Transistor as a power switch

[ricky_wcy]

Transistor can be used as a power switch in power mangement

BJT & MOSFET are commonly-used transistor in electronic design

why sometimes BJT is used as a power switch (because of low current, low voltage, low cost or related vbe, large current leakage?)

why sometimes MOSFET must be used as a power switch instead of BJT (because of high-load current, high voltage or related vgs, less current leakage ?)

 

[dfullmer]

Hi,

some reasons but not all to be sure are

speed of switching
saturation of a transistor vs Rds on of a mosfet
switching losses
transistor turns on with current mosfet with voltage

sometimes a IGBT can give you the best of both worlds but it depends on what you are doing.


you can usually find both in voltage or current ranges you need


regards

dfullmer

 

[kishore2k4]

why sometimes BJT is used as a power switch (because of low current, low voltage, low cost or related vbe, large current leakage?)
->Low on-state voltage drops
->High Current capability
->Relatively cheaper compared to MOSFETs with similar requirements

why sometimes MOSFET must be used as a power switch instead of BJT (because of high-load current, high voltage or related vgs, less current leakage ?)

->BJTs can carry more current than MOSFETs(typically)
->High Voltage is definite yes
->High Frequency switching with simple gate drive requirements(like a pulse will put-it in on state, unlike BJTs which require continues gate drive)

Do note that leakage current is not a big factor, if at all it is a factor, in selecting power switches. As dfullmer suggested IGBTs give you the best of both worlds i.e. with some limitations at the extremes. In the end its just a matter of the application at hand.