[time-nuts] Parallel voltage regulators

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Oct 24 20:17:22 EDT 2007

Alan Melia wrote:
> Hi Tom I dont think you need the resistors these are current limited and the
> sense is inside the chip so the resistors dont do anything (you are thinking
> of a negative feedback effect). All that happens in paralled operation is
> that one may take the majority of the current til it current limits and the
> rest is provided by the other. They will need heat sinking. You can get
> Hi-power versions of these fixed regs as well or use one of them to drive a
> big transistor (the 2N2955 PNP used to be a popular choice up to 5A) for the
> series control. You may ned to lift the common leg with a diode to allow for
> the e-b drop on the pass transistor if you use an NPN.
Nonsense look at the circuit.
The base emitter drop of the pnp booster just increases the composite
regulator dropout voltage.
No diodes required to compensate Vbe drops.
However this circuit is unreliable without current limiting of the PNP
collector current.
These days its simpler to use an LM338.
> Cheers de Alan G3NYK

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