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Why would a guitar effects circuit draw 300mA?
An incandescent light bulb would have to carefully sized for this purpose since they have a very large resistance change, something like 1:10 from cold to their operating voltage.Since the power supply is already regulated the fluctuation will not be there. you could also just put a 3 volt light bulb in series with the 9 volt load to create a 12 volt load. An Incandescent bulb will take up the fluctuation as well. The bulb must be a larger current draw than the amplifier or it will simply act like a fuse.
Hi there!
I have a power supply taken from an old compact pc. It's 12 V - 2.5 A output.
I read the previous posts, so I tried to calculate the value of the "simple-resistor" version.
Could you confirm that I'm right?
from 12 V - 2.5A to 9 V - 2.5 A
R = (12 - 9) / 2.5 = 1.2 ohm
W = (12 - 9)^2 / 1.2 = 7.5 W
So for easly convert the the voltage I need a 1.2 Ω 10W resistor?
Thanks and sorry for my bad English.
i like the sound of a light bulb, because it sounds simple, (like me!) does that mean if i stuck a 3v led in line i could reduce the voltage to 9v? my understanding of an led is that it can still operate with slightly more or less voltage than it's rating, so is it possible that it could act as a kind of buffer? just using up the extra volts?A light bulb uses a fixed amount of current and a resistor can be used to reduce the voltage.
But an electronic circuit changes its current requirement nearly all the time. When it uses a low current then the voltage will be too high if a resistor is used to reduce the voltage calculated when it draws its max current.
sweet... that's what i thoughtA power supply that can supply more current than needed is fine because the circuit draws only as much current as it needs.
this sounds like the proper way to do it, although a bit more complex than my head can easily deal with (without someone to really dumb it down for me!) and I'd like the option of being able to run more than 1A off the psu...With a 12V supply and only 9V at up to 1A is needed then you can use a 7809 voltage regulator plus the input and output capacitors shown on its datasheet. If the load current is near 1A then the regulator will dissipate 3W of heat so a little heatsink will be needed for it.
duh yeah....that makes a lot of sense... how about something like this?Most ordinary LEDs have a max current of only 30mA. If your pedal draws more than 30mA then an LED in series will smoke then die.