TL783 & psu design

[daArry]

Hey,

Does this vreg behave the same way as the LM317 with regards to output voltage? So say I need around 100VDC regulated from recified 120VAC would I use 470R for R1 and 39K for R2 for the TL adjustment resistors?

Cheers!

 

[A Camel]

Hi:

No, you must use another formulae.
This is a link for the TL783 datasheet:
http://focus.ti.com/lit/ds/symlink/tl783.pdf
As you can see the recommended resistor from the out pin to Adjust pin(R1) must be around 82 ohms to maintain a minimum load current and the formula to calculate output V is:Vout=1.25Vx(1+(R2/R1))(aprox.)so to obtain R2 value from desired Out V we have: R2=R1x((Vout-1.25)/1.25) if your desired Vout is 100V the value for R2 would be around 6k47 ohms.

Camel

 

[daArry]

Cheers Camel,

Here's the psu ckt it's used in:

The TL bit is based on the G9 supply which I thought be coo to use as I have some TL783's in. I guess I don't need all 3 of those ZD39's there tho - just 1 ok?

Thanks again :thumb:

 

[alk509]

[quote author="daArry"]Cheers Camel,
I guess I don't need all 3 of those ZD39's there tho - just 1 ok?[/quote]

120VAC yield about 165V of rectified DC. You need the three zeners (or 1 120V zener).

Peace,
Al.

 

[daArry]

coo, thanks al...

good to go then on this one :thumb:

 

[daArry]

Hey,

Just to clear up...

The 2 470R/2W resistors (R7, R12) - are these needed in this psu? I drew them in based on the G9 supply which delivers much higher voltage out on the TL783 - 245V instead of the 100V needed here...

Also, are those transformers connected okay and is the way a single ground has been used been implemented correctly?

Just need to put my mind at rest - spent ages trying to get a psu sorted for prrs' vari-mu comp ere!!

Thanks

 

[daArry]

wellll ok then, thanks for putting my mind at rest...

anyway, transformers are hooked up and nothing exploded so far - verobrd'ed the +/-15, +12 and 1.5V supplies so it's just the 100v big spuds to go....

I'm right in thinking i can omit those 2 resistors i mentioned prior tho right? They act as to lower voltage ye and so are not needed in this instance...?

 

[alk509]

[quote author="daArry"]I'm right in thinking i can omit those 2 resistors i mentioned prior tho right? They act as to lower voltage ye and so are not needed in this instance...?[/quote]

I don't think so... It looks to me like they limit the current, not the voltage. Jakob will know better, I'm sure...

Peace,
Al.

 

[alk509]

Yeah, looking at the schematic I'm pretty sure they're there to protect the zeners at turn on...

Peace,
Al.

 

[daArry]

much obliged al - thanks again :thumb:

nuttin but stress with this fokkin thing tho, hooked up the tranformers as I said and when measured for AC - all good, gettin 113VAC for the 110 outs and 17ishVAC for the 15V outputs...however...

I made a simple diode bridge with 4x 1N4006's for the 110VAC so I could get a ground ref to make sure the +12,15,-15 ckt i made on breadboard was working. I only get like 106VDC with the rectifier :/ and with the +12,15,-15 ckt added to the 15VAC, the 12V is fine but the -15 is only giving out like -8V, the +15 Im not sure yet as I don't have one of those vregs to hand...

Here's the hookup for the **** i've tested so far...def okay ye?

Also noticed a slight buzz coming from the transformers - that normal for the box type ones?

 

[gyraf]

Yeah, looking at the schematic I'm pretty sure they're there to protect the zeners at turn on...

Yes, they are. And at turn-off also..

Jakob E.

 

[Guest]

A buzz on your transformer and the low voltage indicate a problem. Could be miss wired ground on the rectifier or a phase problem on the transformer winding. Chaeck it again before you hook it up. I just quickly fried a small transformer with a missplaced ground on the rectifier.

 

[daArry]

Hey,

I dunno :roll:

I've checked it over n over - even with nothing connected to the tx's (but both joined together as in pic above) theres still a lil buzz...