| 摘要 |
PROBLEM TO BE SOLVED: To increase the lightning surge resistance of an ISDN terminal. SOLUTION: A bidirectional constant-voltage diode 30 is connected between primary-side terminals of a transformer T, two resistances R1 and R3 are connected to one terminal in series, and two resistances R2 and R4 are connected to the other terminal of the transformer T in series. A silicon surge-protecting element 18 is connected between the connection point of the resistances R1 and R3 and a grounding circuit; a silicon surge-protecting element 19 is connected between the connection point of the resistances R1 and R3 and the grounding circuit; and further a silicon surge protecting element 20 is connected between the connection point of the resistances R1 and R3 and the connection point of the resistances R2 and R4. This constitution can protect the transformer T and a secondary-side circuit 23, even against infiltration of lightning surge.
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