817

Operating Instructions

Relays & Sockets

Operating Instructions

Driving Circuit for Relays

1. To ensure correct relay operation, apply rated voltage to the relay coil.

2. Input voltage for the DC coil:

A complete DC voltage is best for the coil power to make sure of stable relay

operation. When using a power supply containing a ripple voltage, suppress

the ripple factor within 5%. When power is supplied through a rectification

circuit, the relay operating characteristics, such as pickup voltage and dropout

voltage, depend on the ripple factor. Connect a smoothing capacitor for better

operating characteristics as shown below.

+

–

R

Smoothing

Capacitor

Relay

Pulsation

Emin Emax

Emean

DC

Ripple Factor (%)¥ 100%

Emax – Emin

Emax

= Maximum of pulsating current

Emin

= Minimum of pulsating current

Emean = DC mean value

Emean

3. Leakage current while relay is off:

When driving an element at the same time as the relay operation, special

consideration is needed for the circuit design. As shown in the incorrect

circuit below, leakage current (Io) flows through the relay coil while the relay

is off. Leakage current causes coil release failure or adversely affects the

vibration resistance and shock resistance. Design a circuit as shown in the

correct example.

Incorrect

Correct

R

Io

TE

R

4. Surge suppression for transistor driving circuits:

When the relay coil is turned off, a high-voltage pulse is generated, causing a

transistor to deteriorate and sometimes to break. Be sure to connect a diode

to suppress the back electromotive force. Then, the coil release time becomes

slightly longer. To shorten the coil release time, connect a Zener diode

between the collector and emitter of the transistor. Select a Zener diode with

a Zener voltage slightly higher than the power voltage.

R

Back emf

suppressing diode

Relay

+

–

Protection for Relay Contacts

1. The contact ratings show maximum values. Make sure that these values are

not exceeded. When an inrush current flows through the load, the contact

may become welded. If this is the case, connect a contact protection circuit,

such as a current limiting resistor.

2. Contact protection circuit:

When switching an inductive load, arcing causes carbides to form on the

contacts, resulting in increased contact resistance. In consideration of contact

reliability, contact life, and noise suppression, use of a surge absorbing circuit

is recommended. Note that the release time of the load becomes slightly

longer. Check the operation using the actual load. Incorrect use of a contact

protection circuit will adversely affect switching characteristics. Four typical

examples of contact protection circuits are shown in the following table:

Power

CR

Ind. Load

This protection circuit can be used when the load

impedance is smaller than the RC impedance in an

AC load power circuit.

•

R: Resistor of approximately the same resistance

value as the load

•

C:0.1 to 1 µF

This protection circuit can be used for both AC and

DC load power circuits.

R: Resistor of approximately the same resistance

value as the load

C: 0.1 to 1 µF

+

–

D

Power

Ind. Load

This protection circuit can be used for DC load power

circuits. Use a diode with the following ratings.

Reverse withstand voltage: Power voltage of the

load circuit x 10

Forward current: More than the load current

Power

Ind. Load

This protection circuit can be used for both AC and

DC load power circuits.

For a best result, when using a power voltage of 24

to 48V AC/DC, connect a varistor across the load.

When using a power voltage of 100 to 240V AC/DC,

connect a varistor across the contacts.

3. Do not use a contact protection circuit as shown below:

Power

C

Load

This protection circuit is very effective in arc suppression when

opening the contacts. But, the capacitor is charged while the

contacts are opened. When the contacts are closed, the capacitor

is discharged through the contacts, increasing the possibility of

contact welding.

C

Load

Power

This protection circuit is very effective in arc suppression when

opening the contacts. But, when the contacts are closed, a current

flows to charge the capacitor, causing contact welding.

Generally, switching a DC inductive load is more difficult than switching a DC

resistive load. Using an appropriate arc suppressor, however, will improve the

switching characteristics of a DC inductive load.

Soldering

1. When soldering the relay terminals, use a soldering iron of 30 to 60W, and

quickly complete soldering (within approximately 3 seconds).

2. Use a non-corrosive rosin flux.

Operating Instructions