HB Controls

𝗦𝗦𝗥 𝗣𝗿𝗼𝗧𝗶𝗽: 𝗨𝗻𝗱𝗲𝗿𝘀𝘁𝗮𝗻𝗱𝗶𝗻𝗴 𝗖𝗼𝗻𝗱𝘂𝗰𝘁𝗲𝗱 𝗘𝗺𝗶𝘀𝘀𝗶𝗼𝗻𝘀

All Power Controllers generate electromagnetic noise—it’s just a matter of how much.

When an input signal is applied to a 𝘇𝗲𝗿𝗼-𝗰𝗿𝗼𝘀𝘀𝗶𝗻𝗴 𝗰𝗼𝗻𝘁𝗿𝗼𝗹𝗹𝗲𝗿, the output won’t conduct until shortly after the AC line passes through zero. Because the output semiconductors need a few volts to trigger (typically ~6 Vpk), they don’t switch exactly at zero. That tiny delay causes a sudden change in load power—producing electrical noise that couples onto the AC network.

In SCR-based Power Controllers, this happens every half-cycle. Even with a continuous control signal, the semiconductors turn on and off twice per AC cycle due to their gate-trigger voltage and holding-current characteristics. The result: continuous conducted noise, 𝘄𝗶𝘁𝗵 𝗵𝗮𝗿𝗺𝗼𝗻𝗶𝗰𝘀 𝘁𝘆𝗽𝗶𝗰𝗮𝗹𝗹𝘆 𝗽𝗲𝗮𝗸𝗶𝗻𝗴 𝗯𝗲𝘁𝘄𝗲𝗲𝗻 𝟭𝟱𝟬 𝗸𝗛𝘇 𝗮𝗻𝗱 𝟭 𝗠𝗛𝘇.

𝗘𝗠𝗖 𝗖𝗼𝗺𝗽𝗹𝗶𝗮𝗻𝗰𝗲

Most zero-crossing controllers meet 𝗖𝗹𝗮𝘀𝘀 𝗔 conducted-emission limits (commercial or industrial use).

𝗖𝗹𝗮𝘀𝘀 𝗕 requirements (medical or residential) are more stringent and almost always require additional filtering.

Proportional or instantaneous-control Power Controllers always need external filtering to achieve Class A or B compliance.

👉 Designing for a noise-sensitive environment? We can help you select the right filtering solution for EMC compliance.

Contact Us | HBControls Solid State Power Controllers HBControls - Please feel free to contact us directly to let us help find the right power switching solution for your specific needs.

𝗦𝗦𝗥 𝗣𝗿𝗼𝗧𝗶𝗽: 𝗨𝗻𝗱𝗲𝗿𝘀𝘁𝗮𝗻𝗱𝗶𝗻𝗴 𝗜²𝗧 𝗥𝗮𝘁𝗶𝗻𝗴𝘀 (𝗮𝗻𝗱 𝗪𝗵𝘆 𝗧𝗵𝗲𝘆 𝗠𝗮𝘁𝘁𝗲𝗿)

It’s not the most thrilling spec on a datasheet—but it’s one of the most important.

I²T represents the 𝘧𝘶𝘴𝘪𝘯𝘨 𝘤𝘶𝘳𝘳𝘦𝘯𝘵 of a Power Controller’s output semiconductor—the amount of energy it can absorb before the silicon literally melts and opens the circuit.

It’s calculated from the manufacturer’s single-cycle surge current rating (typically about 10× the continuous current rating). Here’s the math behind it:

I²T = (Peak Surge Current ÷ √2)² × Half-Cycle Time
(8.33 ms for 60 Hz or 10 ms for 50 Hz)

In simple terms, 𝗜²𝗧 𝘁𝗲𝗹𝗹𝘀 𝘆𝗼𝘂 𝗵𝗼𝘄 𝗺𝘂𝗰𝗵 𝗲𝗻𝗲𝗿𝗴𝘆 𝗮 𝗱𝗲𝘃𝗶𝗰𝗲 𝗰𝗮𝗻 𝘀𝘂𝗿𝘃𝗶𝘃𝗲 𝗱𝘂𝗿𝗶𝗻𝗴 𝗮 𝗳𝗮𝘂𝗹𝘁 𝗲𝘃𝗲𝗻𝘁—before it sacrifices itself to protect the rest of the circuit.

𝗛𝗼𝘄 𝗶𝘁 𝗱𝗶𝗳𝗳𝗲𝗿𝘀 𝗳𝗿𝗼𝗺 𝗱𝗶/𝗱𝘁:
– di/dt measures how quickly current changes, not how much current is flowing.
– A di/dt failure usually results in a shorted die.
– An I²T failure typically vaporizes the silicon, leaving an open device.

So while I²T might sound like “datasheet filler,” it’s actually your Power Controller’s last line of defense in a surge event.

Need help selecting the right I²T rating for your application? Let’s talk:

Contact Us | HBControls Solid State Power Controllers HBControls - Please feel free to contact us directly to let us help find the right power switching solution for your specific needs.

𝗦𝗦𝗥 𝗣𝗿𝗼𝗧𝗶𝗽: 𝗧𝗵𝗲 𝗩𝗮𝗿𝗶𝗮𝗯𝗹𝗲 𝗟𝗼𝗮𝗱 𝗖𝘂𝗿𝗿𝗲𝗻𝘁 𝗥𝗮𝘁𝗶𝗻𝗴 𝗼𝗳 𝗦𝗼𝗹𝗶𝗱-𝗦𝘁𝗮𝘁𝗲 𝗥𝗲𝗹𝗮𝘆𝘀

Over the years, countless solid-state relays have met their demise as a warped puddle of charred plastic and FR-4—victims of excessive internal temperatures. In many cases, the relay was running well below its rated load current, yet still failed catastrophically.

Why? Because an SSR’s true load-current rating isn’t fixed—it depends entirely on the heat sink it’s mounted to.

Our latest TechTip article explains why heat sinks are essential when using SSRs, and how their thermal impedance directly impacts the maximum current your relay can safely and continuously switch.

And if you’d rather skip the trial-and-error, give us a call—we’ve overheated a few ourselves and can help you choose the right heat sink to avoid future failures: 𝟴𝟬𝟬.𝟴𝟳𝟵.𝟳𝟵𝟭𝟴.

www.hbcontrols.net