Author Topic: Help in interpreting safety standard for AC/DC converter  (Read 695 times)

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Offline eecookTopic starter

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Help in interpreting safety standard for AC/DC converter
« on: March 26, 2020, 07:23:49 pm »
Hi All,

I am investigating how IEC 61010-1 (safety) applies to a power supply I have designed.

Power supply description:
  Designed for Overvoltage Category II
  - Input: 100-240VAC - 50/60Hz - 700mA
  - Output: 160VDC - 300mA
                12V - 1A
  - Topology: Flyback (quasi-resonant)
  Note 1: Feedback is done through an optocoupler
  Note 2: There is a Y-cap bridging the insulation between primary and secondary grounds (for EMI)

Background:
The 160VDC output is "turned on" at the output terminals through a relay that separates this 2 secondary circuits. I am trying to understand the creepage/clearance requirements between those 2 secondary circuits.

Problem:
I don't know which one of the following items applies to this case (see image). Item b) seems compelling but primary and secondary aren't separated only by a transformer, there's an opto-coupler and
the Y-rated cap.


Can anybody please help me out with this one?

Copyright notice: I do not own the rights to the shared image but "fair use" arguments apply.
« Last Edit: March 26, 2020, 08:20:25 pm by eecook »
Nullius in verba
 

Offline bjbb

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Re: Help in interpreting safety standard for AC/DC converter
« Reply #1 on: March 26, 2020, 09:24:51 pm »
Requirements for insulation and spacing is based on several things, and can be determined only after the designer has measured the working voltages under the least favorable operating conditions per the Type Test conditions (see clause 4) in the scoped standard; and per the class and category defined by the intended end use. In any case, you must meet the minimum requirements for BI as 'functional' cannot be considered.

A Y1 cap, where any touch leakage limits are met, can be considered the same as the galvanic isolation provided by a transformer. This assumes the capacitor ratings meets the requirements for the conditions of the particular insulation that is being  bridged.

Flybacks typically have messy and 'spikey' waveforms, so annex K should be referenced after all of the working voltages (see annex I) have been tabulated, and figure 1.2 of  IEC61010-2-30 should be referenced.

If your employer has a designated compliance engineer, then she needs to be consulted immediately.
 
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Offline eecookTopic starter

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Re: Help in interpreting safety standard for AC/DC converter
« Reply #2 on: March 27, 2020, 03:07:53 pm »
Requirements for insulation and spacing is based on several things, and can be determined only after the designer has measured the working voltages under the least favorable operating conditions per the Type Test conditions (see clause 4) in the scoped standard; and per the class and category defined by the intended end use. In any case, you must meet the minimum requirements for BI as 'functional' cannot be considered.

A Y1 cap, where any touch leakage limits are met, can be considered the same as the galvanic isolation provided by a transformer. This assumes the capacitor ratings meets the requirements for the conditions of the particular insulation that is being  bridged.

Flybacks typically have messy and 'spikey' waveforms, so annex K should be referenced after all of the working voltages (see annex I) have been tabulated, and figure 1.2 of  IEC61010-2-30 should be referenced.

If your employer has a designated compliance engineer, then she needs to be consulted immediately.

Thank you for the response. I was indeed planning to use annex K for the converter, but this is different as it involves 2 secondary circuits that have basically DC.

I had the suspicion that the Y-cap and the opto-coupler would be part of the same insulation system and hence insulation requirements between 2 secondary circuits would be covered by 6.7.1.5 b).

I am a 'solo gig team' pretty much. Not ideal, but grateful for the experience.  :-+
« Last Edit: March 27, 2020, 03:10:31 pm by eecook »
Nullius in verba
 


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