| 摘要 |
PURPOSE:To prevent excessive current supply to a heat emitting body during repetitive operation of a key switch by measuring the frequency signal from an oscillator after the key switch is turned on, and by stopping the current supply to the heat emitting body when this measurement has attained a constant value. CONSTITUTION:When a key switch 1 is turned on, the output of a timer circuit 6 will be '0' while that of a driver circuit 5 '1', and now a relay 4 is closed to actuate current supply to the heat emitting body 3 from a battery 2. Here the timer circuit 6 is composed of a voltage-frequency converter 6a as oscillating means, which gives the point c a frequency signal repeating between '1' and '0' according to the frequency varying with the potential of the point b and a counter 6b which shifts its output from '0' to '1' when counting has found a rise of the point c from '0' to '1'. Accordingly when the time set on the timer is up, the output of the above-mentioned circuit 6 will be '1' while that of the circuit 5 '0', and now the relay 4 is opened to finish current supply to the heat emitting body 3. |
