[Amps] RF power transistor curve trace question

[Dan Sawyer]

Manfred, as always thank you for your response. Below are the answers:

1. the trace is a collector voltage horizontal and collector current 
vertical. The tracer is a Tek 577, the collector sweep is set to 50 
volts and the step current to 20 ma. The parallel resistor is set to 50 
Ohm.

2. I do not know about transistor ballasting. Is there a standard way to 
measure it? Are there standard values? What value would be sufficient to 
operate in class AB?

Thanks in advance - Dan

On 06/14/2009 01:55 PM, Manfred Mornhinweg wrote:
> Hi Dan,
>
>    
>> When placed in the curve tracer it produces a pattern with almost
>> horizontal trace, based step.
>>      
>
> What are you tracing, exactly? Collector current versus base voltage, or
> what? At what collector voltage, etc?
>
>   >I removed the devices from one of the ENI
>    
>> boards and checked the curves . They were rising with a pattern of
>> between 0 and about 15 degrees, significantly different pattern. (the
>> gain was close.)
>>
>> What determines the 'slope' in an RF power transistor?
>>      
>
> I would think that the first transistor you traced isn't nearly as
> heavily ballasted as the second. But I can't be sure if I don't know
> exactly what you are tracing!
>
>    
>> What is its significance?
>>      
>
> If the difference is the ballasting, then basically it means the "flat"
> transistor is suitable for class-C service only, while the "non-flat"
> one is suitable for linear service too.
>
> If a transistor with no or not enough ballasting is used in linear
> service, it will typically burn out from hotspotting.
>
> Manfred.
>
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