Placid-BP Bipolar Shunt Regulated Power Supply

[Russ White]

Paul what you are seeing is normal. You can readjust both the CCS and the output voltage slightly after the heat sinks are warm. The warm output current will always be just a bit more than it will be cold.

You can decrease the CCS current to just what is needed by turning it down until output starts to sag while connected to the load, then turn it back up a few turns after it comes back to the desired voltage. Now you will have just a bit more current than you need.

By tuning the supply to just what you need you will generate less heat.

Cheers!
Russ

[mourip]

Originally Posted by BrianDonegan

Shunt regulated supplies generate a lot of heat. You must be sure to provide enough ventilation. This alone is a good reason to space them out a little bit. After the supply is at operating temperature, and readjusted, the voltages should remain stable.

PS: I deleted the duplicate post on our support forum so that answers can be found.

Thanks for the reply. I posted in both forums because I had been having trouble reaching you this week when replying to the email you sent out asking for feedback on the Placid. Glad to catch you here...

Today the voltages started out at about 15.5 volts and gradually dropped close to where I reset them yesterday after they had drifted up over a two hour time period. I am letting them settle in and will tweak them once more.

Thanks for comfirming the heat dissipation observation. If someone is looking for a drop-in replacement these might not work for some boxes. I have a Parmetal case with good venting and still my entire box warmed up.

Regarding adjusting the CCS. Are there any other points where a voltage could be taken off? How about the un-populated pads for R1/R2? Would the voltage drop across these two points be directly proportional to the drop across R17/18 when the CCS adjustment pot is changed?

The good news is that the DAC sounds great....

[Russ White]

The voltage reference has a negative tempco. So it will tend to start up slightly higher than it will be at working temperature. So what I usually do is adjust for just under your target voltage. That way you never exceed you desired output voltage.

The movement is not very much and the less you heat the VREF section the less drift there will be. So I would adjust the CCS to deliver just what you need with a bit of overhead for the shunt.

I will edit the manual to makes this clear.

I am glad you are enjoying the DAC.

Cheers!
Russ

[mourip]

Originally Posted by Russ White

The voltage reference has a negative tempco. So it will tend to start up slightly higher than it will be at working temperature. So what I usually do is adjust for just under your target voltage. That way you never exceed you desired output voltage.

The movement is not very much and the less you heat the VREF section the less drift there will be. So I would adjust the CCS to deliver just what you need with a bit of overhead for the shunt.
Russ

Just to clarify for my own understanding. According to the manual "The output current per rail is calculated as V across RE divided by value of RE where RE is either R17 for the positive rail or R18 for the negative rail.

So... if I adjust to the .25v suggested in the manual and R17/18 is 1ohm per the BOM then I must be running my supplies at .250A. If I want to get them down to ~.150A then I would adjust down to ~.15v.

Is that correct?

[BrianDonegan]

Yes.

[planet10]

Discussion moved here

CCS in Placid-BP Bipolar Shunt Regulated Power Supply

[NicMac]

Hi All,
I just tried a set of the Placid supplies with a "stock" Buffalo24, with IVY II, and the improvement is very noticeable. I would like to try them also with my Buffalo32S but this unit is a bit "over-tweaked" for a fair comparison between the Placid's and the LCDPS/LCBPS.
Nic

[avr300]

Originally Posted by NicMac

Hi All,
I just tried a set of the Placid supplies with a "stock" Buffalo24, with IVY II, and the improvement is very noticeable. .............
Nic

Hi Nic.

Powering the IVY ?

[BrianDonegan]

IVYII only exists on B32. I think he means IVY 2.0. Yeah, that's much more clear...

[NicMac]

OK, with an IVY 2.0 (actually moderately tweaked according to TPA instructions). I only have the honor of Sir IVY the 2nd on the B32

Anyway, I did first the change of the VA supply and then afterwards the VD. The change was definitely most evident with the VA supply. I will not test much more with this configurations as I have the Counterpoint I/V that I find quite a bit better than the IVY 2.0. I just have to check a few thing with current draw etc.

Nic