JPH02105089A - Switch circuit - Google Patents

Abstract

PURPOSE:To decrease the maximum input current without using a resistance element of a large value and to eliminate an abnormal oscillation by connecting an output terminal of a current mirror circuit to a control input terminal of a switching element. CONSTITUTION:An emitter of a transistor (TR) Q1 connected to a base through a resistance R1 from an input terminal IN is grounded through a resistance R2. A collector of the TR Q1 is connected to a base of a TR Q2 of a current mirror circuit (CM) whose collector is connected to a power source Vcc, and an emitter of the TR Q2 is connected to a TR Q3 of the CM connected to the Vcc. A collector of the TR Q3 is grounded through a resistance R3, and also, connected to a base of an output switching TR Q4 whose emitter is grounded. The resistance R3 prevents a fact that the TR Q4 causes a malfunction due to an output leak current of the CM. In such a way, the maximum input current is decreased remarkably without using a resistance of a large value of >=100kOMEGA.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an electronic switch circuit suitable for a monolithic IC (integrated circuit).

(Prior Art) The configuration of a conventional switch circuit implemented as an IC will be explained with reference to FIG.

In the figure, a resistor R1□ connected to the base of the emitter-grounded transistor Q11 is a current limiting resistor for limiting the current applied to the input terminal IN, and is connected to the collector of the transistor Qtt and the power supply V. Resistors R, R connected in series with 0 connect transistor Qll and emitter, respectively, to power supply V. This is a resistor for controlling the current of the transistor Q12 whose base is connected to the connection point of the resistor RR. Also, the resistor RR connected in series between the collector of the transistor Q1゜ and the ground causes the leakage of the transistor Q SQ 14ゝ 15
11 12 Output switching transistor Q whose base is connected to the connection point of resistors R and H by current
13 is a resistor for preventing malfunction to prevent it from turning on. The emitter of transistor Q13 is grounded, and the collector is connected to power supply VCC via load circuit RL.

The input current fin supplied to the input terminal IN of the above configuration is 11n=(Vln-V)/R-=
(1) BELL becomes 11.

However, Vin is the control input terminal, and 2 is the base-emitter voltage of the transistor ELL star Q11. Also, the minimum input current 11n (M
I10(MIN)-V/β・R・
... (2) BCl2 11 13 . However, ■ is the ON E1 of the transistor Q1°.
The base-emitter voltage at 2, βIt, is the transistor Q
11 is the current amplification factor of the common emitter. Here, V
-0.7V, β -100, ΩBE to R13-70
12 If 11, then formula (2)
Therefore, I In (M I N) =0. It becomes l ttA.

In other words, in Fig. 3, the input terminal 11n is 0.1 μA
If the current flows more than that, the transistor Q12 turns on, and if it flows less than that, it turns off, and the load circuit RL can be switched.

The input terminal 11n depends on the resistance R as seen from equation (1), and can be reduced by increasing the resistance R1□, but the minimum value Vin (MIN) of the control input voltage Vln and the minimum value of the input terminal 11n The value fin(MIN) determines the maximum value R,,(MAX) of the resistor, R11(MAX)-(Vin(MIN)-V)E
II / I In (M I N) ---
(3) becomes.

Cocote, Vln (MIN) -0,9V, VB
E-0,7V, I in (M I N) -0,
If it is 1tt A, then R11(MAX)-2MΩ. In other words, the resistance R11 only needs to be 2MΩ or less.

When the switching circuit described above is integrated into an IC, a too large resistance element value increases the chip size and is uneconomical.Generally, the resistance element value integrated into an IC is 100.
It is about KΩ or less. Therefore, the maximum value 11n (MAX) of the input current fin is 11n (MAX) = (
Vln(MAX)-V)EII/R1, (4). Here R, l-100KΩ, Vln (MAX)
-3VSV -0.7V, then from equation (4) E
II 11n(MAX)=23μA. As described above, it is difficult to narrow down the input current 11n in the circuit configuration shown in FIG. 3 to 23 μA or less due to the economical constraints associated with the use of IC. Note that if the value of the resistor R11 is set to 100Ω or less, the input current 1 inch will naturally increase further than 23μ8.

