[time-nuts] Adding adjustment pot to 5680

[Attila Kinali]

On Mon, 9 Jan 2012 13:06:12 -0800 (PST)
Arthur Dent <golgarfrincham at yahoo.com> wrote:

> On the inside of the case where the DB-9  
> pins go through the circuit board, I mounted a 7805 fixed regulator. I 
> cut a piece out of pin 4 and connected the output of the 7805 to the 
> board side of the pin with a tantalum cap for bypass. I decided not to 
> use a 78L05 because at the elevated temperature I felt it would be 
> cutting it too close to the 100MA current limit.
[...]
> http://farm8.staticflickr.com/7013/6668466093_90782cf7e9_b.jpg

You are driving the 7805 near its limit. As a rule of thumb,
a TO-220 case can disipate about 1W of power, if it's
free-standing. You have max 100mA with a voltage difference of
10V, resulting in 1W max. Ie the 7805 will be running at a
considerable high temperature. As you have there a good heat sink
already (the case), i'd mount the 7805 against the case and use
wires to connect it.

			Attila Kinali

-- 
Why does it take years to find the answers to
the questions one should have asked long ago?