Re: need help BFG135A
- From: Winfield Hill <hill_a@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: 20 May 2005 02:35:54 -0700
Pooh Bear wrote...
>
> mauri236@xxxxxxxx wrote:
>
>> i need your help! I'm using the Infineon transistor BFG135A
>> (http://www.infineon.com/cgi/ecrm.dll/ecrm/scripts/prod_ov.jsp?
oid=26136&cat_oid=-8959)as
>> unit gain stage (emitter follower)with a periodic impulse 2MHz, 10nsec
>> ON (=duty cycle 0,02). The impulse amplitude is 5Vpp. Which is the max
>> peak current of the collector, that the transistor can support for an
>> unlimited time ?
>>
>> thanks in advance
>
> I assume that you mean the signal at the collector is 5Vpp ?
>
> Depending on the load and the waveform shape, the current may be
> Icmax or Ptot limited.
Wrong, at least for the specified 2% duty cycle. Ptot = 1W is the
continuous power rating, and if the thermal pulses are short enough
(the OP specified 10ns) the dissipated power can be much higher, as
shown in the transient thermal-resistance curves (Infineon calls this
Permissible Pulse Load). For example, the maximum-rated voltage and
current = 25V * 150mA = 3.75W, which is well under 50W implied by 2%,
or about 25W implied by the 2.8K/W thermal-resistance-plot's value
for 100ns 2% duty-cycle pulses.
Looking at the transistor's beta spec at 100mA (Infineon) or beta
plot (Philips), it's likely this part can be operated well above
150mA for short pulses. Transistors that have integrated emitter-
ballast resistors can often give truly amazing performance.
--
Thanks,
- Win
.
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