2N4991

[Pavel Novotny]

SBS v provedeni s klasikymi soucastkami vypada takto
www.4qdtec.com/gifs/sbs.gif
a mate pravdu pouziva se pro zapalovani velkych tricu a nabijeni velkych C
 

Two identical circuits are arranged in anti-parallel as shown, so that one
works for positive voltages, the other for negative. Consider a rising
positive voltage, as on a charging capacitor, on A2. The left hand part of
the circuit will operate, but at low voltages, since the circuit started at
zero, there is no base current so neither transistor conducts. Z1 is forward
biased, but with no current flowing, so the full voltage is across Z2. This
circuit remains non conducting until Z2 starts to conduct at its breakdown
voltage. Now current flows into the base of the left hand PNP and the
transistor pair conducts.

PN


-----Original Message-----
From: hw-list-bounces@list.hw.cz [mailto:hw-list-bounces@list.hw.cz] On
Behalf Of aze
Sent: Tuesday, July 21, 2009 11:42 AM
To: HW-news
Subject: 2N4991

Zdravim. Hledam, kde sehnat/cim nahradit tento prvek, je to "silicon 
bilateral switch", TO-92, 3 nohy, 2N4991 nebo MBS4991. Podle meho se to 
chova jako diac s napetim kolem (6-10) V.
http://pdf1.alldatasheet.com/datasheet-pdf/view/82619/ETC/2N4991.html
Slouzi to ve spojeni s RC clenem 560k / 470n pro rozbeh spinaneho zdroje 
vetsiho vykonu (nejaka stovka W), tranzistory jsou tam 2x BUW13A. Ty jsem 
nasel u TME.
Mozna by stacilo snizit kapacitu kondu a placnout tam nejaky 30V diac.
Co vy na to, nez poslu ty nove BUW do silicon heaven?
AZE 

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__________ Informace od ESET NOD32 Antivirus, verze databaze 4263 (20090721)
__________

Tuto zpravu proveril ESET NOD32 Antivirus.

http://www.eset.cz