All-semiconductor regulated HT PSU

[pwdrive]

With the old style carbon composition resistors the higher the value the less carbon was in them so for any given level of stress (mechanical/electrical or whatever) that stresses effect would be greater as regards reducing current flow, I suspect that the main culprit area would be the interface between the carbon compound material and its connection to the outside world.

Lawrence.

[Nick]

Interesting:

http://www.cliftonlaboratories.com/carbo...istors.htm

Basically, with old carbon resistors, even NOS, you're doomed.

[pwdrive]

We knew that back in the old days, high value carbon resistors used to go for a pastime in the old tv's especially those being fed from the boost rail etc.

Lawrence.

[Skywave]

We've all met hi-stab. resistors: often they have pink coloured bodies; sometimes they're all black. I believe that the pink ones have a spiral cut; not sure about the black ones. But both have one feature in common: their end caps. Unlike traditional carbon composition types, these end caps fit round the ends of the resistor and as such, will significantly reduce moisture ingress, compared to the 'standard' carbon compo. types.
Sounds relevant to me . . . but to what degree?

Al. / Aug. 5, '14 //

[Skywave]

Update to circuit of PSU, Aug. 5, '14.

Modifications (above posts refer).
► 12-v. Zener diode now added: cathode to gate of FET.
► 1-kΩ resistor added to base of Q4.

► Drawing error: between the 240 v.a.c. mains 'L' input and the switch, a 1-amp. A/S fuse should be shown.

Post-modification tests: no change in performance was detected.
Measured hum & noise level at 250 v.d.c. / 100 mA output: 5 mV. peak-peak.

Al.

[Skywave]

Full photo set of this item is now in the Gallery / Homebrew / Test Equipment.

Al. / Skywave / Gallery Admin. / Aug. 7, '14 //

[Alistair D]

Hi Al,
I have been playing around with a similar design In LTspice. The main reason I gave up on it is that I struggled to find a PNP transistor with a high enough VCE for the constant current source.

One advantage(I think) is that the current limiter design on mine is slightly different. Mine would allow the current limit to be reduced to a few mA. It could be worth consideration for your design especially as it would be useful for capacitor reforming.

Alas I cannot post it here as the file is in .asc format. PM me an email address if you want to see this circuit.

Al

[Refugee]

Can't you use a screen shot grabber like the one I used to get this?
Mine is called Ksnapshot.

[Nick]

Alas I cannot post it here as the file is in .asc format. PM me an email address if you want to see this circuit.

".asc" files are just txt files of the netlist. You can open them in notepad and just cut-n-paste them in your reply as a code block inside [code]... [/code] tags...

[Alistair D]

I tried to download ksnapshot and got loads of dross and still did not the program. Can anyone suggest a good mirror.

I have emailed Skywave and told he can post a screenshot of the schematic.

Al