Figure 4 shows the patent application filed earlier by the applicant in 1982-
239822, and is a technique for narrowing down the input current 11n without using a large resistance element.

In FIG. 4, resistor R21 controls the input current to prevent transistor Q2 from becoming saturated and excessive current flowing to input terminal IN when the relationship between control input voltage Vln and power supply Vcc becomes Vjn>Vcc. This is a limiting resistor.

This resistor R2□ is unnecessary (R2□-〇) when used under the condition that the transistor Q21 is not saturated. Resistance R
This is to prevent the output switching transistor Q24 from malfunctioning due to a small current of the transistor Q23.

The collector current of transistor Q2 is amplified by the transistor and fed back to the transmitter of transistor Q2□. Also, the transistor Q23 whose base and emitter are commonly connected to the transistor Q22 is the transistor Q2.
A current equivalent to the collector current of transistor Q2 is supplied to the base circuit of transistor Q24 to control transistor Q24.

The input current 11n in FIG. 4 is 11n-Vin-V/R(1+β21+0.5
BE21 22 ・β ・β )+R...(5) It is obtained as follows. However, ■ is the transistor Q2□E2
β21 is the common emitter current amplification factor of the transistor Q2, and β22 is the common emitter current amplification factor of the transistors Q1 and Q2. Also, the minimum input terminal 1in (MIN) that turns on the transistor Q24 is 11n (MIN) - 2V /β ・β - RBE2
4 21 22 23 ...(6) It becomes. However, ■ is H2 when transistor 24 is on.
This is the base-emitter voltage of 4. In addition, the input current II
The maximum value 11n (MAX) of n can be obtained by substituting the maximum value Vln (MAX) of the control input voltage Vin for Vin in equation (5). Here R21-toKΩ, R-10
KQ, Ω to R-70, V -0.7V.

22 23
8B21V BE22-0, 7 V-β21""I
QQ-β22""40, Vln(MAX)-3V, maximum value of input current fin 11n (MIN), maximum value 11n
When (MAX) is calculated from equations (5) and (6), 11 units (
MIN) -0,005uA, 11n(MAX)=
O, ll, czA.

In the case of Fig. 4, compared to the example of Fig. 3, the maximum input current fi
It can be seen that n(MAX) can be reduced to about 1/20 without using a large resistance element. However, the minimum input terminal 11n (MIN) that turns on the transistor Q24 is 0.
．． 005 u A -50 n A, which is extremely small, and there is a higher possibility of malfunction due to external noise etc. than in the example of FIG. 3. Also, when integrated into an IC, the emitter of transistor Q2□ is connected to transistor Q22.
Since feedback is applied from the NPN transistor Q
There is also a risk of abnormal oscillation due to the difference in the transient frequency fT between the transistor Q21 and the PNP l-transistor Q22.

(Problems to be Solved by the Invention) In the case of the above-described conventional configuration shown in FIG. It has been difficult from an economic standpoint to implement ICs in circuits that require narrowing down the number of components. In addition, in the case of the configuration shown in FIG. 4, the minimum input current fin(M
Since IN) has become extremely small, there are concerns about malfunction due to external noise, etc., and because the configuration is such that feedback is applied from the NPH transistor to the PNP) transistor, abnormal oscillation may occur due to differences in the transient frequency fT. be.

[Structure of the Invention] (Means for Solving the Problems) The switch circuit of the present invention has a base connected to a control input terminal directly or via a resistance element, an emitter connected to a reference potential point via a resistance element, and a collector connected to a current control input terminal. The present invention is characterized in that it has transistors each connected to an input terminal of a mirror circuit, and an output terminal of the current mirror circuit is connected to a control input terminal of a switching element.

