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From: "Don" <g@crcomp.net>
Newsgroups: sci.electronics.design
Subject: Re: KA7500 vs TL494
Date: Tue, 25 Mar 2025 17:03:18 -0000 (UTC)
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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>

The switch supply section at his website is worth a look:

    <https://danyk.cz/index_en.html>

The Badcaps SMPS forum is also worth a look:

<https://www.badcaps.net/forum/troubleshooting-hardware-devices-and-electronics-theory/troubleshooting-power-supplies-and-power-supply-design>

Note.

[1] <https://www.youtube.com/channel/UCQak2_fXZ_9yXI5vB_Kd54g>

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.