At 01:49 PM 7/9/01 -0400, you wrote:
>Hi All,
>
>I'm using a 78L05 to keep a stable 5V supply to a simple microcontroller
>circuit, the power comes from a standard home-use 9V, 380Ma power adapter,
>it works fine so far. However, I want to add a relay to my circuit, which
>will easily take up to 80Ma when being turned ON, the 78L05 is now bearly
>powerful enough to maintain a stable 5V. Other than that, when the relay is
>drawing current, the power adapter output voltage will drop considerably,
>this sudden drop and rise in input voltage to the 78L05 will affect its
>regulated output as well. What is the usual way to handle this situation,
>where a low power consumption circuit is driving a relay, with all power
>being supplied by a domestic grade power adapter?

How stable are you expecting it to be? The 78L05 should be ok for digital
circuits, for analog you may need something better. 78M05/7805 regulators
are still very cheap and have better specs (and can dissipate more power
without a heat sink). At 80mA, I suspect you are running very hot-
considering the poor regulation on these crappy wall-warts, maybe
you need more margin.

Are you running the relay from 5V? If so, consider a second regulator for
the relay or consider running it from the 9V (but 9V relays are not as
easy to source as 12V relays).

Best regards,

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