Frishkorn Posted November 14, 2007 Report Share Posted November 14, 2007 Just wanted a little more into how this circuit outputs 14VDC after the 7809. Am I correct in the assumption that the 7809 sums the +9VDC and the +5VDC to create a +14VDC output? I'm using my SID not only to add a synth to my growing studio but to also understand electronic design a little bit better. Quote Link to comment Share on other sites More sharing options...
Wilba Posted November 14, 2007 Report Share Posted November 14, 2007 You are correct.What can be confusing is connecting what looks like the "ground" of a 9V DC supply to the 5V supply.This is quite OK when the supplies are separate... looking at what goes into the 7809, you can see it is a separate 9V AC supply and therefore does not have the same ground as the 5V supply. The 7809 therefore regulates the input voltage so that it outputs 9V above (relative to) the common pin voltage, in most cases this would be connected to ground, in this circuit it is connected to a 5V supply so the output will be 14V above the "ground" of the 5V supply. Quote Link to comment Share on other sites More sharing options...
/tilted/ Posted November 14, 2007 Report Share Posted November 14, 2007 Am I correct in the assumption that the 7809 sums the +9VDC and the +5VDC to create a +14VDC output?Sort of.The term "sum" in the electronics world is more often used to describe mixing two (usually analogue audio) signals together.The way the 7809 (and all other 78xx and 79xx regulators) work is that they take an input voltage (ideally fairly stable, from a rectified and smoothed supply) and output a voltage which is referenced to the "ground" pin. In most applications, the "ground" pin is connected to 0 volts, so the voltage is (in the case of a 7809) would be +9 volts, reletive to the ground pin.In the case of the SID PSU, the ground pin is referenced to a 7805 regulator.Therefore the 7809 output is +9 volts, referenced to a voltage of +5 volts, referenced to ground.So the output is 0 volts + 5 volts + 9 volts = 14 volts.Which I suppose, is kind of what you said... ;D Quote Link to comment Share on other sites More sharing options...
/tilted/ Posted November 14, 2007 Report Share Posted November 14, 2007 Ahem!...and what Wilba said... ;D Quote Link to comment Share on other sites More sharing options...
Frishkorn Posted November 15, 2007 Author Report Share Posted November 15, 2007 Ahh see I knew there was a reason to join the forums ;D. Thanks for all your fast answers! Glad to see my brain does work every now and again.Most helpful forums I've ever visited and only after 3 short posts.Thanks again.- Frishkorn Quote Link to comment Share on other sites More sharing options...
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