konradIC13
Member
Hello,
Im in middle of a project where i use 6 RC servomotors where 2 are powered from 7.5V and two are powered from 6V, the max current on each of the groups wont exceed 10A (so 20A total for 6 servos).
Servos use PWM signal for setting posision that i get from maestro servo controler.
Due to fact that i need to power servos from two different voltages and they draw high current, while the maestro board allows only one voltage for all of them and is very small, thin traces i decoded to make separate PCB for signal distribution.
It have two inputs, 7.5V from Meanwell SP-200 AC\DC converter and the lower 6V is made from 7.5V from NQR010A0X4 DC\DC converter. Each group of servos is powered by appropriate voltage.
PWM signals from maestro board are delivered to PCB and then directed to appropriate servos.
In addition to that, two digital signals from maestro board are controlling two mosfet transistors SUP50N03 allowing to turn on and off servo power.
Also im reading state of two switches that are connected to PCB with pull up resistors wired to 5V (delivered from maestro board, logic supply voltage).
Worries, doubts?
- i made traces to servos + wide to withstand high current (they are 4mm wide) also i distributed ground with powerplane and tried to do not leave narrow bottlenecks, also the PCB will have 0.125mm copper layer
- logic signal from maestro to mosfet goes through 270 ohm resistor to limit current, also gate is wired to GND with 82k resistor to pull it down (and turn power off) in case something happen to wiring, mosfets are logic lvl type, open with 2.4v and rds(on) 6mili ohms, they have a bit high total gate charge but i im not going to rapidly switch them on/off
- should both 7.5V ground plane and 6V plane be connected together on PCB or make them separate (because they are from same 'source' and they are connected at the AC\DC converter)
-Noise filtration-
the power sources i use are already filtered, i placed PWM signals on the opposite side of PCB than high current traces.
What im worried is noise from servo motors. Motors are not directly connected to power source but they go through stock internal servo electronics (control logic, feedback and h-bridge) and i though about adding just standard 100nF ceramic capacitor between servo supply + and - close to the connector but i started wondering if the capacitor should be placed right between servo connector and mosfet drain pin or should it be placed after mosfet, between voltage input and source pin
- maybe ferrite beads? i have a few of bigger ones that i can wrap around 7.5 and 6v cables coming right from AC\DC converter and some smaller rings that i can wrap around servomotor cables
Im attaching PCB design and schematic
I appreciate feedback and hints
Im in middle of a project where i use 6 RC servomotors where 2 are powered from 7.5V and two are powered from 6V, the max current on each of the groups wont exceed 10A (so 20A total for 6 servos).
Servos use PWM signal for setting posision that i get from maestro servo controler.
Due to fact that i need to power servos from two different voltages and they draw high current, while the maestro board allows only one voltage for all of them and is very small, thin traces i decoded to make separate PCB for signal distribution.
It have two inputs, 7.5V from Meanwell SP-200 AC\DC converter and the lower 6V is made from 7.5V from NQR010A0X4 DC\DC converter. Each group of servos is powered by appropriate voltage.
PWM signals from maestro board are delivered to PCB and then directed to appropriate servos.
In addition to that, two digital signals from maestro board are controlling two mosfet transistors SUP50N03 allowing to turn on and off servo power.
Also im reading state of two switches that are connected to PCB with pull up resistors wired to 5V (delivered from maestro board, logic supply voltage).
Worries, doubts?
- i made traces to servos + wide to withstand high current (they are 4mm wide) also i distributed ground with powerplane and tried to do not leave narrow bottlenecks, also the PCB will have 0.125mm copper layer
- logic signal from maestro to mosfet goes through 270 ohm resistor to limit current, also gate is wired to GND with 82k resistor to pull it down (and turn power off) in case something happen to wiring, mosfets are logic lvl type, open with 2.4v and rds(on) 6mili ohms, they have a bit high total gate charge but i im not going to rapidly switch them on/off
- should both 7.5V ground plane and 6V plane be connected together on PCB or make them separate (because they are from same 'source' and they are connected at the AC\DC converter)
-Noise filtration-
the power sources i use are already filtered, i placed PWM signals on the opposite side of PCB than high current traces.
What im worried is noise from servo motors. Motors are not directly connected to power source but they go through stock internal servo electronics (control logic, feedback and h-bridge) and i though about adding just standard 100nF ceramic capacitor between servo supply + and - close to the connector but i started wondering if the capacitor should be placed right between servo connector and mosfet drain pin or should it be placed after mosfet, between voltage input and source pin
- maybe ferrite beads? i have a few of bigger ones that i can wrap around 7.5 and 6v cables coming right from AC\DC converter and some smaller rings that i can wrap around servomotor cables
Im attaching PCB design and schematic
I appreciate feedback and hints