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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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