Max guidesA technician must decide whether ideal release time is safe before changing controlled clamp voltage on the real device. The result is unresolved until the rule and units are checked. Predict the direction first.
See the relationship before changing it
The figure reads from left to right. The blue card is controlled clamp voltage. The middle card applies this page's rule. The green card is ideal release time. Walk the arrows once: set the input, apply the rule, then read the result with its unit.
The retained audit below checks several chapter fixtures. This model keeps those stated values fixed and changes only controlled clamp voltage, so the numeric fixture does not switch without explanation.
Derive the baseline in four named moves
- 1
Name the input. The chapter baseline is 30 V.
- 2
Name the relationship. release time = 0.100 H x 0.080 A x 1,000 / clamp voltage
- 3
Substitute with units. 8 / 30 = 0.267 ms
- 4
Read the result. Keep the unit beside the value. Use it only inside the technical boundary on this page.
Predict, then change controlled clamp voltage
Try Predict the direction of release time = 0.100 H x 0.080 A x 1,000 / clamp voltage. Test another controlled clamp voltage, then compare ideal release time.
Observe A higher controlled clamp removes the fixed coil energy faster. Reset controlled clamp voltage to 30 and compare ideal release time.
Explain A higher controlled clamp removes the fixed coil energy faster.
Check yourself
What should you do before trusting a moved-control result?
What does this small model leave out?
1. A coil stores magnetic energy
Current cannot stop instantly in an inductor. A flyback path gives it somewhere safe to flow while the magnetic field collapses.
2. Find the plain-diode time scale
Recover coil resistanceR=V/I=5/0.08=62.5 Ω.
Find one time constantτ=L/R=0.1/62.5=1.60 ms.
Use a practical settling ruleFive time constants is 8.00 ms.
3. Hold a larger reverse voltage
If the clamp is roughly constant, current falls almost linearly. More clamp voltage means a steeper fall, but the transistor must survive supply plus clamp.
4. Try the controlled clamp
TryRaise the controlled clamp while watching release time and the remaining margin to the chapter's 60 V transistor figure.
ObserveAt 30 V, R=62.5 Ω, τ=1.60 ms, the plain 5τ estimate is 8.00 ms, boosted release is 0.267 ms, ideal speedup is 30.0×, switch voltage is about 35 V, and stored energy is 0.320 mJ.
ExplainThe higher clamp gives the inductor more opposing voltage, so current falls faster. It also consumes transistor-voltage headroom, so release speed is a rated design trade.
The model treats inductance, current, and clamp as fixed and compares a 5τ rule with a constant-voltage ramp.
- coil motion
- Needs separate evidence
- changing inductance
- Needs separate evidence
- resistance
- Needs separate evidence
- diode drop
- Needs separate evidence
- Zener tolerance/dynamics
- Needs separate evidence
- wiring inductance
- Needs separate evidence
- contact bounce
- Needs separate evidence
- avalanche energy
- Needs separate evidence
- repetition
- Needs separate evidence
- heating
- Needs separate evidence
- safe-operating-area limits
- Needs separate evidence
Use field evidence or a deeper model before release.
5. Keep two decay models honest
The plain-diode 8.00 ms value is a five-time-constant “effectively gone” rule. The 0.267 ms value is an ideal constant-clamp ramp to zero. Their 30× comparison is useful, but they are not identical threshold definitions.
6. Verify release and stress
Measure coil current, plunger motion, switch-node peak, release time, temperature, and repeated-operation energy. Check transistor, diode/Zener, insulation, contact, and default-safe-state ratings.
7. Check yourself
What is the coil resistance at 5 V and 80 mA?
Why does a 30 V clamp release faster than a plain diode?
Why not raise the clamp without limit?
These are the chapter inputs, worked results, and named teaching assumptions.
- 5 V
- Voltage or voltage-step value
- 80 mA
- Current or responsivity value
- 62.5 Ω
- Resistance or impedance value
- 100 mH
- Inductance value
- 1.60 ms
- Time, interval, or service-life value
- five-τ 8.00 ms
- Time, interval, or service-life value
- roughly 10 ms
- Time, interval, or service-life value
- 30 V
- Voltage or voltage-step value
- 0.267 ms
- Time, interval, or service-life value
- 30.0×
- Percentage, ratio, or gain
- 35 V
- Voltage or voltage-step value
- 60 V
- Voltage or voltage-step value
- 0.32 mJ
- Charge or energy value
They are ideal comparisons, not a release-time guarantee.