Zener Shunt Voltage Regulator
For an ideal shunt regulator in breakdown, Vo = Vz, series current is (Vs - Vz)/Rs, and Kirchhoff's current law gives Is = IL + Iz. Valid operation also requires safe minimum and maximum Iz.
Why this shows up in the exam
Finding load and Zener currents · Selecting a protective series resistor · Checking line and load regulation limits
Learn the idea
In regulation, series current splits between the load and Zener while the load voltage remains approximately Vz. The series resistor supplies both branches. The load takes what it needs, and the Zener takes the remaining current, so supply or load changes are absorbed without a large output-voltage change.
🧠 Memory hook: Series current equals load current plus Zener current.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- I_S = (V_S - V_Z) / R_S — current through the regulator series resistor
- I_L = V_Z / R_L — load current while the Zener regulates
- I_Z = I_S - I_L — Zener branch current from Kirchhoff's current law
How to approach it
- 1Set output equal to Vz provisionally
- 2Calculate Is and IL separately
- 3Verify Iz is positive and below Pmax/Vz
Common slip-ups that cost marks
- •Sending the full series current through the Zener
- •Assuming regulation when calculated Iz is negative
- •Checking power at the wrong supply or load extreme
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
A transistor has common-emitter current gain beta = 50. If base current is 20 microA, find collector current.
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