Physics Electronics PMDC Conceptual Practice
PMDC Verified Question 207 of 494
Why must a smoothing filter capacitor in a DC power supply be connected in parallel (shunt) with the load resistor rather than in series with it?
A
A series capacitor would increase the peak DC current delivered to the load
B
A series capacitor blocks steady DC current entirely, preventing DC power from reaching the load
C
A shunt capacitor amplifies AC ripple to match the load impedance
D
A series connection causes the transformer to overheat and short-circuit
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: A series capacitor blocks steady DC current entirely, preventing DC power from reaching the load
Concept:

Capacitors block steady DC current (\( X_C = \frac{1}{2\pi f C} \to \infty \text{ as } f \to 0 \)) while providing a low-impedance path to ground for AC ripple components.

Formula:

$$X_C(f = 0\text{ Hz}) = \infty \quad (\text{Open circuit to DC})$$

Solution:

  • Connecting a capacitor in series with the load creates an open circuit for DC, preventing direct current from reaching the load.


  • Connecting the capacitor in parallel (shunt) allows DC to pass freely through the load while routing AC ripple through the capacitor to ground.


Why other options are incorrect:

  • Option A: A series capacitor blocks DC rather than increasing it.
  • Option C: Shunt capacitors attenuate (smooth) ripple rather than amplifying it.
  • Option D: A series capacitor acts as an open circuit to DC and does not short-circuit the transformer.

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