EPR-9 Datasheet, PDF (23/32 Pages) Power Integrations, Inc. – Engineering Prototype Report 5 W, Universal Input, Dual Output, Isolated, TNY266 (EP9)

03-April-2001
5 W Universal Input Dual Output Isolated TNY266
8.7 Surge Voltage Immunity (2 kV and 6 kV, 1.2/50 µs per IEC1000-4-5)
The surge protection for configuration ”1” (2 kV) and configuration ”2” (6 kV) is illustrated in the schematics
(pages 4 and 5).
R7, R8 limit the maximum surge current to approximately 50 A, the value at which the clamping voltage of
the varistor is characterized.(< 800 V). This voltage level was selected to ensure enough margin for the
diode bridge D1-D4. The 6 kV, 1.2/50 µs pulse at 800 V clipping level is approximately 100 µs (see Fig.
8.7.2). From the graph in Fig.8.7.1 it can be inferred that the unit will survive 10 k surges of 6 kV. Reducing
the value of R7, R8 would reduce the total number of 6 kV pulses the unit can survive.
Figure 8.7.1 - Varistor Life (Number of Surges) as a Function of the Rectangular Pulse Amplitude
and its Duration.
VRV1
Varistor Clamp Voltage
Instantaneous Line Voltage
V_AC
Figure 8.7.2 - Varistor Clamping Voltage.
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