JPH0481894B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a semiconductor switch circuit operated by an optical signal.

(Background Art) FIG. 3 shows a conventional semiconductor switch circuit. In this circuit, two photovoltaic diode arrays 1 and 10 are used so that incident light is simultaneously irradiated onto the two photovoltaic diode arrays 1 and 10. When there is incident light, the driving FET 4 consisting of a depletion mode JFET
is turned off by the output voltage of the photovoltaic diode array 10, and the gate-source capacitance of the output MOSFET 3 is set to the output voltage of the photovoltaic diode array 1.
The output of the battery charges the battery quickly. Next, when there is no incident light, it is used for depletion mode driving.
The charge accumulated between the gate and source of FET4 is discharged through resistor 9, and
The potential difference between the gate and source disappears. Eventually, the depletion mode driving FET 4 turns on, rapidly discharging the charge stored in the gate-source capacitance of the output MOSFET 3, and turning the output MOSFET 3 off.

In this conventional example, in order to rapidly charge and discharge the gate-source capacitance of the output MOSFET 3, a photovoltaic diode array 10, a resistor 9, and a depletion mode driving FET are used.
4, but photovoltaic diode array 1
0 needs to be constructed by arranging ten or more photovoltaic diodes in series, and when trying to manufacture the drive circuit for the output MOSFET 3 surrounded by the broken line in Fig. 3 using a single-chip semiconductor integrated circuit, the chip The problem is that the photovoltaic diode array 10 occupies a large space on top, increasing the chip area and reducing yield.

(Object of the Invention) The present invention has been made in view of the above-mentioned points, and its purpose is to provide output power using only one series of photovoltaic diode arrays.
To provide a semiconductor switch circuit which can rapidly charge and discharge the gate-source capacitance of a MOSFET, increase input sensitivity, and enable high-speed operation.

(Disclosure of the Invention) As shown in FIG. 1 or 2, the semiconductor switch circuit according to the present invention includes a photovoltaic diode array 1 that receives an optical signal and generates a photovoltaic force;
A resistor 2 is connected in series with the photovoltaic diode array 1, and the photovoltaic force of the photovoltaic diode array 1 is applied between the gate and source via the resistor 2 to change the impedance state from the first impedance state to the first impedance state. Output MOSFET that switches to 2 impedance states
3, and the drain and source are connected between the gate and source of the output MOSFET 3, and the gate and source are connected to both ends of the resistor 2, so that when the photovoltaic diode array 1 generates a voltage, the resistor 2 A depletion mode driving FET 4 is biased into the off state with a voltage across the terminals, and a pair of terminals are respectively connected to the pair of ends of the resistor 2, and the depletion mode When a voltage higher in absolute value than the threshold voltage of the driving FET 4 in the depletion mode is applied in a direction that biases the driving FET 4 to the off state, the normally-off element 5 conducts in that direction. A voltage is applied to the normally-off element 5 only through the pair of terminals, and the output current is applied to the normally-off element 5 when it is conductive.
It is connected to charge the gate-source capacitance of MOSFET3.

Examples of the present invention will be described below.

Embodiment 1 FIG. 1 shows a circuit of an embodiment of the present invention. In this embodiment, a Zener diode 5a is used as the normally-off element 5, and this Zener diode 5a has a Zener voltage higher than the threshold voltage of the drive FET 4, and when conductive, the Zener diode 5a For output with current
The polarity is connected to charge the gate-source capacitance of MOSFET3.

As the output MOSFET 3, an enhancement mode N-channel MOSFET is used, and the load 7 and power supply 8 are connected so that the drain side has a positive potential with respect to the source side. In addition, in this embodiment, the depletion mode driving FET 4 is a junction FET (JFET).
is used. The photovoltaic diode array 1 receives optical signals from light emitting elements such as light emitting diodes.

The operation of the circuit according to the embodiment shown in FIG. 1 will be explained below. When an optical signal is received, the photovoltaic diode array 1 generates a current. This current flows to the resistor 2 via the drive FET 4 which is normally in an on state. When the voltage generated across the resistor 2 exceeds the threshold voltage of the drive FET 4, the drive FET 4 is turned off. This allows the current from the photovoltaic diode array 1 to be directed to the output
Charge the gate-source capacitance of MOSFET3,
By increasing the gate potential of MOSFET3,
Move MOSFET3 from OFF state to ON state. During this transient state, the drain potential of MOSFET 3 drops from the power supply voltage to zero potential. Therefore, the potential difference between the gate and drain of the MOSFET 3 also changes significantly, and it is necessary to discharge the charge stored in the capacitance between them through the photovoltaic diode array 1. This discharge time occupies most of the response time of the entire circuit. This discharge time is determined by the current flowing through the photovoltaic diode array 1 and the resistor 2. If the resistance value of the resistor 2 is large, the current flowing therethrough will be small and the response time will be slow. On the other hand, if the resistance value of this resistor 2 is large, the drive FET 4 can be activated by a small amount of photocurrent.
It can be turned off, improving input sensitivity.
Therefore, in order to speed up the response time while maintaining good input sensitivity, a Zener diode 5a is connected across resistor 2, and output MOSFET 3 is turned off.
During the transition time from the ON state to the ON state, current flows through the Zener diode 5a, shortening the response time. When the transient state ends, that is, the discharge of the gate-drain capacitance of the output MOSFET 3 and the charging of the gate-source capacitance are completed, and the gate-drain capacitance of the output MOSFET 3 is completed.
When the source-to-source voltage increases, the current flowing through the resistor 2 decreases, and the voltage drop in this portion decreases, and the Zener diode 5a becomes non-conductive when the voltage drops below the Zener voltage. After that,
A small amount of current flows between the drain and source of the driving FET 4, and the voltage generated across the resistor 2 keeps the driving FET 4 in a high impedance state.

