Transformerless mains power supplies
- Off-line power supply requires few parts - This simple non-isolated off-line power supply can provide up to 150 mA 5V and uses only a handful of components from 110-230V AC input voltage. Note that the low voltage output is directly connected to the mains; it can not be used when the low voltage part can be touched. Rate this link
- Transformerless mains power supply - This power supply does not really excel in power efficiency, but it is the cheapest and most compact solution for a small power supply. Note that the low voltage output is directly connected to the mains; it can not be used when the low voltage part can be touched. With the component values of the schematic, the circuit can supply 12V /15mA max. Rate this link
- Transformerless supply fits CATV applications - coaxial CATV systems derive their power from a 60-Hz square wave that shares the center conductor with the television channelsm this circuit generates 10 mA at 5V DC from it Rate this link
Transformerless power supplies are very useful in some applications, but remeber that eliminating the transformer eliminates the safety factor. You should this type of power supply only if the circuit you want to power has no external connections to anything else (unless they are properly isolated from the rest of the circuit). Line isolation is essential for safety with respect to electrical shock - no part accessible to the user must be connected to either side of the power line. A regular power transformer provides this isolation automatically.
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