If your solenoid is only activated for 0.2s at a time, then you don't 
need a power supply rated for 3 amps.
Use a 24v unregulated wall-wart to power the solenoid with 1000uF 
capacitor filtering it.
To get the 5v, use the old and inefficient (though good enough) MC34063 
as a buck converter. The data sheet (onsemi.com) has many examples of 
circuits that would work with some modifications. There are also 
countless parts from National semiconductor etc.
HTH
--
Martin K


Jake Brownson wrote:
> I am trying to design a power system for a project with two voltages.
> I need 1A@5V for the PIC and some other components, and 3A@24V for a
> solenoid. The solenoid will be activated for very short periods of
> time (roughly .2 seconds) rather infrequently (let's say an average of
> once every minute). My good friend the 7805 just isn't cutting it for
> me here.
>
> The power system must (in no particular order):
> * provide 1A@5V continuously
> * provide 3A@24V for very short periods of  time (solenoid)
> * connect to a US 120V wall socket
> * be as inexpensive as possible
>
> I have explored these options:
>
> Wall AC->DC adapter 4A@24V with a 7805 for the 1A@5V
>    I probably got a few guffaws from this one. Yes, the reg got a bit
> warm. Plus, a wall transformer of this caliber is quite expensive.
>
> Wall AC->DC adapter 4A@24V with a switching regulator for 1A@5V
>    This could possibly work, but the cost is still rather high for the adapter.
>
> Open Case Dual Supply Switching Regulator
>    Anything I found that could handle 3A@24V was $50+.
>   
...
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