Farnell L30 DC Power Supply

[lordvader88]

edit I made an Farnell L30, it's great, posted below



I looked up 1960s power supplies to see how they did it with BJTs, and I got lucky and found this, schematic on p7-1

http://literature.cdn.keysight.com/litweb/pdf/06206-90002.pdf

I have a transformer that does 35V @0.95A from the rectifier. It has a sec. winding that does 12.9V@120mA rectified, its rated for 10.3V @1A .

And I have a 2nd little transformer that does 11.4V @110mA.

So according to LTspice the smaller winding works fine to make that cool reference regulator, it's not center taped but thats ok.

And for the bias transformer I could use the other trans, a TL431 for 5.5V and something for the -2V, I have no idea what most currents should be yet.




I made the model in LTspice, using sinewave soucres, for both windings of my non-CT trans, . I didn't include the meter circuits or the Crowbar on another PCB. But the current limiter is there.

I used 2n3391A/2n2907,  as is actually used in the PSU. I used 2n3055 for the 2 power BJTs. And for the diff. pair I've tried a few high and low gain BJT's. They aren't listed in the manual that I can see. Probably some super matched pair.

I used DC 5.5V and -2V referenced to the output, as the Bias transformer.




So far playing around with the variable resistors, it doesn't seem to work the best, at least it's not very linear at the COARSE voltage adj resistor. Anything over maybe 5K or whatever, and the output is near maxing. I haven'd bothered to add a load resistor, it doesn't idle right.

Also LTspice seems to think 400mA is oscillating through the Current sense resistors. 20mA a piece is going into the 2n3055s. Funny thing is I haven't found where the 400mA exits to ?

I don't know what if anything should be in parallel with R12, so I tried anything under 2k total.

I haven't calculated anything yet, or read the circuit theory, I've been having too much fun making the spice model. I made the diff.amp separate, I should start and try and figure out, if I can, what it should be doing.


I'm going to make it IRL

[MarkF]

If you want a comparison, I have a circuit diagram for the HP-6216A power supplies.

   

[duak]

I'll bet there's a small error in the schematic somewhere.  A net misnamed or misplaced.

I see that you've put 2N3055 in the voltage comparator - Q1A & Q1B.  I think these should be small signal parts instead.  2N3055s are pretty crappy at low currents.

[bd139]

Correct. They are actually dual transistors in these. 2n2219 in LTspice is closest to reality.

[lordvader88]

Ok that that never did work in LTspice, and I never figured out the mesh/node equations for the reference area, let alone the rest of it.

Farnell L30


So I found a Farnell L30 PSU and it worked in LTspice, and so I BUILT IT using a single transformer, with all 3 secondaries.

It's on page 11 of this 1, it's the transistor version.
http://www.introni.it/pdf/Farnell%20-%20L%20series%20Bench%20Power%20Supplies


The service manual  is basically this 1
http://rtellason.com/manuals/FarnellL30PsuIssue2.pdf


My reference rail is about 13V at the rectifier, 43V on the primary. And I used the 4.1VAC winding to just squeeze out 4.3V for a 100V 10A  dual meter.

Ii's regulating pretty well at resistive loads, but that's all I've tried with it so far.

I put the transformer in a little wooden box, and put 2 7x15cm prototype boards on top, and I put it all in a cracker box for now. It looks super powerful though.


Alright so I finally built a non-piece of junk 0-30V PSU, it will do for now, without a heatsink and with a single final ouput 2n3055. Under 200mA total is not bad for brief use. Now I should find an old CPU cooler. I haven't pushed it very hard or for long though. The transformer main rail is rated 36Vdc @1.5A. I'm afraid to do that, gets to hot, let alone a single 2n3055. And for now I never ever ever need more that a few hundred milli-amps.

Now I have to try a bunch of math on how this thing really works. Looks fine on the scope at low loads, never tried scope at high loads, I only have 2x 100uF on the 43V winding rect., (I need a lot more assorted caps)


I want to make a comparator circuit with transistors and some 9-10k thermistors I have. I experimented with whats too hot to touch for the 2n3055. I'm sure I could do it with a opamp, but I can't figure out how to do it with transistors, acting on a resistance that drops, rather than a raising voltage.


Now to make a op-amp version, but I'm going to try a curve tracer circuit today

[lordvader88]

This thing has 2 victims so far.

1)I'm powering a LCD volt/amp with 4.3V from a separate winding, and it shares gnd with the power rail gnd. I hooked up a nice little LCD temperature sensor to the 4.3Vdc winding for power, and touched its nice shiny metal probe to the 2n3055 42V collector, expecting to measure the temperate...NOT expecting that the probe tip was somehow a short or near short to gnd, so a little zap sound and thats it.

I never read anything on it or checked anything 1st, so assumptions fried it. It's 5V regulator is zapped, I hope nothing digital is damaged. I'd use the hotair station on that tiny Reg. but there's a plastic power snap/clip/cable connector 1mm away  basically. I have the special kafton? tape, could that save the plastic 1-2mm away? Very tight for the iron too.



