Electronic – Motor driver board – wingxine – need help with wiring

Yes, the "diode" is the LED.

There is no such thing as "wide open"- the current at the LED is reflected (within limits) at the transistor by the ratio "CTR" = Current Transfer Ratio.

If you put 5 mA through the LED you get somewhere between 2.5mA and 20mA through the transistor (until it saturates)- that's what the minimum/maximum CTR figures of 50% to 400% at If = 5mA and Vce = 5V mean. Vce =5V means that it's far from saturation. So if you use a resistor in series that limits the current to (say) 1mA (eg. 5K on a 5V supply) you'll have it saturate with 5mA into the LED. Note the since they vary over an 8:1 range, the manufacturer has ranked some of them and marked them in different "bins"

N : 50 to 400 (%)

H : 80 to 160 (%)

W : 130 to 260 (%)

Q : 100 to 200 (%)

L : 200 to 400 (%)

Naturally, the N version will tend to be the cheapest since the CTR can vary over the widest range, and includes the worst-performing units (50-80% CTR).

The transistor in the NEC part is rated at 70V and you should not put more than that across the Emitter-collector. There are higher voltage rated solutions.. for example the Sharp PC851XNNIP0F is rated at 350V.

You should make sure you have plenty of CTR- it degrades with temperature and with time (as the internal LED fades). Putting extremely high currents (like 30mA) through the LED will hasten the deterioration.

A proposed model of optocoupler aging is life \$\propto \frac{1}{Ie^{\frac {-E}{kTj}}}\$

Where k is Boltzman's contant 8.62\$\times 10^{-5} eV/K\$

Tj is junction temperature

E is the activation energy of approximately 0.15eV

so if you increase the current you not only get a decrease due to the current itself but an exponential decrease due to self heating. If I plug some plausible numbers into that equation, I get more than a 1000:1 reduction in life at 20mA vs. 5mA, with the same ambient temperature.

Note that if a relatively high current is only seen with a very short duty cycle (perhaps fitting your application) then the life is hardly impacted. It's the current and temperature integrated over time that causes the deterioration.

Bottom line is that you want to keep the current as low as is reasonable to make the thing work (and since operation is guaranteed at 5mA, that's not a bad place to start). You should also make sure it will work at (say) 3mA so even if it ages a bit it will still continue to work. In some cases you may have to buy more expensive optos with higher CTR than the cheapest ones if you need long life. Anecdotally, there is significant difference between different manufacturers' products. Personally, I tend to stick with the best-known Japanese makers.

With an unregulated power supply, the voltage will vary with the current draw. Motor speed is proportional to voltage, so any given motor will experience speed variation according to the current draw of the other motors. When each motor is switched on, it will draw a higher current than the normal running current. Depending on the motor design, that current could be much higher than the normal running current. With the very small motors described, the high current will likely be very brief and not extremely high. Even with brief surges of current, the speed variation of the other motors may be noticeable.

If the power supply has electronic over-current protection, switching-on motors may cause the power supply to shut off or cut the voltage to protect itself.

If the power supply has enough capacity and speed variations are not a problem, switching several motors on and off should not be a problem. The voltage in a car is not particularly well regulated, but the supply has a large capacity. The many motors for fans, windows, seat adjusters etc. turn on and off with no difficulty. However the voltage drops considerably and the lights dim if the starter motor is operated with the lights on.

I missed the mention of motor driver, one for each motor I assume. With proper use of the motor drivers, any change in the supply voltage due to varying load or raw input supply voltage can be compensated for. Attempting to accelerate a motor too quickly or overloading a motor could still shut the supply down.