JPS61166223A - Composition type switch circuit - Google Patents

Abstract

PURPOSE:To simplify the driving power supply and the driving circuit by providing additionally the 3rd FET, a diode, a Zene diode and a capacitor to a conventional circuit comprising the combination of a bipolar transistor (Tr) and an FET. CONSTITUTION:When a positive voltage drive signal is fed between gate and emitter of the circuit of this invention, the bipolar Tr3 is turned on. The energy charged in a capacitor 10 is discharged through a resistor 6 and an n-channel FET5. The charging voltage becomes a bias voltage becomes a bias voltage of an FET4. Thus, the bias voltage is ensured sufficiently by selecting a sufficient capacitance to the capacitor 10 so as to ensure a sufficient bias voltage when the Tr3 is turned off and selecting properly a discharge resistor 6. On the other hand, when the voltage drive signal is zero, the Tr3 is turned off. The capacitor 10 is charged to a constant voltage decided by a Zener diode 9 via a resistor 8 and a diode 7 during this period.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a composite switch circuit composed of a bipolar transistor and a field effect transistor (FET).

[Conventional technology]

One conventional example of such a composite switch circuit is shown in FIG. 3, in which a bipolar transistor 3 is combined with two types of field effect transistors, an N-channel field effect transistor 1 and a P-channel field effect transistor 2. Are known. These field effect transistors
and 2 are inverted positive and negative signals that enable the bipolar transistor 3 to be turned on and off.The gates are connected together to form a common terminal, and the entire circuit is modularized as a three-terminal switch circuit.

Next, to briefly explain the operation, when a positive voltage signal is applied between the gate terminal G and emitter terminal 8 of this modularized circuit, the N-channel field effect transistor 1 is turned on, and the P-channel field effect transistor 2 is turned on.
is off. Conversely, if a negative voltage signal is applied, N
Channel field effect transistor 1 is turned off, and P channel field effect transistor 2 is turned on. This results in
Bipolar transistor 3 is turned on and off, but 41
The P-channel field effect transistor 2 connected between the base and emitter of the bipolar I-transistor 3 is necessary to improve the turn-off characteristics of the bipolar I-transistor 3.

Furthermore, as another conventional example, as shown in FIG. There are also devices in which one terminal is driven separately.

[Problem that the invention seeks to solve]

However, the circuit shown in FIG. 3 requires both positive and negative drive signals to drive the N-channel field effect transistor and the P-channel field effect transistor 2, and therefore has the disadvantage that the drive circuit becomes complicated. The P-channel field effect transistor 2 has a disadvantage in that it is theoretically more expensive than the N-channel field effect transistor 1.

In the case of the circuit shown in FIG. 4, the above-mentioned disadvantage of being expensive can be solved, but voltage drive signals must be separately supplied to each N-channel field effect transistor 1 that constitutes the switch circuit. However, the drive circuit becomes more complicated, and the number of terminals of the switch circuit increases compared to the one shown in FIG. 3, making it difficult to use.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a composite switch circuit which eliminates the disadvantages of the conventional example and which can simplify the drive power supply and drive circuit.

[Means for solving problems]

In order to achieve the above object, the present invention connects a first field effect transistor between the collector and emitter of a bipolar transistor in Darlington, and connects a second field effect transistor of the same type between the base and emitter of the bipolar transistor. , providing a circuit for extracting the gate drive power for the second field effect transistor from between the collector and emitter of the bipolar transistor, and further bridging the voltage applied from this circuit to the gate of the second field effect transistor. The gist of the present invention is to provide a third field effect transistor that enables the above, and to connect the gate of the third field effect transistor to the gate of the first field effect transistor.

[Effect]

According to the present invention, since the second field effect transistor uses the main circuit as its power source, there is no need to provide a separate power supply circuit, and since there is an inverting circuit for matching the drive signals, the drive signals are unified. It can be simplified by reducing the number of input terminals.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram showing one embodiment of the composite switch circuit of the present invention, and the same components as in FIGS. 3 and 4 showing the conventional example are given the same reference numerals.

