bridge rectifier help

[madmurg]

I have just completed a bridge rectifier which I want to use to power my arduino from a 9v ac power supply. I have fitted a 6800uf 10v capacitor across the pos and neg. when testing it I found that I have 19v dc across the pos and neg. any ideas to what I have done wrong. I have not tried it with load on yet as I dont want to fry my arduino. am I right in thinking when I put load on the voltage will decrease.

 

[Harald Kapp]

Your AC source has probably an open circuit voltage (RMS) of 14 V. The capacitor stores the peak value which is 1.4*RMS (minus ~1.2 V for the rectifier diodes). The voltage will drop if you load the circuit. However, I'd recommend to bring down the voltaeg to a level that is more digestible for the arduino. I'd use a simple linear regulator (type 78xx where xx stands for the voltage - I don't know what input voltage the arduino expects) plus some stabilizing 100nF capacitors. Its easy, look it up in the 78xx's datasheet.

Regards

Harald

 

[davenn]

Hi madmurg
welcome to the forums


and speaking of the voltage out of the bridge rectifier. Asa rule of thumb, its a really good idea to have the voltage rating of the electro cap at twice the DC voltage out of the bridge. else the electro cap is likely to go bang.

Dave

 

[madmurg]

Your AC source has probably an open circuit voltage (RMS) of 14 V. The capacitor stores the peak value which is 1.4*RMS (minus ~1.2 V for the rectifier diodes). The voltage will drop if you load the circuit. However, I'd recommend to bring down the voltaeg to a level that is more digestible for the arduino. I'd use a simple linear regulator (type 78xx where xx stands for the voltage - I don't know what input voltage the arduino expects) plus some stabilizing 100nF capacitors. Its easy, look it up in the 78xx's datasheet.

Regards

Harald

But i am testing at the terminals where the a/c comes in and i am getting 9v a/c surely this would be 14v as well on open circuit.

 

[davenn]

But i am testing at the terminals where the a/c comes in and i am getting 9v a/c surely this would be 14v as well on open circuit.

is that with or without the bridge rectifier connected ?


D

 

[madmurg]

that is with the bridge rectifier connected

 

[madmurg]

attached is a scan of my circuit

 

[davenn]

OK ... Using a resistor divider is not a good way to go especially for supplying a uPC
there is absolutely NO voltage regulation and the uPC will NOT react well. Time for you to go to plan B .....

here is a really simple regulated 5V supply using the 9VAC plus or minus a few volts
that I have drawn up for you....

that should be really straight forward for you

cheers
Dave

 

[madmurg]

Thanks i will try this out

 

[BobK]

Or you could pick up a wall wart that outputs 5V at a flea market for $2 like I do

 

[davenn]

Or you could pick up a wall wart that outputs 5V at a flea market for $2 like I do

but there's no fun in that where's your sense of experimentation and adventure, Bob ?? hahaha


Dave

 

[BobK]

Well, I got tired of building power supplies when I was in high school, over 40 years ago. I still have a +- 12 V supply I built back then that uses zener diodes and a pass transistor for each supply and it still works fine. I am a programmer at heart (and by profession) so I spend most of my time using microcotrollers for inappropirate things.

Bob