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Does a RS485 bus preferably have a common ground between connected devices?
Since a RS485 bus uses differential signals between two bus wires I would think not, but reading online comments on chip failures I now think otherwise. Correct?
EDIT: this is with a common power supply for all...
I shouted "victory" too soon: a ripple in approx. 1.5V ac bursts is measured accross the 15V_dc and 7V zener lines when using a transfo centre tab feeding the 7805.
When removing the 7805 from the centre tab then the ripple is gone.
Picture 1: start-up of power supply (yellow = 45V dc...
And ronsimpson Many thanks for those inputs! I changed the LM1117 to a 7805 and a 470µF/35V capacitor on its output, transfo centertab to 7805, and bingo: 5V_dc, virutally no ripple with a load of 100mA.
Magnificent.
I will modify my design to this idea. So no more risk of fireworks at the...
Here is the image from my scope:
1. yellow = rectifier output (45V dc) (10V/div)
2. turquoise = 15V dc line (5V/div)
3. purple: Q1 base (5V/div)
4. blue: 5V zener cathode (2V/div)
20ms timebase (ie @50Hz 2 phasecrossings per 10ms)
I guess the hiccups in the yellow line are the 50Hz...
The 45V is needed for the regulated power supply, which is the actual purpose of this circuit. The design calls for a maximum output voltage of 35 ~40V dc.
The 5V is used for a microcontroller, ina219 current measurement module, temperature measurement modules, LCD display, ...
When my circuit...
Every rare now and then this circuit blows up in smoke on power start-up.
The LM1117 gives fireworks and TIP120 (Darlington) is bust too. All else is ok.
I suspect that on start-up, rarely, the C1815 does not fast enough regulate the base voltage of the TIP120 and subsequently allows the 48V to...
In my posts #17, 18 and 19 I showed how GND of the controller is not connected to PCB and supply GND.
Somehow in my Eagle symbol for this controller I had the GND pins as "nc", ie "not connected", while the symbol VCC pin is connected to "pwr".
This results in Eagle automatically connecting the...
danadak , that is a good idea.
My OP addressed a very specific issue that does not need another design concept. The other posters in this thread have put me on the track to the solution which is great.
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