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FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator

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nctnico:
Well... these kind of switching modules can push quite a bit of HF noise between the input and output. I wouldn't want to use these in a piece of test equipment without a very careful board design and filtering. These modules are nice to provide a lot of power to digital circuitry.

Miti:
Datasheets and link attached.

https://learn.adafruit.com/adafruit-ultimate-gps

Edit: Those are not LDOs, they are Schottky diodes. The question is, what's a PIC doing there? Probably just ON/OFF and supervision?

Johnny B Good:

--- Quote from: Miti on February 22, 2020, 01:36:35 am ---Datasheets and link attached.

https://learn.adafruit.com/adafruit-ultimate-gps

Edit: Those are not LDOs, they are Schottky diodes. The question is, what's a PIC doing there? Probably just ON/OFF and supervision?

--- End quote ---

 Thanks for the gps module link. So, it turns out to be not so useful a module as far as my GPSDO ambitions are concerned (my basic PLL GPSDO using a u-blox NEO-M8N is now completed and housed in a neat extruded aluminium case since my final reworking of the circuit just last night). I think the u-blox module is actually a better bet for this sort of  basic GPSDO project (based in part on Gyro's LEA-6T circuit he posted almost two years back here: https://www.eevblog.com/forum/projects/my-u-blox-lea-6t-based-gpsdo-(very-scruffy-initial-breadboard-stage)/msg1493431/#msg1493431 ).

 I managed to track down a datasheet for the 5v module here: https://www.alldatasheet.com/datasheet-pdf/pdf/606479/DELTA/S36SE05003NRFB.html The specifications don't look too bad but I'd be inclined to test them for noise and ripple before committing myself to using them in a replacement PSU. Those +/-15 volt modules appear to be versions of the Murata modules as per the following pdf: https://power.murata.com/datasheet?/data/power/bei15.pdf. According to this page: https://power.murata.com/bei15-150-q12n-c.html they seem to have a 100mV ripple and noise rating (fairly typical for higher voltage output dc-dc converters).

 The important points of difference between the original smpsu board and a replacement mains voltage transformer based one using these modules is the elimination of the massive amounts of directly emitted RFI by the original mains smpsu and the amenability to additional low pass filtering of the noise and ripple of these modules (the opamps' own PSRR will largely take care of what noise and ripple remains on the voltage rails). The directly radiated switching hash from the original smpsu board which swamps everything can't be so conveniently disposed of by the on board opamps' PSRR.

 If you think you can easily solve the noise and ripple issue with cheap AM1117 LDO ICs, think again! For this trick to work, you'll need special LDOs designed to reject noise and ripple into the low MHz region - your standard off the shelf AM1117s just ain't going to cut the mustard for this job. :(

=============================================================================================
[EDIT 2020-02-22]
 I've just done an ebay search on those +/-15v modules and got this single hit https://www.ebay.co.uk/itm/1pcs-BEI15-150-Q12N-C-Murata-Murata-Power-Solutions-Isolated-DCDC/352744225236?hash=item522131b9d4:g:iGUAAOSwigxdR9Cb. By their deluded reckoning, you've got a tad more than 635 Australian dollars' worth in just those modules alone (around 325 quid's worth)  :wtf:

 The 5v modules are more reasonably priced at just $15.71 each by Octopart... Hmnn, I wonder if they do the 15v modules? Indeed they show a whole bunch of distributor prices at or around the $32 mark which makes X-On Electronic Services a bunch of (deluded - they seem to think they have a monopoly on these parts) piss taking wankers imho. More realistically, you seem to be in possession of around 270 dollars' (American) worth in dc-dc modules in total (assuming the photo represents your complete collection). Still a respectable return on your dumpster diving exploit.  ;)
=============================================================================================

JBG

Miti:

--- Quote from: Johnny B Good on February 22, 2020, 04:05:55 am ---[More realistically, you seem to be in possession of around 270 dollars' (American) worth in dc-dc modules in total (assuming the photo represents your complete collection). Still a respectable return on your dumpster diving exploit.  ;)
=============================================================================================

JBG

--- End quote ---

Add 2 GPS modules priced at $39.95 each, about 80 Li-Po batteries Zeus 2400 mAh, 4 brand new LCDs 800x480 LVDS, pressure sensors, mini vacuum pumps, and many more small things. Not too long ago I found some scrapped boards and I recovered 20+ genuine Ublox Neo M8T modules.
Now if only I could sell them...  :palm:

nctnico:

--- Quote from: Johnny B Good on February 22, 2020, 04:05:55 am --- If you think you can easily solve the noise and ripple issue with cheap AM1117 LDO ICs, think again! For this trick to work, you'll need special LDOs designed to reject noise and ripple into the low MHz region - your standard off the shelf AM1117s just ain't going to cut the mustard for this job. :(

--- End quote ---
There is a very simple solution for that: use an RC filter in front of the LDO. The resistor will also help to dissipate some of the energy lost in the LDO.

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