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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: 25 Apr 2019 at 11:31am
Yes Peter, I'm sure they are Nuvotem Talema RS-Pro branded and made in Czech Republic and India. Took a bit of research to find that out. So much for ISO9000!

And otherwise they're of Polish origin and the Polish seem to know the UK and EU wiring colours.

But I suppose some Czech or Indian thought violet was a pretty colour for neutral... Wink

Anyway, I'm now at the point where I should have been yesterday afternoon, with a working power supply which now needs load testing, and over-voltage testing.

It meant scraping about for bits of heatshrink as the stuff I ordered from RS within minutes of the transformers, didn't arrive, although tracking says "out for delivery". The postman may only knock twice but Parcelforce only knock once...




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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 2019 at 1:15pm
First load test 5V rail

Output adjusted to 5.00 volts at load current of 3.03 amps. After 1 hour the case temperature local to the left hand heatsink rose by 27 degrees C above the 21 degrees C ambient room temperature, with 48 degrees C measured down a tapped lid fixing hole in the top of the heatsink.

The off-load voltage measured 5.1 volts, meaning the load regulation is 2 percent, with the wiring responsible for over 1.5 percent in voltage drop due to its resistance. Measurements at the device (the voltage regulator) showed approx. 0.33 percent which is within the device's specified range of 0.1 to 0.5 percent, and therefore the drop is not due to ripple.

Over-voltage trip (crowbar) at 6.05 volts no-load and 1.25 amp load current.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 2019 at 2:34pm
3.3V rail load test

The 3.3 volt rail is much more sensitive to the over-voltage crowbar trip simply because it has to be, since over-voltage tolerance of 3.3 volt devices is much lower. This trips at 3.58 volts.

Due to the longer connection wires there is a larger voltage drop. There is also greater device dissipation due to it using the same input voltage as the 5 volt section - raw DC being 11 volts on load.

I therefore set it empirically to give 3.23 volts on-load, which equates to 3.4 volts off-load, which I consider safe, the load regulation on the 3.3 volt output is therefore 5 percent. Using heavier duty wire will help reduce it below 5 percent.

The measured current at 3.23 volts is 3.02 amps.

It's just coming up to the one hour point and the temperature is reading 48 - 49 degrees C, and so there is a 28 degree C temperature rise locally on this part of the case.

I must add that I'm operating it with its lid off, and with lid on there will be more heatsinking, but then again, heat from the transformer will be trapped so I will hazard a guess of a maximum temperature rise of 30 degrees C.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 25 Apr 2019 at 10:53pm
Some photos...


The finished bare metal pre-production prototype powering my (out of shot) Bitzie


Load testing the 5 volt rail


Load testing the 3.3 volt rail: reading the temperature this time as it approached 48 C. I had to utilize every load block I have.


And here's a closer picture of the internals.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 26 Apr 2019 at 12:45pm
EuP Compliance

Some wanting a 5 volt power supply may not want a 3.3 volt output and see its inclusion as a waste. However, to comply with EU EuP law it cannot be a single voltage output and use linear components such as a normal mains transformer - it must be capable of more than one voltage simultaneously.

Catcher Diodes and Overvoltage Protection

If used to power more than one item there is a possibility of when disconnecting one that a reverse EMF is generated at the not-instant removal of a connector.

The reverse EMF can amount to a total of twice the rated voltage being injected in the item still connected, which if switched on could be damaged or even destroyed.

Catcher diodes as used on DC coupled power amplifier outputs could be utilised here, but they will only limit the voltage by their forward voltage, which might be more than a volt depending on the current due to the back EMF.

This is where the overvoltage protection comes in handy: placed on each output rail they are set to trigger and shut down the affected rail, leaving only the safer SCR's voltage drop of around one volt on the output.

This extinguishes the LED for that output, and a manual reset is then required by switching off the power switch, waiting a couple of seconds, then switching back on.




Edited by Graham Slee - 26 Apr 2019 at 12:48pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote msphil Quote  Post ReplyReply Direct Link To This Post Posted: 04 May 2019 at 5:34pm
Originally posted by Graham Slee Graham Slee wrote:

EuP Compliance

Some wanting a 5 volt power supply may not want a 3.3 volt output and see its inclusion as a waste. However, to comply with EU EuP law it cannot be a single voltage output and use linear components such as a normal mains transformer - it must be capable of more than one voltage simultaneously.

Catcher Diodes and Overvoltage Protection

If used to power more than one item there is a possibility of when disconnecting one that a reverse EMF is generated at the not-instant removal of a connector.

The reverse EMF can amount to a total of twice the rated voltage being injected in the item still connected, which if switched on could be damaged or even destroyed.

Catcher diodes as used on DC coupled power amplifier outputs could be utilised here, but they will only limit the voltage by their forward voltage, which might be more than a volt depending on the current due to the back EMF.

This is where the overvoltage protection comes in handy: placed on each output rail they are set to trigger and shut down the affected rail, leaving only the safer SCR's voltage drop of around one volt on the output.

This extinguishes the LED for that output, and a manual reset is then required by switching off the power switch, waiting a couple of seconds, then switching back on.



Sounds good! Any idea when they will be available?
'You are, through your soul not your body, a human being.'
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 04 May 2019 at 7:37pm
I need to try out a snubber/zobel network on the transformer secondary to see if I can tweak more body out of the sound.
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