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Scalable PSU/regulator GB

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#582
Just back from the post office. All original orders and the couple of mispacked orders have been shipped.

Actually my son probably mispacked a couple of orders. Check your PSU parts kits. 15V kits are unmarked, 65V its are marked "65V" in poor sharpie penmanship. I should have a couple of leftover 65V kits for myself, but I have none and have more 15V kits than expected. If you receive an unordered 65V kit, let me know and I'll swap it out.

Give it a couple weeks to confirm the number of leftovers and I'll get to the wait listers.
 
#584
D8 and D10 are options if you prefer to use a zener diode as a voltage reference instead of the more accurate lower noise LM4040. Using 1% resistors and the included LM4040 I usually end up with both rails within a few hundredths of a volt.

Within reason you can use the same R2, R11 etc and adjust the voltage reference to adjust output voltage for other than 15V nominal. I find it easier to adjust R2 and R11.
 
#587
Sounds like you used the 3K3 Jens called out for for R11 and R13. That is for use with the trimpots. swap in the leftove 2K resistors and you should get within a few millivolts of 15V.

I put both values in the kit to allow the choice of fixed or adjustable voltage.
 
#589
You can remove R11 and R13 if using trimpots, but leaving them in makes the trimming less sensitive. I'd leave them in if you decide to add a trimpot.

R11/13 at 3K3 in parallel with a 10K trimpot makes a useful range of adjustment around 15V.

Using 2K fixed for R11/13 (replace the 3K3 you installed with 2K and leave out the trimpot) gives you 15V nominal +/- component tolerances. If you have 2K2, that will drop your output voltage to roughly 14.5V.

Output voltage = 10*(R2+R11)/R11 10 is the reference voltage, so if you subsitute a 9.1V zener for D7, use 9.1 as the multiplier. If you have a trimpot installed substitute the parallel equivalent resistance of the pot and R11 for R11 in the equation.

Hope that helps.
 
#591
Should be no problem with proper heat sinking - use at least 1.5" high sinks. The current limiting factor is the diodes - they are 1A devices, 500 ma is reasonable limit. IIRC, the A75 needs about 150 mA for both front ends together.

The spreadsheet I put together takes into account power dissipation in the pass devices to limit junction temperature to 100C. It assumes that your heat sinks are in the case at 35C ambient. You can push that a bit, at the expense of reliability.
 
#594
Hi,
I'm going to be regulating the front-end of a Leach amp with the 65V kit. Just to confirm, this instruction applies to all CT transformer applications, right?

Also, I feed both halves of PSU 2.2 from the same AC tap to get +65 /GND/ -65V? Seems a silly question, but my mind insists that I need both ends of the 50-0-50 transformer.
 
#598
a single board will supply two channels of Leach amp with ease. Purists will say you should have separate regulators.

Keep an eye on heat sinking the pass devices if you have a lot of voltage to drop. The attached spreadsheet will calculate dissipation allowed in the pass device based on keeping the junction temperature below 100C and max current at that dissipation. Keep maximum draw under 500 mA though to keep the rectifiers within their limits.
 

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#600
psu orion+

Hi,

I have some questions concerning the PSU 2.2 15V. I bought the pcb and parts including a transformer from a Cobra2 on this forum. He also kindly added the schematics, the layout of the pcb and the BOM in paper form (Tank you Arne 🙂). I have also read through this thread. Still I have some questions. I realize I am real newbie.

Since I need 15 volts I put 2K into R11 and R13. Therefore I don´t use the 3.3K in these positons. So the first question is then: Should I put the other two 3.3K into R6 and 17 or should I omit them as well?

In the BOM there is listed a quantity of 4 1K resistors but there are ten positions listed, 4 in black (R1, 5, 20 and 21) and the rest in red (R2, 4, 10, 12, 19, 22). Should I only use these 4 in the four positions listed in black or do I need another six and mount all ten?

OK, I hope for clarifying answers.

Best regards,

Ketil
 
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