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PS2633L Datasheet(PDF) 8 Page - NEC |
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PS2633L Datasheet(HTML) 8 Page - NEC |
8 / 38 page 7 The turn-off time can be greatly reduced by the base-emitter resistance (RL). In Test circuit 4, the turn-off time of the test circuit having resistance RL is about 1/30 of that of the test circuit without the resistance. This is because the carrier (photocurrent) stored in the collector-base capacitor (CC-B) is quickly released through the base-emitter resistor (RBE). However, note that part of a photocurrent generating on the base of the phototransistor flows through the RBE resistor and reduces the current transfer ratio (CTR). Compare the voltage level of the output waveform in Photo 4 with that of the output waveform in Photo 2. The current transfer ratio of the test circuit having a base-emitter resistor of 200 k Ω is half or less of that of the test circuit without the resistance. (See 3.3 for reduction of the current transfer ratio CTR.) For reference, Fig. 2-3 shows the switching-time vs. RL characteristics and Fig. 2-4 shows the switching-time vs. RBE characteris- tics. x Sample Solid line: Current transfer ratio of 166% Dotted line: Current transfer ratio of 274% at Ir = 5mA tr td 1000 500 200 100 50 20 10 5 2 1 100 500 1 k 5 k 10 k 50 k 100 k tf ts IF =10mAVcc=5V Vcc=5V Vo RL IF= 10mA 51 Ω I Load Resistance RL ( Ω) VCC = 5 V, IF = 10mA RL = 5 Ω Solid line: Emitter follower Dotted line: Emitter grounded 160 140 120 100 80 60 40 20 0 100 200 500 1000 toff toff Base-Emitter Resistance RBE (k Ω) Load Resistance RL ( Ω) 1000 500 200 100 50 20 10 5 2 1 100 500 1 k 5 k 10 k 50 k 100 k tf ts tr td VCC = 5V Vo RL IF = 5 mA I 51 Ω IF = 5 mA VCC = 5 V x Sample Solid line: Current transfer ratio of 166% Dotted line: Current transfer ratio of 274% at Ir = 5 mA Base-Emitter Resistance RBE (k Ω) Vcc = 5 V, I F = 5mA R 1 = 5 Ω Solid line: Emitter follower Dotted line: Emitter grounded 160 140 120 100 80 60 40 20 0 toff ton 100 200 500 1000 Fig. 2-3 Switching-Time vs. RL Characteristics Fig. 2-4 Switching-Time vs. RBE Characteristics |
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