Which triode will be chosen for this step motor driven circuit?
Different characteristics, want to see the before and after the class relations, the first is to follow the output, high input impedance, output impedance is small, the current level is high voltage low current, and the output voltage is controlled voltage level before, can do limit switch, the output is a voltage source. The second type is the reverse coincident collector output, which is suitable for the low voltage large current, and the output is the high impedance, which is also the current source, and the current is not changed when the load changes. If the previous stage is low resistance, such as TTL, it is suitable for the second type. Additional circuit is a combination of both, light coupling leakage current is easy to be amplified, so let's add R around 2 k (see the parameters of the optical coupling), so relay coil, when the release of low voltage, easy to misoperation, current advantage is can quickly set up the voltage to the coil. In this case, the relay, which is a current drive, is best to output from collector, but also for R.
You are driving solenoid valve, and low power transistor, supplement the drive pipe pressure drop is very big, can only is the second, the valve to the collector, and the drive current 1 a to add another level of pipe.
PLC working voltage is 24 v, optical coupling circuit can need not change, in front of triode can use 8050. Light coupling output side, 10 k resistor can be appropriate in a bit, current-limiting resistance in a bit of light. The triode in the back consists of the darlington form. The model depends on the power of the motor you are driving. Power small words can be used in 8050, large words can be used D882. Or using integrated drive ULN2003 and so on.
