Re: DC Power Supply Question


"kell"
>
> Another issue: some wall warts don't have any filter caps in them.
> That means the voltage drops briefly to zero 120 times per second.


** They are usually called " battery chargers " .


> Here's an idea I had that I would like to put forward.
> You should measure the ripple. Put a non-polar capacitor and a
> resistor in SERIES on the output of the wall wart and measure the AC
> voltage across the resistor. Use a 0.1 uF cap and a ten kilohm
> resistor. If the supply has an electrolytic filter capacitor of any
> size at all you should get only the tiniest AC voltage reading across
> your resistor, less than a volt. If the supply does not have filter
> caps, you will read something like five or ten volts ac across the
> resistor. I have never done this test, but just now did a quick back of
> the envelope thing, could have made a mistake. Let's hear from the
> pros.


** Most DMMs allow you to measure the AC ripple on a DC supply directly
using the AC volts ranges.


> Also, I occasionally find SMPS's in garbage bins, but I live in New
> York -- the dumpster divers' paradise.


** Don't the poor folk live in those things ?



........... Phil


.

Relevant Pages

  • Re: DC Power Supply Question
    ... you have to add your own filter cap across the wall wart's output. ... Put a non-polar capacitor and a resistor in SERIES on the output of the wall wart and measure the AC voltage across the resistor. ... If the supply does not have filter caps, you will read something like five or ten volts ac across the resistor. ...
    (sci.electronics.design)
  • Re: Wanting a circuit to find the average of a fluctuating DC signal ???
    ... increases the voltage across C decreases but is centered around the DC ... filter on the NE-2 relaxation oscillator circuit. ... 1K resistor and .1 uF capacitor. ...
    (sci.electronics.basics)
  • Re: draining filter caps
    ... Each time factor is the time it takes to lose 63.2% of the supply voltage. ... You model it with a resistor in series ... Although the caps build voltage, they don't get anywhere near a full charge back. ...
    (alt.guitar.amps)
  • Re: Lets talk about input protection against ESD (human body).
    ... regulator with a low amount of output capacitance the regulator can ... source that has enough caps to weather the ESD surge. ... voltage drop is much less than the BAV99's. ... what resistor is in front). ...
    (sci.electronics.design)
  • Re: How does it affect power supply operation if filter caps are doubled in size?
    ... Tom Biasi wrote: ... >>comes the filter stage between the supply voltage and ground) ... Are you sure the caps are in series? ... > filter caps are not the norm. ...
    (sci.electronics.basics)