FY6800 (FeelTech et.al.) Linear Power Supply

[jfitter]

If anyone is interested, I have designed a linear power supply for the FY6800 ARB that eliminates many of the problems discussed regarding the SMPS that the instrument is supplied with.

I had 5 PCB's made. Keeping one for myself and one for my son, so there are 3 available to cover my costs. If there is interest I can get a batch run off, or you can use the Gerbers in the archive to get your own made (but the MOQ is 5). You are welcome to the archive but it may be more economical to buy a PCB from me if you only need one.

Cost me $60 incl. shipping from PCBWay for the 5 boards, so sell the rest for $20 + postage each.

The archive is at https://1drv.ms/u/s!AhFYQ1KOpxRroHSUDmyWbZjsuF6Z
This contains all of the high resolution pictures, gerber and drill files, and the PDF document (schematic, assembly drawing, and BOM).

The performance is good and quiet, and is what should be in a test instrument in the first instance. The heatsink is scavenged from an old AT power supply - they are nearly all the same and you get the SilPads as a bonus. The fan is also from an obsolete CPU cooler.

Note. This power supply makes the instrument grounded, ie. the BNC connector shells are connected to mains ground. Know this before you start hooking stuff up to it. You can of course isolate the instrument by simply not connecting the earth at the mains plug, but be sure your wiring is top quality.

What more can I say? It works. Here are some low resolution pics.

[g4wam]

Hi there-Jfitter------do you have any of the psu pcb's left my friend

Mike  G4WAM

[intabits]

Those 3.2VA transformers from RS are cute and cheap, but too piss-weak for the 5v supply in the FY6800.

I was suspicious of their capability, so before making a PCB for my failed FY6800 switching supply, I made a test jig to test the idea.
With a 50R load on the output of one channel, and 75R on the other, the 5v supply was drawing 460mA, and the +/-12v supplies were 75mA each.

My test jig using 3.2VA transformers (9VAC for +5v supply, 2x15V for +/-12V)


 


Top trace shows the +5V regulator input always under the 7V minimum for a 7805 regulator. Bottom trace shows the 7805 output below 5v almost all of the time. The transformer was also getting very hot.





Maybe an LDO regulator, and/or more filter capacitance might have helped, but the transformer was getting way too hot. It just isn't up to the job.
The loose 7VA transformer in the foreground is the same size as the 3.2VA unit, and may have solved the problem, but unfortunately, it was burnt out.
Putting in a larger, 7VA transformer fixed the problem.





Regulator input is now always above 9v, and its output a steady 5v.





New linear power supply PCB installed

[maxwell3e10]

I found this triple linear power supply on Ebay for less than $20
https://www.ebay.com/itm/SL-Power-Electronics-Linear-Power-Supply-MTLL-5W-A-5V-5A-12-12V-NEW/172432850496

It has all three needed voltages and fits nicely in the box. I added a small fan to draw air out of the box and it keeps it cool. There is enough power to use upgraded THS3092 dual output op-amp.

[intabits]

That's a neat solution, at a good price. Outside of the US though, shipping hits hard.

I don't know anything about this THS3092 is it a drop in replacement? And you did it?

I bought a couple of EL2099C video distribution amps to try out what this guy did:-

Not quite the speed as THS3092, but higher current from what I can see.

[maxwell3e10]

Yes, THS3902 is a dual 8-pin op-amp, I soldered it right in.  It provides enough current to drive 50 Ohm load and in principle should even drive a short circuit load (200 mA). There is also THS3091 if your box is configured to use separate amplifiers.

[mawyatt]

That's a neat solution, at a good price. Outside of the US though, shipping hits hard.

I don't know anything about this THS3092 is it a drop in replacement? And you did it?

I bought a couple of EL2099C video distribution amps to try out what this guy did:-

Not quite the speed as THS3092, but higher current from what I can see.

Also, the dual channel Juntek DPA-1698 can supply up to 1A per channel.

Best,