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I would be very grateful if someone could confirm if these are the right sort of values
Measurements
Placid HD BP for Legato 3.1 but no load (one channel)
1. Between TP_Vin and TP_CCS = 0.381v
2. Between TP_Out and TP_Shunt = 0.379v
3. Output 13v when warm
Heatsinks very hot, I would not want to hold my finger on them for more than a few seconds.
Placid HD for Buffalo II with 3.1 Trident and new AVCC but no load
4. Between TP_Vin and TP_CCS = 0.481v
5. Between TP_Out and TP_Shunt = 0.482v
6. Output 5.25 when warm
Heatsinks quite hot (less than Placid HD BP), I would not want to hold my finger on them for more than a few seconds.
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The reason you are getting so much excess heat is that you are running with no load. When you do that the shunt transistor has to sink the entire current. Normally the load uses some of the current and thus the shunt transistor's life is much easier.
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Originally Posted by: Russ White  The reason you are getting so much excess heat is that you are running with no load. When you do that the shunt transistor has to sink the entire current. Normally the load uses some of the current and thus the shunt transistor's life is much easier. That explains the heat thanks Russ ;-) Are the measurement are what you would want/expect for these two power supplies and the boards they will be used with? Edited by user Friday, December 14, 2012 2:19:20 PM(UTC)
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They should be OK, just check the shunt current again once they are connected to the load and adjust as required. :)
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 1 user thanked Russ White for this useful post.
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Originally Posted by: Russ White They should be OK, just check the shunt current again once they are connected to the load and adjust as required. :) Will do Russ, thank you again, I'm just building a Legato so I cannot test it just yet.
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OK, back from the freezing garage, newly minted Legato 3.1 connected to Placid HD BP. Of course the voltage out plummeted to 4v. Adjusting the current I can get the following: Placid HD BP with Legato 3.1 (as load - one channel) 1. Between TP_Vin and TP_CCS = 0.455v 2. Between TP_Out and TP_Shunt = 0.222v 3. Output 14.5v when warm into Legato 3.1 as load Does this look right, I'm not quite sure what the TP_Out and TP_Shunt should be in vdc? If I know I guess adjust the current to get the right amount of shunt, assuming this is the shunt value? Edited by user Saturday, December 15, 2012 10:21:07 AM(UTC)
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The integration manual recommends 50mV between TP_Out and TP_Shunt for most modules - I don't have a Legato so I'm not sure if it's any different. But assuming it's the same as everything else, adjust the current (via VR1) to get 50mV out.
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Originally Posted by: chryses The integration manual recommends 50mV between TP_Out and TP_Shunt for most modules - I don't have a Legato so I'm not sure if it's any different. But assuming it's the same as everything else, adjust the current (via VR1) to get 50mV out. Thanks chryses for the advice, I was thinking it would be less than 0.500v between TP_Out and TP_Shunt for the Legato as it provides a constant load? I could of course be horribly wrong on this which was why I was asking the question. Was the 0.500v between TP_Out and TP_Shunt for the Bufallo II with Trident? Only I cannot seem to find it in the integration guide. Edited by user Monday, December 17, 2012 7:36:46 AM(UTC)
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According to the guide (in the latest version it's on the page below the table that lists the current requirements for each module) I think you want 0.050v (50mV, not 500mV) shunted current for both the Buffalo and the Legato.
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Originally Posted by: chryses According to the guide (in the latest version it's on the page below the table that lists the current requirements for each module) I think you want 0.050v (50mV, not 500mV) shunted current for both the Buffalo and the Legato. When you shunting current you're not talking Volts, but Amperes. It should be 50mA = 0.050A. |
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That's correct, but isn't the resistance across TP_Out and TP_Shunt just 1 ohm? So in this case, doesn't mV = mA?
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The current is exactly the value of the voltage across the test points.
The shunt current is the current the load is not using from the CCS.
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Thank you chryses, I did of course mean 0.050v, typing on an iPad with a plaster on two fingers ;-)
Corpius and Russ, thank you for explanations, they all help, and I think I have it now.
Hopefully later today or tomorrow I'll have the DAC up and running and then we will know for sure ;-) x (crossed fingers)
Seasons greetings to you all and thank you for you patience and help.
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Asked the same question on DIYA while the answer was here... I apologize...
Following this topic now.
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With the BIII SE attached to the Placid HD, I'm eating ~507mA with a shunt current of 40mA. Before attaching the BIII, I measured 488mA for CCS. I hooked a pair of headphones up to the IVY SE outputs and all sounds good for a quick test anyway. BTW, I'm impressed with the noise floor, I had no idea I had the gain up all the way until the music started playing!
I'm slightly concerned about the heat from QN1 with the BIII SE connected. QN2 is barely warm but QN1 is too hot to keep a finger on. The BP supply for the IVY is very cool in comparison to the the single placid for the BIII. Just want to make sure everything is correct before I proceed.
I would have expected the Placid BP to be hotter because it the shunt current is higher per rail? I'm going to shut it down just incase I have something wrong:)
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If you read the chapter "Powering it all" again you'll understand this is to be expected: the IVYIII only presents a load of around 90-150mA to the Placid HD BP. If the temperature of the HD isn't above the 80 degrees/176F you should be fine.
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Thanks for the help Leon!
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