AN1172

Conclusion

15/23

Conclusion

ACS retains the well-known advantages of the triac (high AC voltage blocking capability,

current bidirectionality) and adds high over-voltage robustness and the increased reliability

and compactness that appliance manufacturers now need.

Thanks to the clamping capability and robust break-over characteristics of the ACS

structure, the protection circuits that are usually connected in parallel with the triacs, are no

longer required. The varistor removal increases automatically the reliability of the electronic

board. And the snubber removal allows designers to be free with the dV/dt at off state and

dI/dt at turn-on trade-off when choosing an R-C circuit.

In addition, the triac gate-drive transistor and its associated resistors are also redundant

because ACS devices have built-in logic level drive circuits that allow the power switch to be

safely driven from any MCU output pin capable of sinking 20 mA without over-stressing the

micro-controller output.

Hence, the typical component count falls from eight with triacs, down to two with ACSs (see

Figure 16.).

The new ACS devices represent a real breakthrough in the design of power switches for

home appliances. The enhanced performance, for example their robust off-state and logic

level drive, allied to their inherent compactness will open new perspectives in the design of

compact and reliable electronic power controllers.

Figure 16.

Component count reduction thanks to ACS

References

1.

P.Rault, "Triacs for Home Appliances: present and future", PCIM forum, Honk Kong, pp.

57-65, 1998.

2.

E.Leblanc, "Thyristors and Triacs, an Important Parameter: the Holding Current",

Application Note n°302, STMicroelectronics, February 1989.

3.

P.Rault, "Improvement in the Triac commutation", Application Note n°439,

STMicroelectronics, May 1992.

4.

SCR Manual, General Electric, 6th Edition, 1979.

Vcc

Vcc

ACS

MCU

MCU