Speaking of Colin Mitchell -- Circuit mistakes

his:

On page 9 he claims there's no current coming in or out of the "com" pin of a LM317.

Finding bad circuits on the web is a thankless task.

John

Whoah, that comic seems to imply that these people have someone in their lives that wants to go to bed with them...

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It is worse than that. The masses have been taught what is popular is true, not what is testable and proves itself is very likely to be true. Someone might correct them, and within minutes they will revert to error because it is popular, and being like folks.

It may also be that the diode would need a heat sink but the transistor doesn't. The trade of mechanical for electrical complexity can be worth it.

The transistor is sort of over current protected by not having infinite base current. Since no values are given, we don't know if this could matter.

He also didn't figure out how to get rid of the trim pot. Adjusting that is likely costing more than the transistors.

Way down at the end of the page, there is a circuit that I say will destroy its Zeners after a few times of bing plugged in.

nd

-)

One problem that crops up in Wikipedia is that, while it (like all encyclopedias) is a summary write-up and hence shouldn't be cited as a primary source, you have "traditional" sources such as newspaper that will pick up some incorrect fact in Wikipedia and print it... without citing Wikipedia as their reference. Meanwhile, someone will challenge the erroneous entry in Wikipedia on the grounds that it has no reference, so the error is removed. But then time passes and someone adds the erroneous data back in... this time citing the "traditional source" as their reference, and now the ereror is much more difficult to fix!

The real problem here isn't that Wikipedia is subject to erroneous entries -- both malicious and inadvertent ones --, as everyone is well aware of this problem... but rather than people put far too much faith in the veracity of traditional news sources such as newspapers, books, and TV news. Oh, and circuits published on the Internet. :-)

There are some schools that ban Wikipedia as a source... which is certainly fine so long as they ban all encyclopedia-like references as sources. But some single out Wikipedia, yet allow other web site references, which is an incredibly bad idea if you're trying to encourage veracity in reporting.

---Joel

A lot of them ban Wikipedia entirely, which is unfortunate as it can often be a much faster way to find a reliable source than Google.

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And still the clear ASSumption that any reference is valid.

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The essential requirement is for a current limited LDO regulating at full charge battery voltage, with appropriate temperature coefficient compensation, between the solar cell and the battery/load tie-in point. A simple diode will not do this, the solar cell will attempt to run the battery and ciruit voltage up to the highest voltage/current supported by the irradiation. In the kit original circuit, TR3 is a VBE multiplier, which should remain linear, and maintains the emitter voltage of TR1 at (1+R1/R2)*VBE. This should be set close to VBATT,FC, the full charge battery voltage. TR1 is not necessarily saturated until the battery nears full charge, at which point TR1 base current increases by a factor in the the range of 10-100x with a corresponding increase of the TR3 VBE to be multiplied by 60mV-120mV, overcoming the VEC,SAT loss of TR1. The inherent power limit of the solar cell is relied upon for the overall circuit current limit. Although not as precise as could be, the basic circuit shown in the kit schematic can probably be made good enough for the intended purpose and is way more than just an overcomplicated diode.