nixie supply SMPS to think about

[Ice-9]

Thanks Iccaros, the schematic is very like the SMPS that I build for my valve projects. There are one or two differences which would improve it, The MOSFet has it's source connected directly to ground, an improvement would be to use a 0R05 ohm resistor in there (sense resistor) pin 8 Max1771 (CS) would need to be moved from ground and connected to the source of Q1 also.

Pin 4 of max1771 could be connected to a microswitch instead of directly to ground to turn off the HV line off (say if the enclosure is opened but still powered up the enclosure lid would open the microswitch thus turning off the HV) Much safer against accidental shocks.

The input voltage could be raised up to 30 volts by doing the following. Swap the 5v regulator for a 9v regulator, disconnect pin 2 of max1771 from the positive side of C2 and connect it to the 9v regulated supply then you can hit the input with up to 30v

[iccaros]

Thanks Iccaros, the schematic is very like the SMPS that I build for my valve projects. There are one or two differences which would improve it, The MOSFet has it's source connected directly to ground, an improvement would be to use a 0R05 ohm resistor in there (sense resistor) pin 8 Max1771 (CS) would need to be moved from ground and connected to the source of Q1 also.

can you draw that out? I am not understanding the connection point for pin 8, and is R05 between Q1 and pin 8?

[Ice-9]

Thanks Iccaros, the schematic is very like the SMPS that I build for my valve projects. There are one or two differences which would improve it, The MOSFet has it's source connected directly to ground, an improvement would be to use a 0R05 ohm resistor in there (sense resistor) pin 8 Max1771 (CS) would need to be moved from ground and connected to the source of Q1 also.

can you draw that out? I am not understanding the connection point for pin 8, and is R05 between Q1 and pin 8?

This is the schematic, have a look over it and check out any differences, i'd be happy to answer any questions you have if I can.

http://www.desmith.net/NMdS/Electronics/NixiePSU/MAX%201771%20V5%20schematic.png

[iccaros]

got it, If you added in the protection diode and the fuse, just need a PCB layout as I am sure the MAX1771 is very sensitive to stray capacitance.
Question, is the R050 really a RSense or is it allowing the Mosfet BIAS, changing the point it conducts, allowing it to dump current?
as I see VR1 as a RSense.

[Ice-9]

The CS pin on the max1771 is the current sense input. Here is the datasheet for the max chip.
http://pdfserv.maxim-ic.com/en/ds/MAX1771.pdf

It's a good read but the biggest problem I see with the max1771 is that you can't setup the switching frequency so this could cause problems with noise in the audio range.

[waltk]

It's a good read but the biggest problem I see with the max1771 is that you can't setup the switching frequency so this could cause problems with noise in the audio range.

Looking at the datasheet, it says the switching frequency is "up to 300kHz".  That's well out of audio range, but I wonder if there are conditions that would cause it to drop down to audio frequencies.

The nixie power supply I referred to above runs at 45kHz, and you can change it you want to.

I guess the MAX1771 would give you better regulation under different loads (with its fancy PFM and all), but in the end it's just switching an external MOSFET like the 555 circuit.

[iccaros]

They all just switch something to multiply frequency, and the MAX1771 is out of range, unless you adjust the RSENSE and the feedback, as that adjust voltage by changing the frequency of the oscillator. But There are a lot less parts involved than a 555 based one

[tubegeek]

Thank you Ice-9, I've been meaning to rework that clock!

[iccaros]

It's a good read but the biggest problem I see with the max1771 is that you can't setup the switching frequency so this could cause problems with noise in the audio range.

Looking at the datasheet, it says the switching frequency is "up to 300kHz".  That's well out of audio range, but I wonder if there are conditions that would cause it to drop down to audio frequencies.

The nixie power supply I referred to above runs at 45kHz, and you can change it you want to.

I guess the MAX1771 would give you better regulation under different loads (with its fancy PFM and all), but in the end it's just switching an external MOSFET like the 555 circuit.

sorry I missed your post before, this is close but its tiny.. about the size of a 9pin socket. I will send pictures. I have build a few 555 multiplier.. but if you can by a small one for $20 it saves time to get to the part of the project which is fun..

[Govmnt_Lacky]

Definitely a different layout than the one they show one the website link from the first post. I was looking it over yesterday and could not see how it followed the schematic. This layout looks a bit more correct to the schematic.

I wonder why they went with an SMD inductor 

Everything else is through hole.

[iccaros]

I wonder why they went with an SMD inductor 

Everything else is through hole.

size...

[Govmnt_Lacky]

I wonder why they went with an SMD inductor 

Everything else is through hole.

size...

Yes.. I see however, if you look at the datasheet for the MAX chip.... they have through-hole recommendations that would fit the size aspect.

Must have been one of those situations where they used what was handy at the time. Either way, its a cool little design! 

[Ice-9]

also I can't see the max1771 chip in that picture so I assume that is also a SMD component on the underside oth the PCB ?

[Govmnt_Lacky]

also I can't see the max1771 chip in that picture so I assume that is also a SMD component on the underside oth the PCB ?

Wow! Didn't even notice that. 

[iccaros]

also I can't see the max1771 chip in that picture so I assume that is also a SMD component on the underside oth the PCB ?

yes, I know the datasheet talks about use of ground plains, they have the MAX under the IRF740

[waltk]

Because some folks have asked, here's a PDF containing the schematic, layout, and PCB image for the nixie HV PS described above.  This is the one using a 555 timer (not the MAX1771).
With the parts pictured, it produces ~100 - 270 volts unloaded.

http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=46847

[tubegeek]

Because some folks have asked, here's a PDF containing the schematic, layout, and PCB image for the nixie HV PS described above. 

Thank you very much - this will be well worth investigating.

[iccaros]

FYI
after some testing today, no matter what I do This things puts out a 1.8K frequency that stomps everything else. so I do not see how I can make it work in audio designs.. Will just have to keep it for a NIXIE clock project.

[waltk]

Hmmm... I haven't had that trouble at all.  Mine is dead quiet.  Looking at it on the scope, I can see some little spikes at about 50kHz in the mv range, but only the slightest (sub 1mv) ripple at audio frequency .  Did you try a bigger output cap for smoothing?  The original nixie design has a 2.2uF cap, but I'm using a 22uF cap.

Also this has been used in other designs, like the GTFO: http://www.diystompboxes.com/smfforum/index.php?topic=93936.0

[iccaros]

I used 47uf and 22 with 1K dropping resistors
I can see it clear on the scope with mine. It could be individual units, as it was not designed for audio, its not tested for noise