Searching \ for '[EE]: Regulator grounds...' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=regulator+grounds
Search entire site for: 'Regulator grounds...'.

Exact match. Not showing close matches.
PICList Thread
'[EE]: Regulator grounds...'
2002\07\01@020407 by Pic Dude

flavicon
face
Using 2 regulators (Tait programmer), both in TO-220 packages:
7805 and 7812.  I was planning on securing both of these to the
same heatsink, back to back, but not sure this is such a good
idea now...

The datasheets confirm that the metal tab on each device is
connected to ground, which I will take to mean that it is
internally connected to pin 2.  But the 7812 has its ref pin
offset with 2 diodes (to raise the output to over 13V), so if
I connected both metal tabs together, then the diodes would be
bridged and useless.

So am I assuming correctly here?  I probably don't even need
heatsinks on the 7812 --- I need to calculate that.

Cheers,
-Neil.

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2002\07\01@022308 by Tan Chun Chiek

flavicon
face
Yes, you are correct about the diode bridging. heatsink is not necessary as
i believe 12v is only used as a program mode selector in a programmer and
draws next to no current. However, do that note that 78xx might go out of
regulation if there is very little load on the output, so consider adding a
load resistor.

those transparent mica insulator, (not sure is that a correct name) are used
for insulating TO220 package from heatsink.

Regards,
Tan CC

{Original Message removed}

2002\07\01@034837 by Benjamin Bromilow

flavicon
face
Hi Neil,

You could use a mica electrically insulating washer between the TO220s and
the heatsink... AFAIK that should sort it :)

Ben

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2002\07\01@060359 by Roman Black

flavicon
face
Hi, the easiest solution in not to heatsink the 7812,
you don't need to heatsink them until about 0.5W
dissipation, you will get nowhere near that just supplying
a few mA for the Vpp programming voltage.

If you MUST have them on the same heatsink, use a load
resistor after the 7812, then put the 2 diodes on its
OUTPUT with a series resitor to supply volts. For low
currents this will work ok and give you 12v + 1.4v etc.
Just allow a little more current through the 12v load
resistor than through the diodes.

Current needs are so small here, why not use a 13.6v zener
diode and one resistor??
-Roman



Pic Dude wrote:
{Quote hidden}

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2002\07\01@094907 by Pic Dude

flavicon
face
The mica insulators don't seem like it would work properly cause
they would insulate the screw heads, from the outer surface of
the tabs, but not the threaded body from the inside of the hole
on the tabs.

UNLESS, I was using some sort of plasic or nylon screw, which
I'm not sure would take the heat.

Cheers,
-Neil.




{Original Message removed}

2002\07\01@094914 by Pic Dude

flavicon
face
But what type of screw would I use for this, that would take
the heat?

Cheers,
-Neil.



-----Original Message-----
From: pic microcontroller discussion list
[spam_OUTPICLISTTakeThisOuTspamMITVMA.MIT.EDU]On Behalf Of Benjamin Bromilow
Sent: Monday, July 01, 2002 2:54 AM
To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
Subject: Re: [EE]: Regulator grounds...


Hi Neil,

You could use a mica electrically insulating washer between the TO220s and
the heatsink... AFAIK that should sort it :)

Ben

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2002\07\01@095231 by Pic Dude

flavicon
face
> If you MUST have them on the same heatsink, use a load
> resistor after the 7812, then put the 2 diodes on its
> OUTPUT with a series resitor to supply volts. For low
> currents this will work ok and give you 12v + 1.4v etc.
> Just allow a little more current through the 12v load
> resistor than through the diodes.

You've lost me here.  Load resistor "after" the 7812 =
resistor from output to ground or in series w/app ckt?
Now, if I add the diodes on the output, it'll DROP the
voltage by 1.4v.  Not sure what arrangement could cause
it to RAISE the voltage by 1.4V.

Care you do some more of your awesome ASCII art?

> Current needs are so small here, why not use a 13.6v
> zener diode and one resistor??

This is a much better solution, but I'm still curious
what you meant in the first solution.


Cheers,
-Neil.



