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HI Gustav,

I'm planning the built, I have an 2x0,3A toroid at home and I'm not sure, if that would be enough.
 
I use this one here
http://www.conrad.de/ce/de/product/605767/Ringkern-Transformator-230-V-2-x-15-V-2-x-100-A-30-VA-Sedlbauer
Remember to change the LM317, lm337 resistors for getting +-15V
 
Thanks for your reply.  I will try the transformer I already habe. Since it is2x18, no calculation neccesary :)


If there is a demand, I could post a complete BOM from Reichelt
 
Hi,

there a two different values in the BOM and on the PCB for the Input-Amps. The BOM contains 220pF ceramic capacitors, on the PCB is 200pF printed. What are the right values?

By the way, it is a solid PCB, very easy to work with and feels like high quality.

Thank,

Mike
 
mike76 said:
Hi,

there a two different values in the BOM and on the PCB for the Input-Amps. The BOM contains 220pF ceramic capacitors, on the PCB is 200pF printed. What are the right values?

By the way, it is a solid PCB, very easy to work with and feels like high quality.

Thank,

Mike

200/220pF, makes no difference here.  If it says 200 on the PCB, I must have made a mistake on the silk screen.

Hope that helps :)

Gustav
 
Gustav said:
mike76 said:
Hi,

there a two different values in the BOM and on the PCB for the Input-Amps. The BOM contains 220pF ceramic capacitors, on the PCB is 200pF printed. What are the right values?

By the way, it is a solid PCB, very easy to work with and feels like high quality.

Thank,

Mike

200/220pF, makes no difference here.  If it says 200 on the PCB, I must have made a mistake on the silk screen.

Hope that helps :)

Gustav

It did, thanks :)
 
Is there any explanation, why the test points are different in voltage although using the same resistors? I've got -18,5V and 17,8V on the other side.

I suppose, as I am a newbie, the values should be as equal as possible? Maybe because of tolerances?
 
no, should be quite closer to +-18V or as I prefer +-15,
eg: +18V > 220R and 2,95k(3k)
        +15V > 220R and 2k42(2k4)
check the Ac's coming from the Transformer, if they are the same, check the resistors at the ladder Filter.
Otherwise check the LM317 and LM337
 
You might change it as well but you may also use a voltage devider to be more confident.
Or a trimpot, I would recomend  a 5k Bourns.
 
Greg S. said:
:eek: Better don't refer to this amount of errors/mixups/nonsense in the shown vreg. schematic and formula.
The only correct information seems to be the pic on the right hand side, copypasted from a voltage regulators datasheet.
(make sure to look at the correct parts parameters, because the vregs datasheet most often shows both LM117 and LM317 and parameters are not all the same, IE the current setting 240R resistor is ment for a LM117 that would better be 120R for a LM317 part to ensure draw of minimum load current in order to maintain regulation.)
 
Okay, thanks, I have to work this out. For the beginning, I've ordered a second LM317. I have used several resistor combinations  but ended always in a difference at about 0.5v.

The positive side works as expected, at the moment with gregs recommendation at about 15.04 V.

If the replacement does not work,  I have to dig deeper ;)

Btw, does the elektrocaps need to have 63v? I put 30v in it.

Thanks and sunny greetings from cologne :)
 
'a second LM317' would be for another/different positive supply rail. You want a LM337 for your negative supply rail.
You want to meet the min.load requirement for your neg.rail. Depending on manufacturer of your 337 vreg, this will be in range 5mA ... 14mA. Assuming 10mA for the more common suspects, the current setting R96 (R- resistor) will need a parts value of 1.25V/0.010A=125R. Pick a 120R part for a 1.25V/120R=10.4mA min.current draw. The voltage setting R93 (K- resistor) will have a parts value of (15V-1.25V)/0.0104A=1322R. Picking a 1K3 should be close enough, and ignoring the additional typ.65uA Iadj * 1K3=about 0.09V that would vanish in parts tolerances.
A temporary connected maybe 1K5 between -15V and 0V reference voltage would have a similar -meeting the min.load current- effect before you connect the rest of your circuit, so you might try this first.
Parts come with tolerances, so for usual you design  for worst case conditions in order to not damage or blow up connected parts. (The -from Gustavs schematic- TL072 and TL074s have an absolute max.rating of +/-18VDC=36V between supply pins that you don't want to exceed).
'Btw, does the elektrocaps need to have 63v? I put 30v in it.'
Your 35V (not 30V, be more exact with your numbers) rated electrolytic caps will be sufficient, except for the 1000uF caps C37, C38, C39, C40 that might get close to the edge when you assume +10% high mains voltage and an unloaded or barely loaded mains transformer (typ.+15%) with your -from previous post- dual 22VAC secondaries in front. ((22VAC+22VAC)*1.1*1.15*sqrt(2)-2*0.6V)/2=38.75V raw DC per rail in front of the regulators. The differential between voltage in front of the regulators and voltage at regulator output (from previous numbers worst case 38.75V-15V=23.75V -dropout too much) times current drawn from your circuit will be transfered to heat, so the vregs might require a heatsink attached, further leading to the conclusion that a dual 22VAC secondary probably wasn't the best bet for your wanted +/-15VDC rails.
 
Dear Harpo,

thank you for your extensive explanation. I appreciate that.

I will consider this in my further progress. I'll print this, cause I suppose, I need to read this several times regarding the content :)

Anyway, I ordered 337 not 317 yesterday and 63V caps, too. The transformer was rated to 2x18V and supplies 2x20.05V.

Thanks again, as I can imagine and understand, that questions and requests like mine can be annoying to read and answer for somebody, who might is a professional.

Mike
 
Here we go again  ;D

I changed the LM337 (because I already desoldered it) and changed the resistors as you suggested. It looks much better now: 15.05V at the positive and 15.1V at the negative (15.26 before changing resistors).

I assume, as you wrote, that a difference of 0,05V shouldn't make any headache, does it?

Now if I calculated correct, there are about 28V of raw voltage, minus the 15V equals 13V. Would that be too much for the vreg to handle without cooling or would it be better to go higher with voltage?

Thanks for this important lesson :)

Mike



 
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