That is, in the figure, 3 is a bipolar transistor, 1 is a first N-channel field effect transistor connected between its collector and emitter, and 2 is a second N-channel field effect transistor connected between the base and emitter of the bipolar transistor 3. It is an effect transistor.

The configuration up to this point is the same as the conventional example shown in FIG. 4, but in the present invention, the gate of the second N-channel field effect transistor 4 is connected between the collector and emitter of the bipolar transistor 3, and the gate drive power is obtained from here. I did it like that.

Furthermore, a third N-channel field-effect transistor 5 is inserted and connected between the connection point of the gate of the second N-channel field-effect transistor 4 serving as the gate drive power source and the source of the transistor 4. This third N-channel field effect transistor 5 is used for signal inversion in order to match the two drive signals of the transistor 1.4. 5 and the gate of the first field effect transistor 1 were connected to each other.

In addition, the collector of the bipolar transistor 3 and the third N
A resistor 8 is connected between the drain of the channel field effect transistor 5. Insert a series circuit of diode 7 and resistor 6, and
A capacitor 10 and a Zeli diode 9 are each connected in parallel to the series circuit of the third N-channel field effect transistor 5.

Next, the main operations will be explained.

When a positive voltage drive signal is applied between the gate and emitter of the circuit of the present invention, transistor 3 is turned on, which means that N-channel field effect transistors 1 and 5 are turned on, while N-channel field effect transistor 4 is turned on. This is because when the transistor 5 is turned on, the gate and source are short-circuited and the transistor 5 is turned off. Further, the energy stored in the capacitor 10 is discharged via the resistor 6 and the N-channel field effect transistor 5. The charging voltage of this capacitor 10 becomes the bias voltage of the transistor 4.

Therefore, with regard to this capacitor 10, it is sufficient to have sufficient capacitance in advance to ensure a sufficient bias voltage when the bipolar transistor 3 is turned off, that is, when the transistor 4 is turned on, and if the discharging resistor 6 is appropriately selected. A suitable bias voltage is ensured.

On the other hand, when the voltage drive signal becomes zero, transistor 3 is turned off, but this is because N-channel field effect transistors 1 and 5 are turned off, and N-channel field effect transistor 4 is turned off due to transistor 5 being turned off. This is because it is biased by the charging voltage of the capacitor 10 via the capacitor 10 and the resistor 6 and is turned on. As a result, the bipolar transistor 3 completes its turn-off operation and enters the blocking state. During this period, the capacitor 10 is charged via the resistor 8 and diode 7 to a constant voltage determined by the Zener diode 9 (below the gate-source breakdown voltage).

FIG. 2 shows another embodiment of the invention, which is designed to prevent load current from flowing through the parasitic diode of the N-channel field effect transistor 1.4.
A diode 11 is inserted in series with .

Generally, this parasitic diode is of a low-speed type, and therefore, when used in switching applications, extremely large losses occur. Therefore, in this embodiment, this parasitic diode can be made irrelevant in the circuit configuration.

〔Effect of the invention〕

As described above, the composite switch circuit of the present invention, which combines a bipolar transistor and a field effect transistor, can simplify the drive power supply and the drive circuit, can be manufactured at low cost, and can be made into a module with a small number of terminals. It is also possible to expand.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the composite switch circuit of the present invention, Fig. 2 is a circuit diagram showing another embodiment same as the above, Fig. 3 is a circuit diagram of a conventional embodiment, and Fig. 4 is a circuit diagram showing another embodiment. FIG. 2 is a circuit diagram of a conventional example. 1.4.5...N-channel field effect transistor 2
...P-channel field effect transistor 3...Bipolar transistor 6.8...Resistor 7,11...Diode 9
... Zener diode IO ... capacitor

Claims (1)

[Claims] between the collector and emitter of the bipolar transistor.
A second field effect transistor of the same type is connected between the base and emitter of the bipolar transistor, and the gate drive power supply for the second field effect transistor is connected to the collector of the bipolar transistor. A third field effect transistor is provided which makes it possible to bridge the voltage applied from the circuit to the gate of the second field effect transistor. A composite switch circuit characterized in that the gate of the first field-effect transistor is connected to the gate of the first field-effect transistor.