At 02:12 10/24/2001 +0200, Germain Morbe wrote:
>It deliveres up to 3 mA at 5V and has some advantages over other approaches.
>
>At the 1st glance it is small lightwight and really cheap.
>At the second, due to dividing the series resistor into two parts, you get
>an excellent line filter at no extra costs which is burst proof up to 4kV.
>Given todays EMC requirements, the capacitor approach as mentioned earlier
>by someone else is no longer recommended since the caps impedance drops at
>higher frequencys and therefore prefer burst and surge pulses over line
>voltage to feed your circuit.

These are indeed some advantages, but there is also a disadvantage: power
consumption. Even at only 3 mA, you get close to 1 W. If you need more
current, like 20 mA, this is close to 5 W, which in many applications is
too much. Avoiding excessive power consumption is the main reason for the
use of caps instead of resistors.

Has anybody had to abandon such a capacitor-based power supply because it
didn't fulfill EMC requirements?

ge

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads