High voltage SMPSU

[Top Cap]

Yep, I have had to fit DC-DC converters as isolators to Lascar panel meters and switching noise was a pain. However the meters were tamed from dancing about by applying chokes and decouplers. The latter had to be kept low in value else they caused failure of the isolators.

[timohaveri]

I'll give it a try and see how it works. I'm still gathering the parts for the Sussex so it may be a long time before I actually begin to build it.

Timo

[DAVEHALL]

Was looking for something else ,but if nobody minds ,can I make a suggestion . The circuit idea is from some old telecomms equipment ( getting 28 v on board from standard 24v input) ,and would work from a 12v source .( I did get 240 out -naughtly using a standard transformer - I know losses were horrendous ,but it fired up my zenon strobe for car timing ) .

Used a LM494 IC( smpu chip) .To get losses down ,would need a toroid transformer capable of handling KHZ .Drive output from chip is about 200mA in push pull, but a couple of meaty transformers would soon cure that if more needed .Circuit design is similar to that on Texas pages ,and we found on bench that it gave out very little hash .We did regulate the chip input to 12v with a zener ,which sometimes gave funnies on the output waveforms . Regulation is by feedback ( derived from a regulated portion of the output voltage ) .It is possible also to get overcurrent protection too . Problem might be sourcing this chip -though think that RS still do them .

[DAVEHALL]

Drive output from chip is about 200mA in push pull, but a couple of meaty transformers-from my post -should be "meaty transistors" - but the edit function on my last post has gone walkues .

[DAVEHALL]

That chip should be TL494 ,by Motorola -just found part of a data sheet .

[timohaveri]

Originally Posted by DAVEHALL

That chip should be TL494 ,by Motorola -just found part of a data sheet .

The article that was mentioned earlier is based on computer PSUs that use exactly that same chip, TL494. Apparently it is among the most common chip types used in those PSUs. So an old computer PSU already offers most of the components and to me it is easier to modify an existing circuit rather than design a new one from scratch.

Timo

[DAVEHALL]

Sorry -got MFR wrong ,was TI - http://focus.ti.com/lit/ds/symlink/tl494.pdf

REFERS -IF ANY USE .Used this circuit ( with only voltage side ) on a convertor -works well ( but with massive inneficiencies, only used a 50 hz tx- to step up car 12v to 240 for zenon strobe ) - however the TI data sheet gives winding data for a 28v output -etc - if anyone can give /get equivalent transformer core data -Ferroxcube seems to have vanished .From my research it seems only places like RS stock this chip ( and I'm sore ,as not so long ago Ihad a cleanout of my old stuff -taking up too much room - oin that batch was about 30/40 TL494 .

Good luck .

[DAVEHALL]

Originally Posted by timohaveri

The article that was mentioned earlier is based on computer PSUs that use exactly that same chip, TL494. Apparently it is among the most common chip types used in those PSUs. So an old computer PSU already offers most of the components and to me it is easier to modify an existing circuit rather than design a new one from scratch.

Timo

Timo - I've still got my homebrew 494 circuit( taken from a working design by UK GEC ) - and a copy of the MFR data sheet -so if needed I could reverse eng a circuit diagram of a working circuit .Mine ( even allowing for massive inefficiencies using a 50Hz transformer on a many Khz output ) gave me from 60v DC to 250 v DC on rectification,and with 2uF smoothing and enough output to drive a xenon strobe tied into engine ht output .
So -if it's any use - and ( no promises ) - I might be able to convert the PCB into a drawing ,if needed -so ask ,and I'll try .

[timohaveri]

Originally Posted by DAVEHALL

So -if it's any use - and ( no promises ) - I might be able to convert the PCB into a drawing ,if needed -so ask ,and I'll try .

Thanks for the offer. I was looking for a supply capable of producing about 200 mA so if yours is up to it then it might be of use. However, my PSU projects are on hold at the moment. Too much else to do right now. So I'll let you know if I need the schematic when the time comes.

Timo