore, (i) Diode D, ,D, ,transistor Q.

The ratio of the junction area of the diode D3 to the output current I by selecting the values of the resistors R2 and R8. Set the size of lJr to an arbitrary value and make the temperature coefficient extremely small (it can also be set to zero from the top of the equation)
It can be set.

(Second Embodiment) In the case of FIG. 2, if the common emitter current amplification factor of the transistor Q is sufficiently large, the output current I. R17 is approximately equal to the emitter current of transistor Q, and is the sum of currents 11 and 12.

Here, IIE2 1, - 2 VIE2 V□3 T, - 3 V 81!3...Base-emitter voltage of Q3 However, the base-emitter junction area of transistor Q is set so that vIIE2〉■BE3 holds. , transistor Q
It should be larger than the base-emitter junction area of No.2.

In other words, the voltage ■. 2 exhibits a negative temperature coefficient, whereas the voltage V B E
2 V I E 3 indicates a positive temperature coefficient.

Therefore, Qλ (1) Ratio of the junction area of transistor Q3 to the transistor body 6D By selecting the values of resistors Rt and R3, the current I I+ I t (≧1
It is possible to set the magnitude of (out) to an arbitrary value and to make the magnitude of the temperature coefficient extremely small.

In addition, it should be noted that: (1) The diodes D1 to D in FIG. 1 may be PN junctions, and may also be transistors with collectors and bases connected, such as the transistor Q in FIG. 2, for example. (The base-emitter junction is used.) ■ The transistor Q3 in FIG. 2 may be a simple diode instead of a transistor.

(Effects of the Invention) As explained above, according to the present invention, a constant current circuit that can maintain a constant value against power supply voltage fluctuations and also maintain a constant value against temperature fluctuations is provided. Therefore, if it is applied as a constant current circuit for various electronic devices that are placed in environments with severe temperature fluctuations, it will be possible to maintain the characteristics of those electronic devices (characteristics against temperature fluctuations) constant. It has this effect.

[Brief explanation of the drawing]

1 and 2 show first and second embodiments of the constant current circuit of the present invention, and FIGS. 3 and 4 show the configuration of a conventional constant current circuit. ■1...Positive voltage source Q, -Q,...NPN) transistor D, ~D,...
-Diode R, -R3...Resistance T,...Current output terminal l01jT...Output current

Claims (1)

[Claims] Detecting a voltage generated across a first PN junction element, converting the voltage into a current using a first resistor to create a current, and outputting the current via a transistor. A constant current circuit, characterized in that a circuit in which a second PN junction element and a second resistor are connected in series is connected in parallel to the first resistor.