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5V 3A PSU

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Graham Slee View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 17 May 2017 at 7:11pm
Things were going fine until 3.3V was mentioned. Overvoltage protection is easily implemented on the 5V rail by use of a Maxim IC and MOSFET, but as nobody uses them on 3.3V, nobody stocks them. Blame legislation (the EU) which has sent everybody scrambling for switched mode - the thing we want to avoid like the plague here.

Why bother with overvoltage protection?

1. failure of the voltage regulator
2. an inductive load

Both can lift the voltage above a safe level for the ICs being powered and damage results. I don't want to be paying compensation for that sort of thing.

An explanation of the sort of circuit which can cause an inductive load, is when a BJT 555 timer is used without suitable decoupling. The power supply spike it causes can result in an increase of the DC rail. OK if it's one-shot, but say it was used as an oscillator circuit? The spikes are then a continuous thing leading to a gradually increasing voltage rail. That's a user fault, but most users won't see it that way - experimenters can lack the understanding. Best to have overvoltage protection to shut such a situation down before anything costly breaks.

3.3V is therefore the stumbling block as regards overvoltage protection. I am having the idea of driving a 5V overvoltage chip via a charge pump from the 3.3V rail, if only I can ensure the charge pump outputs 5V from it. Often it's a straight voltage doubling which is 6.6 volts, so I need to make it 5V.

Anyway, it's fun (I suppose) to still be doing such crazy things when I thought I was going to be semi-retired... Wink
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 17 May 2017 at 10:17pm
After many hours of thought I think the 3.3V output fed via a diode drop to a ADM660 charge pump will trick a MAX4840A into thinking it is working on a 5V supply. Indeed it will be, as the output of the ADM660 will be very close to 5V. The gate drive output however, will not be driving a MOSFET on this 5V rail - the gate will drive a MOSFET on the 3.3V rail. I think that should work fine. Just need to build it and test it. Could take a week or two as I will need to get a prototype PCB designed and made for it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 19 May 2017 at 11:28am
On second thoughts Linear Technology's LTC4365 overvoltage chip looks like it will do 3.3V, but the datasheet contradicts itself saying the input voltage needs to be 3.5V to work, and then goes on to discuss operation down to 2.5 volts Wacko
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jwatson Quote  Post ReplyReply Direct Link To This Post Posted: 19 May 2017 at 2:09pm
Hello Graham, I'd also be interested in a 5/3.3 supply for my Raspberry Pi / Hifi Berry Digi + Pro, either as a finished product or kit.
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Majestic DAC -> Solo UL -> HD650
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 19 May 2017 at 11:25pm
I'm still interested in having one of these PSU's please. In making DIY 5V supplies to keep me and Phil going till the proper GSP 5V supply came along I found the Squeezebox Touch is fine with 500mA and 1A is plenty. My PSU's are better sounding IMO than the standard Touch SMPS but are quite crudely laid out and I know from my other GSP gear your expertise in PCB layout will one of several reasons why a GSP PSU is worth waiting for!


Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ServerBaboon Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2017 at 1:10pm
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Like Ian I am interested for my Raspberry pi collection.

On a side note there is a bit of market for these with a usb for Raspberry. I only say bit because a competitor or two has the product or people on diy talk about making there own. Not sure if anybody sells them.

The only problem with the Raspberry pi is due to its low cost people tend to be cheap as well.
Steve

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Various bits of GSP Kit ..well two so far, unless you count the cables that is.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote peterb Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2017 at 12:55pm
How timely i came across this thread, I was contemplating breadboarding a LM317 transistor combination to replace the SMPS currently supplying my PI HiBerry DAC, but it seems GS is going to save me the effort! (but not my bank balance!)
Peter
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Dual 505-1, Cyrus CD T, DIY 80W MosFet amp and PreAmp, 2xKEF 103.2
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