-> In article <
[email protected]>,
->>Hey,
-
->>Forgive me for the simplicity of this question but I'm rather new to
->>electronics. I want to build a homebrew benchtop power supply and would
->>like a bit of feedback before I try:-
-
-<snip>
-
->>2. What sort of current am I likely to require for simple electronics
->>projects?
->
-> Usually less than 1 Amp. This requirement may change if you're building
-> something with electric motors whough.
->
-Would it be necessary to provide current limiting? I've seen some possible
-examples on circuit schematics of manufacturers data sheets but I'm not
-particularly sure if I need it or not?
Nope. Parts like the LM317 are temp limited. If the current gets too high,
the part heats up, then shuts down.
The fuse/circuit breaker I referred to below is also a current limiting
device. The current gets too high, then the fuse blows.
-
-I don't plan to use motors at this point and would like to keep the
-project small and simple (low a current as necessary) until I get more
-adept.
Then 1A should be fine for starters.
->>
->>3. Is isolating a power supply from the mains supply difficult?
->
-> Nope. The component is called a transformer. BTW you'll probably want to
-> put a fuse or circuit breaker on your primary of the transformer in case
-> of a short.
->
-250v @ 2amp ok? Should I go for quick blow or surge resistant fuses? My
-mains supply is a pretty stable 230v (UK) and fluctuates little.
Much smaller current. 250V@2A is almost 500W of power. It's very unlikely that
you'll dissapate more than 25W of power. So you should be looking for something
along the lines of a
[email protected]. It can be slow blow as you already have the
LM317's thermal limiting as another backup.
-
- >>4. What regulator IC should I consider for a beginner project? I was
->>considering LM137, only on grounds of cost and simplicity - is this a
->>good choice?
->
-> As good as any. Did you want variable voltage? This it's the ticket.
-> Just take care with the max voltage and power dissappation on the part.
-> You'll probably have to heat sink it to draw off the excess heat.
->
-Would a fan be a necessity or just passive heatsinks? Variable voltage is
-a definite requirement.
Depends on the power dissapation. Design for the worst, then double it. If
you need a fan at double the worst case scenario, then put one in.
Of course with CPU fans both cheap a plentiful, it may be worth it simply
to throw a small one on the part.
BAJ