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Circuit diagram of constant-current-source type power supply

2014-11-24 13:04  
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Circuit diagram of constant-current-source type power supply and off-hook detection
Circuit diagram of constant-current-source type power supply and off-hook detection The circuit is used for HJD05 –type switching board. The direct current path is + 48V, and the resistances R5, R1, and the transistors Q1, Q3 constitutes a supply circuit in the positive end of the power supply. The upper end of R3 is connected with a end of the extension’s telephone line via a relay. The b end of the extension’s telephone line is connected to upper end of resistance R14 via a relay. The b end then is connected with 0V end of the power supply via R14, transistors Q3, R16, R15, R5, and R7, and the luminous diodes of the photoelectric coupler, which constitute the supply circuit in the negative end of the power supply.