(Function) With the means described above, the maximum input current can be reduced without using a resistive element with a large value, and the minimum input current can also be made to a level that is not affected by external noise. Furthermore, since no feedback loop is formed, there is no need to worry about abnormal oscillation.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

In FIG. 1, a transistor Q1 whose base is connected to an input terminal IN through a resistor R1 has its emitter grounded through a resistor R2. The collector of transistor Q1 is connected to the base and collector of transistor Q2 whose emitter is connected to power supply Vcc, and transistor Q2 is connected to transistor Q3 whose emitter is connected to power supply Vcc. Transistors Q2 and Q3 constitute a current mirror circuit CM. The collector of transistor Q3 is resistor R3
and is connected to the base of an output switching transistor Q4 whose emitter is grounded. The collector of transistor Q4 is connected to the electric current Fi via load circuit RL.
, connected to Vcc. Note that Vin indicates a control input terminal, and resistor R1 is used when transistor Q1 enters saturation (
The resistor R3 is used to prevent excessive current from flowing to the input terminal IN when V In > V cc), and the resistor R3 is used to prevent transistor Q4 from malfunctioning (turning on) due to the output leakage current of the current mirror circuit CM. belongs to.

In the above configuration, the input current 11n flowing through the input terminal IN can be determined from the following equation.

Vln-VBCI 11n-□ (7) R2 (1+β+)+R+ However, VBB+ is the base-emitter voltage when the transistor Q1 is on, and β1 is the current amplification factor of the common emitter of the transistor Q1. Also, the minimum input current 11n (MIN) that turns on the transistor Q4 is VBE4 11n (MIN) = -(8) β1
・ACM・R3. However, VBE is the base-emitter voltage when the transistor Q4 is on, and ACM is the current gain of the current mirror circuit CM.

So: TeR, -10 Ω, R2-10 Ω, R3-70 Ω, VBE+ -0.7V, VBE4-0.7V,
β1-100, ACM=l 5Vln (MAX)
Assuming -3V, the minimum input current is 11n from equations (7) and (8).
(MIN), maximum input terminal fin(MAX) is found as IIn(MIN) -0,1μA, IIn
(MAX) -2.3 pA.

Therefore, the maximum input terminal can be significantly reduced compared to the conventional configuration shown in FIG. 3 without using a large resistor of 100 KΩ or more. Furthermore, the minimum input terminal, in other words, the threshold level, is the same as the configuration shown in FIG. 3, and as shown in FIG. 4, it is not extremely small and there is no fear of malfunction due to external noise. Furthermore, as shown in Fig. 4, since there is no feedback loop, there is no abnormal oscillation, and when integrated into an IC, the threshold level is directly affected by the emitter ground current amplification factor β of the PNP l-transistor, which is difficult to control in the process. In this embodiment, the current mirror circuit is designed to be less susceptible to this influence.

FIG. 2 is composed of transistors Q+' to Q4' of opposite polarity to the transistors Q1 to Q4 in FIG. 1, and the operation and effect are exactly the same as those in FIG. 1.

[Effects of the Invention] As described above, according to the configuration of the switch circuit of the present invention, the control input terminals can be narrowed down without any problem without using a large resistance element, making it suitable for monolithic implementation. Become.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of this invention, Fig. 2 is a circuit diagram showing Fig. 1 with reverse polarity, Fig. 3 is a conventional circuit diagram, and Fig. 4 is a circuit diagram of an application filed prior to this invention. FIG. R,, R2・・・・・・Resistance

Claims (1)

[Claims] The base connects to the control input terminal directly or through a resistive element,
It has a transistor whose emitter is connected to a reference potential point via a resistive element and whose collector is connected to an input terminal of a current mirror circuit, and an output terminal of the current mirror circuit is connected to a control input terminal of a switching element. A switch circuit characterized by: