If there is a bridge rectifier you would probably have 120 Hz, not 60.

>From my experience the C across the diodes will reduce HF interferences =
-
and 4 are really necessary, a rule of thumb says between 0.01=B5F to 0.1=B5=
F
will be OK.

Regards
Enrico

----- Original Message -----=20
From: "Jose Da Silva" <Digital@JoesCat.com>
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Sent: Sunday, November 20, 2005 9:06 PM
Subject: Re: [EE] capacitors on a diode bridge


| On November 20, 2005 11:28 am, Peter wrote:
| > On Sun, 20 Nov 2005, Spehro Pefhany wrote:
| > > You could also have solved the problem of audible noise by using
| > > Schottky diodes for the bridge.
| >
| > Shottkys do not have this problem ? I did not know. But who would use
| > a Shottky in a not-so-low voltage mains rectifier ?
|
| It would improve the hum, but I don't think it would cure it.
| Regular diode drop is about 0.7v while schottky is 0.2v, so the hum
| would drop to 1/3 it's sound level.
| If you were to graph a 60hz cycle and look at the crossover points wher=
e
| one diode stops conducting while the next starts conducting, it is not
| a smooth transition.
| Yes, 0.2v drop is better than 0.7v drop, but doesn't afford the smooth
| transition a capacitor provides.
| Another trick for 60 hz "hum" would be to use a ferrite core choke as
| suggested by the ARRL manual, but the suggestion was probably made when
| winding your own choke was cheap and you had a good-sized cabinet to
| place the ferrite core in... now-a-days, people see a 1cent cap
| (minimal board space) versus a $1.00 choke (plus some PCB realestate)
| as the better way to go.
| I guess the RC resistor solution (vs LC solution) people argue about is
| a compromise in terms of benefit in board space and money.
|
| Cheers!
| --=20
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