| 摘要 |
<p>PURPOSE:To prevent a hot-wire resistance from melting by suppressing a overcurrent which flows through the hot-wire resistance by a hot-wire protecting circuit. CONSTITUTION:The voltage detecting circuit consisting of a transistor (TR) 14, resistances R4 and R5, Zero diode ZD, and diode D is provided so as to detect the terminal voltage VRH across the hot-wire resistance RH. Further, the circuit consisting of TRs 15 and 16 and a resistance R6 is provided as a circuit which operates a power TR 10 in the off-direction according to the output of said voltage detecting circuit. Here, if the voltage VRH across the hot-wire resistance RH rises almost up to the melting voltage of the hot-wire resistance RH, the TR 14 turns on and then the TR 15 also turns on to flow the same current with the TR 14. The TR 16 also turns on with this current to lower the base voltage of the power Tr 10 forcibly, thereby lowering a voltage VCC applied to a bridge circuit. Therefore, the current flowing through the hot-wire resistance RH decreases and the melting is prevented.</p> |
