A while back, when we still bought/got given Linear data books(yes, in paper
format), i recall seeing a circuit incorporating a high power pnp transistor
in a boost configuration, to alleviate the regulator's load.

The PNP derived its drive from a resistor in the input lead of the regulator
and was calculated so that the resistor was just biasing the PNP on when the
regulator was approaching the maximum current available. The output of the
pnp and the regulator were tied together. This bias point i assume could be
reduced to a suitable level by increasing the input resistance to the
regulator.

Hope that helps.

John

On Monday 15 July 2002 04:26 pm, you wrote:
> Jim wrote:
> > Subject: Re: [EE]: 7805 regulator current increase
> >
> > >> I was wondering is is possible to parallel 2 of them
> > >> together to double the current out or do I have
> > >> to use transistors to increase current?
>
> Where regulators have tight regulation (within 10mV from
> 0A to 1A), like 7805 etc, you can parallel them with a small
> resistor on the OUTPUT. Drop about 30mV on the output at
> full current, so about 0.03 ohms is enough. 0.1 ohm
> resistors will do if they are all you can get.
>
> Russell McMahon wrote:
> >As Patrick noted, you can add a SMALL input resistor to each one to
> >encourage them to share the load.
>
> I don't think you can do it with input resistors, they
> have to be on the output, as the output is closely
> regulated by the opamp in the chip regardless of input
> volts. ie, connect one 7805 to 12v and one to 8v, both
> will output the same volts, at least within a couple mV
> chip tolerance. Resistors must be on the output, and YES
> it will work fine.
> -Roman

--
Thank-you for your time.

John Ward

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu