Reed Relays Explained: SIP vs DIP vs 3570 Series — Which One Do You Need?

What Is a Reed Relay?

A reed relay consists of a reed switch (two ferromagnetic contacts sealed in a glass tube) wrapped in a copper coil. When the coil is energized, the magnetic field pulls the reed contacts together, closing the circuit. Unlike electromechanical relays, reed relays have no moving armature — just the contacts themselves flexing — giving them faster switching speeds (typically 0.5-2ms), longer life (100+ million operations), and superior isolation.

Reed relays are widely used in:

• ATE (Automated Test Equipment) — where fast, reliable switching is critical
• Medical devices — where galvanic isolation matters
• Telecommunications — low-level signal switching
• Semiconductor test systems — high-density switching matrices
• Industrial control — sensor interfaces and PLC modules

SIP Reed Relays: Compact and Popular

SIP (Single In-line Package) reed relays are the workhorse of the industry. With a single row of pins spaced at standard 2.54mm pitch, they fit easily onto prototyping boards and production PCBs alike.

Key Specifications (SIP-1A Series)

When to Choose SIP

• You need through-hole mounting with standard 2.54mm pitch
• Board space is not the primary constraint
• You want a proven, widely-available form factor
• Coil voltages from 5V to 24V DC cover most control circuits

3570 Series: High-Performance in SIP Format

The 3570 series (also known as 3570-1331) is a specialized SIP reed relay with higher switching voltage (150VDC Max) compared to standard SIP types. It is commonly found in Coto Technology and compatible designs.

Key Specifications

When to Choose 3570 Series

• Your application requires switching above 100V
• You are replacing or matching Coto 3570-compatible parts
• You need a diode-suppressed version for flyback protection
• Industrial and test equipment applications

DIP Reed Relays: Dense and Versatile

DIP (Dual In-line Package) reed relays use two rows of pins, doubling the contact density in the same footprint. The DIP-1A05, for example, offers the same SPST-NO configuration as SIP types but in a DIP form factor that’s compatible with IC sockets and automated assembly.

Why DIP Matters

• Socket-compatible — can be plugged into standard DIP IC sockets for easy replacement
• Automated assembly — DIP packaging is compatible with pick-and-place equipment
• Compact footprint — two rows of pins maximize PCB density
• Same core specs — 200V/1A, 500mA contact rating, 5VDC coil

SIP vs DIP vs 3570: Quick Comparison

Diode-Suppressed vs. Non-Suppressed

Several reed relays come in two variants: with a built-in flyback diode and without. For example:

• SIP-1A05 — standard, no diode
• SIP-1A05D — with suppression diode
• 3570-1331-051 — standard, 5V coil, no diode
• 3570-1331-053 — 5V coil with diode
• 3570-1331-121 — standard, 12V coil, no diode
• 3570-1331-123 — 12V coil with diode

When should you choose the diode version? If you’re driving the relay directly from a transistor or microcontroller GPIO, the flyback diode protects your driving circuit from voltage spikes when the coil de-energizes. If you’re using an external driver with built-in protection, the non-suppressed version is fine.

How to Source Reed Relays

When sourcing reed relays, verify the following with your supplier:

1. Coil resistance — match it to your driver circuit
2. Contact material — ruthenium or rhodium for dry switching, tungsten for higher power
3. Operate/release time — typically 0.5ms operate, 0.2ms release
4. Insulation resistance — should be 10¹⁰ ohms minimum
5. Life expectancy — 100M+ operations at rated load

Related reading: How to Identify and Avoid Counterfeit Electronic Components | Why Source Electronic Components from China