A diode passes current one way, but even when conducting it keeps a forward drop VF (~0.7 V). Its I-V curve has three regions — forward conduction, reverse block, breakdown — and turn-off isn't instant: the reverse-recovery time (trr) comes back as switching loss. Types split by efficiency (low-VF Schottky), speed (fast-trr switching / fast-recovery) and protection (Zener/TVS using reverse breakdown).
One-way conduction + three I-V regions
Forward (anode +, cathode −) conducts but leaves VF≈0.7 V across it (the first loss); reverse blocks.
Three regions: forward conduction (VF), reverse block (tiny leakage), breakdown (current surges → destruction). Not unlimited current — always check the datasheet max.
Region
Condition
Behavior
Forward
V > VF
Conducts (VF≈0.7 V drop)
Reverse block
−Vbr < V < VF
Blocks (tiny leakage)
Breakdown
V < −Vbr
Surges → destroyed (Zener/TVS use it on purpose)
Three regions by voltage direction & size
Reverse-recovery time trr — the second loss
Cut a conducting diode and current doesn't stop instantly — it briefly flows backward, then recovers. That time is trr; the area under that current is the loss.
In switching circuits that toggle on/off constantly the loss accumulates every cycle, so fast switching needs a short-trr diode.
Forward on
Switch offnot instant
↩Reverse currenttrr window
🔥Switching loss
Turn-off draws reverse current for trr = loss
Six types — split by efficiency, speed, protection
General/rectifier has high breakdown & rating but large VF/trr (poor for switching). Switching (1N4148) is fast-trr for signals; Schottky has VF 0.2–0.6 V (efficient) and very short trr (but high leakage).
Fast-recovery is a low-trr rectifier. Zener/TVS aren't rectifiers — they deliberately use reverse breakdown for voltage regulation and surge/ESD protection.
Type
VF / trait
Use
General
high VF/trr
AC rectify · block reverse
Switching 1N4148
fast trr, low leak
fast signal switching
Schottky
VF 0.2–0.6 V, high leak
power supplies · efficiency
Fast-recovery
very short trr
high-freq rectify
Zener
reverse breakdown
voltage reg · clamp
TVS
fast, absorbs surge
ESD / surge protection
Picking among six diode types
Pitfalls & gotchas
Schottky's low VF (efficiency) is traded for large reverse leakage — you buy efficiency by giving up leakage. Deferred by the lecture: the Schottky-based inverter gate circuit and the MOSFET body diode (recovery). Applied circuits live in the sibling topic 'diode circuits'; for STT errors in the raw transcript, check its correction table.