UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Components and Circuits

Notices

Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

Closed Thread
 
Thread Tools
Old 13th Nov 2019, 5:14 pm   #1
McMurdo
Dekatron
 
McMurdo's Avatar
 
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,263
Default TO247 transistor collector-heatsink

I'm interested in hearing your opinion on using TO247 transistors. The heatsink plate is labelled as the collector, like many tab-type packages.

Is is acceptable to use the tab as the only collector connection? Is the tab-to-heatsink connection likely to be adequate? After all, it is designed to be in very good thermal contact with a flat surface.

Attached Thumbnails
Click image for larger version

Name:	to247.jpg
Views:	51
Size:	10.1 KB
ID:	193673  
__________________
Kevin
McMurdo is offline  
Old 13th Nov 2019, 5:17 pm   #2
HamishBoxer
Dekatron
 
HamishBoxer's Avatar
 
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 8,923
Default Re: TO247 transistor collector-heatsink

I would prefer to hard wire rather than a tag under the screw due to heat sink compound.
__________________
G8JET BVWS Archivist and Member V.M.A.R.S
HamishBoxer is offline  
Old 13th Nov 2019, 6:09 pm   #3
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
Default Re: TO247 transistor collector-heatsink

I've used them [and things like some voltage-regulators with the tab electrically-active] in situations where the tab is bolted down to a tinned area on the 'component side' of a double-sided PCB, and it seemed to work OK.
G6Tanuki is offline  
Old 13th Nov 2019, 6:36 pm   #4
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,786
Default Re: TO247 transistor collector-heatsink

Assuming you are using heatsink compound, I think you should connect the collector leg. I've never had to deal with this though.
paulsherwin is offline  
Old 13th Nov 2019, 7:16 pm   #5
Guest
Guest
 
Posts: n/a
Default Re: TO247 transistor collector-heatsink

If you can ensure contact or not be bothered if it goes O/C (open circuit) it will be fine, the lead frame (bit inside the transistor) collector section is contiguous. Easy enough to solder to as well.
 
Old 13th Nov 2019, 7:51 pm   #6
kalee20
Dekatron
 
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,059
Default Re: TO247 transistor collector-heatsink

Well, the chip is internally bonded to the tab, and then the middle lead is extended from the tab, so the tab itself (collector, drain or whatever) is the most direct connection to the device.

Whether you find it easiest to make a reliable connection of your own to the lead or to the tab, is, of course, under your own control!
kalee20 is online now  
Old 13th Nov 2019, 9:58 pm   #7
Oldcodger
Nonode
 
Join Date: Oct 2014
Location: West Midlands, UK.
Posts: 2,181
Default Re: TO247 transistor collector-heatsink

Thinking out of box .
If using one of these in a series regulator circuit ( or similar), I'd be tempted ( where the negative rail is chassis) to use a negative device and bolt the collector direct to chassis, but I'd still electrically connect to collector tab.
Oldcodger is offline  
Old 14th Nov 2019, 12:08 am   #8
McMurdo
Dekatron
 
McMurdo's Avatar
 
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,263
Default Re: TO247 transistor collector-heatsink

the reason I ask is to do with replacing an old TO218 package with a newer TO247.

See excerpt from a product change notice from ON Semi below:

The hybrid mounting used the collector pin onto a pcb for a voltage reference and the tab mounted to a live heatsink assembly for the power.
I want to avoid having to modify the product if it's not necessary by putting links between the pin and the heatsink.
Attached Thumbnails
Click image for larger version

Name:	onsemi.jpg
Views:	50
Size:	78.9 KB
ID:	193685  
__________________
Kevin
McMurdo is offline  
Old 14th Nov 2019, 1:17 am   #9
Maarten
Dekatron
 
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,184
Default Re: TO247 transistor collector-heatsink

The very good thermal contact isn't really obstructed by a thin layer of aluminium oxide on the heat sink, but the electrical contact is. If you can't find TO-218 devices from old stock or a second source manufacturer, I'd rather make some modifications.
Maarten is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 5:07 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.