Figure 1 shows a simple block using an NPN transistor driving an SMA (electronic muscle) up to 2 A. This circuit needs 20 mA to drive an 1 A SMA and less to drive lower-current muscles. TTL and CMOS outputs can drive low-power SMAs using this block. For higher gain, driving loads up to 1 A from TTL or CMOS outputs, you can replace the transistor with a BD135 or BD137. In any case, the transistor must be mounted on a heat sink.
Figure 1 – Shield for SMA using a PNP transistor
