This is the circuit I have been analyzing. enter image description here

My intention is to calculate the output voltage at the resistance RL when the center tap is removed.

With center tap connection, output voltage VRL(DC) is calculated is given below, enter image description here When center-tap is removed, my understanding,

Secondary output voltage will be the sine wave with peak voltage = 1.414 * 12V = 16.968 V. At the positive voltage diode D3 will conduct and negative cycle D2 will conduct. So each output would be equivalent of half-wave rectifier.

Output (VRL(DC)) voltage (DVM reading) would be = 16.968 V - 0.7 V = 16.268 V

( Note: The reason I am taking the peak voltage as the output voltage is due to the high output capacitance (470 µF). That is why I am not using the average voltage equation Vp/π)

Can you please review the output voltage calculation when the center-tap is removed?


The centre tap is a low impedance source coupled to the primary low impedance.

The load R's are fairly high impedance. When the caps and load R's equal, there is no difference.

To keep the voltages balanced with a mismatched load, the source impedance must be low.

We call this mismatch from loads, load regulation error where the error is due to the voltage divider % (Rs/(Rs+Rl)) that is if one knows the source and load equivalent R's for transformer and diodes.

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  • \$\begingroup\$ So the my understanding is there wont be any change in the output voltage after ,that is it would be 7.1 V after removing the center tap. Also what will happen if one of the load is changed ( example - increase to 10 k or reduce to 1 k) ? \$\endgroup\$ – student7 Nov 28 '19 at 4:05
  • \$\begingroup\$ What does Ohm’sLaw Law tell you? \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Nov 28 '19 at 4:14
  • \$\begingroup\$ Honestly I don't know hoe to apply Ohm's law in that situation. \$\endgroup\$ – student7 Nov 30 '19 at 0:26
  • 1
    \$\begingroup\$ If you remove the tap, so by definition Ground =0V and V+,V- becomes unbalanced if current flows thru R+,R- But if both are the same , then equal. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Nov 30 '19 at 0:29

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