Re: Boomerang Power Supply

[SoundFNR@aol.com]

Hi Bret, hey, someone actually reads my posts.
> Andy,
>  I disagree with your conclusion that using a dc source to an ac
>  (rectified) input of a device like the boomerang can possibly damage
>  the rectifier's diodes or that 'things will get a little hot'.
>  
>  As far as I know rectifier circuits and diodes are rated by max current
>  and max voltage, not power. Diodes will fail if you exceed their
>  current rating, or if you exceed their breakdown voltage rating.  
> 
I just checked, its average current and RMS voltage, for a rectifier.
I think current is specified rather than the power in order to make design 
easier.
(so we don't have to use P=IV)   
>   At a given moment, half of the full wave
>  rectifier's diodes carry ALL of the current.  When the phase of the ac
>  input changes, the other half of the full wave rectifier circuit
>  carries ALL of the current.  So, each of the diodes in the bridge must
>  be rated to carry ALL of the current (plus margin).
  
So each side of the bridge carries full current for half of the time, which
means that the average current is half the full current.

>  The half wave rectifier is simpler.  In this circuit the current flows
>  through the diode half the time when an ac voltage is applied.
 
Actually current only flows for a small portion of the cycle, depending
on the size of the reservoir capacitor.

>  When a 9v dc source is applied to the device's 9v ac (rectified) input,
>  the current through the rectifier is not increased (the device still
>  draws the same current), 

Thats right tho' , if there's a single bridge rectifier component it would 
have the same amount of power/heat to disipate,so should be OK.
If there's discrete components for each half of the cycle, then with DC
I/P one side has to take twice the expected current, so twice the
power, so twice the heat.   
 
>  On an anecdotal note, the Roland GR-09 guitar synth expects an AC
>  input, but I have used a DC input (inside a car) and not seen any
>  problems.
  
Yes, and we've yet to hear any anecdotes along the lines of 
"I used a DC supply and fried my JamMan"

andy