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voltage circuit question
MonMotha:
Basically, you're using an external pass transistor which can handle higher current than the one built into the 7805. This transistor will still dissipate 14W, and it will need to be heatsinked to the excess. In fact, you'll probably need more than one transistor just due to the power dissipation, and then you have to make sure they're well matched. You simply cannot get around the power dissipation issue using a linear solution like this. Total power dissipation MUST be at least 14W due to the nature of this kind of regulator. 14W is a surprisingly large amount of power - things will get TOASTY.
If you are interested in using an external transistor, there should be an example in either the 7805 datasheet or a related app-note. The 7805 with its feedback ends up acting as the "signal generator" in the example you posted. See figure 14 of the fairchild datasheet. May differ in others.
Seriously, just go buy a switcher. These have efficiencies topping 90% in some cases. Even if you don't care about the power efficiency, you won't have to deal with the heat.
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