cupoftea
Advanced Member level 6
Hi,
We have been given a spec for an offline PSU with PFC, 115/230VAC input. Power output is 214W.
Ie, 5V at 6A; 5V at 8A; 48V at 2A; 48V at 1A
The 48V output should fall no lower than 45V, and should be able to source 40A for 120us.
An initial , failed attempt at this supply, (actually sent to us by the customer, and done by a different supplier), shows a non working PSU which comprises a UCC3818 PFC followed by a power module, which is followed by several DCDC converters.
The spec, in places, says the following points......
1…
“At +95°C heat sink temperature, full load and 230 VAC nominal input voltage, the PSU shall have an operational life of no less than 20 000 hours “
…Presumably this means 105degc, 10000 hr electrolytics are not to be used?
2…”Electrolytic capacitors of the vented type shall not be used.”
…presumably this means electrolytics with the “indented pattern” on top cannot be used?
3….”The PSU shall operate at a mounting surface (see 6.1.3) temperature of +95°C.”
….I cannot see this PSU , being done with standard 105degC electrolytics, lasting the 20000 hrs?
4….“The PSU should have a heat output no greater than 15 W whilst providing specified nominal current“
…that means an efficiency of 92%....wow!.....for a PSU with all those outputs!, and PFC front end.
5….“Average RMS current draw shall be no greater than 2 A“
…at 115VAC input, that means input power of just 260W….that would mean an efficiency of 82% which is maybe not possible with the cascaded converters we see.
The spec does not give a range for VAC input…but presume down to 100VAC……so at 100vac and 2A, it cant meet the power requirement.
6...."The PSU shall occupy a space envelope no greater than 178 x 139 x 22.5 mm, including the heads of any fasteners and including any mounting fastener feature."
...That seems very small for this kind of PSU
*****_____*****_____*****_____*****_____*****_____*****_____*****_____*****_____*****_____*****_____*****_____*****_____*****_____*****_____
The spec references an enormous number of standards, which are not freely available.
This spec to me sounds like a trick spec, designed to spot suppliers who are just going to wade in and "do any old thing"....so that that supplier can be crossed off the list of prospective suppliers.
....Would you agree with this assessment?
We have been given a spec for an offline PSU with PFC, 115/230VAC input. Power output is 214W.
Ie, 5V at 6A; 5V at 8A; 48V at 2A; 48V at 1A
The 48V output should fall no lower than 45V, and should be able to source 40A for 120us.
An initial , failed attempt at this supply, (actually sent to us by the customer, and done by a different supplier), shows a non working PSU which comprises a UCC3818 PFC followed by a power module, which is followed by several DCDC converters.
The spec, in places, says the following points......
1…
“At +95°C heat sink temperature, full load and 230 VAC nominal input voltage, the PSU shall have an operational life of no less than 20 000 hours “
…Presumably this means 105degc, 10000 hr electrolytics are not to be used?
2…”Electrolytic capacitors of the vented type shall not be used.”
…presumably this means electrolytics with the “indented pattern” on top cannot be used?
3….”The PSU shall operate at a mounting surface (see 6.1.3) temperature of +95°C.”
….I cannot see this PSU , being done with standard 105degC electrolytics, lasting the 20000 hrs?
4….“The PSU should have a heat output no greater than 15 W whilst providing specified nominal current“
…that means an efficiency of 92%....wow!.....for a PSU with all those outputs!, and PFC front end.
5….“Average RMS current draw shall be no greater than 2 A“
…at 115VAC input, that means input power of just 260W….that would mean an efficiency of 82% which is maybe not possible with the cascaded converters we see.
The spec does not give a range for VAC input…but presume down to 100VAC……so at 100vac and 2A, it cant meet the power requirement.
6...."The PSU shall occupy a space envelope no greater than 178 x 139 x 22.5 mm, including the heads of any fasteners and including any mounting fastener feature."
...That seems very small for this kind of PSU
*****_____*****_____*****_____*****_____*****_____*****_____*****_____*****_____*****_____*****_____*****_____*****_____*****_____*****_____
The spec references an enormous number of standards, which are not freely available.
This spec to me sounds like a trick spec, designed to spot suppliers who are just going to wade in and "do any old thing"....so that that supplier can be crossed off the list of prospective suppliers.
....Would you agree with this assessment?