In electronics, two anti-parallel or inverse-parallel devices are connected in
parallel but with their
polarities reversed.
One example is the
TRIAC, which is comparable to two
thyristors connected back-to-back (in other words, reverse parallel), but on a single piece of
silicon.
Two
LEDs can be paired this way, so that each protects the other from
reverse voltage. A series string of such pairs can be connected to AC or DC power, with an appropriate resistor. Some two-color LEDs are constructed this way, with the 2 dies connected anti-parallel in one
chip package. With AC, the LEDs in each pair take turns emitting light, on alternate half-cycles of supply power, greatly reducing the
strobing effect to below the normal
flicker fusion threshold
The flicker fusion threshold, also known as critical flicker frequency or flicker fusion rate, is the frequency at which a flickering light appears steady to the average human observer. It is a concept studied in vision science, more specificall ...
of the
human eye
The human eye is a sensory organ in the visual system that reacts to light, visible light allowing eyesight. Other functions include maintaining the circadian rhythm, and Balance (ability), keeping balance.
The eye can be considered as a living ...
, and making the lights brighter. On DC, polarity can be switched back and forth so as to change the color of the lights, such as in
Christmas lights that can be either white or colored.
Battery-powered lights, which are wired in parallel, can also create a simulated "chasing" effect by alternating the polarity for each LED attached to the string, and controlling the positive and negative parts of the cycle separately. This creates two "virtual circuits", with odd-numbered LEDs lighting on positive polarity and even-numbered ones on negative polarity, for example. By eliminating the need for extra wires, this reduces costs for the manufacturer, and makes the cords less bulky and obvious for the consumer to string on decorative items. On cheaper sets, this causes strobing and prevents any of the LEDs from getting to full brightness, since both polarities share the same wire pair and cannot be active at the same time, meaning each can only be on during its own half of the cycle. Better lights can adjust the
duty cycle so that any unused "off" time on one polarity can be used by the other, reducing the strobing effect and making it easier to create color blends (such as orange, amber, and yellow from a red/green LED).
ESD
Antiparallel diodes are often used for
ESD protection in
ICs. Different ground or supply domains at the same potential or voltage may be wired separately for isolation reasons. However, during an ESD event across the domains, one would want a path for the high current to traverse. Without the antiparallel diodes in place, the voltage induced by the ESD event may result in the current following an unknown path that often leads to damage of the device. With the diodes in place the current can travel in either direction.
See also
*
Bidirectional LED
*
Charlieplexing
References
{{reflist
* https://www.researchgate.net/post/Why_are_diodes_connected_anti-parallel_across_the_MOSFET_or_IGBT_in_Inverter_Module
* https://www.utdallas.edu/~torlak/courses/ee3311/lectures/lecture3.pdf
* https://ieeexplore.ieee.org/document/4159554/
* https://www.scientific.net/AMR.328-330.32
Electronic circuits