Speed-up capacitor
7 parts
A 25 kHz square wave switches a saturated BJT through a 10 k base resistor whose RC against the explicit 10 nF base capacitance Cb is 100 µs — two and a half drive periods, enough to swallow the drive entirely. The 10 nF speed-up cap across Rb couples half of each 5 V edge straight onto the base (measured kick down to −1.8 V at turn-off), so the collector snaps rail to rail in tens of nanoseconds. Honest note: our BJT is a static Ebers-Moll model with no charge storage, which is why Cb is drawn as a real part — what you see is pure RC base-drive speed-up, not the storage-time or reverse-recovery removal a real saturated power switch adds on top.
- V1 5V·25kHz
- C1 10nF
- R1 10kΩ
- C2 10nF
- Q1
- R2 1kΩ
- V2 9V
