How can I prevent excess voltage drop across BJT during switching.

[AbhimanyuSingh]

In a switching circuit that has to be on for 1second intermittently, the voltage across PNP falls for more than 1 V. Maybe because of high on time. How can I reduce this drop of voltage as I want maximum voltage drop across load.

 

[vGoodtimes]

Can you be more descriptive? 1 second is a VERY long time for any electronic switching device. My first guess would be that the Vce sat is 1V+, or that you just aren't able to saturate the device reliably. Some BJT's have low enough current gain that driving base current can be an issue and cause them to fail to saturate. It is possible the circuit was designed by an engineer more familiar with FET devices, where just having a voltage is enough to switch on.

 

[nitishn5]

Hi AbhimanyuSingh,

Can you post the circuit please...?

 

[BigBoss]

I suggest a simple solution...
Use a MOS transistor instead of a bipolar for switching applications.MOS transistors have much less Rds resistance and drop-out voltage across D-S is much less than Bipolars.

 

[dick_freebird]

What is your load current and what is the datasheet current
at which the manufacturerrates Vce(sat), and at what
forced beta?

High temp runs up Rc (can be > 2X for medium voltage,
more for high voltage bipolars) making the device more
dissipative. What's your cooling situation - what does the
case temp do across that one second?