MAX1771 SMPS Not Playing Nicely.

[Scruffie]

Splitting this off from the Superfly thread...

Right! Designed a PCB for a Superfly using a 12AX7 & U7 Tube and a MAX1771 SMPS, Got it all populated last night and the trouble has begun.

Testing the MAX1771 Section (Before adding the tubes & transformer) I turned it on... first off I was getting a steady 12V, i'm not sure if this was me measuring wrong or something, anyway, checked it, came back, made sure there was no cold joints and when I got back it seemed to have started doing something!

Now I had my multimeter set to 200V... thinking i'd set the trim low and that would be fine, however I forgot i'd moved it when I was getting the steady 12V, turned it to high voltage and it settled around 500V... pretty sure I heard a hissing sound and the cap felt a little warm.

I'm only using 350V Rated Electrolytics in that schematic and a 250V 0.1uF Cap (which i've replaced now, no spare electrolytic though).

Now... with the trimmer the other way I do get a higher voltage but it is fluctuating, it seems to charge up towards 250V then drop down to 100V in increments and repeat this.

I've come to a few possible causes
1) My Multimeter is having trouble dealing with the voltage readings/frequencies and can't settle (it is rather cheap)
2) That Electrolytic is Shot even though it looks okay
3) The added copper I put in the layout for an easier etch is causing parasitic capacitance and buggering something up.
4) I only used a small inductor as it was the only one to fit the layout, I also substituted a 47uF Cap in place of the 100uF as I figured this was just supply filtering... also my Trimmer is 10k rather than 5k and shouldn't the 1M5 be high voltage? It's no noted so on Ricks layout but it gets full voltage... however it's not getting hot or anything.

Here is the MAX1771 SMPS Schematic and my PCB layout, I did try and follow suggestions in the Nixie page about Layout tips but I do understand these are finnicy beasts.







Any suggestions... other than start from scratch.

Edit: Never mind, after playing with it some more i'm pretty sure i've blown either the diode or MOSFET so i'm just gunna have to start from scratch any way.

[Pigyboy]

This is a tricky one. I have finally (kind of) conquered the smps beast using some of Ricks info and info from Nick De Smith that designed one of the pixie clock supplies but I am sure you guys can improve on it. Layout is important and I think it is better to keep it on a separate board to avoid noise but that is just my thoughts. I have this running several hundred volts and it works fine of a 9 or 12 volt input.







This one works good but I'm using a special shielded inductor and a LRC filter.

[iccaros]

I am surprised the 1N4007 has a fast enough recovery...

But do you have the drawing to etch this or the link?
Thanks

[Scruffie]

I am surprised the 1N4007 has a fast enough recovery...

But do you have the drawing to etch this or the link?
Thanks

He's marked it as UF on the parts list after the 1N4007 bit.

Doesn't matter anyway, I cut away the parts to make it an easier etch with a stanley knife then when I fired it up again I think I musta shorted something with my probe and got a spark, after that I just got a steady 34.9 volts then after some tinkering it was stuck at 12V so i'm just gunna replace all the parts with 400V versions and get the right parts were I substituted and hope for the best... the charging and discharging makes me think I did kill a cap, the hissing sound (if it was the SMPS truly giving 500V) can't have been good.

I'll do it properly this time and learn my lesson.

I would do it on a seperate board but i'm hoping to get it all on the one, Rick has managed to and I think my SMPS layout is fairly decent other than the extra copper which i've now removed.

This time i'll work on it without a hangover too 

[iccaros]

He's marked it as UF on the parts list after the 1N4007 bit.

Did not know there is such a thing.. But I do not know everything..

This time i'll work on it without a hangover too 

Where is the fun in that?

I have to get some homework done and honey do, after that I was going to LTSPICE this and see if I can see anything.

[Pigyboy]

I am surprised the 1N4007 has a fast enough recovery...

But do you have the drawing to etch this or the link?
Thanks

Hey Iccaros,
I may have written the wrong numbers but that is an UF (ultra fast) 4007 diode.  Pm me your email and I will send you the pdf files to etch the SMPS.

Chris

[iccaros]

I am surprised the 1N4007 has a fast enough recovery...

But do you have the drawing to etch this or the link?
Thanks

Hey Iccaros,
I may have written the wrong numbers but that is an UF (ultra fast) 4007 diode.  Pm me your email and I will send you the pdf files to etch the SMPS.

Chris

Cool, found the UF4007 ,which is different from the 1n4007 I use for amp rectifier, just wanted to make sure as I have lots of NTE parts around need to do a cross reference, which shows a  NTE575

Thanks for the update and I'll send my email.  Awesome share

[jubal81]

This is an excellent design. Might I also have the design to etch?

[frequencycentral]

Pigyboy's layout is based on one of my layouts. I use a 2.5A axial inductor, but this layout has optional pads for radial too.

[Pigyboy]

Yeah, sorry about that Rick.   I think I mentioned your name in there somewhere   
We are all using your designs everywhere! The check is in the mail 

I did find  that using the DR1030 inductors and the Murata filters cleaned mine up rather well along with shoving as big a capacitor as I could fit in there.

Thanks for the new layout.

Cheers,
Chris

[frequencycentral]

No apology neccesary Chris, I didn't mean it like that. 

[Pigyboy]

None taken

[Scruffie]

Wooo, replaced all the parts and I have a Steady 180V before tweaking... now to get on with the rest of the amp 

[Pigyboy]

Great work Scruff!  Now let's see how quiet it is once you get your amp done.  I just scored a zillion different minitubes for pennies so I'll hook you up if you need. Thanks for all the help.

Cheers,
Chris

[jbgron]

Sorry to resurrect an old thread.  I've built Rick's power supply above and I get ~210V from a 9V supply but I only get 12V from a 12V supply.  I'm using 1N4004 instead of UF4004 but everything else is stock.  I'm stumped, can anyone help?

Many thanks,

Mike

[thomasha]

Hi,
first question, is the 12V supply also center negative? Normally the're all center positive, that mistake happened with me...

I would suggest to use a ultra fast diode, with a slower one the voltage drop with the load will be bigger. Check the mosfet if it is switching with 12V.

Thomas

[jbgron]

Thanks for the fast reply. Yes it is a center negative 12V supply. I'll get some ultra fast diodes on my lunch break today and report back tonight.

Cheers

Mike

[thomasha]

I burned some Max1771 and IRF840 and was reading only 12v, but after changing this two it was back to life again.
Check the max1771 pins too.

[Scruffie]

It has to be an UF diode and yeah, me changing the trimmer value was the issue and that blew a cap and the MAX1771.

[jbgron]

OK I installed a UF4004 diode but now I'm getting a whopping 435V from the thing.  Has to be an error in my layout or I've got the mosfet around the wrong way.