This is for my new amplifier, but thought it deserved a separate thread. I am using multiple ZTX450 and ZTX550 transistors (e-line package - a bit like a thin TO92). The datasheet states the maximum operating temperature as 200 deg C. I am running them at about 200mW and 90 deg C. The thermal resistance die to air is 175 deg C/W (probably allowing for some cooling by the PCB too which I don't have), but I don't know what it is die to case, so I can't calculate die temperature. What do we think? Is 90 deg C too hot?
I have already reduced to bias so now it is only class A for the first watt, the original design ran at 110 deg C
Thanks,
Brian
How hot would you run transistors
#1 How hot would you run transistors
Last edited by brig001 on Sat Sep 14, 2013 1:52 pm, edited 1 time in total.
#2
Well, 175 C/W and 200mw would put the die at only 30C above ambient. I am guess you have measured the outsides being hotter than that?
I guess it will heat up the air around the things, maybe mount them vertically with a plain in front of them to get convection to help with a chimney effect.
Or you could find some of the fluid they used to fill Cray-2's with.
I guess it will heat up the air around the things, maybe mount them vertically with a plain in front of them to get convection to help with a chimney effect.
Or you could find some of the fluid they used to fill Cray-2's with.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#3
I think I'd attempt to get that down a bit, if you have the room...
something like this?
http://www.rapidonline.com/electronic-c ... ink-77178/
something like this?
http://www.rapidonline.com/electronic-c ... ink-77178/
There's nowhere you can be that isn't where you're meant to be
#4
Thanks Nick and Ed. The mistake I made is to put 80 of them in close proximity, so that's a total of 16 Watts in quite a small space. The ambient around the transistors is 55 deg C, so it sounds like the die and the case are at a similar temperature, so I'm not going to worry about it. I think I'll need some holes in the lid before I put it on though.
Brian
Brian
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#5
80 ?brig001 wrote: The mistake I made is to put 80 of them in close proximity,
Brian
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
#6
I thought I could build a class A amp without heatsinks - optimistic with hindsight, but I like the sound, so I'm going to persevere. Instead of one or two large output transistors, I used 20 small ones per amplifier; 10 npn and 10 pnp. Active crossover means 4 amplifiers, so 80 transistors in total. Should have spread them out a bit, or got more space to fit them in. Like every design, it evolves around a set of compromises, and keeping the size down to reduce loop area for noise pickup was one of the considerations. It worked too. My last amplifier picked up noise from a neighbour, or more likely the lift, this one is totally silent. Small loop areas, ground plane, decoupling everywhere and a mains filter sorted it.
Brian
Brian