Placid-BP Bipolar Shunt Regulated Power Supply

[eclectic2k]

Originally Posted by alboran

I noticed that if you adjust the voltage to +15 V and-15V without load, then when I connect the IVY III, the voltage drops to approximately +9 V .... Is this normal?

sounds like your current is not set high enough for the load. Did you check the current? -- the voltage across R1 & R2 on most recent PlacidBP's
(Older PlacidBP's were R17 & R18...) See the manual....

[chipzahoy]

Hi Brian and Russ,

The manual recommends a 7v transformer for the Placid Power Supply. Is is okay to use a 9v transformer, or would the extra voltage drop create too much heat? (350mA, 5.5v output)

[BrianDonegan]

Originally Posted by chipzahoy

Hi Brian and Russ,

The manual recommends a 7v transformer for the Placid Power Supply. Is is okay to use a 9v transformer, or would the extra voltage drop create too much heat? (350mA, 5.5v output)

It should be >=7V for 5V use. We sell a 9V transformer for it.

[chipzahoy]

Thank you Brian! I'll pair a 9v transformer with the Placid

[Boris_The_Blade]

I received a Placid power supply a little while ago and just finally got around to implementing it. Thought I'd post a few comments and suggestions, sort of a mini-review.

Overall, very good board layout, price is decent. I was using a 2x15V secondary transformer with +/-12VDC outputs. I measured about 400uVrms of noise on an output with a 150mA load and 225 mA through the CCS (shunting 75mA). This was even without the best test setup, using an HP 403B. For comparison, a 7812 makes about 1.6mVrms of noise.

My only suggestions would be to:
1) Add test points for R1 and R2. I was using a meter to measure current across them, when one of the meter lead tips peeked through the soldermask and shorted, ruining one of current-setting potentiometers (VR1/VR2).

2) Ship with 50-ohm variable potentiometers instead of 200-ohm. Most of the turning range is wasted getting the current close to most applications (> 25mA).

Otherwise, very nice product!

[glt]

Originally Posted by Boris_The_Blade

...
I measured about 400uVrms of noise on an output with a 150mA load and 225 mA through the CCS (shunting 75mA). This was even without the best test setup, using an HP 403B. For comparison, a 7812 makes about 1.6mVrms of noise.

...

It got to be lower noise than that?. I am not sure how your measurements relate to specifications, but:

According to specifications, an lt1763 regulator is about 8x lower noise than a 78xx class regulator: H I F I D U I N O: Comparing Noise Figures in Linear Regulators

Your measurements show that the Placid is 4x lower noise than a 7812. Does this mean that a lt1763 regulator is 1/2 the noise than a Placid? It seems that from a design point of view (filtered LED reference, low noise opamp and low noise pass transistors) the Placid should be lower noise than an IC regulator using a bandgap reference

[Boris_The_Blade]

The placid very well could ideally be lower noise, however, that is what I measured, under a non-ideal situation (e.g. inside a chassis with other electronic components). Also keep in mind that the LT1763 series only go up to 5 Volts. Noise would likely go up when using a voltage divider for the reference rather than directly connecting the output to the reference (for 12V output).

[Russ White]

All things considered its not a bad measurement at all.

[Boris_The_Blade]

Originally Posted by Russ White

All things considered its not a bad measurement at all.

I agree completely.

[Bassivus]

Hi,

I'm waiting for the next batch of Buffalo IIs and am reading a bit in the mean time ... I just noticed that Placid BP bom says:
"IC1, IC2 2 Precision Low-noise Bipolar Op Amp Burr-Brown OPA227PA Mouser 595-OPA227PA"
but I can see on the picture that your latest boards use SMD versions, don't they?

Ivica