Better to use a higher gain device? I'll be using all 1/4w resistors. I really need to measure the current so I can figure this out.
Higher gain devices don't necessarily have lower saturation voltages but many newer transistors are optimised for low Vcesat. But most of the newer devices are in SMT packages which may or may not be a problem.
If he goes to a smaller device then he might need to run deeper saturation to keep both the Vcesat down and dissipation down.
Ic/Ib = 20:1 will be not a particular issue up to 500mA on the BD140 - it just depends on whether the power loss is acceptable or not.
If he goes to a smaller device then he might need to run deeper saturation to keep both the Vcesat down and dissipation down.
if you switch is running saturated, then @ 130mA output it will drop <<0.2V and a realy good switch will drop ~0.02V.
Taking the worst Vdrop with the highest demand you get a collector dissipation of 0.2V*0.13A = 0.026W
the base disspation will be ~0.8V*0.13/10A = 0.01W.
The total dissipation in the switch is <36mW
You can use a sot23 here not a To126/To220 !
But you NEED to know the maximum current demand and from there determine the required base current to ensure saturation.
Taking the worst Vdrop with the highest demand you get a collector dissipation of 0.2V*0.13A = 0.026W
the base disspation will be ~0.8V*0.13/10A = 0.01W.
The total dissipation in the switch is <36mW
You can use a sot23 here not a To126/To220 !
But you NEED to know the maximum current demand and from there determine the required base current to ensure saturation.
Perhaps not, I don't need them so I didn't look.
More important they have EBC connections and known as TO-202 case.
Mona
- Status
- Not open for further replies.