JPS6192034A - Semiconductor relay using fet - Google Patents

Abstract

PURPOSE:To avoid a control current quantity with other switch element turned on from being affected by ambient temperature by providing a correcting means absorbing the temperature change in a pinch-off voltage of a switch element. CONSTITUTION:The 1st switch element Q1 and the 2nd switch element Q2 are both n-channel FETs and the pinch-off voltage is a negative value. A solar battery B1 is connected between a gate and a source of the element Q1 and a discharge resistor R having a positive temperature characteristic and a solar battery B2 are connected in parallel between a gate and source of the element Q2. When the ambient temperature rises, the pinch-off voltage of the element Q2 is decreased, since the resistance of the R is increased, the voltage drop across the R is increased and the bias voltage reaches the pinch-off voltage of the element Q2 or below so as to turn off the element Q2. The temperature characteristic of the pinch-off voltage of the element Q2 is cancelled and the element Q1 is turned on with the same control current regardless of the ambient temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a semiconductor relay using an FET, and more particularly to a semiconductor relay using a MOS type F'ET as a load control element.

[Background Art] In general, this type of semiconductor relay utilizes the characteristic of a MOS FET that the gate and source are in an on state and an off state at a pinch-off voltage between the gate and source. By connecting a solar cell between the gate and source of a type F'E'T and by placing the light-emitting surface of the light-emitting diode opposite to the light-receiving surface of the solar cell, when a control current is passed through the light-emitting diode and the light-emitting diode lights up, MO
The MOS type FET is configured to be turned on by applying a bias voltage based on the electromotive force of the solar cell to the S type FET. By the way, the rise is gradual at the boundary between the on state and the off state, and when the bias voltage of the MOS FET slightly exceeds the pinch-off voltage, the drain,
Since the resistance between the source and the source is high, when the MO3 type FET is turned on, the resistance between the drain and the source is low and the rise is steep, so as shown in Figure 3, an n-channel MOS The drain and source of the second switch element Q2, which is an 11-channel junction FET, are connected in parallel between the gate and source of the first switch element Q1, which is a type FET, and a discharge resistor is connected between the gate and source of the second switch element Q2. R'' are connected in parallel and the second
A configuration has been considered in which a second solar cell B2 is connected so as to apply a negative bias voltage to the switch element Q2.

In this configuration, the second switch element Q2 is in the on state until the light emitting diode LED reaches a predetermined brightness, and the gate and source of the first switch element Q1 are short-circuited, and the first switch element Q1 is in the off state. It is maintained. When the load control current increases and the brightness of the light emitting diode LED increases, the electromotive voltage of the second solar cell B2 increases, and the date voltage to the source of the second switch element Q2 becomes lower than the pinch-off voltage of the second switch element Q2. , the second switch element Q2 is turned off, the bias voltage from the first solar cell B1 is applied to the first switch element Q1, and the first switch element Q is turned on. As described above, the first switch element Q1 can be turned on by flowing a control current to the light emitting diode LED, and when the first switch element Q1 is turned on, the brightness of the light emitting diode LED is increased. The electromotive voltage of the first solar cell B1 is sufficiently high, and the first switching element Q is turned on when its conduction resistance is low.

By the way, since the second switching element Q2 is a junction FET, the temperature dependence of the drain current on the gate-source voltage is relatively strong, and as shown in Figure @4, the pinch-off voltage has a negative temperature dependence. The pinch-off voltage tends to gradually decrease as the ambient temperature increases. That is, in the above-described circuit, there is a problem in that the control current for turning on the first switch element Q1 varies depending on the ambient temperature. In addition, a chip resistor is used as the discharge resistor R', and since the discharge resistor R' has a negative temperature characteristic, when the ambient temperature rises, the resistance value of the discharge resistor R' decreases, and the ambient temperature When the voltage becomes high, it is necessary to increase the electromotive voltage of the second solar cell B2 in order to turn off the second switch element Q2, and it is necessary to increase the brightness of the light emitting diode LED. That is, when the ambient temperature changes, the first switching element Q1
This is inconvenient because the amount of control current flowing through the light emitting diode LED to turn it on changes. In addition, for this reason, the bias voltage when the first switching element Q1 is in the on state varies depending on the ambient temperature, and the resistance value between the drain and source of the first switching element Q when the first switching element Q1 is in the on state changes depending on the ambient temperature. There is a problem with doing so. In addition, T3, T2, and T3 in FIG. 4 indicate the ambient temperature, and vT old, VTH2, and TH3 indicate the pinch-off voltage corresponding to the ambient temperature.

[Objective of the Invention 1 The present invention has been made in view of the above points, and its main purpose is to absorb the temperature dependence of the second switching element and turn the first switching element into an on state. An object of the present invention is to provide a semiconductor relay using an FET that reduces fluctuations in the control current required to achieve this.

[Disclosure of the Invention] In the present invention, by providing a correction means for absorbing temperature changes in the pinch-off voltage of the second switch element, the amount of control current when turning on the first switch element is not affected by changes due to ambient temperature. A semiconductor relay using a non-receptive FET is disclosed.

