What is the difference between a ZETA and a SEPIC converter?

Both give the same non-inverting Vo = D·Vin/(1 − D). A ZETA has the output inductor in series with the load, giving low output current ripple (good for the load), while a SEPIC has the input inductor in series with the source, giving low input current ripple. The ZETA is effectively the SEPIC's mirror image.

What is the coupling-capacitor voltage in a ZETA converter?

The average voltage across the ZETA coupling capacitor C1 equals the output voltage, Vo. The switch and diode block Vin + Vo.

When would you use a ZETA converter?

Where a positive output above or below the input is needed with low output ripple — for example driving noise-sensitive loads or LEDs from a battery whose voltage crosses the output during discharge.

ZETA (Non-Inverting) Converter Simulator

Q: What is the output voltage of a ZETA converter?

In continuous conduction mode the ideal output of a ZETA converter is Vo = D·Vin/(1 − D), a non-inverting (positive) output that can be lower than the input (D 0.5).

ZETA Converter Simulator

An advanced, physics-accurate simulator of the DC-DC ZETA converter — a two-inductor, two-capacitor topology giving a non-inverting (positive) output that can be above or below the input, with low output current ripple (the mirror image of the SEPIC). Sweep the duty cycle D, switching frequency, the two inductors and capacitors and the load, add a real device model, and watch every waveform on a real-time oscilloscope — validated live against Vo = D·Vin/(1 − D) and coupling-cap voltage Vo, with efficiency and a conduction-loss breakdown.

ZETA DC-DC converter circuit: MOSFET switch, input inductor L1, series coupling capacitor C1, output inductor L2, diode and output capacitor C2 producing a non-inverting output voltage across load R — ZETA converter — a non-inverting step-up/step-down topology with the output inductor L2 in series with the load for low output ripple. V_o = D·V_in/(1 − D).

Parameters

Duty cycle D 50%

Vo = D·Vin/(1−D) · D<0.5 step-down · D>0.5 step-up

Input voltage V_in

Switching frequency 50 kHz

Power stage (L₁ L₂ · C₁ C₂ · load)

Input L₁ 100 µH

Output L₂ 100 µH

Coupling C₁ 47 µF

Output C₂ 220 µF

Load resistance R 15 Ω

Device & parasitics model

MOSFET R_ds(on) 0 mΩ

Diode V_f 0.0 V

Inductor DCR 0 mΩ

Output C ESR 0 mΩ

Ideal (all 0) gives Vo = D·Vin/(1−D) exactly; add parasitics to see the real drooped output, ripple and losses.

Sampling & display

Sampling rate 700 pts/cycle

Points plotted per switching period

Switching periods shown

Run speed (DSO) 1.0×

Show sample points

Presets

Waveforms to display

Waveforms — one steady-state switching period ZETA

Vin v_C1 coupling Vo output i_L1 input i_L2 output i_Q / i_D

LIVE

Efficiency & conduction-loss breakdown

Estimated efficiency (conduction losses)—

Power lost in each component, computed from the true integrated currents: MOSFET R_ds(on), diode V_f, inductor DCR and output-capacitor ESR. Set parasitics above to see the split.

Measurements

Live accuracy check — simulation vs closed-form theory

Output voltage

Coupling cap & ripple

What is a ZETA converter?

The ZETA converter is a DC-DC converter that produces a non-inverting (positive) output that can be higher or lower than the input. It uses two inductors and a series coupling capacitor C₁, and is essentially the mirror image of the SEPIC: where the SEPIC puts its inductor in series with the source for low input ripple, the ZETA puts its output inductor L₂ in series with the load, giving low output current ripple.

How it works — the two switching states

Switch ON (0 → D·T): the MOSFET connects the input to the circuit; L₁ charges from V_in and energy flows through the coupling capacitor to L₂ and the output. The diode is off.
Switch OFF (D·T → T): the diode conducts; L₁ transfers its energy to C₁ while L₂ maintains the smooth output current. Volt-second balance sets the ratio.

Key equations

Vo = D·Vin / (1 − D) (ideal, continuous conduction, non-inverting)

v_C1(avg) = Vo · ΔiL = Vin·D/(L·f_sw)

Switch & diode blocking voltage = Vin + Vo

This simulator numerically integrates the full 4th-order switching circuit (two inductors, two capacitors) with your device parasitics to steady state, then measures V_o, the coupling-cap voltage, the ripple and the losses from the resulting waveforms and compares them to the equations above.

ZETA vs SEPIC vs Ćuk

All three give a step-up/step-down ratio of D/(1 − D). The Ćuk is inverting with low ripple on both ports; the SEPIC is non-inverting with low input ripple; the ZETA is non-inverting with low output ripple (its output inductor faces the load). Choose the ZETA when a clean, low-ripple positive output matters most.

Converter	Polarity	Ideal Vo	Ripple
Ćuk	Inverting (−)	−D·Vin/(1−D)	Low in & out
SEPIC	Non-inverting (+)	D·Vin/(1−D)	Low input
ZETA	Non-inverting (+)	D·Vin/(1−D)	Low output

See the Ćuk and SEPIC simulators for the related topologies.

Applications

Battery-to-rail supplies needing a positive, low-ripple output above or below the source — LED drivers, sensor and RF supplies, and automotive/portable electronics where the input voltage crosses the output during discharge.

Frequently asked questions

What is the output voltage of a ZETA converter?

In CCM the ideal output is Vo = D·Vin/(1 − D) — positive (non-inverting), step-down for D < 0.5 and step-up for D > 0.5.

What is the difference between ZETA and SEPIC?

Same conversion ratio, but the ZETA has low output current ripple (output inductor faces the load) while the SEPIC has low input ripple. They are mirror images.

What is the coupling-capacitor voltage?

The average voltage across C₁ equals the output voltage, Vo — the simulator plots it live.

What must the switch and diode withstand?

Both block Vin + Vo.

Power4All · ZETA Converter interactive simulator. All waveforms are produced by numerical integration of the actual 4th-order switching circuit and validated against closed-form theory.