JPH0364211A - Switching circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching circuit, and more particularly to a switching circuit for large current control using transistors.

[Conventional technology]

FIG. 3 is a circuit diagram showing a conventional switching circuit for large current control. In the figure, Ql and Q2 are NPN) transistors, and these transistors are connected in a Darlington manner. The base of transistor Q1 is connected to input terminal 1, and the common connection point between the emitter of transistor Q1 and the base of transistor Q2 is connected to GN through a leakage cut resistor R1.
At D, common connection points of the collectors of the transistors Ql and Q2 are connected to the constant current source 2, respectively. The leakage cut resistor R1 prevents current from leaking in the direction of the constant current source 2 → the collector of transistor Q1 → the emitter of transistor Q1 and the base of transistor Q2 when transistor Q1 is not completely turned off, and transistor Q2 does not turn ON. In addition, it is provided to allow leakage current to flow to GND. Q3 is a switching NPN transistor in the output stage, and has a collector connected to the output terminal 3, a base connected to the cathode of the level shifting diode D1, and an emitter connected to GND. Also, the base of transistor Q3
A leakage cut resistor R2 is connected between the emitters. The anode of the level shift diode D1 is the transistor Q1. It is connected to the collector common connection point of Q2. The leakage cut resistor R2 is provided to flow the leakage current to GND so that a part of the large current I leaks from the collector to the base of the transistor Q3, causing the base potential to rise and turning the transistor Q3 on. be.

Next, the operation will be explained. When "L" is input to the input terminal 1, the transistor Q1 is turned off, so that the current I2 is not supplied from the constant current source 2 to the base of the transistor Q2. Therefore, the base potential of transistor Q2 is 'L'
Therefore, transistor Q2 is turned off. Current I2 from constant current source 2 is supplied to the anode of diode D1,
Diode D1 is turned on. The current I2 is the diode D
1 to the base of the transistor Q3, and the transistor Q3 is turned on. Large current I is transistor Q3
Flows to GND via. Therefore, the potential of the output terminal 3 becomes "L".

On the other hand, when "H" is input to the input terminal 1, the transistor Q1 is turned on, so that the current I2 is supplied to the base of the transistor Q2. The base potential of transistor Q2 is “
"H" and transistor Q2 turns on. Constant current source 2
The current I2 flows to GND through the transistor Q2, the cathode potential of the diode D1 becomes "L", and the diode D1 is turned off. Then, the base charge of the transistor Q3 is extracted to GND via the resistor R2, and the transistor Q3 is turned off. Since the large current ■ is supplied to the output terminal 3, the potential of the output terminal 3 becomes "H".

Here, the role of the level shifting diode D1 will be described. Transistor Q1. When Q2 is ON,
The potential VA on the anode side of the diode D1 is V −V +V ・(1)A
BF2 5atl V8E2: Base-emitter voltage vsatl of transistor Q2: Saturation voltage of transistor Q1. On the other hand, the potential VK on the cathode side of the diode D1 is VK''=vBE3-(2)V
BE3: Becomes the base-emitter voltage of transistor Q3. Generally, the base-emitter voltage of a transistor is about 0.7 (V), and the saturation voltage is about 0.2 (V). Therefore, the potentials V and VK are expressed by formula (1).

(From formula 2), they are approximately 0.9 (V) and approximately 0.7 (V), respectively. In this case, if the level shift diode D1 is not provided, even though the transistors Ql and Q2 are turned on, Current is supplied to the base of transistor Q3,
Transistor Q3 is always turned on, making switching impossible. Therefore, a level shift diode D1 is provided, and when the transistors Ql and Q2 are turned on and turned low, the diode D1 is turned off to prevent current from being applied to the base of the transistor Q3, thereby enabling switching.

Thereafter, when "L" is input to input terminal 1 again, transistor Q1 is turned off. Then, as the base charge of the transistor Q2 passes through the resistor R1 to GND, the transistor Q2 is turned off, and "H" is outputted to the output terminal 3 as described above.

