An update to the transition from IEC 60950-1 to IEC 62368-1

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On a weblog put up again in March 2015, I discussed Hazard-Based mostly Security Engineering (HBSE) IEC 62368-1 commonplace will likely be changing IEC 60950-1 and IEC 60065, overlaying hazards and hazard prevention for ITE (Data Know-how Gear) and audio / visible tools. The transition date to EN 62368-1:2014 has now been prolonged 18 months to December 20th, 2020 for new submittals (or a major modification of the present 60950/60065 file) in the EU.  UL has additionally introduced that the UL 62368-1 Version No. 2 date is now December 20th, 2020. Quite a lot of different international locations have adopted the commonplace, together with Australia, Singapore, Malaysia, Japan and Russia.  No precise date has been printed for different international locations like China, Taiwan, South Korea and Argentina.

The new commonplace makes use of a Hazard Based mostly Security Engineering (HBSE) science self-discipline, and operates in 4 steps:
  1. Figuring out power sources in the product
  2. Classifying the power for the potential of inflicting harm or hurt
  3. Determine the essential safeguardswanted to shield from these power sources
  4. Qualify the safeguardsas efficient
The Power Source ES classification handles the impact on the physique for a variety of hazards.  See Desk 1 for instance of the two most related to power provides – electrical and thermal power.

Power Source class
Impact on the Physique
Impact on flamable materials
Class 1
Detectible, however not painful
Unlikely ignition
Class 2
Painful, however not an harm
Attainable ignition, however restricted
Class 3
An harm
Probably ignition, progress fast & swift
Desk 1 Power Source classification
As well as, a 3 particular person situation has been adopted for 62368-1 (see Desk 2).       
     
Particular person
Description (See commonplace for full particulars)
Unusual Particular person
An individual who's a person or is shut by to the tools
Instructed Particular person
An individual that's skilled to establish sources of ache inflicting power and keep away from them. Should not be uncovered to harm inflicting power sources, even throughout a single fault situation
Expert Particular person
An individual who has the coaching to acknowledge & keep away from power sources that might trigger ache or harm.  Have to be protected in opposition to unintended contact with harm inflicting power sources
Desk 2: Description of sorts of particular person
Relying on the Particular person kind and the Power Class, Safeguards have to be in place to shield that Particular person.  See Determine 1.

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Determine 1: Protection for an Unusual Particular person with completely different Power Courses

For instance, one small change power provide producers could have to make to their designs to meet IEC 62369-1, considerations “capacitance discharge” of the AC enter. 
Determine 2 exhibits the typical schematic of an EMI filter part of a power provide and the location of a resistor that discharges the Line to Impartial X capacitors after the AC has been eliminated.  This avoids a person unplugging an AC plug, touching the pins and getting an electrical shock.

Fig 2: EMI Filter Schematic

If the line twine was eliminated from the AC plug at the peak of a 240V AC cycle, then the voltage can be 339Vdc.  The time for that to decay to a secure voltage relies upon upon the values of the X capacitor(s), the Line to Impartial resistor and any loading of the power provide converter circuitry.
IEC 60950-1 states that after one second that voltage has to be at a most of 42.4Vpk.  IEC 62368-1 states that for an X capacitance of 300nF or larger, after two seconds, the restrict is 60Vpk in regular situation or 120Vpk in a single fault situation.
A 10W power phone charger may have a really small X capacitance and a high worth discharge resistor. Underneath 62368-1, if that resistor failed (a single fault situation) the power provide would in all probability nonetheless meet the 60Vpk situation after 2 seconds.  From Determine 1, this nonetheless complies with no Primary Safeguard is required, even for an “Unusual Particular person”.
The next wattage power provide on the different hand, may have a a lot bigger X capacitance.  With a single fault situation, the lack of the bleed resistor could end in a voltage of larger than 120Vpk after 2 seconds.  That might then be an ES2 - Class 2 Power Source - and from Determine 1, a Primary Safeguard would wish to be in place.  As an alternative of only one bleed resistor, a second one would wish to be added, in parallel with the first.  The values of the resistor can be sized accordingly to be certain that the lack of one, would nonetheless discharge the X capacitor to a most of 120Vdc after 2 seconds.
Supplementary Safeguards can be utilized in different elements of the power provide circuit in the identical method as bolstered or double insulated is in 60950-1.
One facet impact of the ES1 and ES2 limits is tha IEC 62368-1 deems a 48V or perhaps a 36V output power provide in hiccup mode over present as an AC output.  The ES1 limits for DC are 60V, however for up to 1kHz that drops to 30Vrms or 42.2Vpk.  IEC 60950-1 acknowledges that as SELV, however beneath the new commonplace that will be ES2 and the output shouldn't be made accessible to an Unusual Particular person.  Pins and connectors not accessible by a blunt probe are exempt.