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Power Electronics

Full-Bridge Inverter

A half-bridge can produce at most VDC/2 of amplitude from a single supply. In a full bridge the load is connected BETWEEN two totem-pole outputs; drive the legs in opposite phase and the load sees the full ±VDC.

When the two legs are driven with SPWM at 0° and 180°, the difference voltage becomes bipolar PWM; the fundamental component reaches an amplitude of m·VDC (twice the half-bridge).

The load voltage exists between two nodes: a single-ended probe cannot see it. In the Waveform Analyzer’s Math mode, take the CH1 − CH2 difference to inspect the true load waveform.

Formulas

V_load = V_A − V_B
V₁(fundamental) = m · VDC
Leg phases: 0° / 180°

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Test Yourself

In a full bridge with a 24 V supply, what peak voltage can the load see?
Answer: 24 V — With the legs tied to opposite rails the load sees ±24 V.
What is the full bridge’s advantage over the half bridge?
Answer: Twice the output amplitude from the same supply — At the cost of 4 switches, amplitude ×2 (power ×4).
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