LM317T - where have I gone wrong?

Rigger Mortice said:
If you wanted to supply a 12volt regulated supply from a 12 volt battery (I don't know why though?) then you would need to use one of the step up units.
Click to expand...

Actually, 12v-12v is more complicated as the input can be either higher or lower than the output.

"Buck" configuration to step-down - cheap, basically just a chip and an inductor (plus a few other bits).

"Boost" configuration to step-up - also cheap, again basically a chip and inductor, but wired differently.

Most converters with similar input and output voltages will be isolated - with a transformer and rectifier etc, so more complicated/expensive.

The other way to do it is with a configuration called "Cuk", but I don't think I've seen a ready-built module using this approach. Simpler/cheaper than a transformer, but still more complicated than simple step-up/down

There you go - I bet you didn't want to know all that
 
Rigger Mortice said:
I'm not sure what you mean by "using it for regulated 12v". To source from 12v or to supply 12v? In any event the answer is probably yes to both but the one I posted will have a voltage drop (2volts IIRC) so, from a 12v battery it could supply up to 10volts. The maximum current will also limit it for some applications........but there are other types which could be used.

If you wanted to supply a 12volt regulated supply from a 12 volt battery (I don't know why though?) ...
Click to expand...

I have no need for stable 12v anymore, but a while back before decent regulated LEDs appeared I put a 12v voltage regulator in before LEDs to stop them getting zapped by 14+v when charging, or more when equaising the batts. Think the lowest drop out was about 0.5v, worked OK. Maybe that board could have driven a whole light circuit of cheapo LEDs but 2v dropout sounds too much

Great find though, ta. There's some 9v bits onboard need supplying, sounds like that board will be perfect.
 
mikefleetwood said:
Actually, 12v-12v is more complicated as the input can be either higher or lower than the output.

"Buck" configuration to step-down - cheap, basically just a chip and an inductor (plus a few other bits).

"Boost" configuration to step-up - also cheap, again basically a chip and inductor, but wired differently.

Most converters with similar input and output voltages will be isolated - with a transformer and rectifier etc, so more complicated/expensive.

The other way to do it is with a configuration called "Cuk", but I don't think I've seen a ready-built module using this approach. Simpler/cheaper than a transformer, but still more complicated than simple step-up/down

There you go - I bet you didn't want to know all that
Click to expand...

I am actually interested, even though you are getting a bit technical for me. Maybe it's my inner geekiness coming out!! :)
I had assumed that something like this http://www.ebay.co.uk/itm/DC-3-35V-..._Measurement_Equipment_ET&hash=item3ccbe2adba would be an easy way to provide 12v stabilised from a 12volt battery.
 
Last edited:
Rigger Mortice said:
I am actually interested, even though you are getting a bit technical for me. Maybe it's my inner geekiness coming out!! :)
I had assumed that something like this http://www.ebay.co.uk/itm/DC-3-35V-..._Measurement_Equipment_ET&hash=item3ccbe2adba would be an easy way to provide 12v stabilised from a 12volt battery.
Click to expand...

I've used something similar to float charge a sealed battery (13.6V?) for the VHF from the ship's '12V rail', but I had to make my own.
I would look up the data for the chip on the web.
 
Rigger Mortice said:
I am actually interested, even though you are getting a bit technical for me. Maybe it's my inner geekiness coming out!! :)
I had assumed that something like this http://www.ebay.co.uk/itm/DC-3-35V-..._Measurement_Equipment_ET&hash=item3ccbe2adba would be an easy way to provide 12v stabilised from a 12volt battery.
Click to expand...

Sorry, didn't mean to decend to geekiness - sometimes I can't help it:D

Anyway, that would do it - as far as I recall, buck-boost is AKA Cuk. It uses 2 inductors and a capacitor rather than the usual single inductor, so, as I said more complex/expensive (£2 vs. £1!). The best configuration has both inductors wound on the same core (not a transformer) as all the ripple currents cunningly cancel out - which makes it very useful in some applications.
 
You must log in or register to reply here.

Share this page

Top