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My take on...well, something, anyway

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My take on...well, something, anyway

Postby LongRunner » March 5th, 2014, 3:26 pm

The subject is "Electronics Demystified" (ISBN 0-07-143493-3), authored by Stan Gibilisco and published by McGraw-Hill in 2005. Here's my assessment of it:

What it does right
The fundamental concepts, at least those I checked, are correct. Not a lot else to say here, really.

The stumbling blockade
The first obvious problem is that at no point does it elaborate on the forms of passive components. Then you make your way to chapter 4 (about power supplies)...

In the part about step-up transformers:
The cathode-ray tube (CRT) in an old-fashioned television receiver needs several hundred volts.

If you're thinking of the EHT, I'm afraid you're off by a factor of about 100.

On half-wave rectifiers:
Half-wave rectification usually works all right in a power supply that is not required to deliver much current, or when the voltage can vary without affecting the behavior of the equipment connected to it.

Yeah, right... See this article, which clearly states that the resultant DC bias can easily cause the transformer in a linear supply (ED has no mention of switchers, so...) to saturate, rendering half-wave rectification outright unusable for any significant load. Half-wave rectifiers on the mains are really not advisable either (though some small switching plug-packs do just that, albeit (bizarrely) with two diodes, one each in live and neutral - whether or not you can fit PFC into the budget, the least you can do is use a bridge).

On full-wave rectifiers:
In this circuit [a PSU using either split-phase or bridge rectification], the average DC output voltage is about 90% of the rms AC input voltage.

That's with choke-input filters, which are rare in modern equipment due to the high cost of the choke used. With the common capacitor-input type of filter, the peak DC voltage is the rms AC input voltage times the square root of 2, minus the diode drops, and the average is only somewhat lower.

On voltage doublers:
In practice, voltage-multiplier power supplies work well only when the load draws low current.

The "bridge" type of doubler (as is formed in an old-style PC PSU set for 115V input) - which, of course, is the only one illustrated - doesn't actually have that problem. While each capacitor works at only 50/60Hz, this merely requires them to be sized accordingly. It's the "cascade" type of multiplier (which, bizarrely, isn't so much as mentioned) that suffers.

It goes on to mention Zener-diode shunt regulators, but the resistor required to limit the current is mysteriously missing from the page. Then when you reach the part about line transients, it claims that what are clearly supposed to be Y-class capacitors (which are unlikely to exist in linear PSUs anyway) are used to suppress spikes. I mean, seriously???

In the part about batteries:
Paste-type lead-acid batteries can be used in consumer devices that require moderate current, such as laptop computers and portable camcorders.

In 2005?! (Mind you, it's no ordinary event that gets that much emphasis from me.)

In case it isn't entirely clear, I'm not bothering with nitpicking here, as well...these are not nits. They're much bigger than that.

There is a brief mention of operational amplifiers, but nothing about how to actually use them, which is strange as they're quintessential to modern analog circuits...

So what can I say? A good part of the book is half-baked at best. As for the review, maybe it's not entirely relevant, but at least it gave me something to do.

For what its worth, I don't have "Teach Yourself Electricity and Electronics" (the book targeted at those having completed ED). I can't say I'm inclined to go out and buy it, though.
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Re: My take on...well, something, anyway

Postby c_hegge » March 5th, 2014, 4:08 pm

Yup. That's a bit of a problem. I can't believe how inaccurate and/or out of date some of that information is.
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