Servo driver PCA9685 problem solved using multiple motors

Problems solved for PCA9685 in the simultaneous operation of many servo motors.pca9685 fails if all 16 servo operate same time
There are two types of PCA9685 are available. One with a low-power tiny P channel MOSFET (or a high-power MOSFET) which is in series from the DC supply connector as V+. This MOSFET acts effectively like a diode in series to protect the board from reverse polarity accidentally fed. Using a forward-biased diode as traditionally followed in electronic circuits for reverse polarity protection develops a substantial voltage drop of 0.6 to 0.8 volts depending upon the current passing through it. Using a MOSFET with very low RDS causes a smaller voltage drop and a very low I square R loss. MOSFET IRLML6401 used in PCA9685 having RDS of 0.05 causes a voltage drop of only 0.2 volts in 4A current. While if a simple diode use would have caused of about 0.8 volts for the same amount of current.
Moreover, as this tiny P channel MOSFET has a maximum drain current of around 4 A , over drawl results in burning it. Some costly boards use a high power capable of handling much higher current. Thus if a number of high torque servo motors operate simultaneously drawing about say 8 A, the low power PCA9685 simply smokes. Therefore either uses the high power type or carry out some modifications to simple PCA9685. Remove the tiny MOSFET and connect V+ from the connector directly to the servo pins V+ and similarly the ground. One will lose the reverse polarity protection but one can then drive all 16 high torque servos’ simultaneously if required. However, the DC power supply used needs to handle that much current too and the use of an additional filter capacitor accordingly is also required. As a rule of thumb 1000uF electrolytic capacitor for every 1A current. Thus use of 10,000 uF across the DC bus.
The other problem that arises many a time that the back EMF of the DC motors inside the servo motors develop high voltage spikes on the DC bus and if the control circuit like Arduino also gets supply from the same bus it simply resets. Programmers often try to address the same problem by fiddling with code unsuccessfully not understanding the root cause being the hardware. To overcome this problem use a high power switching diode of 4 to 6A in reverse bias connection across the servo dc supply bus

Видео Servo driver PCA9685 problem solved using multiple motors канала Patnaik UC