Design forward converter power supplies with turns ratio, duty cycle, output inductor, capacitor sizing, and MOSFET stress calculations.
The forward converter is a workhorse isolated DC-DC topology for power levels from roughly 50 W up to 500 W. Unlike the flyback converter, the forward converter transfers energy to the secondary while the primary switch is on, passing it through an output LC filter to produce a clean regulated DC output.
This makes the forward converter behave like an isolated buck converter, delivering lower output ripple and better efficiency at higher power levels than a flyback. The trade-off is an additional output inductor and the need for a transformer reset mechanism — typically a reset winding or an active clamp.
This Forward Converter Calculator handles the essential design equations: turns ratio, duty cycle, output inductor for a target ripple current, output capacitor for a specified voltage ripple, and the maximum MOSFET voltage stress set by the reset winding ratio. Enter your specifications and instantly see whether your components can handle the stresses. Preset buttons provide quick access to common power supply designs used in telecom, industrial, computing, and LED lighting.
Use this calculator when you need a first-pass design check on an isolated forward converter and want the core sizing relationships in one place.
It is useful for power-supply design, topology comparison, and checking whether turns ratio, duty-cycle limit, inductor ripple, and MOSFET stress still fit the chosen architecture. It also helps you compare a forward converter against a flyback or other isolated topology before you commit to the magnetics.
Dmax = Nr / (1 + Nr) Turns Ratio: N = (Vout + Vf) / (Vin × Dmax) Duty Cycle: D = (Vout + Vf) / (Vin × N) Output Inductor: L = (Vin×N − Vout) × D / (fsw × ΔI) MOSFET Stress: Vds = Vin × (1 + 1/Nr)
Result: N = 0.5, D = 50%, L = 20 µH, Vds = 96 V
A 48 V to 12 V / 5 A forward converter at 200 kHz with equal reset winding runs at 50% duty cycle and requires a 20 µH output inductor.
Forward converters are most useful in the power range where a flyback is starting to strain but a bridge topology is still unnecessary. They reward careful coordination between transformer ratio, reset method, switching frequency, and output-filter sizing.
The most common mistakes are overlooking the reset constraint, underestimating switch stress, and choosing an output inductor that drives excessive ripple current. Leakage inductance, snubbing, core flux, and thermal limits also matter, so this kind of calculation should be treated as an electrical starting point rather than the full magnetic design. Real magnetics usually need one more pass for winding layout and thermal margin. That final pass is where parasitics and temperature rise are checked against the actual transformer build. It is also where the reset winding geometry is verified against the core window and insulation plan.
The reset winding demagnetizes the transformer core during the off-time to prevent saturation. Its turns ratio Nr relative to the primary sets the maximum duty cycle and the switch-voltage stress. In practice, it is part of the transformer reset path rather than a separate power output.
The forward converter transfers energy during the on-time through an LC filter, while the flyback stores energy in the transformer and releases it during the off-time. That difference usually makes the forward converter better for cleaner output at higher power.
Dmax = Nr/(1+Nr). With Nr = 1 (equal reset winding), Dmax = 50%. Smaller reset ratios lower the duty-cycle ceiling. That limit ensures the core has enough off-time to reset before the next cycle.
Yes, with Nr > 1 or with an active clamp, but MOSFET stress and reset design both become more demanding. That is why the reset network needs to be checked along with the duty-cycle target.
The transformer secondary produces a pulsed voltage. The LC filter smooths it into a regulated DC output and keeps the ripple current under control. That inductance also gives the control loop a more stable current waveform to regulate.
Typically 50–500 W. Below 50 W a flyback is simpler; above 500 W half-bridge or full-bridge topologies are preferred. The exact boundary depends on efficiency, size, and transformer stress limits.