Can I mount the thermal monitoring transistor, can't think of the name, that sits between the two power transistors directly on one of the power transistors, or behind on the same mounting screw?
I have NO WAY to mount it between them, they have their own separate aluminum rail.
I could place a short piece of flat bar between the power MOSFETs and mount it in the middle. Just there will be three junctions that will require screws and thermal paste.
The designer said to just mount it on one of the power MOSFETs.
And which MOSFET,the positive or the negative?
Are they THAT critical I never crank it up, just like plenty of head room.
He has one smaller watt with out thermal run away and doesn't use it, but will need to replace the 40-0-40 to a 30-0-30.
Thanks
I have NO WAY to mount it between them, they have their own separate aluminum rail.
I could place a short piece of flat bar between the power MOSFETs and mount it in the middle. Just there will be three junctions that will require screws and thermal paste.
The designer said to just mount it on one of the power MOSFETs.
And which MOSFET,the positive or the negative?
Are they THAT critical I never crank it up, just like plenty of head room.
He has one smaller watt with out thermal run away and doesn't use it, but will need to replace the 40-0-40 to a 30-0-30.
Thanks
??? answers are hard to give when there's not enough specifics try uploading a pic or at least tell us what semiconductor devices are at play.
and are you perhaps referring to a bias compensation transistor..?
and are you perhaps referring to a bias compensation transistor..?
That transistor and associated components is commonly called a bias spreader. A Vbe multiplier is a common implementation.
The junction temperature of the transistor in the bias spreader should track the junction temperature of the output devices. Quite a bit has been written on this by both Douglas Self and Bob Cordell in their respective power amp design books. You can mount the bias spreader transistor on top of one of the output devices as long as you can get a good thermal connection between the two.
Is the picture in Post #4 of the circuit in question? If so, why not simply drill a hole in the heat spreader between the two output devices and attach the bias spreader transistor with a machine screw?
Tom
Don't forget that galvanic isolation from the sink is necessary for all the devices,
including the bias transistor. Unless it has an isolated plastic package, in which case
it will not function as well thermally.
including the bias transistor. Unless it has an isolated plastic package, in which case
it will not function as well thermally.
Michael designed this https://www.ampslab.com/hx200.htm amplifier , maybe you should ask him what he considers the best heat sinks mounting .