Forward Converter Calculator — DC-DC Output Voltage
Calculate the output voltage of a forward converter (a common isolated DC-DC switched-mode power supply topology) from the input voltage, transistor duty cycle, and transformer turns ratio. Includes an efficiency-adjusted output and a duty-cycle sweep curve.
V
%
Vout = Vin × D × (Ns / Np) — before efficiency losses
- 1
Turns ratio (Ns / Np)
5 ÷ 10 = 0.5The secondary-to-primary turns ratio scales the coupled voltage. - 2
Ideal output voltage
48 × 0.4 × 0.5 = 9.600
How does this calculator work?
Vout = Vin × D × (Ns / Np). The output voltage is linearly proportional to duty cycle and the secondary-to-primary turns ratio. For a standard single-transistor design the duty cycle is limited to D ≤ 0.5 for reliable transformer reset. Multiply by converter efficiency for a realistic estimate.
Formula
How this is calculated
A forward converter transfers energy through a transformer every switching cycle while the power transistor is ON. During the ON phase, the transformer couples the input voltage to the secondary with a factor of Ns/Np (the turns ratio). The output voltage is then proportional to the duty cycle D (the fraction of each period the switch conducts): Vout = Vin × D × (Ns / Np). This linear relationship between duty cycle and output voltage makes the forward converter straightforward to control via PWM.
A key constraint distinguishes the forward converter from the flyback: the transformer core must be reset — its magnetising energy returned to zero — during each OFF phase to avoid saturation. In the classic single-transistor design with a tertiary reset winding of Np turns, the reset volt-seconds equal the forward volt-seconds only when D ≤ 0.5. Exceeding D = 0.5 prevents full reset, eventually saturating the core. Two-transistor and active-clamp variants relax this limit.
The efficiency field accounts for real-world losses: rectifier forward drops (typically 0.4–1.0 V for Schottky diodes), transformer copper and core losses, switch conduction and switching losses, and output filter ESR. For design estimates use 88–93% for a well-optimised design operating at 100–500 kHz; output the resulting effective Vout to guide component selection and feedback-loop target setting.
Frequently asked questions
The transformer core must be fully demagnetised (reset) during each OFF period. With a 1:1 reset winding, the core sees the same volt-seconds in both directions only when the ON and OFF times are equal — i.e. D = 0.5. Above 0.5, the core accumulates flux cycle by cycle and eventually saturates, destroying the transistor. Active-clamp and two-transistor topologies allow D > 0.5 by resetting the core differently.
Set Ns/Np so that the target Vout is achieved at a duty cycle around 0.35–0.45 for a single-transistor design, leaving headroom for regulation. Rearranging the formula: Ns/Np = Vout / (Vin_min × D_max), where Vin_min is the minimum input voltage and D_max ≤ 0.5.
In a flyback converter, energy is stored in the transformer's magnetising inductance during the ON phase and released to the output during the OFF phase (like a coupled inductor). In a forward converter, energy passes through the transformer to the output directly during the ON phase — requiring an output inductor — and the core must be separately reset during the OFF phase.
Also known as
TG we-Calculate Editorial Team. (2026). Forward Converter Calculator — DC-DC Output Voltage [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/forward-converter
TG we-Calculate Editorial Team. "Forward Converter Calculator — DC-DC Output Voltage." TG we-Calculate. 2026. https://we-calculate.com/calculator/forward-converter.
TG we-Calculate Editorial Team, "Forward Converter Calculator — DC-DC Output Voltage," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/forward-converter
@misc{wecalculate_forward_converter, title = {Forward Converter Calculator — DC-DC Output Voltage}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/forward-converter}}, year = {2026}, note = {TG we-Calculate} }
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