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Break down voltage of BJT

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mrinalmani

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The datasheet of a switching BJT from NXP: PMBT2369 mentions
collector-base break down voltage = 40V (emitter open)
collector-emitter break down voltage = 15V (base open)

Now if we don't leave the base terminal open, say by shunting it with a 10K resistor between base-emitter then can we operate the BJT at higher voltages than 15V. How high can we go safely?

Thanks
 

Hi,

I don´t recommend to do this.

There are many, many bjts rated with higher voltage than your PMBT. Select one of them.

Klaus
 

yes, though I presume OP wants to use this BJT because it is fast?
I think it is strange the big difference between the VBC(E OPEN) and VCE(B open).
But yes there is no figure given for VCE(B not open) so you should stick to the 15V.

**broken link removed**
 

Thanks for the reply.
Any suggestions for other fast switching BJTs in voltage range of around 30V?
 

You could use a pair of devices in cascode connection.
But without having knowledge about your circuit and requirements, this is only a guess.
 

Hi,

You don´t give us any specification..

But there is a good interactive selection tool at nxp.com. (Other manufacturers have similar tools)
Just select the specifications you need:


Have a look at PMST2369

Klaus
 

PMST also has VCEO = 15V
My requirement is simply to level shift a 3.3V output from MCU to nearly 25V inverted output, as quickly as possible. Output current is around 100mA. I can use FETs also, but it appears that for such weak output from the MCU, FETs will switch slower than BJTs.
 

By as quickly as possible I meant as fast as the fastest available switches would permit. My expectations are 15ns or better.
 

15nS switching with transistors is a bit of a dream, esp for turn off, you will need complex base drive to achieve this - how about a high spec comparator or op-amp....?

Can you post a sketched schematic of your ideal intended circuit?

- - - Updated - - -

Also the device you list is only 15V open base, you will need a good gnd plane layout and a ckt that allows B-E resistors to give you a Vcex higher than 15V, you want a 3v3 signal from a uP to generate a 25V signal to drive 100mA at 15nS rise times? (~ 16MHz) are you an RF engineer specialising in BJT circuits? the load will influence the rise time - esp if there is cabling that is not impedance matched, (~250 ohm).
An hysteretic circuit might get you there, but there will be some delay to the o/p....also I doubt if the uP o/p pin rise fall times are that quick?

- - - Updated - - -

Also how often are you driving this? 8MHz? there will be a power consumption in a driver going this fast....
 
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