Ranbeer Singh
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2. Will need of copper ground pour in case of 1Hz circuit?In general resistors are relatively robust against overvoltge and they limit current and divide voltage.. additionally they transform the electrical energy into heat.
Not for a 1Hz circuit as such. But you need stronger ground connections to handle the output currents claimed in the schematic. And you surely need it if you start to add serious ESD and surge protection.Will need of copper ground pour in case of 1Hz circuit?
Did you follow a single point of my recommendations of post#4?
* no GND plane, even a copper pour is far away from being a solid GND plane.
* capacitors are missing, pin32 of PIC isn't connected at all (it's not by accident called VCC)
* you did feed the complete output GND (including ESD) current explicitely under the PIC with a thin wire
* HF filters are only on the signal input lines
* overvoltage filters are missing completely
* LPF filters on sensitive lines are missing completely
Sorry, i have to say it's far away from being a reliable design
******
What's the purpose of Q1?
You have a lot of current at the outputs. Did you follow it's path (it doesn't stop at the ULNs). Did you calculate trace width?
A 1000uF input capacitor will cause a lot of input current when connected to 24V.
GND pins are missing at the input connector and the output connector.
Did you calculate the power dissipation of the output pullup resistors?
Not for a 1Hz circuit as such. But you need stronger ground connections to handle the output currents claimed in the schematic. And you surely need it if you start to add serious ESD and surge protection.
The 0.5/1.0/1.5 A output current specifications are not substantiated by ULN2003 datasheet, by the way. 0.5 A is only valid for one activated output, review the allowable collector current graph.
State-of-the-art suggests short circuit and overcurrent protected smart power switches instead of ULN2xxxx.
--> the capacitor at pin 32 is missing* what capacitors am i missing? Pin32 of controller is VCC and my software connect all same name net pins to each other automatically.
post#4: * HF filtering on each line leaving the PCB* where will need of HF filters except to inputs?
If yo want it small, then use SMD. This additionally increases the chance for a two layer PCB, becuase the pin´s don´t split the GND plane at the bottom side. But it´s no guarantee.* I wanted to make my PCB small as possible. So I skipped knowingly those circuits.
I don´t like switches in the GND line of a power supply. If the switch is open, then you loose GND as reference. This may cause that the resistive dividers at the 24V signal input don´t work anymore.* I used Q1 for power input polarization inversion protection.
Calculate the inruh current. I assume it easiyl can be well above 50 Ampres. Is your design made for this?* what will be wrong with 1000uf capacitor?
No. It´s not nice. IT IS URGENT! Otherwise all the load current is flowing across the complete PCB.* Ground pins with input output connectors is nice prectice. I will implement it.
Did you calculate dissipated power? Can your resistors withstand it?* I do not know pullup resistence calculation according to ULN. Please explain.
Unfortunately the circuit doesn't work. The MOSFET should be turned on with correct polarity and turned off for inverted input voltage, but it isn't. Use a PMOS switch in positive supply line or a NMOS switch in negative supply line to achieve the intended effect.I used Q1 for power input polarization inversion protection.
That's correct, but you need to consider the derating given in the datasheet. The current values written in your schematic can't be achieved.However the ST ULN2003A datasheet says that "Output can be paralleled for higher current outputs". Is it not correct?
post#4: * HF filtering on each line leaving the PCB
Input as well as outputs and power. At least for a good EMV design, where cable induced high voltage/ high frequency signals may affect your circuit.
I don´t like switches in the GND line of a power supply. If the switch is open, then you loose GND as reference. This may cause that the resistive dividers at the 24V signal input don´t work anymore.
--> Check signal integrity when Q1 is open.
I agree. Your signals.But in my circuit no more current & no high frequency.
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