I'm trying to build the power supply described here.
R1: 1K8 1/4W Resistor
C1,C2: 4700µF 25V Electrolytic Capacitors
D1: Diode bridge 100 to 400V, 1.5 to 4A
D2: LED Any type and color
SW1: SPST Mains switch
T1: 230V Primary, 30V Center-tapped or 15 + 15V Secondary, about 45 to 60VA or 1.5 to 2A, Mains transformer
PL1: Male Mains plug with cord
In fact, I already did it and it's working. The problem is that the output voltage is higher than the voltage supported by the IC (ne5534), that should be 22V (maximum).
After I built it, I measured +-24V. I would like to limit it to +-20V. How do I do this?
Searching the internet I found that I could use LM317/337 (since I need +/- output). Or I could use 78xx/79xx (it seems to have a 18 or a 24 version, but not a 20V). Or I could use a resistor. Or diodes (regular or zener).
I would like to use the resistor/diodes solution, since I have some spare/salvaged ones In hand.
If I calculated (V = I*R and P = I^2 * R) correctly, to use resistors, I should use two 4R 4W (one for each output).
If I use standard silicon diodes, it will require a minimun of 6 (in series) for each (12 total).
The approach that I prefer is the use of a zener diode, but unfortunatelly (I'm a hobbyst) I dont know how to calculate it... My problem is with the current. How much power the diode/resistor should accept (considering 1A). I found many papers describing zener theory, but I didn't manage to solve it by myself... It seems that a 20V 1W zener diode would fit, but it will require the same 4R4W resistor to regulate the current...