Author Topic: "Leakage" parameter of typical BJT  (Read 1320 times)

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Offline CodiJackTopic starter

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"Leakage" parameter of typical BJT
« on: July 10, 2020, 03:36:46 pm »
Hi.

For a new design, I'm looking for "leakage" parameter of typical npn transistor like e.g. BC847B.
I'd like to know what is collector current when transistor is off (base has the same potential as emitter) for a certain condition (defined Uce & defined temperature). To me it is Ices.
In the many spec's of BJT it is defined only collector-base cut-off current (Icb0).
Nowhere I could find Ices (base shorted with emitter).
Is there a way to calculate it anyhow or is it the same as ...Icb0... (I doubt, but...) |O?
 

Offline TimFox

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Re: "Leakage" parameter of typical BJT
« Reply #1 on: July 10, 2020, 04:18:09 pm »
Ices should be close to Icbo, since the current gain of the device is removed due to the BE short.   Iceo should be larger than Icbo, since the Icbo flows into the base and is amplified by the current gain.  Checking a typical data sheet, however, I found Icbo > Iceo, but Icbo was measured at Vcb = 45 V, while Iceo was measured at Vce = 5 V.
https://www.mouser.com/datasheet/2/68/2n2484-31162.pdf
 

Offline CodiJackTopic starter

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Re: "Leakage" parameter of typical BJT
« Reply #2 on: July 10, 2020, 04:49:22 pm »
My heart tells me Ices>Iceo>Icbo.
My engineering evil tells "base on what, did you come up to above conclusion?"
To me floating emitter is no delivering carriers to collector, so only small base area via small contact on a "side of npn structure" (red path) deliver carriers.
When emitter is connected to base, a total area capable of deliver carriers is much larger (green path), isn't it (mentioned above diode)?.
Is it like I think or is it large simplification?
 


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