On 5/12/05, Lindy Mayfield wrote: > Is it safe to say then that a ripple or an uneven DC output from an AC to DC converter is due to the omission of some very cheap and simple passive components? And if so, where they left out just to keep costs down because they aren't necessary when charging a battery or providing the input DC supply like a wall-wart does? And as a hobby electronics person, I can just understand that and add them myself if I really need a more filtered DC output? > > (I would like to say I've really learned a lot from this thread and I do really appreciate the time people took to explain things.) > I think you're catching on. What makes this discussion kind of confusing is there are generally two kinds of plug-in adapters: 1) Old-fashioned "wall-wart". AC input->Transformer->diode bridge->big capacitor. These are not very well regulated. Due to resistance in the transformer, the output voltage goes down as you draw more current. At no load they generate a voltage about 40% above rated. At the rated current, should output the rated voltage. If it is made for charging only, the capacitor may be omitted or skimpy. You can compensate with a bigger capacitor in your circuit. 2) New-fangled "brick". AC input->rectifier->high-DC voltage->switchmode regulator->output. These are useally pretty well regulated to the rated voltage and ripple should be pretty small too. It sounds like you've got the second type. If you don't have a scope, you can measure ripple by setting your voltmeter on AC volts with a capacitor in series to block DC. (most multimeters have the capacitor built-in for their AC range, but some analog ones don't) Ripple will go up as the load increases, so measure under the load of your circuit. Note, the ripple is not exactly sinusoidal, so RMS readings will be slightly inaccurate with this method and a typical cheap meter. Still, it's in the ballpark to tell you if ripple will be a problem with your supply or not. Regards, Mark markrages@gmail -- You think that it is a secret, but it never has been one. - fortune cookie -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist