59. DC SSR Load Switching
1. Component Purpose
Like the AC SSR, a DC SSR switches loads without mechanical contacts — giving silent operation and long life for frequently switched loads.
DC solid state relays typically use a MOSFET output (often called PhotoMOS or photorelay). Unlike AC SSRs that use TRIACs, MOSFET-output SSRs work with DC loads and have very low ON-state resistance (≤100mΩ), which means minimal voltage drop and power loss.
Required: SSR/Photorelay · SPST-NO · DC Output · 5V input · ≥24VDC load · ≥3A · Ron ≤100mΩ
2. How to Find It on DigiKey
Go to DigiKey.com → Relays → Solid State Relays
Apply these filters:
- Output Type → DC
- Voltage - Input → Range includes 5V
- Voltage - Load → 24VDC or higher
- Load Current → 3A or higher
- On-State Resistance (Max) → 100mΩ or lower
- Circuit → SPST-NO (1 Form A)
- Part Status → Active
Tip: On DigiKey, DC SSRs may appear under "Solid State Relays" or as "PhotoMOS" / "Photorelays". Both are valid for this application.
3. Key Specifications & What They Mean
| Specification | Required | Why |
|---|---|---|
| Relay Type | SSR / Photorelay | MOSFET output for DC switching. |
| Circuit | SPST-NO | Single NO output channel. |
| Output Type | DC | Switching 24VDC load. |
| Input Voltage | Includes 5V | Controller signal compatibility. |
| Load Voltage | ≥24VDC | Must handle 24V load voltage. |
| Load Current | ≥3A | Load is 2A; 1.5× margin. |
| On-State Resistance | ≤100mΩ | Low Ron = minimal loss and heat. |
| Temp Range | −40°C to +85°C | Industrial conditions. |
| Safety Approval | UL/CSA/TUV | Product certification. |
4. Selecting a Safe, Production-Ready Part
The filtered list will show matching parts. Before you pick one, check: Is it Active? Is stock available? Is the manufacturer reputable? Is a datasheet available?
Full checklist: How to Select a Safe, Production-Ready Component — EWskills Guide