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Don't believe everything you read

Posted by Triode_Kingdom (A) on October 12, 2016 at 11:35:27

In Reply to: RE: I was thinking of trying this. posted by DAK on October 12, 2016 at 10:32:17:

This is another example of a Net-borne design that isn't fully vetted. I only had time for a quick scan of the article, but that's all it took to realize the author may not understand this topic sufficiently to rank as an authoritative source. Here's what I'm referring to:

"In most applications, the pass transistor will not require a heat sink. For example, in a circuit with 50 volts differential across the TIP50 and 100 mA load, the pass transistor is only dissipating 5 watts. The TIP50 is rated 40 watts dissipation."

This statement tells me the author doesn't understand semiconductor ratings, and that throws the validity of the entire article into question. The 40W rating of the TIP50 is based on maintaining the collector at a temperature of 25C. That requires a big heat sink. The datasheet further confirms this error with its 25C ambient (no heat sink) rating of 2W dissipation. Hook it up as the author suggests - 5W and no heat sink - and the part will fry.

That aside, I'm not saying the circuit won't work, or that it's not effective for screen regulation (although it's much more complex and costly than I would find appropriate). It's just worth pointing out that articles and projects like this need to be approached with your eyes open. It's not a commercial design, and it may be burdened with design parameters or advice/technical opinions that will cause failure in your specific application.

This post is made possible by the generous support of people like you and our sponsors:

Kimber Kable

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