Power calculator
Bulk capacitor
A capacitor is a water tower: the rectifier fills it in gulps, the load drinks steadily.
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The example, worked out
Given
- I want
- A ripple after a rectifier
- Load current
- 1 A
- Peak voltage
- 15.6 V
- Ripple allowed
- 1 V
- Mains
- 50 Hz
- Rectifier
- Full wave (a bridge)
Working
- two refills per cycle
- the load drinks I for a whole period, the voltage may drop ΔV
- with 10 mF
Results
The formulas
- C = I / (f ΔV)the load current, the ripple frequency, the dip allowed
- f = 2 × mains (full wave), mains (half wave)two humps per cycle, or one
- C = 2 P t / (V1² − V2²)hold-up: energy for a time
The usual traps
- Full-wave ripple is at 100 or 120 Hz, not 50 or 60: half the capacitor.
- The ripple current through the capacitor is two or three times the load current: check its rating.
- Rate the capacitor a quarter above the peak, and the peak is √2 × the RMS.
Questions
How big must the capacitor after a rectifier be?
C = I / (f ΔV): the load current, the ripple frequency, the dip allowed. f = 2 × mains (full wave), mains (half wave): two humps per cycle, or one. C = 2 P t / (V1² − V2²): hold-up: energy for a time.
What does it give for typical values?
10 mF for 1 V of ripple at 1 A, full wave on 50 Hz. Capacitance: 10 mF; From the shelf (E6, above): 10 mF.
What are the usual mistakes?
Full-wave ripple is at 100 or 120 Hz, not 50 or 60: half the capacitor. The ripple current through the capacitor is two or three times the load current: check its rating. Rate the capacitor a quarter above the peak, and the peak is √2 × the RMS.
In the app
Your circuit, drawn live
Change a value: the schematic redraws with your numbers on the parts.
The part you can buy
Results rounded to standard values (E12, E24, E96) and power ratings.
The working, shown
Every step written out. Try it first by hand, then check.
Into your notebook
One click puts the circuit on a sheet of your project.
Open the calculatorOpens in the app on 1 December, with Circuit Notebook 1.0
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