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4.Twin-relay
coil
simultaneous
operation
For relays which have multiple coils such as twin relay for forward-reverse operation of motor, if the coils
are continuously turned on at the same time, the coil temperature may exceed the tolerance in a short
time due to heat generation of each coil. Please contact us before use.
5. Coil
impressed
voltage
5. Continuous
current
Coil heating due to continuous current applying to coil for extensive time periods will cause deterioration
in insulation performance for coil.
For such circuit types, please consider the fail-safe circuit design in case of contact failure or breaking of
coil.
1. Connection method
Collector connection method is the most recommendable when the relay is driven by means of a
transistor.
To avoid troubles in use, the rated voltage should always be impressed on the relay in the ON time and
zero voltage be done in the OFF time.
6. Coil
impressed
circuit
1. Relay drive
by means of
a transistor
2. Countermeasures for surge voltage of relay control transistor
If the coil current is suddenly interrupted, a sudden high voltage pulse is developed in the coil. If this
voltage exceeds the breakdown voltage of the transistor, the transistor will be degraded, and this will
lead to damage. It is absolutely necessary to connect a diode in the circuit as a means of preventing
damage from the counter emf. In case of DC relay, connection of Diode is effective. As suitable ratings
for this diode, the average rectified current should be equivalent to the coil current, and the reverse
blocking voltage should be about 3 times the value of the power source voltage. Connection of a diode is
an excellent way to prevent voltage surges, but there will be a considerable time delay when the relay is
open. If you need to reduce this time delay you can connect between the transistor's Collector and
Emitter with a Zener diode that will make the Zener voltage somewhat higher than the supply voltage.
Take care of Area of Safe Operation (ASO).
(Good) Collector connection
This is the most common
connection, which operation is
usually stable with.
(Care) Emitter connection
When the circumstances make
the use of this connection
unavoidable, the voltage may not
be completely impressed on the
relay and the transistor would not
conduct completely.
(Care) Parallel connection
As the power consumption of
the entire circuit increases,
the relay voltage should be
considered.
Diode