I am working on interfacing CT to PIC 18f4550 controller. Please find below my rough circuit diagram. my questions are

i)the Recommended Secondary Burden is 47 ohm. i have used in my circuit as 200 ohm is it advisable?

ii) is the below circuit is reliable and better way for interface with micro controller

iii)is there any modifications can be done to make it better?

I am using electrohms CT-1169 max i/p 60A rms,turns 1:7000,suggested burden resistor 47 ohm for datasheet [1] http://www.electrohms.com/data_pdf/CT1169_01.PDF


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ Read the small print at the bottom of the brochure \$\endgroup\$ – Andy aka Jul 10 '13 at 17:07

Some remarks:

  • when 47 Ohm is recommended, why choose 200 Ohm??
  • IIRC the recommended maximum source impedance for the A/D is 2.5k, the DC impedance of your devider is 5k. If power is not a problem I would take two 1k resistors.
  • that direct line from the trafo to the A/D input pin makes me nervous. I would add a series resistor (1k) and two (schottky) diodes for protection, and maybe a capacitor too.

For an explanation of resistor-diode-diode for input protection read what-kind-of-diode-to-use-with-adc-inputs.

| improve this answer | |
  • \$\begingroup\$ i have now understood the importance of source impedance, if source impedance of adc is greater than 2.5 will affect the acquisition time.ya surely i will change it to 2.5k .1) I didn't understood importance of burden resistance , will increasing the value, affect my performance/resolution ???.2)what's c1 capacitor value i should choose ?. 3) if possible could u so some example to use schokkty diode & capacitor to adc input to improve my understanding \$\endgroup\$ – tamil_innov Jul 10 '13 at 14:49
  • \$\begingroup\$ FWIW, the AC source impedance of the input to the MCU ADC will have a much lower impedance, depending on the capacitance of C1. If he's not running the ADC continuously, it'll probably be fine. \$\endgroup\$ – Connor Wolf Jul 11 '13 at 4:23
  • \$\begingroup\$ True, but no value for C1 is shown, so I can't rely on it. \$\endgroup\$ – Wouter van Ooijen Jul 11 '13 at 5:39

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