{Original Message removed}

2002\07\01@095646 by Hazelwood Lyle

flavicon
face
From memory, along with the mica insulators, there are small nylon
shoulder washers that go between the screw head and the tab of the
to-220 package, These washers protrude slightly inside the hole to
prevent the screw from touching the tab at all.
You can find a complete TO-220 kit at Digi-Key PN# 4724K-ND, but they'll
charge you a dollar each (singles)

Lyle Hazelwood

{Original Message removed}

2002\07\01@104205 by Bill & Pookie

picon face
And they make a good heat conductor.  Also if you have the chance, use some
of that white goo between surfaces for good heat transfer.  Messy but fun.

Bi;;

{Original Message removed}

2002\07\01@110411 by Doug Hemingway

picon face
Pic Dude at picdudespamKILLspamAVN-TECH.COM wrote on 7/1/02 9:41 AM:

> The mica insulators don't seem like it would work properly cause
> they would insulate the screw heads, from the outer surface of
> the tabs, but not the threaded body from the inside of the hole
> on the tabs.
>
> UNLESS, I was using some sort of plasic or nylon screw, which
> I'm not sure would take the heat.

The kit with the mica washer includes a nylon shoulder washer for the
mounting screw.

Make sure you use adequate amounts of silicon grease between the heatsink
and the mica washer, and the washer and the device for a low thermal
resistance.  THAT is where the heat must transfer, not the screw.

BTW, if you are getting the heat sink hot enough to melt a nylon screw, you
ain't got enough heat sink!

Doug Hemingway

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2002\07\01@111606 by Roman Black

flavicon
face
Pic Dude wrote:
>
> > If you MUST have them on the same heatsink, use a load
> > resistor after the 7812, then put the 2 diodes on its
> > OUTPUT with a series resitor to supply volts. For low
> > currents this will work ok and give you 12v + 1.4v etc.
> > Just allow a little more current through the 12v load
> > resistor than through the diodes.
>
> You've lost me here.  Load resistor "after" the 7812 =
> resistor from output to ground or in series w/app ckt?
> Now, if I add the diodes on the output, it'll DROP the
> voltage by 1.4v.  Not sure what arrangement could cause
> it to RAISE the voltage by 1.4V.
>
> Care you do some more of your awesome ASCII art?


Here it is, not a great circuit but it will do
what you wanted with the same parts count you
already have.

Vin------*-----------------------------,
+20v?     |                             |
         |                             R  +13.4v
         |                             *--------------
         |                             |          vout
         |                             D
         |          ,--------,         D
         |          |        |         |
         '----------| 7812   |---------* +12v
                in  |        | out     |
                    '--------'         |
                        |              |
                        |              |
                        |              RL
                        |              |
                        |              |
                        |              |
                        |              |
Gnd ---------------------*--------------*-------


I think a much better circuit is just using one R and
one zener diode, the Vpp volts you need are VERY low
current. I'm sure you could even use a 2-resistor
voltage divider as the PIC only needs a signal >13v
to activate Vpp.
-Roman

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2002\07\01@113346 by Josh Koffman

flavicon
face
There are small plastic <?> inserts that go in the mounting hole to
insulate the screw. Then the screw can be metal. Of course, you must
still use the mica insulator.

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

Pic Dude wrote:
>
> But what type of screw would I use for this, that would take
> the heat?
>
> Cheers,
> -Neil.

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2002\07\01@122528 by Bob Blick

face picon face
>
> So am I assuming correctly here?  I probably don't even need
> heatsinks on the 7812 --- I need to calculate that.
>

I've never used heatsinks on either regulator in a Tait programmer. I've
even used a 78L05 regulator (TO-92 package) although that does get rather
hot. 16 or 17 volts DC input.


Cheers,

Bob

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2002\07\01@180608 by Pic Dude

flavicon
face
Ahhh... very ingenious!  If you invented this, my hat's
off to you.  If not, well I still think you're an okay
guy.  :-)

I'm questioning the 13.5V vs. 12V though, cause so far,
I've been running the programmer breadboarded, with an
external PS (pulled from a PC), and my DMM says that
it's putting out 11.7V.  A backup DMM said 11.6V.  And
no probs programming any PIC so far.

Cheers,
-Neil.



{Original Message removed}

2002\07\01@182909 by Pic Dude

flavicon
face
I do have a couple 78L05's laying around, but perhaps I
should use it from the 13.5V output of the 7812, so that
it is not dissipating as much power.  The 7812 should
have no problem absorbing the extra current w/o a heatsink.

