[PIC]

[Michael Johnston]

Happy Thanksgiving Pic guys. I have a project using a PIC16F1847 and it is
a simple Led tracer application.It will be mounted in a truck and will be
powered by the 12volt system in the truck. My choice is the 7805 linear
voltage regulator but My friend told me this was not a good choice for
automotive applications. I found the TI Lm2940 low drop out voltage
regulator. I was going to use this but I noticed that Digi Key states this
device is out dated and not to use in it in new designs. So does anyone out
there know of a newer low drop out 5 volt regulator for this purpose? Any
help would be appreciated
Thank You
Michael Johnston

[Brent Brown]

Nothin wrong with a good old 7805 in an automotive environment... if you wrap some protection around it as appropriate and don't push it too hard. Surviving alternator load dump takes some design effort even with parts that help you more. Ti.com lists the LM2940-C & N as still active. Other similar parts might be LM2941 and LM2931 from the top of my head. You probably don't typically need LDO dropping 12V to 5V, although flat battery cranking is worth considering... be ones a problem at some point no matter what dropout voltage the regulator is.P.S. Thanksgiving not a tradition here but just celebrated my first one ever thanks to some US and Canadian visitors~!
-------- Original message --------From: Michael Johnston <***@gmail.com> Date: 11/23/18 4:07 PM (GMT+12:00) To: "Microcontroller discussion list - Public." <***@mit.edu> Subject: [PIC] Happy Thanksgiving Pic guys. I have a project using a PIC16F1847 and it isa simple Led tracer application.It will be mounted in a truck and will bepowered by the 12volt system in the truck. My choice is the 7805 linearvoltage regulator but My friend told me this was not a good choice forautomotive applications. I found the TI Lm2940 low drop out voltageregulator. I was going to use this but I noticed that Digi Key states thisdevice is out dated and not to use in it in new designs. So does anyone outthere know  of a newer low drop out 5 volt regulator for this purpose? Anyhelp would be appreciatedThank YouMichael Johnston-- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archiveView/change your membership options athttp://mailman.mit.edu/mailman/listinfo/piclist

[Harold Hallikainen]

What is the "LED Tracer?" It might be similar to a project I did about 15
or 20 years ago.

Harold

Post by Brent Brown
Nothin wrong with a good old 7805 in an automotive environment... if you
wrap some protection around it as appropriate and don't push it too hard.
Surviving alternator load dump takes some design effort even with parts
that help you more. Ti.com lists the LM2940-C & N as still active. Other
similar parts might be LM2941 and LM2931 from the top of my head. You
probably don't typically need LDO dropping 12V to 5V, although flat
battery cranking is worth considering... be ones a problem at some point
no matter what dropout voltage the regulator is.P.S. Thanksgiving not a
tradition here but just celebrated my first one ever thanks to some US and
Canadian visitors~!
-------- Original message --------From: Michael Johnston
[PIC] Happy Thanksgiving Pic guys. I have a project using a PIC16F1847 and
it isa simple Led tracer application.It will be mounted in a truck and
will bepowered by the 12volt system in the truck. My choice is the 7805
linearvoltage regulator but My friend told me this was not a good choice
forautomotive applications. I found the TI Lm2940 low drop out
voltageregulator. I was going to use this but I noticed that Digi Key
states thisdevice is out dated and not to use in it in new designs. So
does anyone outthere know  of a newer low drop out 5 volt regulator for
this purpose? Anyhelp would be appreciatedThank YouMichael Johnston--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list
archiveView/change your membership options
athttp://mailman.mit.edu/mailman/listinfo/piclist
--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[RussellMc]

As well as automotive environment specified regulators, consider a front
end of
Series R, zener to ground, series R, zener to ground.
With R's suited to Imax and desired voltages and currents and zeners
clamping voltage at two high enough intermediate points to leave as much as
possible for regulator headroom and car-battery cranking low-voltage.

Used lonnnng ago, such an arrangement on Telecom low energy supplies
powering low voltage electronics (with admittedly much more voltage to work
with), provided near bulletproof protection from the awesomely
lethal-to-electronics telephone exchange 50V power supply. [Very high
energy noise transients exist in locations towards the far end of voltage
feeds. And everywhere else as well :-) ].


Russell.

Post by Michael Johnston
Happy Thanksgiving Pic guys. I have a project using a PIC16F1847 and it is
a simple Led tracer application.It will be mounted in a truck and will be
powered by the 12volt system in the truck. My choice is the 7805 linear
voltage regulator but My friend told me this was not a good choice for
automotive applications. I found the TI Lm2940 low drop out voltage
regulator. I was going to use this but I noticed that Digi Key states this
device is out dated and not to use in it in new designs. So does anyone out
there know of a newer low drop out 5 volt regulator for this purpose? Any
help would be appreciated
Thank You
Michael Johnston
--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[RussellMc]

With 12V in you can add a series resistor to drop say
(V.12Vsupplymin-Vregulator.headroom- Vregulator.out) at Imax.
This will probably drop out during engine cranking but will otherwise
transfer most of the heat dissipation from regulator to series resistor.
Rate resistor power at at least 2x max dissipation in actual mounting
situation. Be aware of possible heat transfer from resistor to regulator.

eg 12V min - 2.5V dropout - 5V = 4.5V in resistor and 2.5V max in regulator
at Imax.
Adjust assumptions to suit.


