SERIES
421
MAGNETIC-LATCHING
ESTABLISHED RELIABILITY
TO-5 RELAYS
SPDT
SERIES
DESIGNATION
RELAY TYPE
421
SPDT basic relay
421D
SPDT relay with internal diode for coil transient suppression
SPDT relay with internal diodes for coil transient suppression and polarity
reversal protection
421DD
The Series 421D and 421DD utilize discrete silicon diodes for coil
suppression and polarity reversal protection.
DESCRIPTION
The magnetic-latching TO-5 relay, originally conceived and
developed by Teledyne, has become one of the industry standards
for low-level switching from dry circuit to 0.5 ampere. Designed for
high-density PC board mounting, its small size and low coil power
dissipation make the 421 relay one of the most versatile
ultraminiature relays available.
By virtue of its inherently low intercontact capacitance and contact
circuit losses, the 421 relay has proven to be an excellent
ultraminiature RF switch for frequency ranges well into the UHF
spectrum. A typical RF application for this TO-5 relay is in handheld
radio transceivers, wherein the combined features of good RF
performance, small size, low coil power dissipation and high
reliability make it a preferred method of transmit-receive switching
(see Figure 1).
The following unique construction features and manufacturing
techniques provide excellent resistance to environmental extremes
and overall high reliability:
• All welded construction.
• Unique uni-frame design providing high magnetic efficiency and
mechanical rigidity.
• High force/mass ratios for resistance to shock and vibration.
• Advanced cleaning techniques provide maximum assurance of
internal cleanliness.
The Series 421 magnetic-latching relays are ideally suited for
applications where coil power dissipation must be minimized. The
relays can be operated with a short duration pulse. After the contacts
have transferred, no external holding power is required.
The magnetic latching feature of the Series 421 provides a “memory”
capability, since the relays will not reset upon removal of coil power.
• Precious metal alloy contacts material with gold plating assures
excellent high current and dry circuit switching capabilities.
PERMANENT MAGNET
MAGNETIC CIRCUIT A
SOFT IRON CORE A
MAGNETIC CIRCUIT B
PRINCIPLE OF OPERATION
Energizing Coil B produces a magnetic field
COIL B
COIL A
opposing the holding flux of the permanent magnet
in Circuit B. As this net holding force decreases, the SOFT IRON
attractive force in the air gap of Circuit A, which also
results from the flux of the permanent magnet,
becomes great enough to break the armature free
of Core B, and snap it into a closed position against
Core A. The armature then remains in this position
upon removal of power from Coil B, but will snap
ENVIRONMENTAL AND
PHYSICAL SPECIFICATIONS
SOFT IRON
CORE A
CORE B
AIR GAP
SOFT IRON
ARMATURE
Temperature
MOVING
CONTACT
–65°C to +125°C
(Ambient)
Vibration
30 g’s to 3000 Hz
STATIONARY
CONTACT
(General Note 1)
back into position B upon energizing Coil A. Since operation depends upon cancellation
of a magnetic field, it is necessary to apply the correct polarity to the relay coils as
indicated on the relay schematic. When latching relays are installed in equipment, the
latch and reset coils should not be pulsed simultaneously. Coils should not be pulsed
with less than rated coil voltage and the pulse width should be a minimum of three times
the specified operate time of the relay. If these conditions are not followed, it is possible
for the relay to be in the magnetic neutral position.
Shock
(General Note 1)
100 g’s,
6 msec, half-sine
Acceleration
Enclosure
Weight
50 g’s
Hermetically sealed
0.089 oz. (2.52g) max.
421 Page 1
SPECIFICATIONS ARE SUBJECT TO CHANGE WITHOUT NOTICE
www.teledynerelays.com
©2005 TELEDYNE RELAYS
421/1205/Q1
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