Phototransistor Amplifier Circuit. One example is a darlington pair phototransistor circuit which provides double amplification of the output current. Figure 6 shows a photocurrent voltage conversion circuit using an operational amplifier.
One example is a darlington pair phototransistor circuit which provides double amplification of the output current. The output volt age vout is given as vout if r1 ip isc. A phototransistor is an electronic switching and current amplification component which relies on exposure to light to operate.
When light falls on the junction reverse current flows which are proportional to the luminance.
And with ludicrously high gain comes a requirement for ludicrously low offset voltage. The common collector and common emitter phototransistor circuits shown above will provide something closer to true digital switching behavior when a larger base resistor rb is used in the circuit. The arrangement utilizes the characteristics of an opera tional amplifier with two input terminals at about zero voltage to operate the photodiode without bias. The collector is taken to the supply voltage via a collector load resistor and the output is taken from the collector connection on the phototransistor.
