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Re: [TCML] Frequencies
Paul Brodie wrote:
Jim,
Thanks. Once again, you are quite correct and I'm really glad you added
your comments. I hadn't thought of the reasons you give for my 3055
failures and they make perfect sense. No wonder I fried so many 3055's.
I was barking up the wrong tree.
I'm not sure overvoltage was the problem and I had been using the
3055HV's rated to 100Vceo for a little extra leeway in this regard and
they are also rated Vbc 100V but I am sure I have been guilty of under
drving the base. I suppose powering the 555 with a nine volt battery
limits the amount of base current somewhat?
depends.. What's the base emitter resistance? VBE on is 1.5V at 4A
collector current
:-) Also, the 3055HV is
advertised as 20hfe mimimum and 100 maximum
At what Ic? The regular old 2N3055 has 20 hFE at Ic=4A, Vce=4V, but
only 5(!) at Ic=10A, Vce=4V. (where it's dissipating only about 40W, to
boot.)
The Vbe reverse limit is also easy to exceed in an inductive load situation.
but I certainly don't
believe they ever produce anything more than 20 and wonder if they even
do this.
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