gino@voder.UUCP (Gino Bloch) (12/06/84)
[stamp out AC] > By the way, my homebrew machine (TI9900) was made from a Technico Super > Starter kit, but I designed and built the power supply. I have 1/6 of a > farad on the +5 supply! (Yes, the lights dim and it goes "buzz" for a > few seconds when I turn it on. But +5 is clean!). On the other hand, 7805 voltage regulators with MUCH smaller capacitors is another approach for very clean volts, and the lights won't dim. The solid state voltage regulators come in other fixed values, including negative, and in variable configurations too. -- Gene E. Bloch (...!nsc!voder!gino) Mr Humility
chris@umcp-cs.UUCP (Chris Torek) (12/08/84)
Yes, but....
7805s are only rated at 1 amp. Now I know you can pull about 1.5 amps
through most of these suckers before they melt (have *you* ever seen
the thermal overload protect *work*?), and that you can get 3 and 5 amp
versions of essentially the same thing, but you are still current
limited by the things.
Also, just having a 7805 doesn't do a whole lot of good. You still
need quite a bit of capacitance, somewhere. In fact, with most real
computers you need lots of caps sprinkled about the boards near each of
the ICs, 'cause when those suckers switch, they want CURRENT. (Not
much actual power, but over a very short time period, so lotsa
current.) If you have lots of switching, you also need lots of
capacitance BEHIND the regulator (that is on the rippled DC input side)
so that it can recharge all the little caps even if the AC cycle is
well below 5 volts (actually, with 7805s, you need about 6.5V min
before regulation, but that's beside the point).
--
(This line accidently left nonblank.)
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (301) 454-7690
UUCP: {seismo,allegra,brl-bmd}!umcp-cs!chris
CSNet: chris@umcp-cs ARPA: chris@marylandkarn@petrus.UUCP (12/11/84)
> 7805s are only rated at 1 amp. Now I know you can pull about 1.5 amps > through most of these suckers before they melt (have *you* ever seen > the thermal overload protect *work*?), and that you can get 3 and 5 amp > versions of essentially the same thing, but you are still current > limited by the things. I seem to recall a lamp flasher which used the current limiting capability of these three-terminal regulators. You put a horrendously oversized lamp on the output of the regulator, and you controlled the flashing rate by varying the size (and thermal inertia) of the regulator's heatsink. Phil