For a "typical" 250W SMPS, I guestimate that the bus cap(s) will contain approx 145 j. I can think of several single fault conditions that would make my product safety Type Tests much more fun and spectacular ...
But note that, for voltage dips and short interruptions according to 61000-4-11, IEC 60601-1-2:2001, table 202, says that "it is recommended that the [EQUIPMENT or SYSTEM] be powered from an UPS or battery." luck, Brian -----Original Message----- From: Rich Nute [ mailto:[email protected]] Sent: Thursday, April 29, 2004 11:27 AM To: [email protected] Cc: [email protected] Subject: Re: Medical devices and voltage dip testing Hi Pat: > If a product is rated for 100-240Vac operation, this > means test levels like 40Vac for 100ms (100Vac/50Hz > nominal input, 60% dip for 5 cycles). The performance > criteria makes this especially difficult - "The system > shall provide essential performance". > > This looks like a major design change for many of our > power supplies. My health insurance premiums are going to go up! The way I read the requirement, the power supply output will need to be maintained through this dip. Most power supplies cannot sustain the output with input that low for that long a period. The requirement does indeed imply a MAJOR design change for "typical" power supplies. The 100 ms time period (5 cycles) is really tough. For a switcher, it means some really big capacitors in both the rectifier and the output. It may also mean the switcher will need to work at even lower voltages. The power supply will be bigger and more expensive. Good luck, Rich
