How to implement negative SMPS for AC switch control
Almost all appliances need a power supply to convert the 100-130 or 220-240 V AC mains voltage to a 3.3 or 5 V DC voltage to supply board electronics. A new regulation to the ECO conception directive (2005/32/EC) and applied for energy using products (or EuP) specifies that the maximum standby-mode or off-mode power consumption has to be between 1 or 2 W by 2010, and below 0.5 or 1 W by 2013. This new regulation will push appliance electronics designers to implement switched mode power supplies (SMPS). SMPS circuits are more often used to provide a positive output voltage. This paper explains that negative power supplies are preferred when AC switches such as snubberless Triacs, ACS and ACST devices are controlled by the electronics board. We present some negative power supplies which are indeed as simple to implement as positive ones.