= H-bridge shoot-through
{c}
<H-bridge shoot-through> is unintended conduction directly between the supply rails through devices in the same bridge leg. It differs from the intended load-current path through opposite legs of an <H-bridge>. Overlapping device conduction during switching can create that rail-to-rail path even when the intended logical states never command it. The manufacturer application note explicitly identifies cross-conduction as shorting the supply and introduces nonoverlap timing to prevent it.<Using power MOSFETs in DC motor control applications by Nexperia>[§4.1, Modes of switching, bipolar-drive discussion and Figure 5]{ref}
An original lumped fault-loop model shows why a short overlap can matter. Let a previously unenergized parasitic loop have <electrical resistance> $R$, <inductance> $L$ and constant supply <electric potential difference> $V_d$. During overlap,
$$
L\frac{di}{dt}+Ri=V_d,\qquad i(0)=0,
$$
so
$$
i(t)=\frac{V_d}{R}\left(1-e^{-t/\tau}\right),\qquad \tau=\frac LR.
$$
For $t\ll\tau$, the initial ramp is $i\simeq V_dt/L$; the steady resistive value $V_d/R$ is not reached instantaneously.
Take stipulated $V_d=24\,\mathrm V$, $R=0.10\,\Omega$ and $L=100\,\mathrm{nH}$, giving $\tau=1\,\mathrm{\mu s}$. An overlap lasting $100\,\mathrm{ns}$ reaches about $22.84\,\mathrm A$. The supply delivers
$$
E_{\rm supply}=\int_0^{\Delta t}V_di(t)\,dt
=\frac{V_d^2}{R}\left[\Delta t-\tau\left(1-e^{-\Delta t/\tau}\right)\right]
\approx27.86\,\mathrm{\mu J}.
$$
Some of this <energy> remains in the loop's <magnetic field> at turn-off; it should not all be labeled heat dissipated in one switch. A $500\,\mathrm{ns}$ overlap in the same ideal model reaches about $94.43\,\mathrm A$, illustrating the nonlinear dependence on duration. Device and supply behavior can invalidate these constant-parameter assumptions.
<Bridge switching dead time> addresses timing overlap by allowing one conduction path to cease before the complementary one starts. An inductive load still needs a recirculation path while the controlled devices are off. TI's primary bridge lesson illustrates current paths during that interval.<Brushed DC Motor 2: The H-Bridge by Hector Hernandez>[Slides 5–7, Dead Time and current decay paths]{ref}
A proposed diagnostic compares actual device control waveforms and supply-current transients with load current during transitions, using a limited-energy test arrangement. A large load current by itself does not identify shoot-through; the timing and path establish the mechanism. The calculated fault-loop pulse is an original model, not an asserted device rating.
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