JPH03136113A - Constant-current circuit - Google Patents

Abstract

PURPOSE:To constitute the circuit so that a variation of an output current is suppressed small even in the case a fluctuation occurs in a current voltage by bringing a part of the output current to feedback and supplying it. CONSTITUTION:A positive voltage source V1 is connected to a current supply terminal T2 of a current mirror CM, and also, connected to an output terminal T4 of the current mirror CM and bases of transistors Q3, Q1 through a resistance R3, and moreover, grounded through diodes D1, D2. Also, an input terminal T3 is connected to a collector of a transistor Q3, and its emitter is grounded through a resistance R4. A collector of the transistor Q1 is connected to an output terminal T1, and its emitter is grounded through a resistance R2. In such a way, a current output terminal of the current mirror CM is connected one terminal of a PN junction element as a current supply means to the PN junction element. In such a way, even in the case a fluctuation of a power supply voltage occurs, a variation of an output current is suppressed small.

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 fluctuations in power supply voltage.

(Prior Art and Problems to be Solved by the Invention) Circuits shown in FIGS. 13 and 14 have been commonly used as circuits for obtaining a constant current independent of fluctuations in power supply voltage. In Figures 13 and 14, ■, is a positive voltage source, Q
, and Q2 are NPN transistors, D and Dt are diodes, R1 and R2 are resistors, and T is a current output terminal. The conventional examples shown in FIGS. 13 and 14 are constructed using NPN transistors, and the direction of the output current (indicated by 1out in the figures) is the direction in which it is drawn from the outside. If you want the output current to flow out to the outside, use a PNP transistor to
It is sufficient to construct a circuit that has a complementary relationship with those shown in FIGS. 3 and 14. This also applies to the embodiments of the present invention shown in FIGS. 1 to 12 (PNP2NPN, PMO3→NMO3,
Replace the positive voltage source → negative voltage source. ).

Now, in FIGS. 13 and 14, the transistor Q,
If the current amplification factor of Q is sufficiently large, the output current IO1+T is approximately equal to the emitter current of transistor Q. The emitter current 11 of the transistor Q is given by the following equation.

1! −(Vo++Vbt VIIEI)/Rz
(Figure 13) Iyu=V+):z/Rz
(Figure 14) VDI, Vnz -Dr, D
Pressure the s communication of t! l+V□2...Q,,Q,
The base-emitter voltage of , that is, the voltage of one stage of PN junction divided by the resistor R2. And VDl+
Since VO21V□1°V02 is the conduction voltage of the PN junction, it is not affected much by the value of the current flowing through the junction, and maintains an approximately constant value (usually about 800+oV). In other words, as the power supply voltage ■1 fluctuates, the diodes D, , D, , ) transistors Q! Even if the current flowing through changes, the output current ■. at and It) maintain approximately constant values. However, if we look in more detail, R+, Dr due to variations in vl.

When the current flowing through Dz, (b increases (decreases), Vtl
,, V□,■, increases (decreases), albeit slightly. Therefore, the output current I. UT also increases (decreases), albeit slightly.

(Specific example) For example, if V, which is 5V under normal conditions, fluctuates by ±5% (among the design conditions of electronic circuits, the power supply voltage fluctuation condition is often about ±5%), then Dr. Dt
, the current flowing through Qz is: 1m5%X5V/ (5V
-0.8V

I+vo! , v□2 is T −Xfn (1,07~0.93)':26vaVx1. (1,07~0.93)=±
It changes by about 1.8 mV T . Here -'i corresponds to 26 mV.

At this time, the amount of change Δ of I or (”:: I out )
I OL+T (both Figures 13 and 14) ΔI OII? : ±1.8 mV/800mV=
±0.2% In the above equation, 0.8V x 2 = VD+, VDx or VIIEI +VllE!
k: Boltzmann constant q: unit charge T: absolute temperature 4- The PN junction voltage vX and junction current IX are related by the following equation.

q l5 I3: Reverse saturation current of the junction In other words, it is difficult to say that the constant current characteristics are sufficient in the conventional configuration.
For example, when it is necessary to suppress current fluctuations to about ±0.1%, such as in constant current circuits used in VCOs (voltage controlled oscillators), it is necessary to suppress fluctuations in the power supply voltage itself. The drawback was that the equipment was expensive.

(Specific Example) For example, in a constant current circuit for a VCO, it has been necessary to create a (secondary) constant voltage using a Zener diode (breakdown voltage of about 6 cm).

Also, at this time, approximately IOV is required as the (primary) power supply voltage, and when mounting it together with other 5V circuits,
A separate IOV power supply is required.

