First time poster - this site's been really helpful for me, so thanks to all of you. I'm working on my first electronics project not from a kit, and am attempting to make a variable power supply. I'm using this schematic as a reference: http://www.ladyada.net/library/equipt/diypsupp.html However, I've modded it a bit:

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I will be using a wall wart to power, and am planning on using a 19V power supply, with the option to use smaller adapters if necessary. I'm not certain if I got the symbols right, but the V and A represent a digital voltmeter/ammeter. My most pressing questions (in order of importance):

  1. What connection do I make with the ground that is located below R2?
  2. I'm interested in having a light-up switch for power. What would be the best way to draw the 12V it requires for the bulb?
  3. I can certainly test this one out, but I'm wondering if I have the voltmeter and ammeter connected properly.
  4. How might it affect my circuit if I increase C3 to be a 2.2uF cap? This may be what's available to me, and it seems like it won't impact the circuit negatively, but I want to be sure.

Thank you for any thoughts or suggestions!

  1. The connection to ground is not required. Sometimes there is an actual connection to ground but like in this circuit the symbol is used only to state that node should be considered as ground.

  2. A resistor in series with the light bulb would work. Pick one with a resistance that drops 7V (from 19V to 12V) at the current that your light bulb draws. If your bulb is a 1W, this resistor would be around 75 ohms and waste about 1/2W. I would recommend using an LED rather than a light bulb.

  3. Yes, the voltmeter and ammeter are correctly placed. With the ammeter in series with the load and the voltmeter across the outputs of the power supply.

  4. Rather than replacing C3, add your additional capacitor in parallel. As the capacitance of a capacitor is frequency dependent and smaller ones react faster to changes in voltage.


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