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Attached is the block diagram of my circuit. Input is 230 VAC. A SMPS module converts it to 14 VDC. The on board regulator then converts it further to 3.3 V.

I have observed that many times when I switch off the main 230 V, my controller reset firsts and then finally it turns off.

I have MOV and an inductor on 230 V line and decoupling capacitors on PIC power input. Any suggestions?

  • \$\begingroup\$ Add caps on PIC power lines , both 0.1uf and 0.01 uf, may this help \$\endgroup\$ – Bharav Jun 9 '16 at 6:55
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    \$\begingroup\$ Maybe post a proper schematic instead of a block diagram, and show the configuration bits, then we can see, for example, if your MCLR may be implicated. \$\endgroup\$ – Roger Rowland Jun 9 '16 at 7:45
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    \$\begingroup\$ Do you mean that it resets and then carries on running for a short while before completely losing power? \$\endgroup\$ – brhans Jun 9 '16 at 11:17
  • \$\begingroup\$ Yes, After turning off main 230V. Controller reset and whole system shut down.I have a LCD connected so I can see controler get reset before system completely got off. any way I added on 0.01uf cap on 230V entrance in my board that solved my problem. But even I have reset problem whenever i connect my RS232 db9 connector to my board to communicate to pc \$\endgroup\$ – Transformer Jun 9 '16 at 16:44

There are following possible explanations:

  1. Make sure Brown Out Reset is disabled for your chip.
  2. Check your MCLR pin connections. It should have the following circuit:


simulate this circuit – Schematic created using CircuitLab

The exact values of of R1, R2 and C1 will vary as per your chip (consult the datasheet's reset section for that). But more or less this circuit acts as a low pass filter, thereby small disturbances in the power-line does not resets your PIC.

  1. After the 14V supply and 3.3V supply add large decoupling capacitors (of the order of ~50 uF or more). Also add 33 (or 22) pF capacitors along side large capacitors. The large one acts as 'local' charge reservoirs, so any small variations in the input side does not directly effect your digital supply. The large one acts as high pass filter. The little (33 or 22 pF) ones act as high pass filters suppressing any high frequency noise.
  2. You said you have decoupling capacitors on the PIC power input. That's good. But what are the values?

Please provide more information regarding your circuit diagram and your configuration bits and i will update my answer accordingly.


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