Selection guides, cross-reference reviews and engineering Q&A for LAN transformers, RJ45, SFP and other communication components, plus the latest from VOOHU.
Selection GuidesOSFP vs QSFP-DD vs QSFP28 vs QSFP112OSFP vs QSFP-DD on the board: QSFP-DD adds a second contact row (76 vs 38) and accepts QSFP modules; OSFP uses 60 pins. Also covers QSFP28 and QSFP112.
Tech BlogTVS Diode vs Zener Diode vs Varistor (MOV): Which One Should Protect Your Interface?Use a TVS diode when a signal or low-voltage DC line must survive ESD and surge pulses with a tight clamping voltage. Use a varistor (MOV) on power inputs, wher
Tech BlogRJ11 vs RJ45 (8P8C)RJ11 and RJ45 jacks belong to the same modular-connector family, but they are not interchangeable. An RJ11-style jack has 6 positions and is usually fitted with
Tech BlogPoE PinoutPower over Ethernet carries DC on the RJ45 contacts, two pairs at a time. Alternative A (called Mode A at the powered device) uses contacts 1-2 and 3-6; Alterna
Selection GuidesIEEE 802.3bt PoE MagneticsIn 4-pair operation, an IEEE 802.3bt (PoE++) port drives DC current through the cable-side center taps of the LAN transformer on all four pairs, so the data-sid
Tech BlogHow to Test a Varistor (MOV)To test a metal oxide varistor (MOV), remove power, discharge the circuit and inspect the part for cracks, burn marks or a bulging coating. Then lift one lead a
Tech BlogWhat Is a Common Mode Choke and How Does It Work?A common mode choke (CMC) is an inductor with two windings on one shared magnetic core, connected in series with a pair of conductors such as a differential dat
Selection GuidesShielded vs Unshielded RJ45 Connector: When Does a PCB Jack Need a Shield, and How Should It Be Grounded?Short answer. Use a shielded RJ45 connector when the product will be cabled with shielded twisted pair (F/UTP, S/FTP and similar), when it sits in a metal enclo
Tech BlogChanging a PoE Device's Output from 12V to 5V: Can You Keep the Same Power Transformer?Changing a PoE camera or AP's isolated supply from 12V to 5V? At the same 13W, a 5V output delivers 2.4× the current of 12V, secondary copper loss rises about 4
Thinking of adding a second molded inductor in parallel to carry more current? Paralleling halves inductance and doubles total ripple, and DC current divides by
Many 1:1 audio transformers are rated 600:290 or 600:301. What goes on the secondary? Using VOOHU selection table data: why the secondary rating is the terminat
A dead Ethernet port after a surge does not necessarily mean the LAN transformer failed. How surges reach the port, a power-off method that measures each side o
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