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| How to check a 5V phone charger for good DC? |
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| vtsteam:
I've got a bunch of 5V phone chargers from old cheap flip phones. I'd like to use one for my DRO project, but it needs to be regulated and fairly clean DC, not a charger which depends on filtering/regulation in the phone itself to clean up the power. I know some chargers are good DC and some not. This is one that does not just have a USB socket, but includes a cord to the phone. The legend on the charger does say 5.0V DC ... but is it good DC? How can I tell without an O-scope to look at the output for noise? I do have a DVM. And/or is it possible also to hook up a headphone and just have a listen? If so I imagine I'd need a fairly high value resistor in series? Or, any other ideas....? |
| awemawson:
Stick an appropriate load resistor across it and measure the AC ripple via a capacitor with your multimeter |
| vtsteam:
Thanks Andrew, but what value appropriate load resistor, capacitor, and what value am I looking for on the multimeter reading? The output is rated at 550 ma btw. |
| awemawson:
Ohms Law is your friend. 5 volts @ 550 mW so about 50 ohm should suit. (47 nearest preferred value). Large electrolytic - actual value unimportant but say 100 microfarad at 15 volts working. It just needs to be low impedance at 50 60 Hz. Ripple voltage should be approaching zero but probably a few 10's of millivolts - hundreds being to much. |
| vtsteam:
Thanks Andrew. Ohm's law is well understood here, but doesn't attempt to set a value for "a load" since there's still the practical question of how much of a load? Looks like you're saying a load at half the charger's max rated current is what you recommend, so I'll go with that. And thanks for the cap and acceptable V values. :beer: |
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