JPH0230207B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bidirectional solid state switch using field effect transistors.

Conventionally, mechanical switches have been used especially when the potential levels of the switch control circuit system and the switched circuit system are different, or when it is desired to keep both potentials independent, such as relatively high voltage AC signals such as commercial voltage. Contact switches and mercury relays have been used.
However, as electronic circuits become more solid-state and more integrated, and electronic devices as a whole become smaller, there is an increasing demand for solid-state mechanical contact switches. Up to now, many examples of solid-state switches in which the switch control circuit and the circuit to be switched are insulated and separated have been researched and developed, such as optically coupled switches using light emitting diodes and optical PNPN elements. but,
When using a PNPN element, it is easy to cause false firing due to surge voltage, and it is difficult to turn off DC current.
It has weaknesses such as the occurrence of offset voltage due to the PN junction near zero voltage. Furthermore, due to the principle of operation, bipolar elements are susceptible to so-called thermal runaway when high voltage is applied and the junctions break down, and when used in high-output control switches, there are significant restrictions on use due to temperature rise. . FIG. 1 is an example of a solid-state AC switch using a field effect element, which has been proposed in order to solve the various drawbacks of switches using bipolar elements.

In Fig. 1, 1 and 2 are MOS field effect transistors whose gate electrodes and source electrodes are commonly connected to each other, and 3 is a transistor that ensures isolation between the input signal source and the circuit to be switched, and only transmits the switch drive signal. It is a transformer for transmission. This switch transmits a pulse-like drive input signal from the input signal end via the transformer 3 to the gate circuit side of the field effect transistors 1 and 2 to control the gates of the field effect transistors. With this type of solid-state switch, there is no erroneous firing due to surge voltage, unlike when a PNPN element is used, the DC voltage can be easily turned on and off, and no offset voltage occurs near zero voltage. Furthermore, since a field effect transistor is used, there is no fear of thermal runaway even when handling high power, and the switch is highly reliable. However, this type of switch uses a transformer that is extremely difficult to miniaturize, so there are essentially limits to miniaturization and integration. In other words, as long as a transformer is used, the entire solid-state switch circuit shown in Figure 1 can be housed in one package, such as various IC packages, or even multiple independent switch circuits can be housed in one package. It was difficult to develop devices that could be housed inside the device. An object of the present invention is to provide a solid-state AC switch that can be downsized and integrated while taking advantage of the advantages of field effect transistors.

According to the present invention, a solid state alternating current is connected between the drain electrodes of two field effect transistors of the same conductivity type, in which the gate electrodes and the source electrodes are commonly connected and a shunt resistance is provided between the gate and the source. In the switch, at least the output end of the driving pulse power source and the gate electrode side end of the field effect transistor, and the ground electrode end of the driving pulse power source and the source electrode side end of the field effect transistor, The output terminal of the field effect transistor is connected to the gate electrode side end of the field effect transistor by a capacitor, and a pulse voltage train is generated between the gate electrode side end of the capacitor and the source electrode side end by a driving pulse input voltage train. A solid-state AC switch is obtained, characterized in that the rectification and smoothing circuit provided between the gate electrode side end of the capacitor and the gate electrode of the field effect transistor performs rectification and smoothing, and serves as the DC gate input of the field effect transistor. It will be done.

