Agreed. But not all the devices you mention operate in the same way. In particular, Sidactors get their high apparent energy absorption because they crowbar the line being protected, to relatively near ground potential. They are basically energy-rated bidirectional breakover diodes (acting like self-triggered triacs). Thus, although the device handles high spike current, the voltage across it is very low during this period (thus power dissipation in the device is much lower). Devices operating off the AC line being protected by a sidactor, will see an interruption in their power supply (the AC line), as a result of the sidactor clamping it to near-zero volts. Because of the Sidactor's crowbar action, it is not likely acceptable as a normal AC line protection device (they are more commonly used to protect data and telecom lines). A transzorb or a MOV simply limits the rise of voltage to a small increment ABOVE nominal line voltage, hence the power dissipation will be much higher than with a Sidactor. But the benefit is that devices operating from the protected AC line will see no interruption in their power when a "hit" occurs. Bob Wilson TIR Systems Ltd. Vancouver. -----Original Message----- From: j...@aol.com [mailto:j...@aol.com] Sent: June 19, 2002 9:51 AM To: Robert Wilson; mpet...@analogic.com; emc-p...@majordomo.ieee.org Subject: Re: Transient Voltage Suppressor - Europe approvals? In a message dated 6/19/2002, Bob Wilson writes:
Transzorbs (or "TVS"s) are basically zener diodes that are rated for their energy absorption capability. Hello All: One thing to keep in mind is that the energy handling capability of a TransZorb is generally not very high compared to other devices such as gas tubes, MOV's, and sidactors. Michael, your original posting did not specify the intended application, but the reference to being "rated for mains voltage" makes me wonder if you are trying to protect from surges on an AC mains input. If so, I do not think that a TransZorb would have adequate energy handling capability. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 http://www.randolph-telecom.com
