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Old 24th September 2011, 09:12 PM   #611
JKC is offline JKC  Canada
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I have build Placid HD that can deliver 800mA at 5.25V. Those components has to be changed in order to get that current safely: both heatsinks to 2.5" high, R2, R2 resistors to 2W and add TO-220 heatsink to A1 bridge. Without heatsink the bridge is too hot (57C). With added heatsink temperature on the bridge is around 43C at 800mA load and 22C ambient.

At 800mA load QN1 heatsink is around 48C hot and QN2 34C. I tried this configuration with 1A load but heatsink is getting too hot for my taste at 58C. You can't get higher heatsink than 2.5" to fit the board, so I set the limit at 800mA. For this test I have used Amveco 70060 2x7VAC 25VA transformer. With 2x9VAC transformer temperature on heatsinks will rise more. With this transformer I got 9.15VDC on C1 with 149mVAC ripple at 800mA. On the load ripple is only 4.6mVAC at 5.25VDC which is good in my book.

Heatsink for the bridge doesn't require any screws. It fits perfectly between AC_IN connector and bridge. You will need to add some thermal compound however. See pictures for details and have fun.

George
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Old 24th September 2011, 09:28 PM   #612
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Nice work! That's a lot of current. the 7V transformer is close to ideal.

I wonder if the 2W R1/R2 resistors really need to be 2W. According to my quick calculations they should only see about .64W max.

One thing to note, is that if you want the CCS to be a bit stiffer you can use a larger value resistor at R1 (R2 remains 1R or less) and a higher voltage reference, but then you will definitely need higher power handling resistors. I had very good success with 4.7R.
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Old 24th September 2011, 09:38 PM   #613
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You can also mount the transistors under the board, using the case as a heatsink, or mount the entire psu on a heatsink.
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Old 24th September 2011, 09:58 PM   #614
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One other thing - your reported ripple at the load is much higher than it should be for some reason. How did you measure? I just cranked one up to 800ma with a 7.5VAC trafo and I too get about 80-120mvac (I varied current from 600ma to 800ma) ripple at the cap, but I get nothing measurable with my (well up to this point seemingly) excellent DMM at the load (which is drawing about 550ma). Not even a 100th of a millivolt showing. I just confirmed with the scope there there is virtually nothing there between 1 and 1mhz. Perhaps you are not shunting quite enough current, or you are shunting too much (which is very possible)?
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Old 24th September 2011, 10:29 PM   #615
JKC is offline JKC  Canada
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Russ,

I know that at 800mA you can get away with 1W R1 and R2 resistors but they are very hot. I have measured the ripple at C1 an on the load using Agilent U3401A multimeter. However, an internal frequency meter in not showing anything at the output so I am not sure what is that. Unfortunately, I have no scope to verify what is exactly I am measuring here, 120Hz or some HF noise. I have about 20" wires going to the load plus even longer measuring leads so maybe I am picking some other noise than actual ripple. I will try later with different current settings to see if it makes any difference, ether way I am not too concerned about it.

George
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Old 24th September 2011, 10:33 PM   #616
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Ah ok, thanks for the information, and again good work!
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Old 26th September 2011, 03:16 PM   #617
Bunpei is offline Bunpei  Japan
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Quote:
Originally Posted by staccatiss View Post
What IV converter did you use when you tested with doubled output?
what is that black "thing" in the middle?
In my case, I usually use no active IV converter. Instead, a direct connection of earphones (minimum impedance is about 5 ohm) or line transformers. Wires for those are bound to pins in the first floor DAC board.

The black parts are my standard decoupling capacitors, copper foil & polyphenylene sulfide (PPS) film capacitors.

I2S input and analog output wires are respectively shared by two boards at the pins that bridge the first and the second floor boards.
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Old 28th September 2011, 05:01 PM   #618
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What's the next stampede date?
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Old 28th September 2011, 09:37 PM   #619
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That's probably all now. Next will be BIV
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Old 28th September 2011, 09:38 PM   #620
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No, I don't think I have the time or energy for another major revision for quite some time.
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