[Problem to be solved by the invention]

Conventional switching circuits are configured as described above, so if you try to increase the switching speed, the resistance R
1, the resistance value of R2 is made small, and the transistor Q2. Q3
It is necessary to allow the base charge to quickly escape to GND. Furthermore, it is necessary to increase the switching ability of the transistors Ql and Q2.

However, if the resistance value of the resistor R1 is reduced and the transistor Q1 is completely turned on, the current summer 2 through the transistor Q1 will flow not only to the base of the transistor Q2 but also to the GN
There is also a problem that the current is shunted to D, increasing wasteful current. Furthermore, if the resistance value of resistor R2 is reduced, when diode D1 is turned on, current I through diode D1
There is a problem in that the current is shunted not only to the base of the transistor Q3 but also to GND, increasing unnecessary current.

Furthermore, in order to increase the switching ability of the transistors Ql and Q2, it is necessary to increase the size of the transistors Ql and Q2, which inevitably causes a problem that the pattern area becomes larger when integrated circuits are formed.

The present invention has been made to solve the above-mentioned problems, and aims to provide a switching circuit with increased switching speed without increasing unnecessary current and pattern area.

[Means to solve the problem]

A switching circuit according to the present invention includes at least a constant current source and a first transistor whose control electrode is supplied with a human input signal, whose first electrode is connected to the constant current source, and whose second electrode is grounded. It includes a buffer that outputs a current according to the human input signal, and a 0N output according to the current given to the control electrode.
10 F F L, applied to a switching circuit including a switching transistor that switches current, and a diode whose anode is connected to the output of the buffer and whose cathode is connected to the control electrode of the first transistor.

In the switching circuit according to the present invention, the control electrode is connected to the second electrode of the first transistor, the first electrode is connected to the control electrode of the first transistor, and the second electrode is grounded. Equipped with transistors.

[Effect]

The second transistor in this invention is turned on in conjunction with the first transistor to extract charge from the control electrode of the switching transistor.

When the diode is on, the second transistor is off, and all current from the constant current source is applied to the control electrode of the switching transistor. Since the control electrode of the second transistor is supplied with the signal amplified by the first transistor, there is no need to increase the degree of signal amplification, and the second transistor can be made smaller.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of a switching circuit according to the present invention. In the figure, the difference from the conventional circuit shown in FIG. 3 is that the resistor R2 is eliminated and an NPN (NPN) transistor Q4 is newly provided in its place. The transistor Q4 has a base connected to the emitter of the transistor Q1, a collector connected to the base of the transistor Q3, and an emitter connected to the emitter (ground) of the transistor Q3.

Other configurations are the same as before.

Next, the operation will be explained. When "L" is applied to the input terminal, as in the conventional case, the transistor Ql.

Q2 turns OFF. Further, transistor Q4 is also turned off. Therefore, electricity! I2 is supplied to the base of transistor Q3 via diode D1, and transistor Q3 is turned on.
do. Since the large current I flows to GND via the transistor Q3, the potential of the output terminal 3 becomes "L".

Next, when the potential of input terminal 1 changes from "L" to "H", transistors Ql, Q2 . Q4 turns on. When the transistors Ql and Q2 are turned on, the current I2 flows to GND via the transistor Q2, as in the conventional case. Since the anode potential drops, the diode D1 is turned off. On the other hand, transistors.

4 is turned on, the base charge of transistor Q3 is quickly extracted, and the transistor Q3 is turned on. 3 is instant OF
F. Therefore, the potential of the output terminal 3 is also instantly reversed from "L" to "H".