Russell

[Neil]

A low-dropout regulator won't do anything for you here as you have more
than enough overhead voltage.
A 7805 is fine as long as (a) you can heatsink the wasted power away,
and (b) you don't need to put the PIC into low-power/sleep mode.
I find that 100mA or maybe even 150mA is fine with a small heatsink,
otherwise you'll need a proper heatsink, or a switching regulator would
be better.
And in sleep mode, the quiescent current of the 7805 will consume far
more than the PIC (IIRC 5-6mA).

Cheers,
-Neil.

Post by Michael Johnston
Happy Thanksgiving Pic guys. I have a project using a PIC16F1847 and it is
a simple Led tracer application.It will be mounted in a truck and will be
powered by the 12volt system in the truck. My choice is the 7805 linear
voltage regulator but My friend told me this was not a good choice for
automotive applications. I found the TI Lm2940 low drop out voltage
regulator. I was going to use this but I noticed that Digi Key states this
device is out dated and not to use in it in new designs. So does anyone out
there know of a newer low drop out 5 volt regulator for this purpose? Any
help would be appreciated
Thank You
Michael Johnston

[Michael Johnston]

Hi Harold, A LED tracer is a series of LEDs tied to each port pin and a
current limiting resistor tied to VCC. In the original design each port pin
was tied to the cathode of the Led and the anode is tied to a current
limiting resistor and this is tied to VCC . The idea is turn an led on and
then keep it on for seconds then it would turn off and the next pin would
turn on and off and so on. This will look very similar to the KIT Car from
the Night Rider TV show of the 1980s. I am going to mount 8, 10mm high
brigthness LEDS in a piece of plexi glass and it will be mounted behind the
grill of a friends vehicle. Each Led will be connected to a custom
designed PCB board that will be mounted in a metal case which will be tied
to the chassis ground.
I thought the 7805 would work great for this purpose and my friend thought
a choke would help with noise environment of an automobile. My other friend
says not to use the 7805 as it cant handle this situation. So I came up
with the Lm2940 from TI and was going to use this but on Digi Key's website
its listed as obsolete and not to use it in a new design. Another friend
say use it and see how it works. If you look at my schematic you see that I
tie each port pin the to base of through a base resistor of 43k ohms the
collector is tied to the anode of LED a current limiting resistor of
330Ohms was a choosen but I will change to a large value because I have the
top tied to the unregulated 12volts which I will setup and simulate in
LTspice when I get the chance.
Thank You
Michael Johnston

Post by Neil
A low-dropout regulator won't do anything for you here as you have more
than enough overhead voltage.
A 7805 is fine as long as (a) you can heatsink the wasted power away,
and (b) you don't need to put the PIC into low-power/sleep mode.
I find that 100mA or maybe even 150mA is fine with a small heatsink,
otherwise you'll need a proper heatsink, or a switching regulator would
be better.
And in sleep mode, the quiescent current of the 7805 will consume far
more than the PIC (IIRC 5-6mA).
Cheers,
-Neil.

Post by Michael Johnston
Happy Thanksgiving Pic guys. I have a project using a PIC16F1847 and it

is

Post by Michael Johnston
a simple Led tracer application.It will be mounted in a truck and will be
powered by the 12volt system in the truck. My choice is the 7805 linear
voltage regulator but My friend told me this was not a good choice for
automotive applications. I found the TI Lm2940 low drop out voltage
regulator. I was going to use this but I noticed that Digi Key states

this

Post by Michael Johnston
device is out dated and not to use in it in new designs. So does anyone

out

Post by Michael Johnston
there know of a newer low drop out 5 volt regulator for this purpose?

Any

Post by Michael Johnston
help would be appreciated
Thank You
Michael Johnston

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[Harold Hallikainen]

Thanks for the explanation of the project! I did something similar 15 or
20 years ago. This was strobe lights for motorcycles. I don't remember
what the regulator for the PIC was, but I used an LM317 as a current
regulator off the raw +12V. It connected to the anode of each LED series
string. I used high power white LEDs designed for camera flash. I think I
had four in series in each string. At the bottom of each string was an FET
driven by the PIC. The PIC sequenced the LED strings. The pulse width was
reduced for night use, reducing the apparent brightness. I MAY have used
another LM317 t regulate the +12V down to 5V to reduce the variety of
parts. Since the PIC was only driving FET gates, the power consumption
(and the regulator dissipation) was very low.

There are concerns about voltage spikes due to load dump in automotive
applications. There are some regulators designed especially to handle
this, but a series R and a transient voltage suppressor may be cheaper. If
the 5V power consumption is high, a switching regulator would be
appropriate. There are some inexpensive modules from muRata and others
that are drop in replacements for an LM7805. I think the muRata one can
take more than 32V input.

Good luck!

Harold