| 摘要 |
PROBLEM TO BE SOLVED: To surely limit an output voltage even when a microprocessor operates without control. SOLUTION: A PWM pulse generating circuit within a micon-chip outputs a PWM pulse by single edge modulation from a voltage command. The rise edge of the pulse is detected by a D-flipflop 41 and an AND gate 42 to reset an upcounter 31 for each PWM cycle. The coincidence circuits 32, 33 provide an output with the count corresponding to the minimum and maximum pulse widths, an OR gate outputs the pulse of which lower limit is limited to the maximum width and an AND gate further outputs a pulse of which upper limit is limited to the maximum width. Since the coincidence circuit 34 resets the up-counter 31 with the signal of one PWM cycle via a NOR gate 42, even when a voltage command is saturated and rise edge does not exist in one PWM cycle, the PWM pulse is limited to the predetermined width for one PWM cycle. Since pulse width limitation is performed outside the chip, the pulse width is surely limited. |
