steve said:
I have a friend who needs to convert 10-11v AC to 9v DC. This is for a
small foot pedal on a guitar.
Can anyone diagram something like this. I have a basic understanding of
circuits and am fairly positive I could build it if I have a diagram,
as I dont think it would be very hard. Perhaps even just a diode. But
the diode might cause too much voltage drop.
Regards
10V AC is 14V peak to peak, so this would work. How did you measure this
voltage ? If it is the open circuit voltage, you may have a too large
voltage drop under load to be able to use this suply.
You'll need a basic regulated power supply like this :
Bridge ____
rectifier 1000uF 100nF | | 50uF 100nF
+-+----+----+----|7809|---+----+--- +9V
A A | | I|____|O | |
AC ----+ | --- --- | --- ---
in ----(-+ --- --- | --- ---
A A | | | | |
+-+----+----+------+------+----+--- Ground
(created by AACircuit v1.28.6 beta 04/19/05
www.tech-chat.de)
I'll explain the different parts a bit :
The diode bridge is used to rectify the AC, that is invert all negative
portions of the waveform and get only positive half-sines.
Next, the 2 capacitors in parallel filter this rectified waveform, the
big 1000uF (use 25V type at least) to filter ripple and the 100nF to
filter higher frequency noise. You have about 13V DC at this point.
The 7809 regulates the voltage down to 9V. You need at least 2V higher
voltage at input for this to work, so 13V would do, but as I said before
under load your power supply may not be able to keep this voltage.
When looking at the regulator with the inscriptions facing you, the
three leads are in order : input, ground, output.
After the regulator, add two more capacitors for improved filtering (use
16V models at least).
That's it.
vic
