AN954: Off-Line Capacitive Power Supply


* 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:

  • Significantly smaller than a transformer-based power supply.

  • More cost effective than a transformer-based or switcher-based power supply.

  • Power supply is more efficient than a resistive transformerless power supply.

Disadvantages of Capacitive Power Supply:

  • Not isolated from the AC line voltage which introduces safety issues.

  • Higher cost than a resistive power supply.

* Efficiency calculated as (4.1V x 9mA)/(120V x 16mA).


Manufacturer Microchip Technology
Category AC/DC and DC/DC Conversion
Sub-Category AC/DC SMPS - Single Output
Eval Board -
AC Voltage 115 V
Outputs and Type 1 Non-Isolated
Voltage Out 4.1 V
Current Out 9 mA
Output Power 37 mW
Features Soft Start
Efficiency @ Conditions >1%, 120V in, 4.1V @ 9 mA
No-load Input Power @ Voltage 1.92 W @ 120 V
Switching Frequency
Internal Switch
Component Count + Extras 8 + 0
Voltage In 120 VAC
Design Author Microchip
Application / Target Market Power: Auxiliary Power Supply
Main I.C. Base Part
Date Created By Author
Date Added To Library 2011-10