(Example) Hereinafter, an example of the present invention will be described based on the drawings. 1st
As shown in the figure, the circuit configuration is similar to the conventional one, with the drain and source of the first switch element Q1, which is an MO3 type FET, connected to the load, and connected to the gate and source of the first switch element Q1, respectively. The drain and source of the second switching element Q2, which is a type FET, are connected. Both the first switch element Q and the second switch element Q2 are n-channel FETs, and have negative pinch-off voltages. A first solar cell B1 is connected between the gate and source of the first switching element Q1, with the gate on the positive electrode side. A discharge resistor R and a second solar cell B2 are connected in parallel between the gate and source of the second switch element Q2. The second solar cell B2 is connected with the gate of the second switch element Q2 as the negative electrode. A diffused resistor is used as the discharge resistor R, and its resistance value has a positive temperature characteristic. That is, when the ambient temperature rises, the pinch-off voltage of the second switching element Q2 decreases, but at this time, the discharge resistance R increases, so the voltage drop across the discharge resistance R increases, and the bias voltage increases
2, the second switch element Q2 becomes lower than the pinch-off voltage of Q2.
is turned off. Since the discharge resistor R has a positive temperature characteristic in this way, it is possible to cancel out the temperature characteristic of the pinch-off voltage of the second switching element Q2, and the same control current is applied to the first switching element Q regardless of the ambient temperature.
1 can be turned on, and the discharge resistor R using a diffused resistor acts as a correction means.

Here, the temperature coefficient of the diffused resistance increases as the concentration of impurities to be implanted increases, and a desired temperature coefficient can be obtained by adjusting the amount of impurities. Furthermore, unlike a chip resistor, since it is a diffused resistor, it can be incorporated into the same chip of an integrated circuit together with the first switch element Q1 and the second switch element Q2, and the overall size can be reduced.

FIG. 2 shows an embodiment of the pond, in which a Zener diode Z is connected as a correction means between the gate and source of the first switching element Q1, and the cathode of the Zener diode Z is connected to the first switching element Q1.
It is connected to the gate of switch element Q1. The breakdown voltage of the Zener diode Z is set to be lower than the electromotive voltage of the first solar cell B1 when the second switch element Q2 is in the OFF state within the operating temperature range l2. However, even if the electromotive voltage of the first solar cell B1 when the second switch element Q2 is in the off state is different, the bias voltage applied to the gate of the first switch element Q1 by the Zener diode Z remains a constant value. It is a thing,
The resistance value between the drain and the source when the first switching element Q1 is in the on state can be kept at a substantially constant value regardless of changes in the ambient temperature. Also,
If a high voltage is applied to the gate of MO3 type FET when it is not connected to the circuit, the data Y may be destroyed, but since the Zener diode Z is connected to the gate, the high voltage can be applied to the data. This prevents the gate from being damaged by static electricity or the like.

As described above, in the embodiment of FIG. 1, the control current for turning on the first switching element Q1 is approximately constant, and in the embodiment of FIG. 2, the first switching element Q1 is in the on state regardless of the control current. When this occurs, the resistance between the drain and the source is kept approximately constant, and a combination of both may be used.

[Effect of the Invention 1] As described above, the present invention includes a first switch element made of a MOS FET with a load circuit connected between the drain and the source, a drain between the gate and the source of the first switch element,
A second switch element consisting of a junction FET whose sources are connected in parallel; a discharge resistor connected in parallel between the gate and source of the second switch element; and a control means for applying a negative bias voltage to the second switching element at the same time as applying a negative bias voltage to the second switching element. In a semiconductor relay in which two switch elements are non-conductive, a correction means is provided to absorb temperature changes in the pinch-off voltage of the second switch element, so that the control current amount when turning on the first switch element and the first switch This has the advantage that the resistance between the drain and the source when the element is in the on state does not change due to ambient temperature and remains a substantially constant value.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing an embodiment of the pond of the present invention, Fig. 3 is a circuit diagram showing a conventional example, and Fig. 4 is a circuit diagram showing the same problem as above. FIG. B1 is the first solar cell, B2 is the second solar cell, LED
is a light emitting diode, Q is a first switching element, Q2 is a second switching element, R is a discharge resistor, and Z is a Zener diode. Agent Patent Attorney Ishi 1) Chief 7 Figure 1 Figure 2

Claims (1)

[Claims] (1) MO with a load circuit connected between the drain and source
a first switch element made of an S-type FET; a second switch element made of a junction FET whose drain and source are connected in parallel between the gate and source of the first switch element;
A discharge resistor is connected in parallel between the gate and source of the switch element, and as the load control current increases, a positive bias voltage is applied to the first switch element and a negative bias voltage is applied to the second switch element. control means;
In a semiconductor relay that makes a second switch element non-conductive when a bias voltage to the first switch element makes the conduction resistance of the first switch element less than or equal to a predetermined value, a temperature change in the pinch-off voltage of the second switch element is absorbed. A semiconductor relay using an FET, characterized in that it is provided with a correction means.