JP2973654B2 - Static auxiliary relay circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a static auxiliary relay circuit in which an input and output are electrically insulated by an optical element and an on / off output is obtained at an output semiconductor element.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional circuit diagram. The on / off input signal is applied to the input element of the photocoupler 2 through the current limiting resistor 1. Output element voltage V of photocoupler 2
_in is applied to the gate of the FET 4 that becomes an output element through the resistor 3. A parallel circuit of a resistor 5 and a capacitor 6 as a time constant circuit is provided between the gate and the source of the FET 4.

In the above-described configuration, the operation time T when the FET 4 is turned on / off with respect to the on / off of the input signal.
_OP and return time T _RE are as follows.

[0004] T _OP =-(C ₆ + C _SS ) × (R ₃ // R ₅ ) ln (1-V ₂ / V ₁ ) where V ₁ = V _sn (R ₃ / (R ₂ + R ₃ )) C ₆ : Capacitance of capacitor 6 C _SS : Input capacitance of FET R ₃ : Resistance value of resistor 3 R ₅ : Resistance value of resistor 5 V ₂ : Operating voltage (threshold) of FET T _RE = − (C ₆ + C _SS ) × R ₅ × ln (V ₃ / V ₁ ), where V ₃ : FET return voltage

[0005]

In the conventional auxiliary relay circuit, since the output capacity of the photocoupler 2 is small, the resistance values R ₃ and R ₅ of the resistors 3 and 5 must be R ₃ << R _5. . For this reason, it is general that the operating time _TOP and the return time _TRE generally _{satisfy TOP} < _TRE, and there is a problem that _TOP > _TRE cannot be satisfied.

In order to obtain a short operation time _TOP , the capacitance C ₆ of the capacitor ₆ must be reduced. However, if this capacitance is reduced, desired characteristics are obtained due to variations in the input capacitance C _SS of the FET 4. Design becomes difficult. vice versa,
If the resistance value R 3 of the resistor ₃ is reduced and the capacitance C ₆ is made sufficiently larger than C _SS , the return time T _RE becomes longer, and T
_OP << T _RE and the expected value cannot be obtained between the return time.

SUMMARY OF THE INVENTION An object of the present invention is to provide a static auxiliary relay circuit for arbitrarily setting a magnitude relationship between an operation time and a recovery time and setting a value.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a photocoupler for receiving an ON / OFF input signal in a state of being electrically isolated, a capacitor provided in parallel with an output element of the photocoupler, and a first circuit. A parallel circuit with a resistor, a second resistor connected in series with the parallel circuit, and a connection point between the first resistor and the second resistor provided between the output element of the photocoupler and the gate of the output semiconductor element. The semiconductor device includes a transistor that is turned on by a voltage to turn off the semiconductor element, and a diode that is provided between a collector and an emitter of the transistor and forms a current path that turns on the semiconductor element.

[0009]

According to the present invention, by providing a transistor between the output element of the photocoupler and the output semiconductor element,
The operation time for turning off the semiconductor element depends on the time until the transistor turns on, that is, the time constant of the capacitor and the first and second resistors.

Further, by providing a diode between the collector and the emitter of the transistor, the recovery time for turning on the semiconductor element depends on the input capacitance of the semiconductor element or the external capacitor capacitance and the time constant of the first and second resistors. .

[0011]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, and the same components as those in FIG. 2 are denoted by the same reference numerals. Photocoupler 2
Are provided in parallel with a parallel circuit of a capacitor 7 and a resistor 8 and a resistor 9 in series therewith. An emitter-collector of a PNP transistor 10 serving as a switch is connected between the output element of the photocoupler 2 and the gate of the FET 4, and the base of the transistor 10 is connected to a resistor 8
And the resistor 9 are connected. Further, a diode 11 is provided in a forward direction from the collector to the emitter of the transistor 10 to form a current path for turning on the FET.

In this embodiment, the operation time T _OP is determined by the time until the transistor 10 is turned on, that is, the resistance values R ₈ and R 9 of the resistors ₈ and ₉ and the capacitance C _{7 of the} capacitor 7. Not dependent on _SS . The operation time T _OP is input impedance R ₄ is R ₄ of FET 4>
If> R ₈ + R ₉ , the following equation is obtained.

T _OP = −C ₇ × (R ₈ // R ₉ ) × ln (1-V _BE / V ₁ ) where V ₁ = V _in (R ₈ / (R ₈ + R ₉ )) V _BE : On the other hand, the recovery time T _RE is the time required for the diode 11 to conduct and discharge the charge of the input capacitance C _SS , that is, the resistance values R ₈ and R 9 of the resistors ₈ and ₉ and the input capacitance. It is determined by C _SS and does not depend on the capacitance C _{7 of the} capacitor 7. This return time T
_RE is given by T _RE = −C _SS × (R ₈ + R ₉ ) × ln (V ₃ / V ₁ ).

Therefore, according to this embodiment, the operation time T _OP
And the recovery time T _RE can be determined by different capacities C ₇ and C _SS , respectively, and can be arbitrarily set to a circuit configuration where T _OP > = T _RE and a configuration of T _OP <T _RE .

Further, operation time T _OP is dependent on the capacity of the capacitor 7 can be reliably and set in a wide range from short to long, without being affected by variations in the input capacitance C _SS of FET 4.

Since the recovery time T _RE depends on the input capacitance C _{SS of the} FET 4, its dispersion may deviate from the designed value. However, the input time is determined by adding an external capacitor between the gate and source of the FET 4. The effect of the variation in the capacitance C _SS can be suppressed.

In the above-described embodiment, the case where an FET is used as an output element is shown. However, this can be replaced with another semiconductor element such as a transistor or a thyristor to obtain the same operation and effect.

[0018]

As described above, according to the present invention, an off transistor and an on diode are provided between the output element of the photocoupler and the gate of the output semiconductor element, and the capacitors of both the output element side and the semiconductor element side are provided. Since the operation time and the recovery time can be individually set according to the capacity, there is an effect that the operation time and the recovery time can be set to any time required for the relay circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment.

FIG. 2 is a conventional circuit diagram.

[Explanation of symbols]

2 ... Photocoupler, 4 ... FET, 7 ... Capacitor, 8,
9: resistance, 10: transistor, 11: diode.

Claims (1)

(57) [Claims] 1. A photocoupler for electrically isolating and receiving an on / off input signal, a parallel circuit of a capacitor and a first resistor provided in parallel with an output element of the photocoupler, and a second circuit connected in series to the parallel circuit. A transistor provided between the output element of the photocoupler and the gate of the output semiconductor element and turned on by a connection point voltage between the first and second resistors to turn off the semiconductor element; and the transistor And a diode provided between the collector and the emitter of the above to form a current path for turning on the semiconductor element.