What is a half-bridge converter?
A half-bridge converter is an isolated DC-DC topology that drives the transformer primary with ±Vs/2 using just two switches and two split bus capacitors. The capacitors are connected in series across the input to create a Vs/2 midpoint; the primary sits between that midpoint and the node between the two switches. Two power pulses per period are full-wave rectified into a buck-like LC filter. Because the series capacitors block any DC current, the half-bridge is inherently immune to the flux-staircase saturation that plagues the push-pull, and each switch only blocks Vs — half the push-pull's stress.
How it works
- Switch 1 (top) ON: the primary sees +Vs/2 (switch node = Vs, midpoint = Vs/2); the secondary applies
n·Vs/2to the LC filter. - Dead-time: both switches off; the rectifier freewheels (node = 0).
- Switch 2 (bottom) ON: the primary sees −Vs/2; the full-wave rectifier again applies
n·Vs/2— a second power pulse of opposite primary polarity. - Dead-time to the end of the period.
Key equations
This simulator numerically integrates the real half-bridge circuit — the split-capacitor midpoint, the ±Vs/2 primary drive, the magnetizing current and the output LC — to steady state, then compares the measured Vo and ripple to the equations above in the accuracy panel.
Split capacitors, midpoint balance & DC block (topic-specific)
The two series bus capacitors do two jobs. First, they set the Vs/2 midpoint, which self-balances: any tendency toward asymmetry shifts the midpoint slightly until the volt-seconds equalise again. Second — and crucially — they block DC current from flowing in the primary, so the transformer cannot walk into staircase saturation the way a push-pull can. This simulator integrates the midpoint voltage as a real state so you can watch it settle to Vs/2, and the magnetizing current stays symmetric about zero regardless of small mismatches.
Dead-time & shoot-through
The two switches are in series across the input, so they must never conduct together — that would short the bus (a destructive shoot-through). A dead-time between them keeps each duty below 0.5. The simulator's guard shows the remaining dead-time margin and warns as the duty approaches the limit.
Advanced options in this simulator
- Split-cap midpoint analyzer: watch the Vs/2 midpoint self-balance and block DC.
- Dead-time / shoot-through guard: live margin as duty approaches 0.5.
- Vs switch-stress meter: half the push-pull's stress — ideal for high-voltage buses.
- Device model: MOSFET Rds(on), diode Vf, inductor DCR and capacitor ESR; the accuracy check stays locked to the ideal Vo.
- Ripple spectrum: a real FFT showing the dominant ripple at twice fsw.
- Export & capture: CSV data, a text report, or a PNG screenshot of the scope.
The six isolated DC-DC converters
| Converter | Switches | Ideal Vo | Switch stress |
|---|---|---|---|
| Flyback | 1 | n·Vs·D/(1−D) | Vs + Vo/n |
| Forward | 1 | n·Vs·D | Vs·(1+Np/Nr) |
| Push-Pull | 2 (center-tap) | 2·n·Vs·D | 2·Vs |
| Half-Bridge | 2 + split caps | n·Vs·D | Vs |
| Full-Bridge | 4 | 2·n·Vs·D | Vs |
| Phase-Shifted FB | 4 (ZVS) | 2·n·Vs·Deff | Vs |
Explore the others: Flyback, Forward, Push-Pull, Full-Bridge and Phase-Shifted Full-Bridge simulators. For the full theory see the Half-Bridge converter tutorial.
Applications
Off-line 400 V-bus supplies, server and telecom power, medium-power isolated rails, and any high-input-voltage design where the Vs (not 2·Vs) switch stress and inherent DC-block are valuable.
Frequently asked questions
What is the output voltage of a half-bridge converter?
In CCM the ideal output is Vo = n·Vs·D, where D is the duty of each switch (≤0.5). The split caps apply ±Vs/2 to the primary, so each pulse is half a full-bridge's.
Why does it use split capacitors?
They set the Vs/2 midpoint and block DC current, preventing flux-staircase saturation and letting two switches apply a bipolar ±Vs/2 primary drive.
What is the switch voltage stress?
Only Vs — half the push-pull's 2·Vs — which makes the half-bridge attractive for high-voltage input buses.
What is shoot-through?
Both series switches conducting at once, shorting the bus. A dead-time between them prevents it; the simulator's guard shows the margin.
Half-bridge vs full-bridge?
The half-bridge drives ±Vs/2 with two switches (Vo = n·Vs·D); the full-bridge drives ±Vs with four switches (Vo = 2·n·Vs·D) for the same switch stress and double the power.