Transformer, rectifier and reservoir
Periodic numerical capacitor-charging model with winding resistance, diode drop and constant-current load.
Development preview. Check the assumptions below before relying on a result. Calculations run in your browser.
How it calculates
Charge equation: C dVC/dt = max((Vrect − VC)/Rsource, 0) − Iload
Assumptions
- Secondary voltage is rated-load RMS; no-load rise determines the ideal source voltage and equivalent winding resistance.
- For center-tap, enter the RMS voltage of one half-winding; reported VA includes both half-windings. Half-wave operation can impose transformer DC bias and is not rated by this scalar model.
- Constant diode drop and series resistance; leakage inductance, transformer heating, mains safety and diode reverse recovery are omitted. ESR ripple is a conservative additive estimate; ESR is not included in the charging ODE.
- Numerical step is 1/2400 of a line cycle. Extremely narrow charging pulses need a higher-resolution circuit simulation.
Worked example
These are the calculator's default inputs. Change any input above to recalculate.
Inputs
- Rectifier
- bridge
- Secondary RMS (one half for center-tap)
- 9 V
- Line frequency
- 50 Hz
- Input voltage tolerance
- 10 %
- Transformer no-load rise
- 10 %
- Rated secondary current
- 1 A
- Additional series resistance
- 0.5 Ω
- Each conducting diode drop
- 0.8 V
- Effective reservoir capacitance
- 0.0022 F
- Constant load current
- 0.25 A
- Reservoir ESR (ripple estimate)
- 0.05 Ω
Results
- Nominal average DC
- 10.689 V
- Ripple bound including ESR
- 0.856216 V
- Low-line minimum DC
- 8.95004 V
- High-line maximum DC
- 12.4341 V
- Nominal capacitor voltage ripple
- 0.79663 V
- Capacitor RMS ripple current
- 0.418559 A
- Peak charging current
- 1.19172 A
- Each diode RMS current
- 0.34474 A