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Questions on the 2N2222A transistor...

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wakiki

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Hi all,

I'm currently using a 2N222A for one of my projects. The problem is dunno what is the manufacturer of the transistor, so i'm having trouble determining which datasheet should i refer to. Does the beta or Hfe of the transistor varies a lot for transistors of different manufacturers?

By the way, the transistor is of the black casing package type and it has KSP 2222A - E38 written on it... Anyone has any idea? :eek:
 
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You're really looking at it the wrong way, you need to design your circuit so that the gain doesn't affect it - it's poor design to reply on specific gains.
 
If you post the schematic then we might be able to suggest improvements so the gain of the transistor isn't important.
 
wakiki said:
Hi all,

I'm currently using a 2N222A for one of my projects. The problem is dunno what is the manufacturer of the transistor, so i'm having trouble determining which datasheet should i refer to. Does the beta or Hfe of the transistor varies a lot for transistors of different manufacturers?

By the way, the transistor is of the black casing package type and it has KSP 2222A - E38 written on it... Anyone has any idea? :eek:
All manufacturers that make the part have pretty much the same data sheet, which as numerous other responders have said is only a guide or a starting point. It is not good practice to rely on the mean value of any parameter and assume that the variance is vanishingly small.

In reading a datasheet I interpret a typical value to be the mean of a normal distribution. I interpret a MIN and a MAX to represent the three sigma points of that normal distribution. That leaves 1% of all the parts with parameter values outside the min and the max. What are you going to do with parts that don't meet spec and cost a penny? Are you going to return them, test them, throw them on the floor, or ship them in your product? BTW there is no right answer to this question, it depends on the circumstances.
 
It is really tricky to choose a transistor.
I used to work with Pre-Amplifiers and sometimes,the amplifier did not turn on instantaneously and made a sizzling sound.We tried to find out reasons,but could not find any possible reasons.Anyhow,after about 1 minute,the sound started to come out of the loud speakers.

After consultation with the manufacturer of the amplifier modules and subsequent tests,we came to a conclusion that if the amplifier modules were changed while they were charging or discharging,it had an adverse affect on the transistor.The transistor went into a thermal runaway and eventually died when the pre-amplifier stopped working.

Transistor is an important aspect in designing so choose the one which is free of flaws.In other words,choose a transistor on which,the whole circuits failure would not depend.
 
gauravbijlani said:
It is really tricky to choose a transistor.
I used to work with Pre-Amplifiers and sometimes,the amplifier did not turn on instantaneously and made a sizzling sound.We tried to find out reasons,but could not find any possible reasons.Anyhow,after about 1 minute,the sound started to come out of the loud speakers.

After consultation with the manufacturer of the amplifier modules and subsequent tests,we came to a conclusion that if the amplifier modules were changed while they were charging or discharging,it had an adverse affect on the transistor.The transistor went into a thermal runaway and eventually died when the pre-amplifier stopped working.

Transistor is an important aspect in designing so choose the one which is free of flaws.In other words,choose a transistor on which,the whole circuits failure would not depend.
Sadly, there is virtually nothing in the datasheet that would help you make this determination. There are no datasheets that say "this is a pretty good transistor except that it might under some obscure conditions have flaws that we don't want to talk about." As some of the other responders have implied it may be the fault of the design rather than the component.
 
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Yes but any transistor can go into thermal runaway when incorrectly used; good design is the only way to avoid this.
 
Hero999 said:
Yes but any transistor can go into thermal runaway when incorrectly used; good design is the only way to avoid this.

Yes, bad design is the only reason for thermal runaway - and if it was in a preamplifier?, exceedingly bad design would be required!.
 
Nigel Goodwin said:
Yes, bad design is the only reason for thermal runaway - and if it was in a preamplifier?, exceedingly bad design would be required!.
Actually "bovine stupidity" was the phrase that came to mind for a design which allowed thermal runaway.
 
The art of electronic design is to design a reasonably precise circuit with imprecise components. Transistors have a very wide spread in their parameters and the parameters are temperature sensitive. This applies to all other components to a greater or lesser extent.

Often you can use virtually any transistor. eg. if you wanted to drive a LED, then any small signal transistor would do. All you have to ensure is that there is enough base current to saturate the transistor, so the rule of thumb is to make Ib about one tenth of the collector current.

However, in some cases more care needs to be taken. For example, for an audio amp you would need to consider the transistor noise and design the circuit to avoid thermal runaway.
 
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