JPH0480807A - constant current circuit - Google Patents

Abstract

PURPOSE:To compensate the Early's effect of a transistor TR and to always ensure a fixed current by using a simple structure applying the current feedback. CONSTITUTION:When the current value of an equivalent current source is re ferred to as I together with the mirror coefficients of the current mirror circuits 8, 9 and 14 set at 1 respectively, the current IC3 flowing to the collector of a TR 3 is specified as the following equation with the collector current of a TR 2 referred to as IC2. That is, IC3=(1+VCB/VA).IC2={1-(VCB/VA)<2> }.I, where VCB shows the base-collector voltage of the TR 3 with VA showing the Early's voltage of the TR 3 respectively. If (VCB/VA)<2> 0 is defined, IC3=I is satisfied. Then the current shown by the preceding equation flows to an output terminal 6. Thus it is possible to compensate the Early's effect of the TRs and to always ensure a fixed current despite the change of the power voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a constant current circuit that can always obtain a constant current even if the voltage of a voltage source changes.

BACKGROUND OF THE INVENTION Generally, when it is desired to obtain a constant current, the configuration shown in FIG. 3 is often used.

The circuit of FIG. 3 consists of an equivalent current source 1, a current mirror circuit 8 consisting of an NPN transistor 23 whose emitter is grounded and which has a common base, and a PNP transistor 45 whose emitter is connected to the voltage source terminal 7. The equivalent current source 1 is connected to the collector and base common connection point of the input transistor 2 of the current mirror circuit 9, and the collector of the output transistor 3 is connected to the input transistor 4 of the current mirror circuit 9. The collector and base of the transistor 5 are connected to a common connection point, and the collector side of the output transistor 5 is used as an output terminal 6.

If the current value of the isometric current source is I and the mirror coefficient of the current mirror circuit 8 is 1, then the collector current Tc3 of the transistor 3 is expressed by the following equation.

I c+= (1+VCB/VA) ・l ・
... - (IIVc8 Heath-to-collector voltage VA of transistor 3: Earth voltage of transistor 3 Also, if the voltage value of voltage source terminal 7 is ■.C, then (1)
The formula is as follows.

I C3= (1+(VCCVBE3 VIIE4)
/ V, A) 1... (2) Vcc3 - Voltage between emitter and base of transistor 3 ■BE4 Voltage between emitter and base of transistor 4 Here, the mirror coefficient of current mirror circuit 9 is 1, If the current flowing to the output terminal 6 is 10, o-Ic3 ,', I o'' (1+(Vcc V[1E3V8
E4)/VA) 1...(3) Normal VBE3= VBE4” 0.7 V, V
A” 30 V, formula (3) is I o= (1+(Vcc 1.4 V)/30
V) J (4) Therefore, if the voltage source voltage Vcc changes, the output terminal current Io will change as shown in FIG.

Problems to be Solved by the Invention As mentioned above, the conventional circuit has a problem in that the current to be obtained changes as the power supply voltage changes.

The present invention solves the above problems, and aims to provide a constant current circuit that can compensate for the earth effect of transistors and always obtain a constant current even if the power supply voltage changes. It is something.

Means for Solving the Problems In order to solve the above problems, the present invention provides an isometry current source connected to a common connection point between the collector and base of an input NPN transistor whose emitter is grounded, and a collector of a first transistor on the output side of the first current mirror circuit is a common connection point between the collector and base of an input side PNP transistor whose emitter is connected to a voltage source. a second current mirror circuit having a plurality of output side transistors, and a collector of a second transistor on the output side of the first current mirror circuit connected to the second current mirror circuit having a plurality of output side transistors; Input side NP connected to the collector of one transistor and whose emitter is grounded
The third current mirror circuit is connected to a common connection point between the collector and base of the N-type transistor, and the collector of the output transistor is connected to the base of the first current mirror circuit.

As described above, the present invention compensates for the Early effect of the transistor by using a simple configuration using current feedback, making it possible to always obtain a constant current even when the power supply voltage changes.