The present invention was proposed in order to improve the above-mentioned drawbacks, and its purpose is to provide a constant current generating circuit in which changes in output current due to fluctuations in power supply voltage are smaller.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a PN junction element,
A base is connected to a means for supplying current from a first constant potential point to the PN junction element, a connection point between one end of the PN junction element and the current supply means, and an emitter is connected to the first constant potential point. A constant current circuit including a first transistor connected to a second constant potential point via a resistor and connected to the other end of the PN junction element, and having a collector of the transistor as a current output terminal. 2 transistors are provided, the base of this transistor is connected to the base of the first transistor, and the emitter of the second transistor is connected to the second constant potential point via a second resistor, The collector of the second transistor is connected to the current input end of a current mirror whose current input end is connected to the first constant potential point, and the current output end of the current mirror is connected to the PN junction element. As a current supply means,
The current mirror is connected to one end of the PN junction element, and the current output end of the current mirror is connected to the first constant potential point via a third resistor, or the current input end of the current mirror is connected to the first constant potential point through a third resistor. or connect the first and second constant potential points to the third and fourth constant potential points via a third and fourth resistor connected in series, and The gist of the invention is a constant current circuit characterized in that the connection point of the fourth resistor and the current input end or current output end of the current mirror are connected through a diode.

(Function) The present invention does not directly supply the current to the PN junction that generates the constant voltage that is the source of the constant current from the voltage source via the resistor, but by feeding back a part of the output current. The most important feature is that

Thereby, even if there is a fluctuation in the power supply voltage, the change in the output current can be kept extremely small.

7 The present invention differs from the conventional technology in that a voltage-to-current conversion resistor and an output transistor are separately provided, and the current of the added output transistor is supplied to a PN junction element for creating a reference voltage via a current mirror. The difference is that

(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.

1 to 8 show first to eighth embodiments of the constant current circuit of the present invention, in which CM is a current mirror 3- and Q4 are NPN) transistors, D3 and D4 are diodes, R1 to R, is resistance. The other circuit elements are the 13th
It is the same as FIG. 14. Also, Tz, Ts, Ta
are the current supply terminal, input terminal, and output terminal of the current mirror CM, respectively.

9 to 12 show specific examples of the above-mentioned current mirror, where Q and Q are PNP transistors.

and Q, are P channel J and MOS) transistor, R+ and R
Il is a resistance. Further, Tz, Ts, and Ta are current supply terminals, input terminals, and output terminals, respectively, and are indicated by 72. in FIGS. 1 to 8. It corresponds to,T,,T,.

First, the current mirror will be explained with reference to FIGS. 9 to 12.

For example, in FIG. 9, the current supply terminal T2 is a PNP
) is connected to the emitters of transistors Q,,Q,, the bases of both transistors are connected to each other, and this connection point is connected to the collector of transistor Q,. Further, the collectors of the transistors QS and Q are connected to the terminals Tx and T4.

Note that FETs are used in FIGS. 11 and 12.

Next, the operation will be explained.

When a current (input current IA) is drawn out to the outside via the input terminal T, a current (output current 1.) is also sent out to the outside from the output terminal T4. Therefore, the input/output current ratio (
The so-called mirror ratio) ■, /IA is the transistor Qsa
Emitter area ratio (Si/Ss) of Q-, or transistors Q and Q.

-VBEl, so do it. However, the ratio of resistance R1° and R11 (RIl/RI
0) Keep them equal. In particular, S5 = 36, WT
=We.

L? = L e , RIo-R+ If set to +, it is equal to IA and 1. is obtained (Miller ratio -1).

In the following explanation, for simplicity, the discussion will proceed assuming IA=IB.

Next, the output current will be explained with reference to FIGS. 1 to 8.

In FIGS. 1 to 8, the output current I. LIT is calculated by the following formula: %))))) In particular, if the shapes and dimensions of transistors Q3 and Q and the emitter currents are made the same, VBE3■. LIT
≧VllE4/R2 (Fig. 2.4.6.8), which is the same formula as in the conventional example.

Next, a first embodiment (FIG. 1) and a second embodiment (FIG. 2) will be described. In this explanation, the explanation of the second embodiment is given in parentheses (...) after the explanation of the first embodiment.
) is explained.

To explain the configuration of FIG. 1 of the first embodiment, the positive voltage source v1 is connected to the current supply terminal T2 of the current mirror CM, and is connected to the output terminal T4 of the current mirror CM and the transistor Q through a resistor R8. Q, and is further grounded via diodes D+ and Dz. Further, the input terminal T3 of the current mirror CM is connected to the collector of a transistor Q, and the emitter of this transistor is grounded via a resistor R1. The collector of transistor Q1 is connected to output terminal T, and the emitter of this transistor is grounded via resistor R2.

