F39-EU1E Omron, F39-EU1E Datasheet - Page 128

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➌-➀-4 Contact Protection Circuits

Using a contact protection circuit is effective in increasing contact

durability and minimizing the production of carbides and nitric acid.

The following table shows typical examples of contact protection

circuits. Use them as guidelines for circuit design.

Typical Examples of Contact Protection Circuits

Do not use the following types of contact protection circuit.

Note: Although it is thought that switching a DC inductive load is more difficult than a resistive load, an appropriate contact protection circuit can

➌-➀-5 Countermeasures for Surge from External Circuits

Install contact protection circuits, such as surge absorbers, at

locations where there is a possibility of surges exceeding the Relay

withstand voltage due to factors such as lightning. If a voltage

exceeding the Relay withstand voltage value is applied, it will cause

line and insulation deterioration between coils and contacts and

between contacts of the same polarity.

Diode

Diode +

Zener diode

Varistor

Power

supply

achieve almost the same characteristics.

Circuit example

Load

http://www.ia.omron.com/

Power

supply

Power

supply

This circuit arrangement is very effective for diminishing

arcing at the contacts when breaking the circuit. However,

since electrical energy is stored in C (capacitor) when the

contacts are open, the current from C flows into the

contacts when they close. This may lead to contact

welding.

Power

supply

Power

supply

Power

supply

Inductive

load

Inductive

load

(Yes)

Yes

Applicable

current

Yes

* Load impedance must be much smaller

The release time of the contacts will be

increased if the load is a Relay or

solenoid.

The electromagnetic energy stored in the

inductive load reaches the inductive load

as current via the diode connected in

parallel, and is dissipated as Joule heat

by the resistance of the inductive load.

This type of circuit increases the release

time more than the CR type.

This circuit effectively shortens the

release time in applications where the

release time of a diode circuit is too slow.

This circuit prevents a high voltage from

being applied across the contacts by

using the constant-voltage characteristic

of a varistor. This circuit also somewhat

increases the release time.

Connecting the varistor across the load is

effective when the supply voltage is 24 to

48 V, and across the contacts when the

supply voltage is 100 to 200 V.

than the CR circuit impedance when

using the Relay for an AC voltage.

When the contacts are open, current

flows to the inductive load via CR.

Features and remarks

1. Depending on factors such as the nature of the load and the Relay

2. When a contact protection circuit is used, it may cause the release

Power

supply

characteristics, the effects may not occur at all or adverse effects

may result. Therefore be sure to check operation under the actual

load conditions.

time (breaking time) to be increased. Therefore be sure to check

operation under the actual load conditions.

Load

This circuit arrangement is very useful for diminishing

arcing at the contacts when breaking the circuit. However,

since the charging current to C flows into the contacts

when they are closed, contact welding may occur.

Use the following as guides for C and R

values:

C: 0.5 to 1 μF per 1 A of contact current (A)

R: 0.5 to 1

These values depend on various factors,

including the load characteristics and

variations in characteristics. Confirm

optimum values experimentally.

Capacitor C suppresses the discharge

when the contacts are opened, while the

resistor R limits the current applied when

the contacts are closed the next time.

Generally, use a capacitor with a

dielectric strength of 200 to 300 V. For

applications in an AC circuit, use an AC

capacitor (with no polarity).

If there is any question about the ability to

cut off arcing of the contacts in

applications with high DC voltages, it may

be more effective to connect the capacitor

and resistor across the contacts, rather

than across the load. Perform testing with

the actual equipment to determine this.

Use a diode having a reverse breakdown

voltage of more than 10 times the circuit

voltage, and a forward current rating

greater than the load current. A diode

having a reverse breakdown voltage two

or three times that of the supply voltage

can be used in an electronic circuit where

the circuit voltage is not particularly high.

The breakdown voltage of the Zener

diode should be about the same as the

supply voltage.

The cutoff voltage Vc must satisfy the

following conditions. For AC, it must be

multiplied by

If Vc is set too high, its effectiveness will

be reduced because it will fail to cut off

high voltages.

Vc > (Supply voltage

Precautions for All Relays

Element selection

per 1 V of contact voltage (V)

1.5)

C-6

F39-EU1E Omron, F39-EU1E Datasheet - Page 128

F39-EU1E

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