CPC1580

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4. CPC1580 Over-Voltage Protection

Over-voltage protection is generally required for the

CPC1580 because of parasitic inductance in the load,

wires, board traces, and axial leads of protectors.

Purely resistive loads or loads with low voltage

switching may be able to rely on the transistor to

handle any parasitic energy and thereby not require

protection for the CPC1580. For very low inductance

loads and traces, over-voltage suppression may be

Figure 2). For more moderate load inductance, or

remote switching of a load (i.e. through a long cable) a

voltage suppressor can be used. For heavily inductive

across the load element is recommended, see

Figure 2.

The energy not consumed in switching losses must be

absorbed by the over-voltage protection element. Most

protective devices are designed to withstand certain

peak power, in the case of a Transient Voltage

Suppressor (TVS); or maximum avalanche energy, in

the case of a MOSFET. Understanding the switching

losses and load dynamics is absolutely essential.

One simple way to reduce the amount of stored

inductive energy is to increase the energy dissipated

in the switch. This can be accomplished by adding a

larger capacitor in parallel with the gate-drain

connection of the MOSFET, however care must be

taken so that the rise time and peak current do not

exceed the Safe Operating Area (SOA) rating of the

transistor.

The consequence of increasing the gate-drain

effective capacitance is reduced dV/dt tolerance.

When used in a circuit with an inductive load,

precautions must be taken to prevent damage to the

circuit from inductively generated voltage spikes. The

circuit shown in Figure 2 includes such protection

across the inductive load.

4.1 Other Protection Techniques

Switching loads with higher inductance characteristics

requires consideration of other circuit protection

techniques, device ratings, or protector types. Of

paramount importance is that the designer know the

characteristics of the load being switched.

Figure 2. CPC1580 Over-Voltage Protection for Inductive Loads

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CPC1580

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