App note: How to implement an SCR or a Triac in hybrid relay applications


Another app note from STMicroelectronics on SCR or Triac hybrid with mechanical relay to decrease power loss and manage inrush current. Link here (PDF)

This document gives some key information about the design of the solid-state silicon AC switch stage of a hybrid relay, which can drive resistive, capacitive or inductive AC loads, such as: heater resistors, motors for industry, power tools or appliance applications.

App note: AC switches – Is a positive power supply mandatory for my application, or could a negative output work also?


App note from STMicroelectronics about the usage of a negative supply in controlling AC switches and their benefits, Link here (PDF)

In this application note we explain the reasons why some appliance designers might choose a positive power supply. This selection is based mainly on the choice of switched mode power supply (SMPS). Some specific applications cases, may also lead to the choice of a positive power supply.

Using a power supply with a positive output is not convenient for all applications. For example, a negative supply is preferred to drive AC switches. We provide here an alternative solution which allows a negative output to be implemented whenever possible. Further, many solutions allow both a negative and a positive output (for the microcontroller) to be implemented.

App note: How to select the Triac, ACS, or ACST that fits your application


Choosing the right AC switch for your application based on specification like current rating, voltage rating and triggering quadrant. Here’s an app note from STMicroelectronics to guide you on selecting the right part. Link here (PDF)

This document gives basic guidelines to select the AC switch device according to the targeted application requirements. These guidelines will allow the appropriate Triac, ACS or ACST to be selected, for most of the applications. Some very specific cases could require a higher level of expertise to ensure a reliable and efficient operation.

App note: A logic-level transient-voltage protected AC switch


STMicroelectronics’ AC switch directly controlled by microcontroller. Link here (PDF)

Home appliances such as washing machines, refrigerators and dishwashers employ a lot of low power loads such as valves, door lock systems, dispensers or drain pumps. Since these loads are powered by the mains in ON / OFF mode, they were initially controlled by relays. Recently, relays have been replaced by triacs, due to their smaller size and lower driving energy. Nevertheless triacs don’t fulfill alone the new requirements that users now need and are used with others components.

Power switches must now be directly driven by a microcontroller unit (MCU) and must be robust to withstand the A.C. line transients so that systems may fall into line with electromagnetic compatibility (EMC) standards. ACSs (for Alternating Current Switches) have been designed with this goal mind, i.e. to offer logic level and more robust semiconductor devices.