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Old 6th September 2012, 11:42 AM   #1761
cersepn is offline cersepn  United States
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1. Okay, will this transformer do? I'm on 230v. Any advantages/disadvantages you personally found with r core vs toroid vs ei?
2. 150 mA is load consumption. Okay, 300 mA CCS good to go?
3. "Its either you use 1k trimmer and one red led, or 2 red leds and a diode for 5V"
If i'm reading you right, 2 red leds + diode (D301), everything else jumpered, no need for trimmer in R305 and no need for R303?
"The diode position can alternatively be a ~220R for easier filtration by C301" means instead of diode in D301, alternatively it can be ~ 220R?
4. Okay, does the quality of resistor matter much here?
5. Will 1000 uF be better than 220 uF for C301?
6. For 300 mA CCS, will 4700 uF be ok?

Thanks a million, Salas!
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Old 6th September 2012, 12:11 PM   #1762
Salas is online now Salas  Greece
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1. It will do when you will use only 2 terminals representing 12V and half the VA. This is a 12+12V transformer. Better not waste half of it if you can find just a 12V 2 terminal secondary one. Unless you got a use for the spare secondary. You can parallel those secondaries also but the VA rating is already overkill. Rcore is great when magnetic field is an issue and is good for all other specs too. Ei is lower capacitance than toroid, toroid wins Ei for bulk and efficiency in large applications. Not an issue here. I prefer a good Ei in small apps.
2. 300mA is a fine plan.
3. 2x 1.9V Vf Leds + 0.6V Vf 1N4003 diode or alike= 4.4V. Add 0.6V Q304Vbe which is there by default, =5V. Orient diode reversely than PCB printed for D301 Zener using its place. Alternatively a ~220R for R303. If circa 3mA runs it then a 200 Ohm will do 0.6V. Its all about what Q303 IDSS you got when installed. You measure the output and you trim the final value. Just one Led and a trimmer is for skipping calcs and fixes but not as perfect for ppm and robustness.
4. Use good resistor. A plain one won't kill it but a good one is superior ppm.
5. Don't know the sensitivity of your circuit for lowest freq noise, that would take an on hand analysis with a lab spectrum analyzer. Use 470uF to be on the safe side.
6. More than enough.

Nothing much, keep diying.
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Old 6th September 2012, 12:34 PM   #1763
cersepn is offline cersepn  United States
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Quote:
Originally Posted by Salas View Post
You can parallel those secondaries also but the VA rating is already overkill.
1. But will it cause any problems in terms of excess heat? I can't find any non-2x12/15v EI..

Quote:
Originally Posted by Salas View Post
3. 2x 1.9V Vf Leds + 0.6V Vf 1N4003 diode or alike= 4.4V. Add 0.6V Q304Vbe which is there by default, =5V. Orient diode reversely than PCB printed for D301 Zener using its place. Alternatively a ~220R for R303. If circa 3mA runs it then a 200 Ohm will do 0.6V. Its all about what Q303 IDSS you got when installed. You measure the output and you trim the final value. Just one Led and a trimmer is for skipping calcs and fixes but not as perfect for ppm and robustness.
2. I see. Is 0.6V referring to the forward voltage? I can't seem to find any 1N4003 with 0.6V. I don't suppose the diodes i have now will work, right?

Thanks again!
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Old 6th September 2012, 12:47 PM   #1764
AndrewT is offline AndrewT  Scotland
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All the 1n400x diodes have a voltage drop around 600mVf.
The exact voltage drop varies witht he current that is passing at any instant.
At very low currents the Vf could be around 400mVf
At very high currents (transient not continuous) the Vf could exceed 1000mVf.
At our "normal currents" of 10mA to 300mA expect diode drop to be between 600mVf and 700mVf.

Look at a datasheet. You will see how Vf varies with Id and with temperature.

BTW,
Rapidonline will sell you 1A diodes for about 2 per 100.
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regards Andrew T.
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Old 6th September 2012, 01:01 PM   #1765
Salas is online now Salas  Greece
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Quote:
Originally Posted by cersepn View Post
1. But will it cause any problems in terms of excess heat? I can't find any non-2x12/15v EI..


2. I see. Is 0.6V referring to the forward voltage? I can't seem to find any 1N4003 with 0.6V. I don't suppose the diodes i have now will work, right?

Thanks again!
1. No. Paralleling same spec secondaries just makes a double secondary transfo fully potent for VA in just one secondary. This is for when needing the grunt and having a small transfo though. Better leave it spare in this case, you may find a use for another reg or something else.

2. There is a chart for Vf VS forward current. At 10mA those 4003s are 0.6V, here it will be even less current running, so you get bit less than 0.6V possibly.
The Schottky you got don't show chart below 100mA, such are low Vf anyway, if they will be say 0.3V in our circuit you will need two. You can test that by using a 2SK117GR as CCS to feed your leds and diodes in a string to avoid soldering and de-soldering. Hook drain on a 9V battery plus, tie gate and source together and from there insert your reference string to battery minus. Measure the drop across the leds and diode(s) string, change something if not about 4.4V, and when OK install those. Install that particular 117 as Q303 also.
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Old 6th September 2012, 01:06 PM   #1766
cersepn is offline cersepn  United States
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Thank you both, Salas and Andrew. Your explanations make perfect sense. I will order the 1N4003 and call it a day
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Old 6th September 2012, 03:44 PM   #1767
cersepn is offline cersepn  United States
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Where's everyone getting their 4700 uF/63 Panasonic FC and Nichicon Muse from? Having trouble trying to get those values. Can only find FC in 4700 uF/25V
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Old 6th September 2012, 03:47 PM   #1768
Salas is online now Salas  Greece
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Why you would need a 63V filter capacitor in a 12 VAC rectified input reg? 25V cap is the right one.
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Old 6th September 2012, 03:53 PM   #1769
cersepn is offline cersepn  United States
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Quote:
Originally Posted by Salas View Post
Why you would need a 63V filter capacitor in a 12 VAC rectified input reg? 25V cap is the right one.
I should be thinking more. A LOT more. Salas to the rescue again!!
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Old 6th September 2012, 04:15 PM   #1770
Salas is online now Salas  Greece
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No worries, I do worse all the time. Its just a hobby.
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