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A forward converter transfers energy directly through a transformer while the switch is on (unlike a flyback, which stores it first). Because the transformer core must be actively demagnetized each cycle, a reset winding (or reset circuit) returns the magnetizing energy to the input, which limits the maximum duty cycle to keep the core from saturating.
| Quantity | Formula |
|---|---|
| Output voltage | Vout = Vin×D×(NS/NP) |
| Maximum duty cycle | Dmax = NR/(NR+NP) |
| Switch voltage stress | Vswitch(max) = Vin(1 + NP/NR) |
With the common 1:1 reset winding, Dmax = 0.5 and the switch sees up to 2×Vin. A smaller reset-to-primary ratio raises Dmax but increases switch stress — a key design trade-off.
An isolated buck-derived converter that transfers energy through a transformer while the switch is on. Unlike a flyback, it needs an active reset mechanism to demagnetize the core each cycle.
The transformer core stores magnetizing energy while the switch is on. If not removed before the next cycle, the core saturates. The reset winding returns this energy to the input during the off-time.
Dmax = NR/(NR+NP), set by how much off-time is needed to reset the core through the reset winding. Exceeding it risks core saturation.
A 1:1 reset winding needs exactly as much off-time as on-time to fully reset the core, capping the duty cycle at 50%.
The peak voltage the main switch must block, which rises above Vin because the reset winding forces the switch node above the input during reset. It depends on the reset winding ratio.
A trade-off: fewer reset turns relative to primary raises Dmax (more output range) but increases switch voltage stress, requiring a higher-rated (often costlier) switch.
Vout = Vin×D×(NS/NP), just like a buck converter but scaled by the transformer's secondary-to-primary turns ratio.
Forward converters suit moderate-to-higher power (100–500 W) with lower output ripple; flyback suits lower power and simpler, cheaper designs without an output inductor.
Besides a reset winding, designs use an RCD clamp, a two-switch (asymmetric) topology, or active clamp reset — each trading efficiency, complexity, and voltage stress differently.
Yes — like a buck converter, its output stage has an inductor and diode/rectifier that smooth the pulsed secondary voltage into a steady DC output.
The core cannot fully reset before the next switching cycle, so magnetizing current builds up progressively, driving the core into saturation and risking switch failure from excessive current.
Yes — additional secondary windings with their own rectifier and inductor stages provide extra isolated output voltages from the same transformer and switching cycle.
Flyback Transformer • DC-DC Duty Cycle • Push-Pull Converter • All Calculators