* From page 10 of AN954:
Figure 10 shows a capacitive power supply with several UL considerations designed in. A fuse is added to protect the circuit during an over-current condition.
Adding R2 in parallel with C1 creates a filter that will attenuate EMI from traveling back onto the line. A varistor, or MOV, provides transient protection.
Advantages of Capacitive Power Supply: - 1. Significantly smaller than a transformer-based power supply.
- 2. More cost effective than a transformer-based or switcher-based power supply.
- 3. Power supply is more efficient than a resistive transformerless power supply.
Disadvantages of Capacitive Power Supply:
- 1. Not isolated from the AC line voltage which introduces safety issues.
- 2. Higher cost than a resistive power supply.
* Efficiency calculated as (4.1V x 9mA)/(120V x 16mA).
