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AFE3010: Power conversion from AC to DC - AFE3010

Prahaladh S
Prodigy 50 points
Part Number: AFE3010

Tool/software:

Hi,

Greetings...

I have gone through the datasheet of AFE3010. In the application diagram, I have seen that the phase of AC is directly connected to bridge rectifier (a resistor is connected for current limiting) & given to the VDD of the IC. 

From the specs, I understand that the max. voltage of VDD is 26V & this IC used in 230V & 120V AC applications.

As per my understanding, the input AC needs to be stepped down before rectifying. If AC step down isn't there, then the input AC will be rectified. For example, 120V AC will be available as ~170V DC after rectification.

Kindly guide me in understanding how the AC is stepped down in the circuit shown in the application diagram of AFE3010 IC.

Best Regards,

Prahaladh S

  • 0
    TI__Mastermind 29555 points

    Hey Prahaladh,

    Thank you for your question. I can understand the question.

    inside the device is a 20-V Zener regulator. The rectifier full wave rectifies, and the approximate 18-24kOhm and 3.3uF input low pass filter smooths out the rectified signal enough so that Zener remains in a stable reverse breakdown mode.

    if AC voltage increases, there will be increased current into VDD pin and this regulator and thus increased power dissipated across input resistors. However internal 20-C supply will remain the same.

    Sincerely,

    Peter

  • 0 in reply to Peter Iliya
    Prodigy 50 points

    Dear Peter,

    Thank you so much for your response.

    Curious to know, how the AC voltage from 120V be stepped down to a lower voltage before the rectifier without the use of a step down transformer.

    Kindly provide your comments on the same.

    Best Regards,

    Prahaladh S

  • 0 in reply to Prahaladh S
    TI__Mastermind 29555 points

    Hey Prahaladh,

    The AC Line voltage does not need to be stepped down. The internal Zener regulating diode help keep VDD clamped to 20V. The resistors help limit input current, the capacitor helps smooth the rectified close to DC, and the Zener goes into reverse breakdown to keep VDD stable at 20V. 

    This means that RMS currents into VDD pin (into Zener) can be relatively high as R decreases, but keep under 15mArms.

    Sincerely,

    Peter