| 摘要 |
PURPOSE:To prevent damages to a transistor because of an overcurrent, by preventing an on/off control signal after detection by a detection circuit from being applied to a transistor base. CONSTITUTION:When a voltage of a resistor 17 is lower than the normal voltage a comparator 18 outputs a logic 1, and when higher it outputs a logic 0. And because the comparator 18 possesses a latching function, a state in which the output is 0 is retained after an output is changed 1-0. When an input current valve to a switch circuit 11 surpasses a corresponding valve of the normal voltage, an output from a pulse width modulation circuit 15 is prevented from being input to a base driving circuit 16 because of a gate circuit 19. Therefore all transistors 11-1-11-4 fall into a state of noncontinuity. Consequently by setting the normal voltage of a normal voltage generator 20 at a lower value than that corresponding to the maximum valve of the permissible current of the transistors 11-1-11-4, a flow of overcurrent to each transistor can preliminerily prevented. |
