I apologize if this question has been tackled, I can't find any good resources... I am building a device which has a light sensor and light emitter (LED array). The sensor is very sensitive to changes, and as such the emitter has to provide a very constant supply of power.
The emitter runs on 9V at 800 mA. I have a 12V AC adaptor (wall wart) and am using two LM7809 regulators with bypass capacitors on both sides. Unfortunately the voltage still oscillates at 60hz with about 400mV peak-peak, which is much too high. I can't seem to get it any lower by adding capacitors.
Any resources which will help me smooth out the power??? Thanks!
I apologize if this question has been tackled, I can't find any good resources... I am building a device which has a light sensor and light emitter (LED array). The sensor is very sensitive to changes, and as such the emitter has to provide a very constant supply of power.
The emitter runs on 9V at 800 mA. I have a 12V AC adaptor (wall wart) and am using two LM7809 regulators with bypass capacitors on both sides.
Probably best to show the circuit diagram. You mention two LM7809 regulators. How are you using those TWO regulators? And did you use rectification diodes and things like that in your circuit?
terryking228:
Hi,
WAIT.. you said
12V AC output?? You need 12V DC and your regulators should then give you 9V with only millivolts of ripple...
It's 12V DC output (sorry, I'm used to calling them AC adapters cause it's 110V AC input), rated for 1000 mA and I'm drawing 800 mA. I'm getting over 400 mV of ripple at the adapter and 200 mV once it's filtered past the 7809
Tyguy:
Diagram attached, note there are two of these arrays and each one has a 7809.
The source is DC, so no need to use rectification diodes???
Ok.... I was just assuming when you mentioned '12 AC adapter', then it could have meant a 12 V AC source, since there really are such AC sources out there.
According to this link here .....click here..... the manufacturer recommends (in ADDITION to your big capacitors).... might be beneficial to put in additional small CERAMIC capacitors in parallel with your existing big capacitors. Like 0.33 uF on input and 0.1 uF on output. Note CERAMIC.
