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Old 20th October 2011, 05:31 PM   #611
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So
What current is your transformer providing for each secondary?
What value have you for R101?
Four LEDs green, correct?
What is the voltage drop across each green LED?
What value for C105?
Chris

Last edited by Backbones; 20th October 2011 at 05:33 PM.
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Old 20th October 2011, 05:46 PM   #612
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Quote:
Originally Posted by Backbones View Post
So
What current is your transformer providing for each secondary? 30VA
What value have you for R101? 3R3
Four LEDs green, correct? YES
What is the voltage drop across each green LED? 1.8-1.9V
What value for C105? 10.000Uf
Chris
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Old 20th October 2011, 06:01 PM   #613
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Transformer current sufficient.
4 times 1.9V = 7.6V
Say current draw of 700mA = Vgs of about 5.5V.
7.6-5.5=2.1V
I=V/R. I=2.1/3.3. I=640mA.
Not enough current for 700mA. R101 needs to be 3ohm or lower (2.1/0.7). I don't know up to what current the BiB is designed to go.
chris
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Old 20th October 2011, 06:08 PM   #614
cersepn is offline cersepn  United States
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Quote:
Originally Posted by Salas View Post
Use 3 1.9V leds and 1.2R 2W setting resistor (R101 etc.) for 0.5A available if you can't find 1.3R.
Hmm, Salas just to confirm, 1.9V = RED LEDs, yes? Because i saw other people who used the regs in the same application and they used the green LEDs in Dx02,x03,x04 instead. Is it because their current used is different?
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Old 20th October 2011, 06:09 PM   #615
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by coolhead View Post
Voltage across R301:
6.3Vac trans = 1.31V
9Vac trans = 1.36V

R301 is 10ohm

The output is the same 3.3V, the different will be CCS current of 50mA.
and now turn the mains supply voltage down to suppliers specified minimum. Measure again.

The fact that you have already lost 50mV tells me you are getting close to dropping out.
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regards Andrew T.
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Old 20th October 2011, 06:09 PM   #616
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Measured voltage accross R1 2.37 V : 3R3 = 718mA

BTW enough for B3...
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Last edited by merlin el mago; 20th October 2011 at 06:12 PM.
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Old 20th October 2011, 06:11 PM   #617
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Quote:
Originally Posted by cersepn View Post
Hmm, Salas just to confirm, 1.9V = RED LEDs, yes? Because i saw other people who used the regs in the same application and they used the green LEDs in Dx02,x03,x04 instead. Is it because their current used is different?
Different voltage.
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Old 20th October 2011, 06:13 PM   #618
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Quote:
Originally Posted by merlin el mago View Post
Measured voltage accross R1 2.37 V : 3R3 = 718mA
OK. After calculation errors it is about the right current levels. The drop across the LEDs depends on their current I believe to some degree.
If you are supplying the right current at the reg level one has to ask if the load is drawing more than this?
Chris
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Old 20th October 2011, 06:16 PM   #619
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Quote:
Originally Posted by Backbones View Post
OK. After calculation errors it is about the right current levels. The drop across the LEDs depends on their current I believe to some degree.
If you are supplying the right current at the reg level one has to ask if the load is drawing more than this?
Chris
Extracted from leonvb BIII manual in the TP site:

"The standard board requires an input voltage of 5.25V and it draws approximately 440mA when one is using the recommended set of Trident shunt regulators"
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Old 20th October 2011, 06:16 PM   #620
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Quote:
Originally Posted by Salas View Post
Looks 5ish to me, better calculate based on Vgs=5V. Also your LEDS maybe ~1.9V at the small current they will run, their spec voltage drop Vf is given at 20mA nominal usually.
From an earlier post.
Chris
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