The present invention will be explained in detail below with reference to drawings showing embodiments. FIG. 2a shows an equivalent circuit of an embodiment of the present invention in which two capacitors are used at the input end of the drive signal. In the figure, 1 and 2 are
a field effect transistor; 4 and 5 are switched ends corresponding to the drain of the field effect transistor;
6, 7 A capacitor installed between the input signal circuit system to cut off direct current and pass only pulse signals,
8 and 9 are drive signal input terminals, 10 is a rectifier diode for obtaining the desired gate voltage polarity and magnitude, 11 is a resistor for gate-source shunt, and 12 is a resistor for gate voltage smoothing. 13 is a drive pulse signal source, 14 is a power supply in the switched circuit that is electrically independent from the drive pulse signal source 13, and 15 is a load. In order to operate the solid-state AC switch of this embodiment efficiently, it is necessary to consider in advance the gate input capacitance of the field effect transistor, the capacitance of the diode 10, the frequency of the driving pulse signal to be used, etc., and set the resistors 11, 12 and the capacitor 6. , 7 must be selected so that most of the divided voltage of the drive pulse voltage appears at the diode 10 end. For example, in the case of this embodiment, the resistors 11 and 12 are set to 100KΩ for the gate input capacitance of approximately 100pF, and
The capacitor capacity of is set to 100pF. First, when there is no input pulse signal, field effect transistors 1 and 2
Since the gate of is grounded to the common source 16 of the transistor through resistors 12 and 11,
Field effect transistors 1, 2 are off and therefore switch ends 4, 5 are off. Next, from the pulse signal source 13, for example, the repetition frequency is
500KHz, positive pulse with pulse width 0.5μs (Figure 3a),
Alternatively, a negative pulse (FIG. 3b) with the same frequency and pulse width of 1.5 μs is applied between input terminals 8 and 9. In the series connection circuit connecting capacitor 6, diode 10, and capacitor 7 when viewed from the input terminal side, input terminal 8
When a positive pulse voltage is applied to the diode 10, since the diode 10 is in the forward direction, current flows through the diode, and charges corresponding to the applied voltage are induced in the capacitors 6 and 7. In this case, a negative charge is generated between the capacitor 6 and the diode 10, and a positive charge is generated between the diode 10 and the capacitor 7. On the other hand, in the case of a voltage of opposite polarity, the diode is in the opposite direction, and the applied voltage is connected to capacitors 6 and 7 and diode 1.
Divide into 0 and add. Here, the positive and negative charges generated between the capacitor 6 and the diode 10 and between the diode 10 and the capacitor 7 are only neutralized through the resistor 11. However, the time constant for discharging capacitors 6 and 7 and resistor 11 is 100pF×
100KΩ = 10 ^-5 sec = 10μsec, the input signal has a repetition frequency of 500KHz and a pulse width of 0.5μs, so the 6 ends of the capacitor connected to the gate electrode side will be negatively biased with respect to the source electrode side. . That is, in contrast to the input waveforms shown in FIGS. 3a and 3b, a voltage having a waveform as shown in FIG. 3c is generated at the end of the diode 10, with the source electrode side set to zero potential. Now, the gate input capacitance and resistance 12 of the field effect transistors 1 and 2 to be controlled are relative to the frequency of the driving pulse.
By choosing the value of resistor 12 to form a CR filter, the pulsed voltage across diode 10 is smoothed to produce a negative DC gate input voltage as shown in Figure 3d. When the gate input voltage exceeds the gate threshold voltage, the field effect transistor is turned on and the solid state AC switch of this embodiment is turned on. When the input pulse signal is turned off, the gate voltage is attenuated through resistor 12 and resistor 11, so that the switch returns to the off state. Here resistance 11,
Since the size of 12 is related to the on/off speed of the switch, the margin for malfunction due to noise, etc., it is necessary to select it appropriately according to the purpose and conditions of use of the switch. As explained above, the solid state AC switch of the present invention is kept in the on state if a pulsed signal voltage train is continuously input to the input signal terminals 8 and 9, and turns off when the input is cut off. Operates as a switch. That is, in the solid-state AC switch of the present invention, the input signal source side circuit and the switched side circuit are DC-separated by the capacitors 6 and 7, and on the other hand, even if the two circuits are in independent potential states, , the switch can always be controlled from the input signal source circuit side via the capacitor. Therefore, the solid state AC switch of the present invention inherits the advantages of the conventional solid state AC switch using field effect transistors shown in FIG. Since the input signal source side circuit and the switched circuit are separated using a small capacitor that can be easily switched, the switch has the feature that it is possible to downsize and integrate the entire switch.

By using a high-voltage, high-output transistor and high-voltage capacitors 6 and 7 in the solid-state AC switch of the present invention, the switch can control high voltage and large power.

FIG. 4 shows another embodiment of the present invention, which differs from the previous embodiment in that only one capacitor is provided at the signal input end on the gate input end.
However, the operation of this embodiment is almost the same as that of the switch of the first embodiment. The circuit shown in FIG. 4 is operable because there is capacitive coupling between the terminal 8 side and the switch side circuit, and this point is different from the conventional example.

The operation shown in FIG. 4 will be explained. The drive pulse signal source 13 and the switched ends 4, 5 are in a potential floating state, and accordingly, there are voltages 17, 1 between the switched ends 4, 5 and the ground potential.
8, and it can be seen that a closed circuit is apparently formed between the drive pulse signal source 13 and the ground potential of the drive pulse signal source 13 through the capacitance. Therefore, by applying a portion of the pulse voltage from the pulse signal source 13 to both ends of the diode 10, a DC bias that turns on the transistor is generated, similar to the circuit operation of FIG. 2. For this reason, the circuit shown in FIG. 4 can operate similarly to the circuit shown in FIG. 2. Therefore, when the pulse train of FIG. 3a or b is applied to the circuit of FIG. 4, the diagrams corresponding to FIGS. 3c and d are also the same.

