AN3168 Datasheet, PDF (19/20 Pages) STMicroelectronics – In alternating current applications

AN3168
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Conclusion
Conclusion
This application note has presented circuits that can be used to control SCR, Triacs or
ACS / ACST devices, as far as a non-insulated circuit is allowed.
It has been shown that a negative power supply is the best topology as it can be used for all
AC switches. Moreover if an SCR has to be controlled with a board using a negative supply
to trigger AC switches, a simple schematic has been presented to control the SCR with the
same supply.
Schematics for negative switched mode power supplies have been presented.
Even if the first reflex of a designer is to implement a positive power supply, negative power
supplies are as easy to implement as positive ones. There are also some benefits with a
negative supply topology such as, for example, the removal of output overvoltage protection
for non-insulated SMPS (buck-boost topology compared to buck topology), optotransistor
removal (for flyback converters) and the use of NPN transistors instead of PNP to amplify
the gate current.
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References
1. “Latching current”, Application note AN303, STMicroelectronics.
2. “QII and QIII Triac triggering with positive power supply”, Application note AN440,
STMicroelectronics.
3. “VIPower: Low Cost Power Supplies Using VIPer12A in Non Isolated Applications”, N.
Aiello - F. Gennaro - R. Santori, Application note AN1357, STMicroelectronics, 2001.
4. “Discontinuous Flyback transformer description and design parameters”, Technical
note TN0023, STMicroelectronics.
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Revision history
Table 7. Document revision history
Date
Revision
09-Mar-2010
1
Initial release.
Changes
Doc ID 17193 Rev 1
19/20