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Old 10th February 2007, 04:15 AM   #1
yusuf is offline yusuf  India
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Default Dual Power Supply Design for LM4780

I was looking at audiosector PSU for LM4780 and wondering why dual bridge rectifier with dual secondary transformer is used. Does it have any advantage over FWCT configuration which requires half the diodes and center tap transformer which is easier to obtain compared to two secondaries transformer.

I am refering to this: http://www.audiosector.com/lm4780%20psu.pdf
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Old 10th February 2007, 01:14 PM   #2
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National used 2 transformers in their LM4702 amplifier application note -- (AN-1490) they are smaller, (not smaller by volume than one transformer with the same VA rating), but perhaps more easy to configure in the chassis -- further -- they shielded the transformers with Mu-Metal.

At one time several DIYAUDIO participants were recommending regulating the power supply for the chipamps -- while the PSRR of the devices was more than sufficient it was thought that regulation improved the performance -- these designs were based upon a conventional off-the-shelf, positive-side-only regulator so 2 transformers or a transformer with dual secondaries was necessary.
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Old 10th February 2007, 04:15 PM   #3
yusuf is offline yusuf  India
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Thanks jack. I understand National's consideration for two smaller transformer. However, I am not able to follow your point on regulator. Any two regulator could be used with common ground, it really does not require two secondaries. or am I missing something.

Morever, I was comparing dual secondaries with bridge vs FWCT.
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Old 11th February 2007, 09:59 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
centre tapped can produce a dual polarity DC supply. The regulators MUST be +ve type for the +ve rail and -ve type for the -ve rail.

Dual secondaries can produce either a dual polarity supply with a common 0Volt and follow the centre tapped topology.
or
give two independant DC supplies which can each be regulated with any combination of +ve or -ve regulators.
Then the resulting pair DC outputs can be connected to form a dual polarity supply.
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Old 11th February 2007, 12:56 PM   #5
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Like so -- with the appropriate resistor values for your app:
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