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Old 7th October 2012, 12:51 PM   #1
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Red face Regulated Power supply design suggestions and updates for LM1875 stereo amplifier

Hi,

Here is the circuit diagram for LM1875 stereo amplifier build power supply. Suggestions and improvements are welcome.

Please, check out the polarity of the MJE2955 transistors (used across each positive and negative supply rails) in this split power supply design with 25-0-25 volts center tap transformer. Did i implemented the use of MJE2955 correctly?

Plz, Check out the RC's. if they are done/implemented the right way.

I will be using the 8ohms speaker each for left and right channel, with this power supply for LM1875 stereo amplifier design.

LM/LT 317 and LM/LT 337 regulators are used for positive and negative rails respectively. MJE2955 (PNP Transistor) is used for increasing the current capacity of the circuit up to 5 Ampere, at least. KBPC3510 Bridge (that's what is easily and only available here) is used for rectification.

Combination of 2200uf and 10,000uf is used as a smoothing tank reservoir.

Will this power supply work best? Is everything OK in the schematic? Sorry! i don't have power supply testing instruments with me. So, this is only a conceptual schematic. No measurements are performed, yet. Is there any other possible design better than this for LM1875 stereo Amp. build? Is there any other modification required to make this power supply perform even better, with noise figures, distortions, sound sonics and sound clearity?

Thanks.
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Last edited by noddy55; 7th October 2012 at 01:13 PM.
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Old 7th October 2012, 03:03 PM   #2
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Your LED's are backward.
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Old 7th October 2012, 03:45 PM   #3
Art M is offline Art M  United States
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C35 non-polarized 47000uF@400V may be an unpractical component. Some polarized capacitors and a few diodes can serve this DC blocking function.
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Old 7th October 2012, 04:22 PM   #4
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The transistor in the negative rail should be an NPN. What does your SIM show? The -25V should be ok, but no current/power in that PNP.
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Old 7th October 2012, 05:09 PM   #5
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Quote:
Your LED's are backward.
I think you are talking about polarity? If yes than, thanks, i will invert the LED symbol in the schematic.

Thanks
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Old 7th October 2012, 05:14 PM   #6
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Quote:
C35 non-polarized 47000uF@400V may be an unpractical component.
C35 is not 47000uf@400V. It is .047uf/400V which is equivalent to 47000 pico farad which is equivalent to 47 nano farad and who's EIA code is 473.

Thanks.
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Old 7th October 2012, 05:27 PM   #7
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Quote:
The transistor in the negative rail should be an NPN. What does your SIM show? The -25V should be ok, but no current/power in that PNP.
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.
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Last edited by noddy55; 7th October 2012 at 05:50 PM.
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Old 7th October 2012, 06:07 PM   #8
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You do not want 47nF in series with your primary. If you want an X capacitor connect in parallel to the mains and use an X approved type.
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Old 7th October 2012, 06:26 PM   #9
Art M is offline Art M  United States
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Default What the hell is a Farad

Quote:
Originally Posted by noddy55 View Post
C35 is not 47000uf@400V. It is .047uf/400V which is equivalent to 47000 pico farad which is equivalent to 47 nano farad and who's EIA code is 473.

Thanks.
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.

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.

You will probably wish the value was 47000uF to get anything
to work properly under load.

Presenting a schematic with bogus values requiring us to read
your mind is a silly endeavor. Clean up your schematic !!!
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Old 7th October 2012, 06:33 PM   #10
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Quote:
You do not want 47nF in series with your primary.
But somebody asked me to: Add some MOV's or an AC rated polyester cap or RC at transformer Primary.

What does this really means? How can i implement the same and with what values?

Thanks.
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