Am I crazy or...

[pseudolobster]

I was scrounging around my junk bin looking for some kind of regulator I could use to build some sort of driver... most of the regulators I've found are for regulating 36v down to 18v or similar... anyways I found a tiny SO-223 package LVDO regulator called a APL1117 I was figuring maybe I could use...

So I look up a datasheet and find this example circuit... I'm about 90% of the way through building it when I realize, if I'm not mistaken, that V[sub]in[/sub] shorts directly to GND (through an optional filter capacitor C1)... Am I crazy or will this not work?

 

[john_lawson]

:-?

 

[pseudolobster]

yeah so I finished it and sure enough it has only TWO wires coming off it... V[sub]in[/sub]/GND and V[sub]out[/sub]..

I'm not sure how this is supposed to work... invisible diodes? sorcery?

 

[chido]

I'm just as confused as you are????? :-?

EDIT: Could you post a link to the datasheet?

 

[Hemlock_Mike]

Don't look right to me

 

[pseudolobster]

here's a link to the datasheet:
http://www.anpec.com.tw/products/download/APL/APL1117/APL1117.htm

I'm wondering if that "optional" capacitor is acting as a diode somehow? do polarized caps prevent reverse flow?

 

[woop]

WHAT?
um whats the problem?
it looks pretty standard to me
the input capacitor is to smooth any ripples from the power supply, it only conducts when there is a change in voltage, for DC, it will not short the input

 

[pseudolobster]

WHAT?
um whats the problem?
it looks pretty standard to me
the input capacitor is to smooth any ripples from the power supply, it only conducts when there is a change in voltage, for DC, it will not short the input

right, but it says the capacitor is optional... if you remove the capacitor it soon becomes clear you're simply connecting the + wire to the - wire before it gets to the regulator. In electronics this is called a short circuit, which rarely produces anything but smoke.

 

[woop]

sorry but i don't see the short.
if you remove the capacitor, you would remove the wires to the cap as well, not just short them together

 

[pseudolobster]

sorry but i don't see the short.
if you remove the capacitor, you would remove the wires to the cap as well, not just short them together

Hmm... you're probably right...

I really do need to stop building circuits when I'm hungover... thanks for putting it in perspective.

 

[woop]

thats ok. everyone has mental blanks every now and then. especially after a big night ;D

 

[chido]

sorry but i don't see the short.
if you remove the capacitor, you would remove the wires to the cap as well, not just short them together

I see what you mean, I can't believe I didn't notice that either.

 

[pseudolobster]

Ohhhkay.. So I removed the short and put it together... sure enough it works now...

here it is regulating 12v down to 1.2v... fully adjustable, though I think I need a different pot.. this one's 10k so the adjustment is pretty touchy.

Anyways, thanks guys... remember, never underestimate the power or prevalence of human error.