JPS58105626A - Switch using photocoupler - Google Patents

Abstract

PURPOSE:To save electric power by using two semiconductor light emitting elements and a photocoupler connecting photodetectors consisting of diodes opposed to said elements between the gate and source of an FET in parallel. CONSTITUTION:An LED8 is opposed to a photocell group 10, and an LED7 is opposed to a photocell group 9 and a photodiode 12 which are optically insulated from the LED8 and photocell group 10. In case of using an n channel type MOS FET11 when the titled switch is to be turned on, the LED8 is turned on to generate photoelectromotive force in the photocell group 10 and positively charge the gate capacity of the MOSFET11. Since the charge of the gate capacity is not almost reduced even if the LED8 is turned off and electromotive force disappears from the photocell group 10, the switch can be driven by a pulse-like signal. When a switch is to be turned off, the LED7 is turned on to generate electromotive force in the photocell 9 and simultaneously connect the photodiode 12, so that the gate capacity is discharged. By said configuration it is unnecessary to continue to turn on the LED8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a circuit for driving an MO8 field effect transistor (hereinafter referred to as MOS FET) switch using a photocoupler at low power. There are horizontal and vertical types of MOSFETs, but the horizontal type is often used to create a structure that can be applied to semiconductor integrated circuits, but in order to achieve a withstand voltage, the conduction resistance is large, and the withstand voltage conduction resistance ratio is ftI type. is more advantageous.

On the other hand, in order to obtain a bidirectional switch, it is necessary to connect two MOS FgTl, 2 in opposite directions in series, as shown in FIG. If this is done, there will be a practical problem in the potential relationship of the gate drive, and it will not be possible to switch higher voltages within the practical fishing force voltage range of about 5V.

What is the purpose of this invention? The object of the present invention is to obtain a switch using a semiconductor element that can handle i6% pressure.

The switch of the present invention uses two semiconductor light-emitting elements, and a diode light-receiving element facing each other is a MOS F.
A switch using a photocoupler connected in parallel between the ET gate and source is obtained.

Compared to conventional optical coupling switches, the optical coupling switch circuit of this invention can drive the switch with pulses, enabling high-speed operation. The conventional circuit shown in FIG.
A photocell 4 is provided opposite to 3, and this photocell 4 provides the gate voltage of the MO8FETs together with a resistor 6, so it is necessary to keep the LED 3 lit when the switch is ON. By using the high insulation properties of the gate, it is possible to drive with low duty pulses and save power. Furthermore, the ON and OK'F speeds of the MO8FET can be freely controlled up to the optical coupling speed.

Next, the structure and operation according to one embodiment of the present invention will be explained with reference to FIG. That is, I, ED8 and photocell # (connect in series f to obtain the voltage necessary to drive the photocell)
The LED 7, the photocell group 9, and the photodiode 12 face the LED 7 while being insulated from the photocell group 9 and the photodiode 12. First, when turning on the switch, MO8F
When using an N-channel type for ETt 1, the LED 8 is turned on to generate a photovoltaic force in the photocell group 10, and the MO8
Charge the gate capacitance of FnT11 positively. After this LWD
8 disappears and the electromotive force disappears in the photocell group 10, the charge in the gate capacitance hardly escapes, so that driving can be performed in a pulsed manner. Also, when turning the switch to 0FFK, the LED 7 is turned on to generate a force to the photocell 9, and the photodiode 1
By simultaneously making 2 conductive, the charge from the gate capacitance is discharged.

In the conventional photocoupler MO8FET switch shown in FIG. .

[, WD3 has the disadvantage that the power consumption also increases.

According to the present invention - HMtJ8 FETI 1 turns on? ! : L W D 7 point mf Lou 4-tldMO
8PET 11 Since the light continues to be ON, there is no need to keep the LED emitting light.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram when MO8FET switch and switch are made bidirectional. 1 and 2...MO8PET. FIG. 2 is a circuit diagram of a switch using a conventional photocoupler. 3...LMDl 4...Photocell, 5
...MOSFET, 5...Leak resistance. FIG. 3 is a circuit diagram of a switch using a photocoupler according to an embodiment of the present invention. 7...LED, 8...LED, 9...
...Photocell, 10...Photocell, 11.
...MO8F E T0 million l Figure 6.3 Figure

Claims (1)

[Claims] Two semiconductor light-emitting elements that can be driven independently are provided, one of which is opposed to the first circuit consisting of multiple photocells and a reverse-biased photodiode connected in series, and the other is connected with multiple photocells in series. The second professional electrodes are connected in series, and the midpoint potential is applied to the gate of the field effect transistor.
A switch using a photocoupler, the other end of which is connected to the source of the field effect transistor.