When no optical signal is incident, the current from the photovoltaic diode array 1 disappears. For this reason, the gate-source voltage of drive FET4 decreases,
Drive FE4 turns on and output
The charge accumulated in the gate-source capacitance of MOSFET 3 is rapidly discharged through drive FET 4. As a result, the output MOSFET 3 is turned off, and the connection between the relay output terminals 6 and 6' is cut off. Note that the accumulated charge in the gate-source capacitance of the drive FET 4 will be discharged via the resistor 2, but the drive FET 4 is connected to the output MOSFET.
Since the capacity is much smaller than that of Type 3, the time required for its discharge is short.

Embodiment 2 FIG. 2 shows another embodiment of the present invention. In this embodiment, the normally-off element 5 includes:
An enhancement mode FET5b with the gate and drain shorted is used, and this FET5b
has a threshold voltage higher than the threshold voltage of drive FET 4, and when conductive, its drain current flows through the gate of output MOSFET 3.
Connected to the polarity to charge the source-to-source capacitance.

In enhancement mode FET 5b, when no voltage is applied between the gate and source, the drain and source are in the OFF state, and when a voltage higher than a predetermined threshold voltage is applied between the gate and source, The drain and source become conductive. Therefore, if the gate and drain are used with a short circuit, the drain and source will become conductive only when the voltage between the drain and source exceeds a predetermined threshold voltage, and the first It can be replaced with the Zener diode 5a in the illustrated embodiment. The other operations of the embodiment shown in FIG. 2 are the same as those of the embodiment shown in FIG. 1, and therefore redundant explanation will be omitted.

In each of the above embodiments, a junction type FET is used as the depletion mode driving FET 4.
(JFET), but a depletion mode MOSFET or SIT may also be used. Also,
The output MOSFET 3 can also be replaced with a P-channel type or depletion mode type.

(Effects of the Invention) As described above, in the present invention, the photovoltaic force of the photovoltaic diode array is applied between the gate and source of the output MOSFET via the resistor, and the photovoltaic force is applied between the gate and source of the output MOSFET. Since the depletion mode drive FET connected to is biased off by the voltage across the resistor, the output MOSFET and drive FET are controlled by a 1 series photovoltaic diode array. Can also be used for driving in parallel with the resistor
A voltage higher in absolute value than the threshold voltage of the FET is used to drive the depletion mode.
Since we connected a normally-off element that conducts when the voltage is applied in a direction that biases the FET into the off state, during the transient period when the photovoltaic diode array generates voltage, the output is output via the normally-off element. This has the effect that the gate-drain capacitance of the MOSFET can be rapidly discharged, and the switching time can therefore be shortened.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of one embodiment of the present invention, FIG. 2 is a circuit diagram of another embodiment of the present invention, and FIG. 3 is a circuit diagram of a conventional example. 1 is a photovoltaic diode array, 2 is a resistor,
3 is an output MOSFET, 4 is a drive FET, 5 is a normally-off element, 5a is a Zener diode,
5b is an enhancement mode FET.

Claims (1)

[Claims] 1. A photovoltaic diode array that receives an optical signal and generates a photovoltaic force, a resistor connected in series with the photovoltaic diode array, and a photovoltaic diode array that generates a photovoltaic force. The output MOSFET is switched from the first impedance state to the second impedance state by applying power between the gate and source via an electrical resistor, and the drain and source are connected between the gate and source of the output MOSFET. is,
A depletion mode driving FET is connected between the gate and the source to both ends of the resistor, and is biased to an off state by the voltage across the resistor when voltage is generated for the photovoltaic diode array; The depletion mode driving FET has terminals connected to the pair of ends of the resistor, and a voltage higher in absolute value than the threshold voltage of the depletion mode driving FET is applied between the pair of terminals. and a normally-off element that conducts in that direction when a voltage is applied in a direction that biases the terminal to an off state, and the normally-off element conducts in that direction when a voltage is applied only through the pair of terminals, The output MOSFET is
A semiconductor switch circuit characterized in that the semiconductor switch circuit is connected to charge the gate-source capacitance of the semiconductor switch circuit. 2. The semiconductor switch circuit according to claim 1, wherein the normally-off element is a Zener diode having a Zener voltage higher in absolute value than a threshold voltage of a driving FET. 3 The normally off element is an enhancement mode element having a threshold voltage higher in absolute value than the threshold voltage of the driving FET.
2. The semiconductor switch circuit according to claim 1, wherein the semiconductor switch circuit is a FET, and the gate and drain of the FET are short-circuited.