I Next, the operation of the circuit shown in FIG. 1 will be explained. In this case, the operation of FIG. 2 is explained in (...).

Resistor R8 is a resistance for starting up the circuit,
This resistor is sufficiently larger than the resistor R1 of the conventional example (FIG. 13) (it may be about 100 times as large as R). That is, first diode DI, D2.1-transistor Q3. When Q+ (Q4.Q3.Q in FIG. 2) is off, first the diode Dr,
Dz, ) transistor Q3. Q, (in Figure 2 Q,
,Q,,Q,). This minute current flows into the base of the transistor Q3, turns on the transistor Q3, the current is amplified by the transistor Q, and becomes the collector current of the transistor Q3, that is, the input current IA of the current mirror CM. Then, from the positive voltage source 1 through the output terminal T4, 18, which is the same amount as IA, is connected to the diode D+.

Dz (Q4 in Figure 2) and diode DI
, D2 (Q in FIG. 2) is turned on. As a result, the entire circuit shifts to normal operation. That is, most of the current supplied to the diodes D+ and Dz (Q4 in Figure 2) is equal to the collector current Ic of the transistor Q3, and its value is Ic-(Vn+ + VO2VBE3) /R4 (Figure 1) r , =v□4/R4 (Figure 2) VIIE3, VBE4-Q+, Q40) is the base-emitter voltage. Compared to this (because the value of R3 is large), the resistance R
3 through the positive voltage source ■, from the diode DI, Dz
The current supplied to CQa) is negligible.

In other words, the voltage Vo1. The current that determines Vnz (VBt4) is the voltage MD1. It is determined by the value of Vゎ2 (V□4) itself. This allows I. Voltage VD+ that determines UT,
Vnz (VllE4) is less affected by power supply voltage fluctuations, and I0tlT is kept constant even when the positive voltage source vI fluctuates.

Next, a specific example will be described.

For example, current 1. If v1/R3 is set to about 1/10 or less compared to
Diode D even if it fluctuates by 5%.

The change in the current supplied to D2 (Qa) is ±5%X
1/10-±0.5% or less, and the voltage VD.

VDZ (V04) (7) The change is T x 1fi (1,005 to 0.995) Cloud ±0.18
The amount of variation Δl0UT in the emitter current ('= I out ) of the transistor Q at this time is suppressed to below mV.
(in both Figures 1 and 2) is 800 mV, which is about one order of magnitude smaller than the conventional one.

Next, a third embodiment (FIG. 3) and a fourth embodiment (FIG. 4) will be described. In this case, regarding Figure 4 (...
).

The embodiment shown in FIG. 3 (FIG. 4) is different from the embodiment shown in FIG. 1 (FIG. 2) in that after transitioning from the startup state to the steady state,
．． This prevents current from flowing into Qa (D3, Qa, Q+) from the positive voltage source (1) via the resistor R3, so that the voltage (1) of the power supply becomes the output current I. u7
It is possible to further reduce the influence on That is, the diode Rs + Rb is set to a value larger than the conduction voltage for two stages of PN junctions and smaller than the conduction voltage for three stages of PN junctions. Then, if the transistor Q3 is initially off, a sufficient forward bias is applied to the diode D, and
The base current of the transistor Q3 flows through the path →R5→D3→Q3, and the transistor Q3 is turned on.

As a result, the diode D, via the current mirror CM,
.

A current is supplied to D2 (Qa), and the diode D.

D2 (Qa) is turned on. Then, diode D
A voltage equivalent to two stages of PN junction will be applied to the cathode of diode D3, and the voltage between the anode and cathode of diode D3 will be:
There is no longer enough forward bias applied to keep diode D3 on, and the current flowing through diode D3 becomes negligibly small. This causes the diodes DI, D2(Q
The current supplied to a) is purely the voltage V D I +V
D2 (VBE4) is determined by itself and does not depend on the magnitude of power supply voltage v1. Therefore, the output current I. LIT is no longer affected by fluctuations in the power supply voltage ■1.

Next, a fifth embodiment (FIG. 5) and a sixth embodiment (FIG. 6) will be described. In this case, the explanation for Figure 6 is (
) is shown.

