Power Electronics Interview Questions
The single most common topic in hardware interviews. Be able to draw a buck converter cold, with waveforms, and to talk through component choice, control loop, layout and protection.
Before you start
What you should already be comfortable with:
- V = L·di/dt and I = C·dV/dt
- MOSFET and diode basics; conduction loss vs switching loss
- Average and RMS values of a waveform
- Bode plots, crossover and phase margin
What interviewers are really testing
- Drawing a buck converter cold, with switch-node, inductor and capacitor waveforms
- Deriving Vout = D·Vin from volt-second balance
- Choosing L, C and FETs with numbers, not catalogue habits
- Explaining loop stability — Type II/III compensation, the boost RHP zero — and how you measure it
- Knowing which loop is "hot" in layout, and how a power tree is sequenced and protected
Start with these two — free full answers
Explain how a buck converter works in synchronous and non-synchronous form. Draw the voltage and current waveforms at the switch node, the inductor and the output capacitor.
Think first: Before you read on: in steady state, what must be true about the inductor current at the start and the end of every cycle? Write that as an equation and Vout falls out.
How do you choose the inductor for a buck converter?
Think first: Before you read on: an inductor has two different current ratings. Which are they, and which number in the converter must each one beat?
Study order
Work through the stages in order. ● screening · ●● onsite technical · ●●● design / senior. Pages marked "Going deeper" add explanation that is not in the book; the two marked "Free answer" show the full answer; every page tells you where the full answer is in the book.
- The buck converter
- PW-01 — How a buck converter works ● Free answer
- PW-02 — Synchronous vs non-synchronous ● Going deeper
- PW-03 — CCM vs DCM ●● Going deeper
- PW-06 — Switching frequency trade-offs ●
- Choosing parts
- PW-04 — Choosing the inductor ●● Free answer
- PW-05 — Choosing a buck regulator IC ●● Going deeper
- PW-07 — LDO vs switcher ●
- The control loop
- Layout and noise
- Systems and protection
- Design problems
Related questions in other chapters
- PC-07 — MOSFET loss trade-off ●●
- PC-08 — Inductor soft vs hard saturation ●●
- PC-01 — Choosing a capacitor type ●
- PI-05 — Inrush when hot-plugging ●● Going deeper
The book
The book has all 20 questions in this chapter with the full answer: how to explain it on a whiteboard, the numbers worth quoting, and the follow-ups that come next.
More topics
PCB Design Interview Questions · Signal Integrity Interview Questions · Analog & Op-Amp Interview Questions · Embedded Hardware Interview Questions · Power Integrity Interview Questions