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Simple High Performance DC Coupled Class A HPA with sub PPM THD
Simple High Performance DC Coupled Class A HPA with sub PPM THD
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Old 27th June 2018, 05:49 AM   #71
pstech is offline pstech  United States
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Old 27th June 2018, 01:06 PM   #72
xrk971 is offline xrk971  United States
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Simple High Performance DC Coupled Class A HPA with sub PPM THD
Quote:
Originally Posted by stellarelephant View Post
Wow, X, looks like you nailed it!
Thanks. To get this performance requires use of the TP7A4xxx LDO regulaors which are only available in quad flat pack with no leads and underside power pad for heatsink. They are rather tricky to solder (must be done with reflow) as needs a hot air gun from above and a hot plate from below, plus the pin pitch is 0.5mm. They don't make them in a larger package like SOTxxx or even SOIC where legs are visible. JPS64 is looking into getting some made to conform to a standard larger trough hole adapter board to resemble an LM3x7 TO220. One could use an LM317N or LM337N in SOT223, but the noise is about 10x higher at 38uV rms vs 4uV rms.
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Old 27th June 2018, 01:39 PM   #73
badboygolf16v is offline badboygolf16v
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Could they be ordered from someone like say www.ldovr.com? Maybe we could do a GB for them?
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Old 27th June 2018, 01:55 PM   #74
xrk971 is offline xrk971  United States
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Simple High Performance DC Coupled Class A HPA with sub PPM THD
Quote:
Originally Posted by badboygolf16v View Post
Could they be ordered from someone like say www.ldovr.com? Maybe we could do a GB for them?
I have bought one from there before - they are kind of pricey at $23 ea. Some Chinese ones are now in the circa $8 range (but not TO-220 pin compatible -but that's ok).

TPS7A3301 -5V -9 -12 -15V -18V 1A Ultra Low Noise LDO Negative Voltage Regulator 699924389058 | eBay

TPS7A4700 Low Noise Power Module DC-DC 3-36V to 3V 3.3V 5V 12V 15V 1A Adjustable 699901905578 | eBay

So these are also an option.
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Old 27th June 2018, 02:11 PM   #75
JPS64 is offline JPS64  Germany
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In progress...


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Old 27th June 2018, 04:23 PM   #76
xrk971 is offline xrk971  United States
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Simple High Performance DC Coupled Class A HPA with sub PPM THD
Hi JPS64,
This looks great. Can you please add a M3 screwhole so that we can bolt a TO220 heatsink to make contact with thermal pad vias on the back?
Thanks,
X
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Old 27th June 2018, 08:29 PM   #77
JPS64 is offline JPS64  Germany
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Hi X,


to small for M3 screwing. Im prefering folling:
- SK 104 25,4, Extruded heatsinks for PCB mounting, Heatsinks f.cool, Fischer Elektronik
- https://www.fischerelektronik.de/web_fischer/en_GB/heatsinks/A06/Retaining%20springs%20for%20transistors/PR/THF104_/$productCard/parameters/index.xhtml


Isolating electrically the PCB using foil.


JP
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Old 27th June 2018, 09:40 PM   #78
xrk971 is offline xrk971  United States
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Simple High Performance DC Coupled Class A HPA with sub PPM THD
Hi JPS,
Yes, those are similar the heatsinks I get from eBay for about $7 for 10. I would probably use silicone TO220 insulator sheets or one layer of Kapton tape works too.

Thanks,
X
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Old 27th June 2018, 10:34 PM   #79
JPS64 is offline JPS64  Germany
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Last progress. Ill give datas for control to X.


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Old 27th June 2018, 10:45 PM   #80
xrk971 is offline xrk971  United States
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Simple High Performance DC Coupled Class A HPA with sub PPM THD
Looks good! So use a spring clip to clamp voltage regulator to heatsink vs screw hole. I need to get some clips.

For system with single DC-DC we will be limited to about 150mA bias current per channel as overall current limit is 310mA.
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