Vce(sat) -Hfe, was Protecting FETs
Russell McMahon email (remove spam text)
* Delayed 12 hrs due to email hiccup*
Ah -still in outbox - I'll grab the new better subject line.
> Zetex (or Farnell) seem to have deliberately
> chosen to show a beta of 160, at a totally
> unreasonable current for a 3A transistor. When
> operated as a low-sat transistor the beta is
> VERY POOR.
Are you SURE you have the pinout right on your Zetex parts ????
I imagine you almost certainly have BUT they do have a strange case and
unusual pinouts. They may just be providing that Beta while reverse polarity
Also, there are Zetexes and Zetexes alas.
The table at http://www.zetex.com/3.0/b1-2.asp
provides very precise statements about what you should be able to expect.
And it's not what you are getting !
eg ZTX1047A E-line
Vceo = 10V (low!)
Ic max continuous = 4A
Hfe 300-1200 @ 1A
240-1200 @ 4A
Vsat 70 mV at 1A at 10 mA Ib = Beta of 100
Vsat 190 mV at 4A at Ib = 20 mA = Beta of 200 !!!!!!!!
ZTX1048A seems similarly blessed with Vceo = 17.5v (how precise :-) )
Certainly many (most?) are worse than these specs and the results get
generally worse with higher Vceo but there are some good specs there and
Zetex themselves are very open about the spec.
Here's the equivalent 30-50v table
The frabjous FCX890B in SOT89 seems to have the best of all worlds except,
no doubt, price :-)
Vceo = 45V
2A max cont
400 beta min at 1A
150 beta min at 2A
80 mV sat at 100 mA at Beta = 200
300 mV sat at1A at Beta = 200
Even the FZT1049A in SOT223 is no slouch at
30 V Vceo
330 mV Vsat at 5A with beta = 100
That's a bright LED !!! :-)
Zetex, by the way, are located in the UK within easy reach of the Lake
Once known AFAIK as "Newmarket Transistors" long long long ago.
Pictures of 47 year old transistors
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