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5V 3A PSU

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Post Options Post Options   Thanks (0) Thanks(0)   Quote peterb Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2018 at 7:59pm
I seem to recall radians were a useful way of describing angles in the many equations that I was exposed to doing my degree. The fact they included PI offered equation simplification and like many units under the SI system, it is defined as 'derived'.
The much maligned Wikipedia has some useful things to say about them and dBs, worth a look if want to consolidate the learning!
This link gives a nice visualisation of 2PI radians.
Peter
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Dual 505-1, Cyrus CD T, DIY 80W MosFet amp and PreAmp, 2xKEF 103.2
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2018 at 10:05pm
Yes, six and a bit. Near enough, but if you need better I recommend a simulation tool, or use a trimmer and AOT.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2018 at 9:37am
As seen on another topic -



This had to be done to make the voltage regulators do their advertised "guaranteed 3 Amps". They are also supposed to do in excess of 3 Amps. But if you look at the small-print you will see the qualification "at 25 degrees C".

I have yet to test the above to see if it will do a continuous 3 Amps. What happens is that if the voltage regulator heats up, as it will because of the power dissipation (there is a voltage drop across it which multiplied by the current equals watts), it starts to current-limit to protect itself.

Many years ago I was given the job of making an 18-0-18 V plus 12 V version, and that needed a tunnel heatsink with a fan, and then 6 Amps was ordered which required two such circuits in parallel with "diode steering". The 6 Amp unit used two fans.

What we tend to forget (me included) due to today's fantastic high current plug-top power supplies, is that linear is very wasteful of energy. A little plug-top or desk-top SMPS can do 3A and run cool.

But mincing high current ultrasonic square waves in inductors is a rather silly thing to do. Politicians are not interested in physics you see, and have zero respect for engineering (or engineers). Politicians are only interested in a different kind of power: "only power, pure power... power is not a means; it is an end." (O'Brien, Eric Blair's 1984).

The earliest long distance radio transmitters did very much the same; I made one as a child and screwed up radio reception on my street...

Linear, because it switches a sine wave at low frequency, with low and controlled ripple, radiates very little energy (sod-all in fact).

The voltage regulator used can dissipate up to 30 watts (suitably cooled), which at a current draw of 3 Amps means a maximum input output differential of 10 volts. The device itself needs 2.5 volts. Any less than that and it drops out of regulation. So we have 7.5V to allow for component and mains tolerances/fluctuations, and ripple, which we will always have no matter how big we make the reservoir capacitors.

Its maximum output however is 15 watts (5V x 3A) which makes it wasteful. As such, seeing that it's an external power supply, it is not legal to sell it.

It is OK if it is inside another product, such as a wasteful class A amp!

But because the politicians wanted to ban the little linear wallwarts, which are predominantly single voltage - only one voltage at a time, which means switchable output wallwarts also got banned - they left multiple voltage (at the same time) external power supplies alone... for the time-being.

Therefore, if a 5V linear external power supply also does 3.3V at the same time, it is OK to sell it.

If you're following me so far (Pinch) it will now be seen why there is a heatsink on both sides. One allows 5V 3A and the other allows 3.3V 3A. It would also look odd I suppose if it was lopsided...

But you will not be able to get 5V and 3.3V both at 3A. The 3A is the total load, EG: 2A on one voltage, 1A on the other.

That's enough rambling for this session. Load test coming up.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2018 at 11:12am
Oh, a point for Pi users...

This power supply uses internal wiring which is up to the job, but all wires have resistance, and although the regulators do their advertised load regulation, the wiring alters it from 0.3% to 1.4%.

Therefore the voltage will be around 0.07 volts less on load than it is off load.

Now look at the Pi power connector. It has to have skinny wires to solder to it's hair width terminals. You will get a bigger voltage drop due to its wiring when it requires its 2.5A. It will not be this power supply's fault.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote msphil Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2018 at 12:57pm

Looks good to me. I'm really looking forward to hearing the results on my system when the final load test is done. My mouth is fair watering at the prospect of getting the finished product. Sounds like it will be really worth the wait!

'You are, through your soul not your body, a human being.'
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BackinBlack Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2018 at 1:14pm
I have noticed that it is not uncommon on devices (Tablets, Phones) that charge via micro usb that the connectors and adjacent cable often become warm, if not hot. The cables/connectors often fail prematurely, particularly if they have suffered fatigue due to flexing of the cable at the connector. They are then replaced by cheap lightweight aftermarket cables that usually have very light gauge conductors, even less capable of carrying the higher current without overheating.
As has been mentioned before these micro usb connectors are not designed or specified for more than 500mA, although the supplied chargers are capable of 1A or more.  I'm surprised there aren't more incidents caused by the overheating of these connectors and cables.
At least the recommended Pi PSU, rated at 2.5A has a heavier cable, but still relies on the micro usb connector. A properly rated connector, cable and power supply will make the Pi much more reliable and safe.
Just listen, if it sounds good to you, enjoy it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ash Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2018 at 7:38pm
Looking forward to its release.
We do not see things as they are. We see things as we are.
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