Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!rutgers!elbereth.rutgers.edu!ron.rutgers.edu!ron From: ron@ron.rutgers.edu (Ron Natalie) Newsgroups: sci.electronics Subject: Re: 60 Hz hum filter Keywords: any ideas Message-ID: Date: 20 Feb 89 18:59:51 GMT References: <2313@rayssdb.ray.com> <4004@midas.STS.TEK.COM> Organization: Rutgers Univ., New Brunswick, N.J. Lines: 10 Well your average AC adapter/Ni-Cad charger is a pretty cheap thing. What it is is a step down transformer (with enough resistance in the windings to be a current limitter as well) and a diode. When charging NiCad's you don't need filtering and you don't need voltage regulation. When running the calculator/radio/whatever off the charger the battery pack provides the voltage regulation, hence the warning not to operate without the batteries in place. You probably need to add a some nice capacitance accross the rectified AC to smooth it out enough not to be obnoxious. -Ron