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Old 7th October 2012, 06:48 PM   #11
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Quote:
C35 is shown as .047/400V. When a capacitor value prefix
is not otherwise indicated as in uF, nF, pF, it is assumed that the no prefix
value is in Farads (F). LTspice certainly assumes this.
I agree 100%. And, my apologies for forgetting to show "uf" in the schematic. Please, check out, I rectified the mistake in the last diagram.

Quote:
The reactance of your newly invented C35/ .047uF capacitor is
over 50Kohms at 60 Hz. Your supply will not work. I know you
have not run a simulation with load, successfully.
Actually, i wanted to, Add some MOV's or an AC rated polyester cap or RC at transformer Primary. But i don't know how to do this and with what proper values. So, i end up using .047uf/400v AC cap at primary input, which is actually an X capacitor connect in parallel to the mains(parallel to power on off switch primarily). Offcourse, power supply won't work until this cap is bypassed or the power on/off switch is in ON position.

Can you tell me how to Add some MOV's or an AC rated polyester cap or RC at transformer Primary, and with what proper values in my design?

Thanks.

Last edited by noddy55; 7th October 2012 at 07:07 PM.
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Old 7th October 2012, 07:34 PM   #12
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Quote:
Originally Posted by noddy55 View Post
Thanks!. This is really i was confused about. So i asked, to check the polarity and implementation of Q1 and Q2 transistors. Actually, this is first time i am creating a split rail power supply. With single supply i know how to use NPN as well as PNP. But, i had no idea and experience about the negative rail transistor, its type and polarity.

So, i think now i conclude that the opposite type pair goes together in a split supply?
If i use NPN in positive rail then i have to use PNP in a negative rail and if i use PNP in a positive rail then i have to use a NPN in a negative rail with Center tap traffo. Am i right?

However, with dual secondary supply traffo, The case is different. We can use both PNP. With dual supply traffo, the negative wire of one supply is shorted with the positive wire of another supply, thus forming the center ground and we can then use both transistors as PNP.

Am i all right about this? Will this all goes this way?

I have not build the power supply practically yet. Once, the design will be final and approved by here at diyaudio members, I will then go for an actual implementation.

I think the new design will be as such:

Thanks.
1. LED D9 is mounted wrong. Should flip vertically;
2. R10 and R11 values ​​are rather small. Assuming 35Vdc potential for one LED about 5mA, then each resistors should be about 7K;
3. R1, C31, or R3, C32 is just a fad, especially as talk of a power supply whose frequency is 50/60Hz. I recommend you give up that's snubber and then you can use in the primary side of the transformer more useful circuit (see the circled in red in the attached picture below);
4. Should you give up R2 and R4. If you quit mount these resistors, then you can quit and C1 and C2.
5. The output LT317/337 should be connected ballast resistor, which is especially useful when you want to test power suplly at no load operation (ie without connecting power amplifiers). This resistor is dimensioned for the lowest current which are provided to stabilize performance, typically 10mA. For example, 25Vdc, you need a resistor 2k2 - 1W.
6. In parallel with the BE junction of Q1 and Q2, I recommend you install two diodes in series, type 1N4007.
7. If you want, you could implement the Slow Turn-On as recommended in the LM317 datasheet, see page 16 from here.
8. C23 ... 26's better to be 22nF or 47nF.
9. C21 and C22 should be of greater capacity, for example 1000uF.
10. Diodes D3 and D4 should be moved in parallel with the collector and emitter terminals of the transistors Q1 and Q2. In this case, instead of 1N4007 should use something like BY255 or 1N5404.

