JPH0234027A - Solid-state relay - Google Patents

Abstract

PURPOSE:To attain the prevention of destruction of a circuit due to an overcurrent by providing a MOS transistor(TR) in parallel with a power MOS TR, a resistor connected in series with the MOS TR and a MOS TR turned on by a voltage due to the overcurrent flowing to the MOS TR. CONSTITUTION:If an overcurrent flows between output terminals OUT1, OUT2, a voltage is generated between a drain and a source of an N-channel MOS TR 1 of the power MOS TR. As a result, an N-channel MOS TR 3 is turned on as soon as the N-channel MOS TR 1 is turned on and a large voltage is generated across a resistor R3 by selecting the resistance of the resistor R3 sufficiently larger. On the other hand, a voltage between a gate and a source of an N-channel MOS TR 5 whose gate is connected to a terminal of the resistor R3 is equal to a voltage across the resistor R3 and the N-channel MOS TR 5 is turned on. When the N-channel MOS TR 5 is turned on, it short-circuits an output of photodiodes PD1-PDN, then the output level is lowered. Thus, the N-channel MOS TR 1 is turned off thereby preventing the overcurrent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to solid-state relays, and more particularly, to a solid-state relay that is provided with an overcurrent prevention function and has a low on-resistance.

[Conventional technology]

In a conventional solid-state relay, as shown in Figure 2, a power MO3) and a transistor (NMOS1, NM), which plays the role of a switch, are connected between switch terminals (OUTI, 0UT2) that turn on and off the current flowing to the load.
These power MOS
Transistor (NMO8I.

A resistor (R
1, R2) were connected. In order to detect overcurrent, the voltage drop generated across the detection resistors R1 and R2 is connected to an NPN transistor (NPNI).

By exceeding the threshold voltage of NPN2), bipolar transistors NPNI and NPN2
It can be detected by turning on. When the bipolar transistors NPNI and NPN2 are turned on, the collector potential of the transistors drops to near the ground potential, so the transistors NMO81 and NMO82, which are switches, are turned off and the current flowing to the load is cut off.

When operating this solid state relay as a control relay, connect a load to the load connection terminals 0UT1.0UT2 and apply voltage to the control input terminals IN1 and IN2 to cause the LED to emit light, and by optical coupling. The photodiodes PD1 to PDN are activated. The voltage generated in one photodiode PD is approximately 0.6V (actually.

0.5), and the switch NMOS transistor (
NMOS 1, NMOS 2) + 7) X L/ Since the hold voltage is approximately 10V, 27 photodiodes PDI to PDN are connected, resulting in a total of 13.5
Generates a voltage of about V. The voltage generated by the photodiode PD is applied to the switch transistor NMO8I,
Turn on NMO82 and output 1.

Current flows through the load connected between the 0UT2 terminals.

Regarding solid state relays, for example,
Electronic Communication Handbook, March 30, 1978, published by Ohmsha Co., Ltd., page 415.

[Problem to be solved by the invention]

A voltage proportional to the resistance value is generated in each on-resistance of the switch transistors NMO51, NMO52, overcurrent detection resistors R1, R2, and load resistance, and heat is generated proportional to the square of the resistance value. Therefore, when an overcurrent flows, a large amount of heat is generated, which may destroy the transistor and the load. To prevent this, bipolar transistors NPNI and NPN2 for overcurrent prevention and overcurrent detection resistors R1 and R2 are provided.

Conventional relays use switch transistors (power MO
The overcurrent detection resistors R1 and R2 connected in series with 8) have high resistance values because it is necessary to increase the on-resistance of the relay.

For example, in FIG. 2, if an overcurrent flows from ○UTI toward 0UT2, the voltage appearing across resistor R1 increases. Now, if R1 = 2Ω, R1
When a current of 250 mA flows through R1, a potential difference of 500 mV appears between both terminals of R1. This voltage turns on the bipolar transistor NPNI, so the output voltage of the photodiodes PDI to PDN decreases, and the NMOS
l, the gate voltage of NMO82 decreases, and NMO5l,
By turning off NMO 82, the overcurrent is interrupted. Therefore, in this case, in order to limit the current at a load current of 250 mA, both of the resistors R1 and R2 need to have a value of 2Ω.

However, increasing the on-resistance of the relay will have an adverse effect on the load. Therefore, it is desirable to lower the on-resistance as much as possible.

An object of the present invention is to solve such conventional problems and provide a solid state relay that has low on-resistance and is provided with an overcurrent prevention circuit.

[Means for Solving the Problems] In order to achieve the above object, the solid state relay of the present invention includes a light emitting element, a plurality of photoelectric conversion elements optically coupled to the light emitting element, and an output voltage of the photoelectric conversion element. on·
A solid state relay including a power MOS transistor that is turned off, a second MOS transistor connected in parallel to the power MOS transistor, and a resistor connected in series to the second MOS transistor.

a third MOS transistor that is turned on by a voltage generated by an overcurrent flowing through the resistor;
By turning on the transistor.

By short-circuiting the output voltages of the plurality of photoelectric conversion elements.

The feature is that it prevents damage to the circuit due to overcurrent.

