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L487 +5 volt regulator... help...
Posted: Sun Jun 18, 2006 5:35 pm
by Jonathan KC8RYW
What are those two extra lines for?
One is RESET, if I recall.
Posted: Mon Jun 19, 2006 3:55 am
by AEC
The number you listed is not familiar to me, how many leads does this regulator have, and what's the case style?
TO-220, TO-3 Etc...
If more than the standard 3-pin regulator, you'll have input, control, gnd, output with maybe one 'extra' pin for reference voltage.....uncertain here.
Posted: Mon Jun 19, 2006 5:12 am
by kcbooboo
Also, what radio product is this used in? Those of us with manuals might be able to shed some light on it.
Bob M.
Posted: Mon Jun 19, 2006 9:31 am
by Jonathan KC8RYW
OK.
it is TO-220 package,
5 pins.
Here is how they are labeled in the schematic:
1 VI
2 RST OUT
3 GND
4 CD
5 VO
It's used in Motorola Smart Status/Message units.
Pin 1 is the juice from the battery
Pin 2 is the reset out line, which goes to the reset pin of the micro-p
Pin 3 is ground, duh
Pin 4 ("CD") goes to a small cap connected to ground.
Pin 5 is the regulated +5 out.
I'm just wondering what pin 2 and 4 are for. I'm only familar with 78xx series regulators with three pins.
Thank you,
Posted: Mon Jun 19, 2006 9:44 am
by kcbooboo
The MaxTrac uses a similar chip. It is a standard 5V 3-terminal regulator that happens to have a microprocessor reset circuit built into it. There are a bunch of similar chips, including this one, an L387:
http://www.datasheetcatalog.com/datashe ... L387.shtml
You can download the PDF datasheet from this page.
Bob M.
Posted: Mon Jun 19, 2006 10:02 am
by JohnWayne
Pin 2 (RST OUT) should go low when the output of the regulat gets below about 4.75V. There is a delay that occurs before the RST OUT goes high again when the voltage goes back to above 4.75V, and that delay is controlled by the external cap between pin 4 and ground.
Jeff
Posted: Mon Jun 19, 2006 11:03 am
by AEC
Here is how they are labeled in the schematic:
1 VI
2 RST OUT
3 GND
4 CD
5 VO
From what I see, pin #4 is the Capacitive Delay which sets a time delay for the discharge rate according to the capacitor's 'size' in Microfarads.