Replacing a off-line switcher IC to a higher switching frequency IC - Page 1
Forum section: electronics / repair

author: Yamin
author_rank: Frequent Contributor
timestamp: November 11, 2022, 11:40:17 am
content: I've got a power supply which came into repair with a blown TOP258MG IC. There were couple of diode shorted and leaky caps. I have replaced them all.The issue is I have only got TOP258MN, everything is identical except the switching frequency.TOP258MG = 66kHzTOP258MN = 132kHz (the one I have)My question is could it be replaced, and if there would be any side effectsThanks

author: coromonadalix
author_rank: Super Contributor
timestamp: November 11, 2022, 11:58:19 am
content: normally the xformers or coils are calculated for the "normal" 66khz working frequency, not the higher one

author: Yamin
author_rank: Frequent Contributor
timestamp: November 11, 2022, 12:01:31 pm
content: Thanks, I wonder what would happen if the switching frequency is higher. (higher freq should result in less switching losses right?)Would the PS work as it should though?Also what might happen to the output voltage of the ps

author: ingalopez
author_rank: Contributor
timestamp: November 14, 2022, 06:48:10 pm
content: Probably bad things may happen!As previos post remarks, the filters Transformer, etc has been calculated for a much lower frequency.In the best case something may get very hot , and prone to fail unexpectedly.

author: Yamin
author_rank: Frequent Contributor
timestamp: November 14, 2022, 10:58:53 pm
content: Thanks for the insights, I am a bit confused regarding the two ICs. From the datasheet of the TOP ICs there is no mention of a TOP258MG. It talks about only MN.Only a google search shows these two as different IC, but the datasheet link goes to datasheet I mentioned.Any idea on how to double check this?

author: Audiorepair
author_rank: Frequent Contributor
timestamp: November 14, 2022, 11:32:13 pm
content: The data sheet says:In the M, P and G packages and the TOP259-261 Y package option, the full frequency PWM mode is set at 66 kHz, for higher efficiency and increased output power in all applications.From this data sheet:https://www.mouser.co.uk/datasheet/2/328/tophx_family_datasheet-1511305.pdf

author: Yamin
author_rank: Frequent Contributor
timestamp: November 14, 2022, 11:44:15 pm
content: Quote from: Audiorepair on November 14, 2022, 11:32:13 pmYes exactly that's what I mean, the datasheet does not mention about the last letter (N or a G or any significance of that). But a google search of TOP258MG vs TOP258MN yields a result showing that it has got two different switching frequency with everything else the same. The same parameters are displayed on mouser but when I click the datasheet link it directs to the one you also have attached for both the ICS

author: fzabkar
author_rank: Super Contributor
timestamp: November 15, 2022, 12:00:47 am
content: The E and Y packages for the TOP258 have an F pin (pin #4) which sets the frequency to 66kHz or 132kHz. This pin is missing from the M package.QuoteI wonder if TOP258MG and TOP258MN differ in pin#4, ie perhaps the 132kHz version retains pin #4 rather cutting it off.Edit:I just answered my own question (pin #4 is missing in both):https://www.google.com/search?q=TOP258MN&tbs=isz:m,itp:photo&tbm=ischhttps://www.google.com/search?q=TOP258MG&tbs=isz:m,itp:photo&tbm=ischEdit #2:The manufacturer's web page for the TOP258MN specifies Switching Frequency (max) = 66kHz.https://www.power.com/products/topswitch/topswitch-hx/top258mnThere is no TOP258MG part on the web site:https://www.power.com/products/topswitch/topswitch-hx

author: Audiorepair
author_rank: Frequent Contributor
timestamp: November 15, 2022, 07:55:38 am
content: Digikey show it as a 66kHz device.https://www.digikey.co.uk/en/products/detail/power-integrations/TOP258MN/1657675Perhaps the AiPCBA data is incorrect, or they sell a clone not made by Power Integrations.