6.3v indirectly heater valve PCB (possible group buy?)

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IslandPink
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#31

Post by IslandPink »

I love the smell of Veroboard in the ... evening .
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#32

Post by Mike H »

Compact and bijou :D
 
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#33

Post by Andrew »

Mike H wrote:Compact and bijou :D
I imagine it will get even better when on a proper PCB as the layout won't be quite so constrained by the strips on veroboard.

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#34

Post by Mike H »

Wotchit with them strips, easy get short across if you're not careful - hint, bend component leads INLINE with the strips, not 'the normal intuitive way' at right-angles to.
 
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#35

Post by Andrew »

Quick update.

I have a working breadboard but the FET we decided to try isn't ideal, since we want to isolate the packages so we can use a single heatsink I have spent item looking for a suitable FET or bipolar in the same TO-200F plastic package.

This one looks promising http://www.st.com/internet/com/TECHNICA ... 001254.pdf

I'll get some in to try and report back.

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#36

Post by Andrew »

OK, here we go!

The TIP22 is installed, I used a green LED plus 1N4181 bias. The slight current difference is down to being on a slightly different part of of the TIP122 curves.

I'll do a layout now.

Andrew
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400mA load was 15R
400mA load was 15R
900mA load was 6R8
900mA load was 6R8
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#37

Post by Andrew »

Some progress towards a PCB

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#38

Post by Andrew »

Here's the spectral output of the heaters at 900mA. Not much to see really, which is exactly what you want!

The worse is the 3rd harmonic at roughly -100db down. Also please bear in mind this is an unshielded breadboard and so will be picking up EMI. Full scale here on my magic box is 200mV on the lowest scale so 100db down is 200mv / 100000, so, basically, a fart in thunder!

cheers,

Andrew
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#39

Post by Paul Barker »

Andrew wrote:Here's the spectral output of the heaters at 900mA. Not much to see really, which is exactly what you want!

The worse is the 3rd harmonic at roughly -100db down. Also please bear in mind this is an unshielded breadboard and so will be picking up EMI. Full scale here on my magic box is 200mV on the lowest scale so 100db down is 200mv / 100000, so, basically, a fart in thunder!

cheers,

Andrew
Looks a lot cleaner than my signal generator!
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#40

Post by Andrew »

Getting there, needs a double check, if anyone spots anything please let me know.
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#41

Post by James »

Hi Andrew,

Not sure what it will do to the price but it mat be worth making the tracks between the main input capacitor, bridge and input termianls as thick and short as possible as the capacitor charging pulses are significantly higher than the average current.

It may also be worth putting some holes under the heatsink fins to facilitate convection cooling.

I assume the input and output pad spacings are standard to allow termals to be fitted?

Best Regards,

James.
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#42

Post by Andrew »

Yes, the pads are standard spacing so you can fit connectors. I checked against some spares I had from those e-bay mini24-96 DACs.

I have increased the track widths a bit on the ground line and on the input section.

I also fixed a bug I found, I picked the wrong part and so the pin out was wrong. As a result of changing the part I have now managed to get it all onto one side of the PCB :)

Here's the latest, suggestions are welcome. I'm seriously considered doing a one off using a light box and photo resist and chem etch process to make sure I have this right; especially if we're doing quite a few of these.

I was wondering what people expect in terms of a delivery date and if folks are willing to wait for me to verify that the artwork produces an OK PCB before I press the button on a run of 50 or so?

Andrew
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#43

Post by IslandPink »

I'm happy for you to do a prototype first, Andrew - you'll probably pick up something you can improve, and it's best in the long run that it's got the bugs sorted .
What are the dimensions of this board currently ?
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#44

Post by Andrew »

Eagle does things in inches, its 2.4" * 3.55" or 61mm * 90mm in new money.

cheers,

Andrew
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#45

Post by Mike H »

Track layout seems to pan out to me OK. :)
 
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