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Old 8th February 2009, 05:02 PM   #981
RCruz is offline RCruz  Switzerland
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Here you have a pdf showing how many jfets for each current.

Is 8.5 a good value or should I look for 6.5 mA ? (I still have some jfets to measure).

Ricardo
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Old 8th February 2009, 05:42 PM   #982
Salas is offline Salas  Greece
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8.5mA is very good for the Rsource resistors I recommended.
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Old 8th February 2009, 05:45 PM   #983
Salas is offline Salas  Greece
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Quote:
Originally posted by ikoflexer


I hear you sir. Any pointers to particular makes of polyprop caps with low ESR? I have quite a bunch of them of different makes, and not one has low ESR but I do have already have some electrolytic ones with low ESR.

I forgot to mention something else different in the buffered regulator. The power mosfets are COLD. They run at much lower quiescent current. The simulation does not show especially much current going through the darlington, yet it gets warmest of them all. I am not inclined to change it again for a highest current through the mosfets, it if works already so well.
Do you have a Solen 0.1-0.22uF to parallel your low ESR electrolytic, so to do even better? Canadian distributor of SCR I believe?

The current is governed by the CCS. Must be 212mA with Vbe/3R3. Can you measure it at the input?
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Old 8th February 2009, 06:46 PM   #984
hoktuna is offline hoktuna  Sweden
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My local supplyer do not stock 550`s nor 560`s.
I have bc549b and bc559b,will they do the job in the shunt?
Im almost done with the wireing,just have to fix the ac inlet and switch and maybe a fuse.
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Old 8th February 2009, 07:00 PM   #985
iko is offline iko  Canada
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Quote:
Originally posted by hoktuna
My local supplyer do not stock 550`s nor 560`s.
I have bc549b and bc559b,will they do the job in the shunt?
Im almost done with the wireing,just have to fix the ac inlet and switch and maybe a fuse.
I can only speak of my experience with the BC550B instead of the BC550C. It worked for me just fine. The higher gain of the C is desirable, but I cannot say how much it affects performance. The scope trace looked very good.

The 549 seems to have a bit lower maximum allowed voltage, 30V, instead of 50V for the BC550. But in this circuit, I don't think you'll get more than 25V across the transistor anyway.
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Old 8th February 2009, 07:05 PM   #986
iko is offline iko  Canada
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Quote:
Originally posted by salas


Do you have a Solen 0.1-0.22uF to parallel your low ESR electrolytic, so to do even better? Canadian distributor of SCR I believe?

The current is governed by the CCS. Must be 212mA with Vbe/3R3. Can you measure it at the input?
Don't have a solen, but I'll see what I can get. I'll measure the current probably tomorrow, as I have to get ready for some guests.

Later.
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Old 8th February 2009, 08:01 PM   #987
Salas is offline Salas  Greece
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Quote:
Originally posted by hoktuna
My local supplyer do not stock 550`s nor 560`s.
I have bc549b and bc559b,will they do the job in the shunt?
Im almost done with the wireing,just have to fix the ac inlet and switch and maybe a fuse.
No, if you do the 36V version as I think you do. In that, the driver npn is going to see 33.5V across. Don't you have access to some 45 or 60V npn low noise high hfe part?
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Old 9th February 2009, 01:52 PM   #988
RCruz is offline RCruz  Switzerland
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Hi Salas

Yesterday I noticed the 560r (554r real) resistor I was using to load the shunt during testing, was really hot so I decided to measure the current flowing.

By my calculations: (I=V/R) ;R load = 554 ohms; Vout = 28.2 Volts, the current should be 50.9 mA.

In reality I am reading 78.2mA

I decided to change the loading resistor to a 1kr (988r real) and now the current reading is 43.3 mA

Am I missing something ?

Is there a problem with my DMM ?

Regards

Ricardo
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Old 9th February 2009, 03:41 PM   #989
Salas is offline Salas  Greece
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Did you measure with your DMM set for current in series with the dummy load? There it is just I=V/R. We use 500R so to have about 50mA, which is comparable with 2 phono channels of your version, so to judge the reliability with given sink on the shunt Mosfet, stability over time, and correct voltage output. Maybe the dummy resistor isn't so big for the heat it develops so its resistance plays way off?. Or the DMM does tricks?. I usually use 3 times the Wattage of actual dissipation on resistors. So I would use a 5W dummy in your case. If it has 28.2V across, and it is 500R and holding, there is no way than running anything different than 56.4mA through it. But being able to measure correctly as expected or not what the dummy consumes, is irrelevant to the PSU. As long as the dummy sinks some current and nothing oscillates, when the voltage is stable at nominal, all is working well.
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Old 9th February 2009, 04:17 PM   #990
RCruz is offline RCruz  Switzerland
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I measured with the DMM set for mA, in series with the load resistor.Maybe my DMM is not correctly set.
Tonight I will try and measure with an analog MM.

The shunt delivers 28.2v steady with any of the loads (and even without any load).

Ricardo
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