In Figure 5 (Figure 6), compared to Figure 1 (Figure 2), the startup resistor R7 is connected to the lower power supply (in this case, ground).
The difference is that it is connected to In other words, if the resistor R1 is set to a sufficiently large resistor, when the circuit is initially off,
First, a minute current flows along the path V1→T3→R1→earth, and the same amount of minute current is applied from vl to the base of transistor Q3 via output terminal T4, turning on transistors Q and l. The circuit operation thereafter is the same as in the case of FIG. 1 (FIG. 2). That is, current mirror C
Most of the current applied to the diodes D+, Dz (Qa) via M is determined by the voltage VDI, Voz (Vs□)6 itself, and is determined by the current component flowing from the positive voltage source ■1 to the ground through the resistor R1. is extremely small because the resistance R1 is large. As a result, the output current I. . The influence of fluctuations in the positive voltage source 1 on the voltage source 7 becomes extremely small.

Next, a seventh embodiment (FIG. 7) and an eighth embodiment (FIG. 8) will be described. In this case, the explanation for Figure 8 is (
...).

Figure 7 (Figure 8) shows that in contrast to Figure 5 (Figure 6), after the transition from the startup state to the steady state, no current flows from the input terminal T3 of the current mirror CM to the ground via the diode D4. As a result, the power supply voltage (■) becomes the output current (I). The influence on UT can be further reduced. However, Figures 7 and 8
The configuration shown in FIG. 9 is applicable to the current mirror commercial shown in the figure.

That is, the cathode point of the diode D4 and the positive electric current R, +R
7 Set to a value larger than the conduction voltage for two stages of N junctions and smaller than the conduction voltage for two stages of PN junctions +R1°xxc (he is the collector current of transistor Q in a steady state). Then, first transistor Q,
, Q, is in the off state, a sufficient forward bias is applied to the diode D4, and ■1→R1°→Q, →D4→R7
→A current flows through the earth path, and the same amount of current flows as ■1
→ R11 → Q6 → Q3 flows into the base of transistor Q3, and transistor Q is turned on. After this, as described above, the state shifts to a steady state. In the steady state, sufficient forward bias is no longer applied to diode D4, and the current flowing through diode D4 becomes negligibly small. As a result, the output current I. ljT is no longer affected by fluctuations in power supply voltage vI.

(Effects of the Invention) As described above, according to the present invention, there is provided a PN junction element, a means for supplying current from a first constant potential point to the PN junction element, and one end of the PN junction element. A base is connected to a connection point with the current supply means, an emitter is connected to a second constant potential point via a first resistor, and a second electrode is connected to the other end of the PN junction element. 1 transistor, the collector of the transistor being a current output terminal, a second transistor is provided, the base of this transistor is connected to the base of the first transistor, and the second transistor is connected to the base of the first transistor. The emitter of the transistor is connected to the second constant potential point via a second resistor, and the collector of the second transistor is connected to a current mirror whose current input terminal is connected to the first constant potential point. The current output terminal of the current mirror is connected to one end of the PN junction element as a current supply means to the PN junction element, so that even if there is a fluctuation in the power supply voltage, the current output terminal of the current mirror is connected to the current input terminal. Since the change in the output current can be suppressed to an extremely small value, the power supply voltage generating device can be simplified. That is, there is an advantage that tolerance to power supply voltage fluctuations is increased.

Furthermore, a Zener diode is not required, and a voltage as high as IOV is not required as a power supply voltage.

[Brief explanation of the drawing]

FIGS. 1 to 8 are diagrams showing first to eighth embodiments of the constant current circuit of the present invention, and FIGS. 9 to 12 are diagrams showing examples of current mirrors applied to the embodiments of the present invention. , FIG. 13 and 1
Figure 4 shows a conventional example. ■1...Positive voltage source T, ~T4...Terminal Q, ~Q,...Transistor D1-D4...Diode R1-R11...Resistance ■. U7...Output current CM...Current mirror 2,

Claims (1)

[Claims] A PN junction element, means for supplying current from a first constant potential point to the PN junction element, and a connection point between one end of the PN junction element and the current supply means. , a first transistor having a base connected to the base thereof, an emitter connected to a second constant potential point via a first resistor, and a first transistor connected to the other end of the PN junction element, the collector of the transistor being connected to the first transistor. In a constant current circuit as a current output terminal, a second transistor is provided, the base of this transistor is connected to the base of the first transistor, and the emitter of the second transistor is connected via a second resistor,
connected to the second constant potential point, the collector of the second transistor is connected to a current input terminal of a current mirror whose current input terminal is connected to the first constant potential point,
A current output terminal of the current mirror is connected to one end of the PN junction element as a current supply means to the PN junction element, and the current output terminal of the current mirror is connected to the first terminal via a third resistor. or connecting the current input end of the current mirror to the second constant potential point via a third resistor, or connecting the first and second constant potential points, 3rd and 4th connected in series
A constant current circuit, characterized in that a connection point between the third and fourth resistors and a current input end or a current output end of the current mirror are connected through a diode.