Solid-state relay

Details Solid-state relay Solid-state relay

2001-05-07

2003-04-29

Jackson, Stephen W. (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

With specific current responsive fault sensor

C361S018000, C361S058000, C361S118000

Reexamination Certificate

active

06556406

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a solid state relay, and more particularly to a novel solid state relay in which less EMI noise leaks in to a power source, and which can be produced without especially increasing the cost and the size as compared with a relay of the conventional art.
BACKGROUND ART
Usually, a solid state relay is configured so that an input circuit and an output circuit are electrically insulated from each other by a photocoupler, and a main switching element (thyristor, triac (triode bilateral thyristor), or the like) interposed in the output circuit is operated in accordance with an electric signal applied to the input circuit, thereby closing or opening a load connected to the output circuit.
As a solid state relay of the conventional art, for example, known are a first conventional art example shown in
FIG. 8
, a second conventional art example shown in
FIG. 9
, and a third conventional art example shown in FIG.
10
. In the solid state relay of the first conventional art example, a trigger system is employed in which the main switching element is triggered by a triac coupler. In the solid state relay of the second conventional art example, a trigger system is employed in which the main switching element is triggered by a diode bridge and a thyristor. In the solid state relay of the third conventional art example, a trigger system is employed in which the main switching element is triggered by a diode bridge and a thyristor coupler. These three trigger systems can be realized at a low cost, and hence are used in many solid state relays.
FIG. 11A
shows a connection example in the case where the solid state relays shown in
FIGS. 8
,
9
, and
10
are used. In the figure,
1109
denotes a solid state relay (SSR),
1107
and
1108
denote input terminals of the solid state relay,
1104
and
1103
denote load terminals of the solid state relay (and serving also as a pair of external connection terminals which are conductive with the ends of the incorporated main switching element),
1111
denotes an input signal voltage in this case it is a symbol for a DC power source,
1122
denotes a load which is to be driven, and
1123
denotes an AC power source for driving an external load.
The details of the solid state relays shown in
FIGS. 8
,
9
, and
10
will be sequentially described.
In the first conventional art example shown in
FIG. 8
, a triac (triode bilateral thyristor)
816
serving as a main switching element is triggered by a photo-triac(triode bilateral thyristor) coupler
813
. In the figure,
807
and
808
denote a pair of input terminals to which the input signal voltage
1111
(see
FIG. 11A
) is supplied,
812
denotes an input circuit which functions as a buffer or the like for an input signal,
813
denotes the photo-triac coupler (configured by optically coupling a light emitting diode
814
with a photo-triac
815
) which electrically insulates the input circuit
812
and an output circuit from each other,
816
denotes a power triac incorporated into the output circuit and serving as a main switching element,
817
denotes a current limiting resistor for the photo-triac
815
,
818
denotes a gate bias resistor for the power triac
816
, a resistor element
819
and a capacitor element
820
are connected in series to constitute a surge absorbing circuit, and
804
and
803
denote a pair of external connection terminals which are conductive with the ends of the triac serving as the main switching element.
The operation in the case where the solid state relay of the first conventional art example is employed as the solid state relay (SSR)
1109
shown in the connection diagram of
FIG. 11A
will be described with reference to
FIGS. 11B and 11C
.
The relationship between the load current I and the voltage V
T
between the terminals
803
and
804
during the operation of the solid state relay are indicated by the broken and solid lines in the waveform chart of FIG.
11
B. In this case, a resistance load is as the load
1122
. In the figure, when the terminal-to-terminal voltage V
T
reaches a specified on-start voltage V
ON
in accordance with the voltage of the power source
1123
as indicated by the sold line in the figure the power triac
816
serving as the main switching element is turned on, thereby causing the load current I to start flowing through the load
1122
. At the same time, the terminal-to-terminal voltage V
T
instantly drops to a specified power-chip ON voltage (ON-state voltage) V
TM
P
.
The change of the terminal-to-terminal voltage (voltage between the terminals
803
and
804
) V
T
before and after turning on the power triac
816
is enlarged and shown in FIG.
11
C. As shown in the figure, the on-start voltage V
ON
that is equal to the terminal-to-terminal voltage V
T
at which the triac
816
is triggered (hereinafter, indicated as V
ON1
in the first conventional art example) is determined by the sum of the voltage drop (I
G
×R
GS
) of the current limiting resistor
817
due to the operation current I
G
of the photo-triac
815
, the on-state voltage V
TM1
of the photo-triac
815
, and the voltage drop V
GT
of the resistor
818
as indicated by following expression (Eq. 1):
V
ON1
=I
G
×R
GS
+V
TM1
+V
GT
.  (Eq. 1)
As apparent from this, in the trigger circuit of the first conventional art example, the on-state voltage V
TM1
of the photo-triac
815
which serves as a triggering element is high, and hence the on-start voltage V
ON1
at which the triac
816
which serves as the main switching element is triggered is inevitably made higher. This causes a problem in that the noise terminal voltage is high.
Next, in the second conventional art example shown in
FIG. 9
, a triac(triode bilateral thyristor)
916
serving as a main switching element is triggered by using a diode bridge
917
and a thyristor
922
. In the figure,
907
and
908
denote a pair of input terminals to which the input signal voltage
1111
(see
FIG. 11A
) is supplied,
912
denotes an input circuit which functions as a buffer or the like for an input signal,
913
denotes a phototransistor coupler (configured by optically coupling a light emitting diode
914
with a phototransistor
915
) which electrically insulates the input circuit
912
and a trigger circuit
921
in an output circuit from each other,
916
denotes a power triac incorporated into the output circuit and serving as a main switching element,
917
denotes the diode bridge which rectifies the power source voltage and then applies the rectified voltage to a thyristor
922
,
922
denotes the thyristor which is triggered by the trigger circuit
921
to trigger the main switching element,
918
denotes a gate bias resistor for the power triac
916
, a resistor element
919
and a capacitor element
920
are connected in series to constitute a surge absorbing circuit, and
904
and
903
denote a pair of external connection terminals which are used to lead out the ends of the triac which serve as the main switching element to the outside.
Also the operation in the case where the solid state relay of the second conventional art example is employed as the solid state relay (SSR)
1109
shown in the circuit diagram of
FIG. 11A
which will be described with reference to
FIGS. 11B and 11C
in the same manner as the first embodiment. Also in the second embodiment, the on-start voltage V
ON
that is equal to the terminal-to-terminal voltage V
T
at which the triac
916
is triggered in the same manner as the first conventional art example (hereinafter, indicated as V
ON2
in the second conventional art example) is determined by the sum of the on-state voltage V
TM2
of the thyristor
922
, the on-state voltage (2×V
F
) of diodes in the diode bridge
917
, and the voltage drop V
GT
of the resistor
918
as indicated by following expression (Eq. 2):
V
ON2
=V
TM2
+2×V
F
+V
GT
.  (Eq. 2)
As apparent from this, in the trigger circuit of the second conventional art example, the on-state vol

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