Documentation sections
Flyback Converter Calculator
POSThttps://rftools.io/
Slug flyback-converter. Calculate flyback converter turns ratio, peak primary and secondary currents, and power levels for isolated DC-DC converter design.
Inputs
Send every one of these in inputs, in the units shown. Most are required: a call without one is refused (400) and costs nothing; one the calculator can do without takes the default shown. An input outside its range is still computed and flagged in the provenance.
| Name | Unit | Range | Default | Description |
|---|---|---|---|---|
| vinnumber | V | 1 … 1000 | 48 | DC input voltage |
| voutnumber | V | 0.5 … 500 | 12 | Desired output voltage |
| ioutnumber | A | 0.01 … 100 | 1 | Maximum output current |
| efficiencynumber | % | 10 … 99 | 85 | Expected converter efficiency (typical: 80-90%) |
| fswnumber | kHz | 10 … 5000 | 100 | Switching frequency |
| dutyCyclenumber | % | 5 … 90 | 40 | Primary switch duty cycle (typical: 30-50% for flyback) |
| vinMinnumber | V | 0 … 1000 | 0 | The lowest input the converter must work from; 0 for the nominal. The transformer designed at the nominal runs in continuous conduction below it. |
| vinMaxnumber | V | 0 … 1000 | 0 | The highest input the converter must work from; 0 for the nominal. It sets the switch's and the rectifier's voltage. |
| rdsOnnumber | mΩ | 0.1 … 100000 | 50 | The switch FET's on-resistance at its operating temperature. |
| tFallnumber | ns | 0 … 10000 | 20 | The switch turns off at the peak current: the switching loss is ½·(V_in + n·V_out)·I_pk·t_f·f_sw. It turns on at zero current at the boundary. |
| qgnumber | nC | 0 … 10000 | 15 | The switch's gate charge at the drive voltage: the gate drive takes Q_g·V_g·f_sw. |
| vGatenumber | V | 1 … 20 | 10 | Gate Drive Voltage |
| vDiodenumber | V | 0 … 3 | 0.5 | The output rectifier's forward voltage: it dissipates V_F·I_out. |
| rPrinumber | mΩ | 0 … 100000 | 50 | Primary Winding Resistance |
| rSecnumber | mΩ | 0 … 100000 | 20 | Secondary Winding Resistance |
| coreLossnumber | mW | 0 … 1000000 | 100 | From the core's datasheet at this flux swing and frequency. |
| leakageInductancenumber | μH | 0 … 100000 | 2.6 | Primary leakage inductance, measured with the secondary shorted; typically 1 to 3 % of the primary inductance. Its energy goes to the clamp. |
| clampRationumber | none | 1.1 … 10 | 2 | The clamp voltage as a multiple of the reflected output voltage; AN-4147 suggests 2 to 2.5. A lower clamp spends more of the magnetizing energy in the clamp, a higher one stresses the switch more. |
Outputs
Returned in values, by key. A value that is unbounded or undefined is null.
| Field | Unit | Description |
|---|---|---|
| turnsRatioheadline | none | Primary-to-secondary turns ratio |
| iinAvg | A | Average DC input current |
| ipPeak | A | Peak current in primary MOSFET switch |
| isecPeak | A | Peak current in secondary diode/rectifier |
| outputPower | W | Total output power: Vout × Iout |
| primaryInductance | μH | Magnetizing inductance at which the primary current ramps from zero to the peak in each on-time (boundary conduction): Vin·D/(fsw·Ipk) |
| dutyMin | % | At the maximum input voltage, in discontinuous conduction |
| dutyMax | % | At the minimum input voltage, in continuous conduction |
| ipPeakWorst | A | The transformer's saturation current must be at least this |
| ipPeakWorstVin | V | Input at the Worst Primary Peak |
| isecPeakWorst | A | Peak Secondary Current, Worst Case |
| isecPeakWorstVin | V | Input at the Worst Secondary Peak |
| primaryRmsA | A | In the switch and the primary winding |
| primaryRmsVin | V | Input at the Worst Primary RMS Current |
| secondaryRmsA | A | In the rectifier and the secondary winding |
| secondaryRmsVin | V | Input at the Worst Secondary RMS Current |
| reflectedVoltage | V | The output as the primary sees it while the secondary conducts |
| clampVoltage | V | Above the input rail, where the clamp holds the drain after turn-off |
| vdsPeakWorst | V | The maximum input plus the clamp voltage |
| vdsPeakVin | V | Input at the Worst Drain Voltage |
| vdsRating | V | The rating sold at or above the clamped peak drain voltage |
| diodeVrWorst | V | The output plus the maximum input over the turns ratio, while the switch is on |
| diodeVrVin | V | Input at the Worst Reverse Voltage |
| diodeVrRating | V | The rating sold at or above 1.5 times the worst reverse voltage |
| lossConduction | W | Switch Conduction Loss |
| lossSwitching | W | Switch Turn-off Loss |
| lossGateDrive | W | Gate Drive Loss |
| lossDiode | W | Rectifier Conduction Loss |
| lossCopper | W | Winding Copper Loss |
| lossCore | W | Transformer Core Loss |
| lossClamp | W | The leakage energy ½·L_lk·I_pk²·f and the magnetizing energy the clamp takes while the leakage resets |
| lossTotal | W | Total Loss |
| efficiencyLossModel | % | At the nominal input and load, from the loss model. The currents are sized with the efficiency input; set it to this value and they follow the loss model |
Calling it
- Calculate: one call, the request and response in full, and its errors.
- Batch: this calculator with others, or a sweep, in one request.
- Solve for a target: the value of one input that brings an output to a target.