In this embodiment, the base charge of the transistor Q3 is quickly drawn out by turning on the transistor Q4 in conjunction with the transistors Ql and Q2, so the current I is a large current and there is a large residual charge at the base of the transistor Q3. Quick switching is possible even in the case of Also, connect the base of transistor Q4 to transistor Q
1, the base current of transistor Q4 becomes a current amplified by transistor Q1. The amount of current that transistor Q4 draws from the base of transistor Q3 is (base current of transistor Q4) x
(current amplification degree of transistor Q4), and this current amount is set to I2, which is the same as the current value of constant current source 2. The reason for this setting is that the maximum current supplied to the base of transistor Q3 is I2. Since the base current of transistor Q4 is given the amplified current as described above,
Compared to the case where the base of the transistor Q4 is directly connected to the input terminal 1, the current amplification degree of the transistor Q4 can be reduced, and the size of the transistor Q4 can be reduced. Therefore, when integrated circuit, transistor Q1.
The increase in pattern area is smaller than when the pattern area is increased to increase the switching ability of Q2. Further, when the diode D1 is ONL, the transistor Q4 is 0FFt, so the current I2 through the diode D1 is all given to the base of the transistor Q3, and there is no need to divide it as in the conventional case. As a result, wasted current is eliminated. Note that transistor Q3 is 0FF.
Since transistor Q4 is ON when the voltage is L,
Leakage current from the collector to the base of transistor Q3 flows to GND via transistor Q4.

FIG. 2 is a circuit diagram showing another embodiment of the switching circuit according to the present invention. In this embodiment, the transistor Q4 is removed from the circuit shown in FIG. 1, and the connection is changed so that the transistor Q2 serves as the transistor Q4.

In other words, the collector of transistor Q2 is connected to transistor Q
It is connected to the base of 3. The rest of the configuration is the same as the circuit shown in FIG.

Next, the operation will be explained. When "L" is manually applied to input terminal 1, transistor Q
l, Q2 is turned off. The current I2 is supplied to the base of the transistor Q3 via the diode D1, the transistor Q3 is ONL, and the potential of the output terminal 3 becomes "L".

When the potential of the input terminal 1 changes from "L" to "H", transistors Ql and Q2 are turned on. When transistor Q2 turns on, charge is quickly extracted from the base of transistor Q3, so transistor Q3 turns off instantaneously. Therefore, the potential of output terminal 3 is also instantaneously “
The signal is reversed from "L" to "H", allowing quick switching as in the above embodiment.

In this embodiment, the role of transistor Q4 shown in Figure 1 (the role of quickly extracting charge from the base of transistor Q3) is assigned to transistor Q2, which exists in the conventional circuit (Figure 3), so the number of elements increases. Without,
Can be made smaller. Therefore, the pattern area can be made smaller than when the switching circuit is integrated.

In the embodiment shown in FIG. 1, a case has been described in which the base of the transistor Q4 is connected to the emitter of the transistor Q1, but the base of the transistor Q4 may be connected to the emitter of the transistor Q2. In this case, the current amplification degree that transistor Q4 should have can be further reduced, and transistor Q4
It is possible to reduce the size of the circuit, and when it is integrated into an integrated circuit, the pattern area can be further reduced.

〔Effect of the invention〕

As described above, according to the present invention, since the second transistor is provided which is turned on in conjunction with the first transistor and extracts the charge from the control electrode of the switching transistor, even when switching a large current, it can be done instantly. This has the effect that the switching transistor can be turned off and high-speed switching can be performed. Also, when the diode is ONL, the second transistor is OFF.
This has the effect that all the current from the constant current source is applied to the control electrode of the switching transistor, eliminating wasted current. Furthermore, since the signal amplified by the first transistor is given to the control 71ttM of the second transistor, there is no need to increase the degree of signal amplification, and the second transistor can be miniaturized. In this case, there is an effect that the pattern area does not become significantly large.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the switching circuit according to the present invention, FIG. 2 is a circuit diagram showing another embodiment of the switching circuit according to the present invention, and FIG. 3 is a circuit diagram showing a conventional switching circuit. It is a diagram. In the figure, 2 is a constant current source, Ql, Q3 and Q4 are N
The PN transistor and Dl are level shift diodes. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] (1) A first transistor including at least a constant current source and a first transistor whose control electrode is supplied with an input signal, whose first electrode is connected to the constant current source, and whose second electrode is grounded; a buffer that outputs a current according to a signal; a switching transistor that switches the current by turning ON/OFF according to the current applied to the control electrode; an anode connected to the output of the buffer, and a cathode connected to the first
diodes each connected to a control electrode of a transistor, the control electrode being connected to a second electrode of the first transistor, and the first electrode being connected to a control electrode of the first transistor. 1. A switching circuit comprising: a second transistor whose second electrode is grounded;