mwtheplumber
New Member
Is it possible to use more than one regulator such as 7812 in parallel to increase the current available, always assuming the transformer is man enought to supply it?
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Some applications need the clean, no-switching-noise output of a linear regulator.aussiepoof said:Why not use a switchmode IC which can output 3A or 5A??? One IC, one inductor, one schottky diode and one low-esr cap... so easy!
I've used National Semiconductor's SimpleSwitcher IC's to great effect.
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Roff said:I haven't built and tested this, but the simulation works really well. The basic idea is to use one of the regulators as a master, and then use a diff amp to force the current through the slave regulator to be the same as that of the master. The op amp output forces the ADJ (or GND) pin on the slave to whatever voltage is required to make the currents equal.
If you use a slave with a nominally lower output voltage than the master, you can get away with a single supply. For example, the master could be a 7812, and the slave a 7805. They both wind up dissipating the same power, because the 7805 will have +7V on the GND pin.
If you use two identical regulators, e.g., 7812's, you will need a low-voltage, low-current negative supply for the op amp, because the slave might need to have the GND pin pulled negative by as much as a few hundreds of millivolts.
The op amp needs to have a common-mode range that includes the positive rail. I played around with other amplifiers, including a discrete PNP differential pair, but the op amp is the easier, and performs better.
If you add short circuit protection for the pass transistor, it raises the dropout voltage by another 0.7V on top of the ~1V added by the pass transistor, and the pass transistor is still not thermally protected, as an extra regulator will be.Hero999 said:Whilest I don't see why that wouldn't work, it's much easier to add a pass transistor as suggested on the datasheet. The only benifit I can see is that a pass transistor increases the dropout voltage significanty and your idea doesn't.
I understand that... my question was posed to mwtheplumber not as a generic "why oh why do people not do this?" you assumed it to be.Roff said:Some applications need the clean, no-switching-noise output of a linear regulator. For whatever reason, this question comes up time and time again.
Be my guest.aussiepoof said:I understand that... my question was posed to mwtheplumber not as a generic "why oh why do people not do this?" you assumed it to be.
More helpful would have been to list those applications for which a switchmode might be inappropriate so that mwtheplumber might learn more... and make a decision.
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