Diskusní téma: Úvodní stránka

Datum	07.04.2018
Vložil	Deltatrqabt
Titulek	Ошибка частотного преобразователя

wire connects to safety ground when the supply is plugged in. Optoisolating Optoisolators transfer signals across an isolation barrier. An optoisolator consists of a photodiode coupled to a phototransistor. Current through the photodiode causes the photodiode to emit energy in the visible or infrared spectrum. The energy switches the phototransistor on, creating a low resistance between the transistorвЂ™s emitter and collector. The phototransistorвЂ™s base can be left unconnected. Adding a resistor from base to emitter results in faster switching but lower output current. The interfaces in Figure 5-7 use 6N139 optoisolators, which are designed for direct interfacing to LSTTL logic. Their gain is high: 400% with a photodiode current of just 0.5 mA. In the TTL-to-RS-232 circuit, a logic low at pin 3 of the 74LS14 inverter causes current to flow through the photodiode. The current switches on the corresponding phototransistor, bringing its collector low. The MAX233 inverts the signal and transmits a positive RS-232 voltage. A logic high on pin 3 of the 74LS14 switches the photodiode and phototransistor off. The MAX233вЂ™s internal pull up at pin 2 results in a negative RS-232 voltage. The other direction works in a similar way. A negative RS-232 input causes the MAX233 to output a logic high. This signal switches the photodiode and its phototransistor on, resulting in a logic low at pin 1 and a logic high at pin 2 of the 74LS14. A positive RS-232 input causes the MAX233 to output a logic low. The logic low switches the photodiode and its phototransistor off. A pull up brings pin 1 of the 74LS14 high, resulting in a logic low at pin 2. The RS-232-to-RS-232 circuit shows how to isolate an existing, non-isolated RS-232 interface by using an RS-232 output to drive a photodiode directly. When the RS-232 voltage is positive, the photodiode is on, and the isolated RS-232 output is also positive. When the non-isolated output is negative, the photodiode is off, a 1N914 diode clamps t prom-electric.ru