Surging
Ideas
TVS Diode Application Note
PROTECTION PRODUCTS
Unidirectional & Bidirectional Operation
Unidirectional Protection
Figure 1 illustrates a large transient at the input of a
circuit protected by a unidirectional TVS diode. During
the positive spike, the TVS diode junction is reversed
biased. The device acts in avalanche mode as the
transient current i
1
flows. The spike is clamped at or
below the maximum clamping voltage of the device.
During the negative spike, the TVS diode junction is
forward biased. The negative spike is clamped to one
diode drop as the device conducts i
2
in the forward
direction.
Bidirectional Protection
Figure 2 illustrates a large transient at the input of a
circuit protected by a bidirectional TVS diode. The
positive and negative spikes are both clamped at or
below the maximum clamping voltage of the device.
During the positive spike, D
1
conducts in the forward
direction (i
3
) and D
2
is reversed biased conducting in
avalanche mode. The action is reversed (i
4
) for the
negative spike.
Figure 1 - Unidirectional Device
(Asymmetric Clamping)
SI96-05
Figure 2 - Bidirectional Device
(Symmetrical Clamping)
Revision 9/2000
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