| 摘要 |
<p>PURPOSE:To prevent change in the impedance of a phototransistor on the output side due to temperatue by a system wherein two phototransistors are closely located on the same pellet, a allowing them to equally receive light from one LED. CONSTITUTION:When phototransistors PT1, PT2 equally receive light from an LED, and when their internal impedance is Z1=Z2, the relation between an operating AMP input Ein and the current Ic flowing from the constant-current regulated power to PT1 is Z1=Z2=Ein/Ic. As the temperature rises, the PT increases hFE and a light current. Therefore, the output impedance to the PT2 is reduced, but Z1 decreases because of the increased light current in the PT1, while the negative feedback volume to the operating AMP increases. Thus, the operating AMP output is lowered. For this reason, light volume from the LED decreases, which prevents an increase in light current toward each PT. As the temperature falls, hEF as well as the negative feedback volume to the operating AMP decrease, while output voltage increases so that the light volume of the LED is increased. Therefore, input voltage can be always correctly delivered by impedance coupling without being affected by temperatures, thus making it applicable to an analogue circuit.</p> |