The 2nd victim was itself, I'm not quite sure what did it. I never had the protection diodes in, I had a short/wire for R12 S.O.T. meter circuit for some reason, which I'm not using, I never had the CV/CI part added to the bottom. Could have been solder debris, I just made it this week

Turns out I fried the lower 5.1V Zener and the coarse V adj. pot, I used 44k for the 25k (I know that it basically maps the kilo-ohm's set there, to the output voltage, I never went over 33V)

Just before I was running a LM317/LM337 circuit from this...I never added a load to it, so that unit used a few mA. Did that fry it, with no protection diodes on either the PSU or LM317/ unit? IDK (I added them to the LM317 circuits I've made)

Then I had that unhooked, and all seemed find and I quickly turned voltage down to zero to check something, last I saw before smoking was -15V on the volt/amp meter (the ouput put LCD I added).

I had it down to zero several times before and it did go a bit negative according to DMMs and the LCD vol/amp meter , so I quickly went back positive.

So somehow that 44k coarse voltage pot. and the xener fried.



So I didn't really know what smoked , I found the zener, the rest checked out in circuit, but I missed the 44k pot. So I pulled it apart and checked the diff. amp and amplifier transistors, they were all fine.





So now I'm have it working again, but I added some higher wattage resistors and more stable resistors in a few places, a bunch of switches, protection diodes, the full constant current and V(-)output. I haven'y tied that function at all yet tho.


The 10.3VAC rail is not really enough, just idling, I get about 13.8Vdc w/30-40mV ripple w/ 4700uF across the rail. I haven't tried playing with the zener voltages, lots to try, later. Lots of fun, lots of fun, no sleep, crazy electronics party all week.



Right now, I'm getting a lot of noise or oscillation at the base of transistor Q4, for the current limit divider. The red overload LED I have used, is coming on and off, to varying amounts, when it should not be I don't think. I have a 10cm wire running from the 1k P3 to the power rail board. If I clamp my hand over that wire, I can sometimes short the AC and the LED turns of.


Cheers to anyone still reading,

So there's a few mV of 120Hz ripple at the base of Q4, but, there's also something much higher frequency, (my scope sees radio 99.1MHz a lot). When that picks up and the LED is conducting I'd start getting 10-20mV (I just shut off the scope). But I can see the signal grow and shrink and any freq/, its very real.


I know the basics and equations for high/low pass filters...but not their subtitles, .so far I only tried 2 caps from the  -5.1V rail to the base, it's an improvement, but still not consistent.

thats enough rambling for now

[lordvader88]

I found a ringing of 286kHz at the base of Q1, of the diff amp and tied to the output.  It was over 1.24Vpp, then dropped off in a few cycles. So I put a 20n cap across there and the reference regulator V(-) and that got rid of it. 

Then I notice a +600mVpp spikes at 5.62kHz also on QB1, it's beating at that frequency, but the underlying ringing is at 1.57Mhz, the spikes/beat is about 3.8us, and there's higher frequencies too, 2 or 3 or 5MHz or whatever. The ringing drops super fast and fades into the noise in 10-10 cycles or so anyways.

Putting 0.22uF cap there reduced and smoothed the overall ripple of 1.57Mhz part a bit, thats was at a few mV or tens of mV, when it's not spiking every @5.6kHz

So I turned it off and notice it's the transformer thats ringing at a few MHz and beating at 5.6kHz just from being attached. There was 0.8V left on the primary tank cap of 330u. Now it's still ringing and there's 1.14V leaked back on the cap, 30minutes later. The 10Vac winding is drained to zero, never checked the 4V rail.


I'm aware that sometimes RLC circuits are used on transformers to damp this, like putting 4 caps around the rectifier. There's 3 secondary winding on this, any adive ? should I even worry about it ?

I'm going through the PSU with all major nodes and recording values and looking at the wave forms.


My Vbe of Q3 is locking around +0.5V, I haven't figured out how to adjust it. That sounds super low. Puting a variable resistor on the Q2 collector, basically never changed the Q3 base. So I'm tugging on the wrong string. Lot's of fun.

I have the rough current limit for set for full current, and @10.00V w/22ohm it drops too 9.76V

That LED and current control circuit is not biased right or something AC is turing it on, it keeps turning on a bit when there's no load, or half random.

There's a big hedge of output ripple on the scope tho, overall atm. About 75mVpp(max) at 60Hz, and it's 20mV wide made of all the other frequencies.

If I zoom in at 5ns, it's 100mVpp (max), some dominant stuff around 2.36 and 7.6MHz. How much of all that part is real, or my scopes, IDK? I can quite clearly see them changing and try oscillating for a few seconds when touch the load resistors.

back at it, but what about the transformer ringing ?