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by corax 08/21/2003, 10:28am PDT |
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Dunc wrote:
Choson wrote:
Also, I've got an AC-DC adapter here from a friend that works on Beijing AC input, and has rated output DC4.5V 1A. I've been trawling Google News for a definitive answer, but those places are full of people arguing about whether or not that extra 0.4A is no big deal or if it'll blow the load up. Anyone want to give this one a shot? I have no idea how to tell if it's a "regulated adapter", also.
I say go ahead and use it. The deal with DC adaptors is they're supposed to look (electrically) like Ideal Voltage Sources - that is, for any amount of current you draw from it (up to the current rating) the voltage remains constant - 4.5V in your case. To your MP3 player, a 4.5V supply with a 0.6A limit should look no different than a 4.5V supply with a 1A limit, since the player shouldn't be exceeding the 0.6A limit anyway. People don't design electronics expecting to hit the limit of their DC supplies in normal operation; they always over spec the current by a certain percentage. So your friend's adapter can supply more current than your old one, but should do the job just as well.
Dunc
Not so fast there, Sparky. Your average DC adaptor doesn't contain a fancy-shmancy voltage regulator, so it doesn't behave like an ideal voltage source. For example, a transformer rated at 9V/300mA will typically measure 11+V unloaded, dropping to around 10V at 50mA load. A 9V/1A supply will measure nearly 13V unloaded, and still push a full 12V across a 50mA load. Pull out some wall warts and take some readings, you'll be (HURF) *positively shocked* at what you find!
The net result is that driving a small a load with a large a transformer can result in operating voltages well outside the value printed on the transformer. This may not be a problem if the device you're connecting to the transformer has its own voltage regulator that can handle the input voltage adequately. But if you want to play it absolutely safe, you should match both the voltage *and* current ratings on the transformer to the ratings on the device. |
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