| 摘要 |
PURPOSE:To obtain a stable voltage detecting circuit which detects abnormality of the voltage of a DC power source regardless of its variation in direction and speed, by interposing a DC/DC converter between the DC power source and a load. CONSTITUTION:The DC/DC converter 4 is constituted by adding a constant voltage function which holds a + or -5% output voltage even when load current fluctuation is added, to >=+ or -10% level input voltage fluctuation. Therefore, a threshold value is set within a range of + or -5-10% abnormal voltages at a point, e.g. + or -6% and a power supply cutoff preannouncement signal Vpf is outputted: the D/D converter 5 holds <=+ or -5% voltage range of the voltage at a point D continuously until the voltage at the point A deviates from + or -6% and attains to + or -10%, so a comparing circuit 3 sends out the secure power supply cutoff preannouncement signal Vpf in an enough margin time. |