These would be the most important observations should be aware.
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Old 7th October 2012, 08:01 PM   #13
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Let's not confuse you!
You have drawn a schematic with a really big 0.047F cap in series with the primary. In fact there are (few) diyers who do something like that. They want to avoid DC current from the mains to saturate the primary of the transformer. A practical solution has eben presented to you by donpetru. If you ask me, save that idea for later.
Add an X capacitor to the primary. Just connect it in parallel with the primary. Yes, there will be mains voltage across the cap all the time as Long as the amp is on. That's why it has to be a special type of capacitor. Look out for an X2. 47nf is a reasonable value. What does it do? It Shorts out some high frequency noise from the mains and/or your amp. And: Even when your amp is idle there is some (magnetizing) current flowing through the primary. This current is limited by the prim. inductance. When the AC switch is opened the X capacitor gives the induktive current a path and thus avoids inductive peaking. Good for the switch, and no switch-off-popp.
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Old 7th October 2012, 08:06 PM   #14
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You are using LTspice as a schematic editor.
Use it as what it is: a powerful simulation tool.
It is fun and you can learn a lot.
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Old 7th October 2012, 09:41 PM   #15
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Thanks! for the reply Mr.donpetru.

The attached picture by you, shows the circuit attached in series with the mains neutral terminal. It consists of a KBPC 352 bridge and four electrolytic capacitors(4700uf/6.3v). Can we use diodes in place of a bridge and 4700uf/25v electrolytic capacitors instead of 6.3v capacitors?

Quote:
4. Should you give up R2 and R4. If you quit mount these resistors, then you can quit and C1 and C2.
I want to use at least one CRC network in this power supply. Giving up R2 and R4 will totally defeat the purpose.

Quote:
5. The output LT317/337 should be connected ballast resistor, which is especially useful when you want to test power suplly at no load operation (ie without connecting power amplifiers). This resistor is dimensioned for the lowest current which are provided to stabilize performance, typically 10mA. For example, 25Vdc, you need a resistor 2k2 - 1W.
Let me see if i can get a 2.2k - 1w Ballast resistor, here at the shop. I save this idea for later.

Quote:
6. In parallel with the BE junction of Q1 and Q2, I recommend you install two diodes in series, type 1N4007.
Done! Please check if its implemented the right way. Specially check the polarity of diodes at each positive and negative rail.

Quote:
7. If you want, you could implement the Slow Turn-On as recommended in the LM317 datasheet, see page 16 from here.
What are the actuall benefits of Slow Turn-On?

If i opt to use Slow Turn-On implementation, does that imply that i won't be requiring, extra "speaker saving on/off relay circuit", at the amplifiers output stage during power supply on and off?

Actually, I want to save it for later once when the Amplifier will be up and running and i feel the need to do so.

Rest all points are check and done. Please verify them in the newly updated schematic here:

Thanks.
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Last edited by noddy55; 7th October 2012 at 10:01 PM.
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Old 7th October 2012, 09:52 PM   #16
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Thanks! Mr.grommeteer,

Quote:
Add an X capacitor to the primary. Just connect it in parallel with the primary.
Its done! please check out the last schematic.

Thanks.
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Old 7th October 2012, 11:29 PM   #17
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Diodes D11, D12, D13, D14, must be connected backwards because you did not properly connected.
Then, should give up resistance of 3.3 Ohm 10W and apply my instructions from the point no.3 above.

Slow Turn On option will not eliminate the need for a relay on each amplifier output but will bring a slight improvement of the amplifier power supply.
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Old 8th October 2012, 01:12 AM   #18
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The CRC filter R2 & R4 is unnessary. It only serves to reduce the voltage headroom that the active regulator has to work with.

I would also remove C5, C6, C7, C9, C13, C15, C17 & C18. These only serve to keep the LM3XX regulators and the series pass transistors from reacting to load induced voltage fluctations. The effect of this is to increase the output impedance of the supply at higher frequency. Try similating this with an active load of a current source offset at desired load current and a 1K sign wave, then remove those Cs and watch the voltage at the output smooth out. The higher the frequency the more load induced ripple you will get with those caps in place.
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Old 8th October 2012, 08:31 PM   #19
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Thanks, Mr. donpetru,

Plz, check the updated schematic.
I hope its OK Now?

Thanks.
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Old 9th October 2012, 01:28 PM   #20
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I corrected the above diagram.
It would be better to use two transistors MJE2955 in parallel and two 2N3055 in parallel. In this case PSU will be more reliable. Or you could try to use MJ15024 / MJ15025. I know there are more expensive but higher power.
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