EXAMPLE An example of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention, and the same components as in the conventional example shown in FIG. Voltage terminal 8.9 is a current mirror circuit. The isometry current source 1 is connected to a common connection point between the collector and base of the input side NPN transistor 2 of the current mirror circuit 8 whose emitter is grounded,
The collectors of the output side N P N-type transistors 3 and 10 are the collector and base common connection point of the input side PNP type transistor 4 of the current mirror circuit 9 whose emitter is connected to the power supply voltage 7, and the output side PNP type transistor 5
are connected to the collectors of transistors 5 and 5.
The collector of the input side NPN type transistor 12 of the current mirror circuit 14 whose emitter is grounded,
The collector of the output side NPN type transistor 13 is connected to the common base of the current mirror circuit 8, and the output side P of the current mirror circuit 9 is connected to the base common connection point.
The collector of the NP type transistor 11 is used as the output terminal 6.

In the above configuration, if the current value of the equivalent current source is 2 and the mirror coefficient of the current mirror circuit 8.9.14 is 1, as in the conventional example, then the collector current IC3 of the transistor 3 is expressed by the following equation.

I c3= (1+ Vca/ Vwa・I...
(1) However, VCB and VA are the same as in the conventional example.

Here, the current IC5 flowing out from the collector of the transistor 5 of the current mirror circuit 9 is I cs '= I C3--f21 Also, the current flowing into the transistor 10 of the current mirror circuit 8 is I, so from equation (2), I The current Ips obtained by subtracting the current Ips flows into the input transistor of the current mirror circuit 14. Here, IFB is 1 1FB=IC51 = (VC8/VA) ・I
--13) The current IFII in equation (3) is the equivalent current source I
Since the current l flows into the input transistor of the current mirror circuit 8. 2 is as shown in the following equation.

IC2=I IFB - (I Vca/VA) · I - (4 Therefore, the current IC3 flowing to the collector of the transistor 3 is expressed by the following equation.

I C3-(1+ Vca/ VA) ・I c knee(1-(VCB/V, t)2)・1-...15Here, if (V ca/Vwa:!=o), equation (5) is IC
3=I (6), and the current in the above equation will flow to the output terminal 6.

Therefore, as shown in FIG. 2, it is possible to compensate for the Early effect of the transistor and always obtain a constant current even if the power supply voltage changes.

As described in detail, according to the present invention, the Early effect of the transistor can be compensated for by a simple configuration using current feedback, and the Early effect of the transistor can be compensated for by using a simple configuration using current feedback. Even if the power supply voltage changes, it is possible to always obtain a constant current.

[Brief explanation of drawings]

Fig. 1 is a constant current circuit diagram of an embodiment of the present invention, Fig. 2 is a characteristic diagram of the relationship between output current and power supply voltage according to the present invention, Fig. 3 is a conventional constant current circuit diagram, and Fig. 4 is a conventional constant current circuit diagram. FIG. 3 is a characteristic diagram showing the relationship between output current and power supply voltage. 1... Equivalent current source, 2, 3, 10, 12.
13...NPN transistor, 4,5.11.
... PNP transistor, 6 ... Output terminal, 7 ... Power supply terminal, 8, 9.14 ... = - ...
current mirror circuit. Name of agent: Patent attorney Shigetaka Awano Haka12 Figure 2 Q, 'ji, 21) Shi) Tomira

Claims (1)

[Claims] An equivalent current source is connected to the common emitter ground NP of the first current mirror configuration, the collectors and bases of the input side transistors of the N-type transistor pair, and a plurality of output side transistors of the transistor pair are connected. and each collector of a second current mirror configuration consisting of a pair of PNP type transistors whose emitters are connected in common and connected to a voltage source is attached to each collector of the plurality of transistors on the output side of the first current mirror configuration. A common connection point between the collector and base of one transistor of a third current mirror configuration consisting of a pair of common-emitter NPN transistors is connected to the collector circuit of one of the transistors of the first and second current mirror configurations. , and the collector of the other transistor is connected to the common base of the first current mirror configuration.