Radiant energy – Photocells; circuits and apparatus – Signal isolator
Reexamination Certificate
2000-10-13
2002-11-26
Pyo, Kevin (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Signal isolator
C250S216000, C327S514000
Reexamination Certificate
active
06486485
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optocoupler such as a solid-state relay, etc., and more particularly to an optocoupler capable of controlling an off-state thereof with a prescribed timing.
2. Description of the Related Art
A conventional solid-state relay
900
, as illustrated in
FIG. 9
, has a structure including: a light emitting element
901
(generally, a GaAs LED or a GaAlAs LED) which converts an electric signal into a light: a light receiving element
902
(generally, a phototriac) which converts a light into an electric signal; a driving triac
903
which is coupled to the light receiving element
902
: and a resistance element
904
. The driving triac
903
is also coupled to a load
905
.
When an input current is applied to the light emitting element
901
, the light receiving element
902
is activated and the light receiving element
902
drives the driving triac
903
so that the driving triac
903
is switched over to an on-state.
Once the triac
903
is turned on, even if the input current is turned off immediately afterward, the driving triac
903
maintains the on-state until a load current flowing therethrough reaches a zero value (which is a basic operation of solid-state relays).
One method for activating the solid-state relay
900
involves phase control. As illustrated in
FIG. 10A
, phase control is realized by adjusting the timing of turning on the driving triac
903
based on the timing of applying the input current, thereby controlling the load current. Arbitrary control of the load current is generally possible depending on the application timing of the input current (
FIGS. 10A
,
10
B and
10
C).
Now, consider the case where the load
905
must be activated with a half amount of electric power (
FIG. 10B
) as compared to that required for a full-phase on-driving mode. Activating the load
905
with the half amount of electric power in comparison to that of the full-phase on-driving mode may be achieved by setting the timing of the input current application, as illustrated in
FIG. 10B
, so as to occur at phase angles of 90° and 270° of a load current waveform.
As illustrated in
FIG. 11
, when the input current is applied, the load current is at a peak. Thus, a substantial inrush current may flow into the solid-state relay
900
immediately after the input current is applied, depending on the type of the load
905
, thereby adversely affecting the solid-state relay
900
.
Once the driving triac
903
is turned on, even if the input current is turned off immediately afterward, the driving triac
903
maintains an on-state until the load current flowing therethrough reaches a zero value. is As illustrated in
FIG. 12
, especially in the case of a load which gives rise to a load current whose phase is shifted with respect to the phase of a supply voltage, e.g., an inductive load, a steep voltage is applied to the triac
903
as the triac
903
is turned off. Accordingly, there is a possibility that commutation failure may occur.
As described above, the solid-state relay
900
has characteristics such that once the driving triac
903
is turned on, the driving triac
903
maintains the on-state until the load current flowing therethrough reaches a zero value. Therefore, the problems described above may arise depending on the application timing of the input current or the type of the load.
The conventional solid-state relay
900
is not provided with a function of compulsorily turning off the triac
903
when the ambient temperature rises to an extremely high level. At present. the product safety Is sought more than ever. Accordingly, it is desired that any solid-state relay be provided with a function of turning itself off when any abnormality occurs.
As described above, the solid-state relay
900
has characteristics such that once the driving triac
903
is turned on, the driving triac
903
maintains the on-state until the load current flowing therethrough reaches a zero value. Therefore problems such as an increase in the inrush current, commutation failure, etc., may arise depending on the application timing of the input current, the type of the load, etc.
SUMMARY OF THE INVENTION
An optocoupler of the present invention includes a driving triac and at least one normally-on driving element coupled in series to the driving triac, thereby accomplishing objects of the present invention.
The optocoupler may be a solid-state relay.
The driving element may include a MOSFET.
The driving element may include a mechanical relay.
A timing of turning off the driving element may be synchronized with a phase point substantially corresponding to 0 V level of a supply voltage on an output side of the optocoupler.
The driving element may include a light emitting element for controlling the MOSFET. The optocoupler may further include a temperature detecting means coupled to the light emitting element.
The driving element may further include a light emitting element for controlling the MOSFET. The optocoupler may further include a resistance element coupled in series to the light emitting element and the resistance element may have a negative temperature coefficient.
The driving element may further include a first light emitting element for controlling the MOSFET. The optocoupler may include a second light emitting element corresponding to the driving triac and an integrated circuit coupled to the first light emitting element and the second light emitting element. The integrated circuit may have a delay function.
There may be more than one driving triac.
According to one aspect of the present invention, when a solid-state relay is turned on, an input current is applied to a light emitting diode so as to activate a driving triac. When the solid-state relay is turned off afterward, a trigger pulse is applied to a normally-on driving element. Therefore, it is possible to prescribe the timing for turning off, as well as turning on, the solid-state relay.
According to another aspect of the present invention, when the solid-state relay is turned on, an input current is applied to a light emitting diode associated with the light receiving element/driving triac, so as to activate the driving triac. When the solid state relay is turned off afterward at a predetermined time, an input current is applied to the light emitting diode associated with the MOSFET so as to turn off the normally-on MOSFET. Therefore, it is possible to prescribe the timing for turning off, as well as turning on, the solid-state relay.
According to still another aspect of the present invention, when the solid-state relay is turned on, an input current is applied to a light emitting diode so as to activate the driving triac. When the solid-state relay is turned off afterward at a predetermined time, a trigger pulse is applied to a normally-on mechanical relay. Therefore, it is possible to prescribe the timing for turning off, as well as turning on, the solid-state relay.
According to still another aspect of the present invention, it is possible to prevent a steep voltage from being applied to the solid-state relay in the off-state. Accordingly, it is possible to prevent commutation failure from occurring.
According to still another aspect of the invention, by preconditioning the solid-state relay so,that an input current will flow into the light emitting diode (which controls the MOSFET) when an abnormality occurs, e.g., an ambient temperature rises to an extremely high level, the normally-on MOSFET is turned off, thereby compulsorily turning off the device. Accordingly, it is possible to prevent an abnormal operation of the device at high temperatures, for example.
According to still another aspect of the present invention, by preconditioning the solid-state relay so that an input current sufficient to turn off the normally-on MOSFET will flow into the light emitting diode (which controls the MOSFET) by reducing a-resistance value of the resistance element having a negative temperature coefficient when an abnormality occurs, e.g., an ambient tem
Pyo Kevin
Sharp Kabushiki Kaisha
Sohn Seung C.
LandOfFree
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