Cheers,
-Neil.


{Original Message removed}

2002\07\01@194318 by Pic Dude

flavicon
face
Bingo!




-----Original Message-----
From: pic microcontroller discussion list
[.....PICLISTKILLspamspam.....MITVMA.MIT.EDU]On Behalf Of Josh Koffman
Sent: Monday, July 01, 2002 10:55 AM
To: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
Subject: Re: [EE]: Regulator grounds...


There are small plastic <?> inserts that go in the mounting hole to
insulate the screw. Then the screw can be metal. Of course, you must
still use the mica insulator.

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

Pic Dude wrote:
>
> But what type of screw would I use for this, that would take
> the heat?
>
> Cheers,
> -Neil.

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2002\07\01@223504 by Michael Rigby-Jones

flavicon
face
> -----Original Message-----
> From: Pic Dude [SMTP:picdudespamspam_OUTAVN-TECH.COM]
> Sent: Monday, July 01, 2002 2:42 PM
> To:   @spam@PICLISTKILLspamspamMITVMA.MIT.EDU
> Subject:      Re: [EE]:  Regulator grounds...
>
> But what type of screw would I use for this, that would take
> the heat?
>
> Cheers,
> -Neil.
>
>
You use a normal steel/stainless screw and nut, but insulate it from the
device using the standard "top hat" washer that is widely used on power
semiconductors.

Regards

Mike

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2002\07\02@115848 by Brendan Moran

flavicon
face
----- Original Message -----
From: "Pic Dude" <KILLspampicdudeKILLspamspamAVN-TECH.COM>
To: <RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU>
Sent: Monday, July 01, 2002 3:02 PM
Subject: Re: [EE]: Regulator grounds...


> Ahhh... very ingenious!  If you invented this, my hat's
> off to you.  If not, well I still think you're an okay
> guy.  :-)
>
> I'm questioning the 13.5V vs. 12V though, cause so far,
> I've been running the programmer breadboarded, with an
> external PS (pulled from a PC), and my DMM says that
> it's putting out 11.7V.  A backup DMM said 11.6V.  And
> no probs programming any PIC so far.

I guess PICs aren't that PICky

--Brendan

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics


2002\07\02@161244 by Dwayne Reid

flavicon
face
At 08:41 AM 7/1/02 -0500, Pic Dude wrote:
>But what type of screw would I use for this, that would take
>the heat?

I use nylon 6-32 screw and metal nut.  I also use sil-pads in place of the
mica washers but there is nothing wrong with the mica washers except that
you need to use that white Wakefield heatsink grease if you want good
thermal contact.  That grease is optional with the sil-pads.

The advantage to bolting both regulators together is mechanical stability -
there is much less chance of bending a regulator. either by accident or
from vibration.

dwayne

--
Dwayne Reid   <spamBeGonedwaynerspamBeGonespamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

Celebrating 18 years of Engineering Innovation (1984 - 2002)
 .-.   .-.   .-.   .-.   .-.   .-.   .-.   .-.   .-.   .-
    `-'   `-'   `-'   `-'   `-'   `-'   `-'   `-'   `-'
Do NOT send unsolicited commercial email to this email address.
This message neither grants consent to receive unsolicited
commercial email nor is intended to solicit commercial email.

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics


2002\07\02@162302 by Roman Black

flavicon
face
Pic Dude wrote:
>
> Ahhh... very ingenious!  If you invented this, my hat's
> off to you.  If not, well I still think you're an okay
> guy.  :-)
>
> I'm questioning the 13.5V vs. 12V though, cause so far,
> I've been running the programmer breadboarded, with an
> external PS (pulled from a PC), and my DMM says that
> it's putting out 11.7V.  A backup DMM said 11.6V.  And
> no probs programming any PIC so far.


No I didn't "invent" it, i'm not even sure I recommend
it. :o)
With your Vpp voltage, I really do think the best solution
is a resistor/zener divider or even a resistor/resistor
divider. The Microchip datasheest say the Vpp only has
to EXCEED the 13v etc, it does not have to be precise or
regulated in any way. As you have found out, it seems.
:o)
-Roman

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics


More... (looser matching)
- Last day of these posts
- In 2002 , 2003 only
- Today
- New search...