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From: "Don" <g@crcomp.net>
Newsgroups: sci.electronics.design
Subject: Re: KA7500 vs TL494
Date: Thu, 27 Mar 2025 05:31:29 -0000 (UTC)
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legg wrote:
> Don wrote:
>>legg wrote:
>>> Chinese commodity power supplies have tended to use recognizable
>>> configurations from times gone by. In doing so, it's easy to
>>> miss some of the 'small stuff' that actually produced a reliable
>>> product, in the day.
>>>
>>> Even more so, when pricing reaches the 'replace vs repair' threshold
>>> - why even bother with burn-in, in that case? If no burn-in or field
>>> return failure analysis is ever consudered, the small errors persist,
>>> particularly if vendors play wack-a-mole with the same hardware
>>> offered under different brand names and paperwork.
>>>
>>> Case in point is a 5V 40A unit advertised 'for use in LED sign',
>>> commonly used in Onbon product. In the application where a repair
>>> or replace decision was made, actual consumption was in the 35W
>>> range, though a test sequence could draw much higher power.
>>> replacement with an identically rated unit was Cdn$22.00.
>>>
>>> The replacement was physically and schematically identical, but
>>> relaid as a mirror image for component placement. Different
>>> brand name.
>>>
>>> Anyways - a basic self-oscillating bipolar transistor half bridge
>>> with forced beta, synchronized/steered and pwm'd by opening and
>>> shorting the resistor-limited, center-tapped 'drive' winding.
>>> Open collector drive out of a KA7500.
>>>
>>> What's a KA7500 ? Turns out to be pin compatible to TL494, but
>>> mfrd by Samsung/Fairchild/ONS.
>>>
>>> http://ve3ute.ca/query/TL494_vs_KA7500.pdf
>>>
>>> Oodles of data and apps for the 494, not so much for the 7500.
>>> If anyone's got app info published for the KA7900, in any
>>> language, I'd be interested to see it.
>>
>>As you say, KA7500 specific notes are nearly non-existent; other than
>>this circuit schematic of an application available at DiodeGoneWild [1]:
>>
>>    <https://danyk.cz/s_atx01h.png>
>>
> <snip>
>
> That's basically the controller drive and regulation section found in
> commodity single output jobs, but they use output copper track and
> links to develop a bulk current limit, within the input compliance
>  range of the error amp inputs (one would hope).

> I note that in the Sunny Tech schematic, the slow start and aux
> overvoltage line is disconnected from either regulation path.
>
> The 12V 40A unit used MBRF30100 output rectifiers (fully insulated
> TO220). I'll believe the part msrkings/ratings when I see it.

My knowledge of SMPS is limited. Where are the slow start and aux
overvoltage lines?

It seems like the thermister, tau set from R34 and C16, and the output
control (pin 13) ought to contribute something to a slow start.

Does the circuit around pin 15 sense overvoltage?

Danke,

-- 
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.