Here, to supplement the functions of the two transistors 1 and 2, the source 1 of the two transistors
6 are connected through the substrate. Transistors 1 and 2 are connected in opposite directions, so when a voltage (alternating current) is applied, one operates in the forward direction and the other in the reverse direction. In other words, one operates as a diode and the other as a capacitor. (The drain of the transistor and the board are not connected, but there is a pn
A junction is formed. The drains of the transistors 1 and 2 serve as switched ends 4 and 5, respectively. ) That is, if there is a closed circuit surrounding the pulse signal source 13, this switch, and the switched circuit for the pulse signal for driving the switch, the pulse signal can be transmitted. In the switch of this embodiment, since the capacitor 7 is eliminated, the leakage of the signal on the switched circuit side to the pulse signal source ground potential is reduced, making it possible to switch an AC signal with a higher frequency. Of course, it goes without saying that it will become easier to downsize and integrate the switch.

FIGS. 5, 6, and 7 show still other embodiments of the present invention, all of which have improved rectification and smoothing circuits. In the switch of the present invention,
Since it is desired to input the drive signal to the gate side of the switch via the small capacity capacitors 6 and 7, the input signal must be a high-speed pulse train. On the other hand, if there is a ripple in the gate input signal of a field effect transistor, the conductivity of the transistor will be modulated, so it is desirable that the DC gate input be smooth. The switch of the embodiment shown in FIG. 5 attempts to obtain a DC gate voltage with less ripple by devising a pulse input smoothing circuit.

The embodiments of FIGS. 6 and 7 attempt to rectify the pulse input signal more efficiently and obtain a higher DC gate input voltage for the same pulse input voltage. The rectifying and smoothing circuit for the pulse input signal may be of various forms and combinations other than those shown as an embodiment of the present invention, and may be of any suitable form according to the purpose of use of the switch and in keeping with the gist of the present invention. A rectification and smoothing circuit may be used. Furthermore, if it is desired to obtain an efficiently smoothed gate input voltage, it is effective to use a sine wave that does not contain high frequency components as the drive input signal.

In the embodiments of the present invention, a so-called insulated gate transistor is used as the field effect transistor, but any field effect transistor may be used, for example, a junction field effect transistor or a static induction transistor. The solid state alternating current switch of the present invention can also be realized by using a transistor called .

[Brief explanation of drawings]

Figure 1 shows a conventional solid-state AC switch, Figure 2 shows
One embodiment of the present invention, FIG. 3 is a diagram showing drive signal waveforms of a switch of the present invention, and FIGS. 4 to 7 are diagrams showing other embodiments of the present invention. In each figure,
1 and 2 are field effect transistors, 3 is a transformer,
4 and 5 are switched terminals, 6 and 7 are input signal terminal capacitors, 8 and 9 are input signal terminals of the switch, 10 is a rectifying diode that determines the gate signal polarity, and 11
is a gate shunt resistance, 12 is a smoothing resistance, 13
14 and 15 are the AC power supply and load in the switched circuit, 16 is the common source of the field effect transistor, and 17 and 18 are the parasitics between the switched circuit and the ground terminal of the drive pulse power supply 13. Equivalent capacitances 19, 20 and 21, 22 are resistances and capacitors for smoothing, and 23 to 27 are diodes for rectification, respectively.

Claims (1)

[Claims] 1. In a solid state AC switch in which the switched end is between the drain electrodes of two field effect transistors of the same conductivity type, the gate electrodes and the source electrodes are commonly connected, and a shunt resistance is provided between the gate and the source. Among the output end of the pulse power source and the gate electrode side end of the field effect transistor, and the ground electrode end of the driving pulse power source and the source electrode side end of the field effect transistor, at least the output end of the driving pulse power source and the end thereof are connected to each other. The gate electrode side end of the field effect transistor is connected with a capacitor, and the pulse voltage train generated between the gate electrode side end and the source electrode side end of the capacitor by the driving pulse input voltage train is connected to the gate electrode side of the capacitor. side edge and
The solid-state AC switch is characterized in that it is rectified and smoothed by a rectification/smoothing circuit provided between the gate electrodes of a field effect transistor, and is used as a DC gate input of the field effect transistor.