[For production]

In the present invention, overcurrent detection is performed using resistors connected in parallel with the power MOS transistors (NMOS 1 and NMOS 2), and the resistors directly connected to the power MOS transistors are removed. That is,
In addition to the first current circuit that includes a power MOS transistor that switches the current flowing to the load, a second current circuit that includes a resistor for detecting overcurrent and a second MOS transistor that causes the overcurrent to flow through the resistor. A circuit is provided in parallel with the first current circuit to reduce the on-resistance of the first current circuit. Then, an overcurrent is detected by passing an overcurrent through the resistor of the second current circuit and the second MOS transistor, and turning on the third MOS transistor with the voltage generated by the overcurrent flowing through the resistor. When the third MO81 to transistor are turned on, the photodiode output is short-circuited to prevent destruction due to overcurrent. This makes it possible to realize a solid state relay with low on-resistance.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to one drawing.

FIG. 1 is a block diagram of a solid state relay showing one embodiment of the present invention.

In Figure 1, INI and IN2 are control input terminals, LE
D is a light emitting diode, PDI to PDN are multiple (for example, 27) photodiodes connected in series, and NMO
3I, NMOS2 is a power MOS that serves as a switch
Transistor (connected to the first current circuit), NM
OS3. NMOS4 is a MOS transistor connected in parallel to the power MOS transistor (connected to the second current circuit), R3 and R4 are overcurrent detection resistors (connected to the second current circuit), NMOS5. NMOS6 is a MOS transistor (connected to the third current circuit) for shorting the output of the photodiode, 0UTI, 0UT
2 is an output terminal connected to a load.

The solid state relay of this embodiment includes one light emitting diode LED and a photodiode PDI optically coupled to it.
It is completely the same as the conventional device in that it is composed of a PDN and power MOS transistors NMO8I and NMOS2 that are controlled on and off by the photovoltaic force generated by these photodiodes. Note that the power MOS transistor N
The reason why two MOS1 and NMOS2 are generally connected in series is to correspond to AC signals, and the output terminal 0
Either UTI or 0UT2 may be + or -.

As shown in FIG. 1, in this embodiment, there is a pad between terminals 0UTI and 0UT2 for turning on and off the load.
Only MO8 transistors NMO81 and NMO82 are connected in series, so the on-resistance between 0UT1 and 0UT2 is equal to that of power MOS transistors NMO3I and NMO
It is determined only by the on-resistance of S2. As a result, it is possible to realize a solid state relay with lower on-resistance than before.

When operating as a normal control relay.

When a voltage is applied between the control terminals INI and IN2, the light emitting diode LED starts emitting light, and a voltage is generated by the photoelectromotive force of the photodiodes PDI to PDN due to optical coupling, and this voltage is applied to the power MOS transistors NMOSI and NMO.
By turning on S2, the output terminals 0UTI, 0UT
A current flows between the two. When the voltage applied between the control inputs INN and IN2 becomes low or disappears, the current between the output terminals 0UTI and 0UT2 is also cut off.

Next, the overcurrent prevention function of the solid state relay shown in FIG. 1 will be described in detail.

For example, output terminal 0UT1. ．． If an overcurrent flows between 0UT2 and 0UT2, voltage and voltage will be generated between the drain and source of power MOS transistor NMO3I.
When the on-resistance of O8I is 1Ω, the voltage cursed between the drain and source of NMO8I is 250 mA. Further, since the gate of NMOS3 and the gate of NMO8I are commonly connected, NMOS3 is turned on at the same time as NMO8I. By making the resistance value of resistor R3 sufficiently large compared to the on-resistance of NMOS3, a large voltage will be generated between the terminals of R3.
When the on-resistance value of NMOS3 is 100Ω and the resistance value of R3 is IOKΩ, the voltage applied to R3 is approximately 0. ．． 02
At 5mAX10, Ω=250mV. On the other hand, since the gate-source voltage of NMOS5 whose gate is connected to the terminal of R3 is also 250mV, if the threshold voltage of the second NMOS85 is 250mV, the NMOS
5 is turned on. By turning on NMO35,
Since the outputs of the photodiodes PDI to PDN are short-circuited, the photodiode output is reduced.

As a result, the power MOS transistor NMOSl is turned off and overcurrent is prevented. Note that since the threshold voltage of the NMO 35 can be arbitrarily determined depending on manufacturing conditions, it is also possible to change the limiting current by controlling the threshold voltage of the NMO 85.

In this way, in this embodiment, overcurrent detection is performed by the second MOS transistor and resistor connected in parallel to the power MOS transistor, so the power MOS
The resistor that was directly connected to the transistor can be removed. As a result, the on-resistance of the solid state relay can be lowered.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to realize a solid state relay that has low on-resistance and has a function of preventing destruction due to overcurrent.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a solid state relay according to an embodiment of the present invention, and FIG. 2 is a diagram showing an example of the configuration of a conventional solid state relay. PDI~PDN: Photodiode, LED: Light emitting diode, NMO8I~NMO86: N channel MOS
Transistor, R1-R4: Resistor. INI, IN2: Input terminal, OUT 1, ○UT2:
Output terminal.

Claims (1)

[Claims] (1) A solid state relay comprising a light emitting element, a plurality of photoelectric conversion elements optically coupled to the light emitting element, and a power MOS transistor that is controlled on/off by an output voltage of the photoelectric conversion element, in which the power MOS a second MOS transistor connected in parallel to the transistor;
a resistor connected in series to the second MOS transistor;
and a third MOS transistor that is turned on by a voltage generated by an overcurrent flowing through the resistor, and when the third MOS transistor is turned on, the output voltages of the plurality of photoelectric conversion elements are short-circuited. , a solid stay relay that is characterized by preventing circuit destruction due to overcurrent.