AN3168 Datasheet, PDF (1/20 Pages) STMicroelectronics – In alternating current applications

AN3168
Application note
Non-insulated SCR / Triac control circuits
Introduction
In alternating current applications the direct current power supply for low-voltage electronic
devices (MCU, LEDs, optocouplers, Triacs and so on) can be provided using one of several
different circuits. There are traditionally two major types of power supplies used in
appliances, capacitive power supply and linear power supply using a step-down transformer.
Today, designers are using more and more switches mode power supplies (SMPS) to
achieve higher output current levels and especially lower standby power consumption. The
power supply choice is a trade-off between several parameters. These are the cost, the
required power, the output voltage level and polarity, the standby power consumption and
the necessity or not of an electrical insulation between the mains and the low output DC
voltage.
This application note considers only non-insulated power supplies. After a brief description
of the triggering quadrants and key parameters for SCR, Triac, ACS and ACST, the usual
control circuits are described according to the output voltage polarity of the power supply.
Finally, some examples of negative power supply circuits are introduced.
March 2010
Doc ID 17193 Rev 1
1/20
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