zachtheterrible said:I just tried using my 5v SWMPS for my cell phone as a powersupply for a circuit that I'm building. The SWMPS has a ripple voltage at around 625HZ. Unfortunately it is wreaking havoc on my circuit.
Just wondering if there is any way of suppressing this? I tried decoupling capacitors with absolutely no change. Would an inductor in series w/ the supply work?
zachtheterrible said:Its not that audio, it runs fine off of 4.5v from AA batteries. The circuit that I'm doing is an RX module, HT12E decoder, and a 555 to drive a piezo buzzer when the decoder output is activated.
I did some calculations, and I'm not sure if they're right but here they are:
@ 625HZ:
100uf cap- 2.5 ohm capacitive reactance
1000uf cap- .25 ohm capacitive reactance
100uh ind- .39 ohm inductive ractance
1000uh indu- 3.9 ohm inductive reactance
I'm thinking that I'll have to use capacitors instead of inductors because it would take a ridiculously large inductor to introduce any sufficient reactnace to 625HZ. Unless my calculations are off? I'm still struggling with converting uF and uH to F and H. I don't have a scientific calculator unfortunately.
A low ESR 10000uF capacitor would probably work because it would only have .025 ohm capacitive reactance.
I just bought another phone charger switcher supply off ebay for a couple bucks, and they seem much smaller in the picture than mine, so I'll bet that the frequency is much higher like yours. Maybe I'll get it in the mail today and itll solve my problem :lol:audioguru said:Hi Zach,
I bought some 5V/2A switching tiny wall-warts for only a couple of bucks each. They have a very small ripple voltage that is easily filtered with a small cap because they switch at 30kHz.
Change your 625Hz power supply to a linear regulated one or make one. :lol:
I guess switching supplies are quite a bit different than normal wallwart supplies. In a normal supply, its basically just a full-wave bridge rectifier that supplies DC, and I thought that the capacitor just smooths the output out. From what you're saying, it seems that in a switching supply, the capacitor supplies the load all by itself because the transformer supplies it with pulsing DC? I'm kind of confused here :roll:Regarding ripple voltage, the main thing to understand is that when your transformer is not charging the output capacitor and supplying load current, the capacitor all by itself is supplying the load current. Over a small interval of time , this discharges the cap causing the voltage to droop (the cause of the ripple voltage).
So how exactly do I find C? Isn't the equation set up to find I?I=C*(( the change in voltage of ripple) / ( the time period of the ripple voltage))
zachtheterrible said:I guess switching supplies are quite a bit different than normal wallwart supplies. In a normal supply, its basically just a full-wave bridge rectifier that supplies DC, and I thought that the capacitor just smooths the output out. From what you're saying, it seems that in a switching supply, the capacitor supplies the load all by itself because the transformer supplies it with pulsing DC? I'm kind of confused here :roll:
I=C*(( the change in voltage of ripple) / ( the time period of the ripple voltage))
So how exactly do I find C? Isn't the equation set up to find I?
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