Electronics > Beginners
Speed up BJT switching
Zero999:
Since the drive voltage from the MCU is higher than the voltage being switched, an NPN transistor can be used to switch the high side. There are no Miller capacitance issues, the base is discharged quickly, thanks to the low value base resistor and when it turns off the base voltage by definition falls below the emitter voltage, this turning it off quickly.
It's much faster than the other circuit. The on loses will be higher, especially if the driving voltage is lower or the supply voltage higher, but it's still fairly good, even if the 3.7V is increased to 4.2V.
xavier60:
I'll try Tim's idea tonight.
I'm also wondering about which mode the converters will operate in. Continuous-conduction-mode might be difficult to manage without having current sensing for each converter.
xavier60:
Adding the complementary buffer made a dramatic improvement to the switching speed, 50ns.
The efficiency rose to only 83%. The powdered iron inductor has been lossy the whole time.
A ferrite inductor is needed, especially if operated in Discontinuous-Conduction Mode.
And a less than perfect switching speed would matter even less because of the lower operating frequency.
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