Regulator Chips for LM3886

svbear · 6th July 2007, 02:20 PM

Hi,

I was considering to regulate my power supply to an acceptable voltage for 4ohm load on a lm3886 from a 25.2vac transformer.

These are the options,
1) 3 LM317 paralleled per rail. (guranteed 1.5 amps per regulator)
2) 2 LM350 paralleled per rail. (guranteed 3 amps per regulator)
3) 1 LM2677 per rail. (guranteed 5 amps per regulator)

(I prefer to-220 chips to match the extra computer heatsinks I have.)
Any guidance on using these chips or any preferences?
I was leaning towards option 3.

Many Thanks,

Adrian

AndrewT · 6th July 2007, 03:01 PM

Hi,
the output current limit for a 3886 is specified as 7A minimum and 11.5A typical. These are peak values into complex loads.
With 4ohms speakers these peaks could/will be approached.

How will your amp draw these peak currents, from the capacitors after the regulators, or direct from the regulators?

Just some thinking for you to do and arrive at some conclusions before committing to a particular regulator design.

svbear · 6th July 2007, 03:24 PM

Hi Andrew,

I was thinking of having large caps (47000mf + 4700mf + 100uf(beside the chipamp)) after the regulator to smooth ripple and to cache extra current for the chipamp.

This is part of my 5.1 amp project, so I was figuring that I would not be running the chipamps to their full potential.

I saw your last posting about using two postive regulators verses a pos plus a neg regulator combo. That was something I wasn't sure about, but I trust your recommendation and will go with 2 pos - also makes bulk chip purchases easier

.

Any opnions on the regulator chips?

Adrian

AndrewT · 6th July 2007, 03:35 PM

My recommendation is to trust the designers who originally suggested the twin positive regs for a dual polarity supply.

Your output caps should be able to source the peak currents demanded. That then places the regulators in an easier regime. They only have to meet average demand. Your 5A may just about do for a 6channel amplifier, but might be stretched. Be prepared to having to build a second pair of regs to ease their workload.

Archwn · 6th July 2007, 06:22 PM

Hi Adrian,

LM338, LT1085, 84, 83 if you dont stick with to-220 would be your additional list?

Cheers,

AK

6th July 2007, 02:20 PM	#1
svbear diyAudio Member Join Date: Aug 2004 Location: Toronto	Regulator Chips for LM3886 Hi, I was considering to regulate my power supply to an acceptable voltage for 4ohm load on a lm3886 from a 25.2vac transformer. These are the options, 1) 3 LM317 paralleled per rail. (guranteed 1.5 amps per regulator) 2) 2 LM350 paralleled per rail. (guranteed 3 amps per regulator) 3) 1 LM2677 per rail. (guranteed 5 amps per regulator) (I prefer to-220 chips to match the extra computer heatsinks I have.) Any guidance on using these chips or any preferences? I was leaning towards option 3. Many Thanks, Adrian

6th July 2007, 03:01 PM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, the output current limit for a 3886 is specified as 7A minimum and 11.5A typical. These are peak values into complex loads. With 4ohms speakers these peaks could/will be approached. How will your amp draw these peak currents, from the capacitors after the regulators, or direct from the regulators? Just some thinking for you to do and arrive at some conclusions before committing to a particular regulator design. __________________ regards Andrew T.

6th July 2007, 03:35 PM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	My recommendation is to trust the designers who originally suggested the twin positive regs for a dual polarity supply. Your output caps should be able to source the peak currents demanded. That then places the regulators in an easier regime. They only have to meet average demand. Your 5A may just about do for a 6channel amplifier, but might be stretched. Be prepared to having to build a second pair of regs to ease their workload. __________________ regards Andrew T.

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6th July 2007, 03:24 PM	#3
svbear diyAudio Member Join Date: Aug 2004 Location: Toronto	Hi Andrew, I was thinking of having large caps (47000mf + 4700mf + 100uf(beside the chipamp)) after the regulator to smooth ripple and to cache extra current for the chipamp. This is part of my 5.1 amp project, so I was figuring that I would not be running the chipamps to their full potential. I saw your last posting about using two postive regulators verses a pos plus a neg regulator combo. That was something I wasn't sure about, but I trust your recommendation and will go with 2 pos - also makes bulk chip purchases easier . Any opnions on the regulator chips? Adrian

6th July 2007, 06:22 PM	#5
Archwn diyAudio Member Join Date: Oct 2006	Hi Adrian, LM338, LT1085, 84, 83 if you dont stick with to-220 would be your additional list? Cheers, AK

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