PSU Based Off The Velleman K7200

[yngndrw]

Hi guys. (And girls.)

I have an old kit for the Velleman K7200 (Well actually, it's not the 7200 because that was the 10A version, mine is the 5A version.) but it was discontinued a long time ago. At the time I didn't have much money (Some things never change. ) so I was building it in parts. I had the main board and the transformer, then they decided to discontinue it. I was missing the case / heatsinks and the display and at the time I was way too young to bother making these myself.

Now, things have changed. I'm in Uni and hence have a bit of disposable income. (Thank you student loan.) Electronics is "just" my hobby, yet I seem to spend quite abit of money on it. I currently have a Palstar PS-30M as my PSU. It's not a "big brand", but it provides 0-15V at upto 30A so it plenty powerful, however it doesn't have adjustable current limiting.

I searched around a bit and although I couldn't find a K7200 for a reasonable price, I did find this thread on it:
**broken link removed**

In this thread one member, Wizpic has redesigned the K7200 slightly and has published a document about it. I've attached the pdf here so you don't have to register.

Now I'm quite interested in building this, however I thought I'd ask you guys for some input on the design. It's based upon the K7200 as I said, so the document doesn't make much sense in some places. (It kind of assumes you know about the K7200, so here's the link to that datasheet. Look at the very bottom for the diagrams: http://www.velleman.be/downloads/0/manual_k7200.pdf)

So my questions:
* Are there any changes you would make to this design ?
* What would you change in order to make it into a dual PSU with tracking ?
* What's an alternative to T3 (BD646) that can be bought from http://maplin.co.uk ?
* Is a 15-0-15V transformer as suggested good enough ? Should the voltage be slightly higher ?

Also relating to the K7201 (The digital display in the K7200 document, again the diagram's near the very bottom. Here's a pic of the K7201: http://www.velleman.be/nl/en/product/view/?id=9377#):
* What IC could IC1 & 2 be in the display ?

Thank you for any help !
-Andrew. hm:

Edit:
Also for the transistor, I could buy from: http://cpc.farnell.com

Maplin used to have a massive range or transformers, but now they have about two.
Therefore I looked at CPC for one and I'm unsure.
Here is their range of transformers: http://cpc.farnell.com/toroidal

This is the best option I could find, with 2x 25V secondaries at 10A it should be able to handle two channels of the PSU. However it's quite a bit over the voltage range I was looking for and being 500VA it will be quite big:
http://cpc.farnell.com/FF01589/components-spares/product.us0?sku=MULTICOMP-MCTA500-25

 

[mneary]

* What IC could IC1 & 2 be in the display ?

ICL7106 was popular.

15V is enough for 0-15VDC. Any more and your power dissipation of the pass transistors goes through the roof. And any 25V parts need to be changed to 40-50V.

 

[audioguru]

The ICL7106 is for an LCD display. The power to operate it is very low.
The ICL7107 is for the LED display that uses a lot of power to light up to 24 LEDs.

 

[yngndrw]

Thanks for the replies guys.

I just checked the ICL7107 datasheet's pinout against the circuit diagram and it matches, so it must be that. Makes life much easier for me as now I don't have to find / design a panel meter.

I guess for the transformer, I'll have to go with separate transformers for each PSU as I can't get a 300VA transformer with 15V secondaries at my local supplier.

I can however get a 160VA transformer with 15V secondaries. (It's actually 2x 15V @ 160VA each, which totals 30V at over 10A.)

Come to think of it, the circuit uses a relay to lower the transformer's voltage when it's not needed, by dropping one of the windings. This would keep the power dissipation down if I decide to go for a higher voltage.

I have just ordered a load of rotary encoders. I might use these along with a PIC and a 4x20 Blue / White LCD to set the voltage / current and also to replace the panel meter.

What do you think of the circuit ? Are there any flaws or improvements which could be made ?

Thanks again.