No high voltage, no help from the seller...

More
9 months 3 weeks ago #11075 by jonboy
Hi again,
So I have changed a few things on my circuit.
I have replaced bits so the match the schematics rather than build manual.
C6 with a 390pf instead of a 680pf (should be 360pf, but couldn’t find one on the site I use)
Replaced R22 with a 110k instead of a 390k
Replaced R23 with a 1.8k instead of a 2.2k
Replaced L1 with a 150uh instead of a 100uh.

Now I am getting as per Ty’s post above, exactly what he says I should be getting on the mc34063.
“Negative meter probe goes on any ground test point and stays there.
Positive probe:
Pins 1, 6, 7, 8 all approx +5V
Pin 4 zero volts
Pin 5 somewhere between +0.5V and +2.5V” (getting 1.24)

However I still have the 10k pot on (as per picture) not the 5k it tells me to.

Happily I am now getting above 5 volt on the 50v test points, but.....

I am only getting 20.4 volt with the pot turned all the way up, not 50 volt.

So what’s next?
Should I change the 10k pot to a 5k pot and see what that does?
Change out any of the other bits?
Wait for Ian!

Thanks guys for your help.
Jonathan

Please Log in or Create an account to join the conversation.

More
9 months 3 weeks ago #11076 by Torsten Lang
Hi Jonathan,
there still must be something wrong. The comparator threshold is 1.25V, with the resistor values given you should be able to reach about 65V..70V, no matter if you use a 5k or a 10k potentiometer. At the highest set point both are near short, so the 1k8/100k voltage divider determines the output voltage. Depending on the potentiometer used you should be able to reach about 12V (10k) or 20V (5k) as the lowest possible voltage.

With best regards,
Torsten

Please Log in or Create an account to join the conversation.

More
9 months 3 weeks ago #11077 by jonboy
So just changed the 10k pot to a 5k pot and still only getting 21v turned all the way clockwise.

Starting to get a bald patch with all this head scratching!

What to change next??

Please Log in or Create an account to join the conversation.

More
9 months 3 weeks ago #11078 by Ty_Eeberfest
Just want to confirm: if you turn the pot does the voltage at the 50V test point change? If so, what exactly is the highest and lowest voltage you get at the test point?

The 1.25V at Pin 5 suggests strongly that the boost converter is at least running now. it seems that it's regulating, just not regulating to the desired voltage.This makes me very suspicious of the voltage divider (R22, R23 & the pot).

All I can suggest now is that you double check the values of R22 and R23. The pot seems to be fine. The math says the schematic values are correct and will produce an output of 11.8 to 70.7 volts with your 10K pot.I suspect that either R22 or R23 are the wrong value. Check with a meter, do not depend on reading color codes or the labels on packages!

Look into it later when the dust is clearing off the crater.

Please Log in or Create an account to join the conversation.

More
9 months 3 weeks ago #11079 by Torsten Lang
Hello Ty,
I just received an answer from threeneurons: He really did place C1 on purpose as it is to delay the turnoff. The design was changed over time.

I still think there's a certain risk. The threeneurons PSU set the peak current much higher anyway, so the capacitor has somewhat less influence as in Ians design.

Regards,
Torsten

Please Log in or Create an account to join the conversation.

More
9 months 2 weeks ago #11080 by jonboy
Thanks guys for sticking with me!!
I have got to the root of the problem, eventually.
After changing all the bits above, I checked the values of R22-R23, and found the problem.
R22 should be 100k, but had a 100R in it, and because it was still a 100 I didn’t realize what setting the multimeter was on.
R19 somehow I put a 100k in it not a 1K as well

After doing this I was able to change the voltage output on the pot and tuned it at 40volts.

Maybe I need to take multimeter classes again.

Damm, just went and checked it was still holding at 40v, and it’s dropped down to 20volts again, and the pits not changing anything.

I suppose I must gave a faulty pot now, even though I still get signal to ground on legs 2&3 and leg 1 still connects to R23.

Here I go again!

Please Log in or Create an account to join the conversation.

Time to create page: 0.104 seconds

Search

Tube Suppliers

Go to top
JSN Boot template designed by JoomlaShine.com