Bypass Diodes which in electronics we know as free-wheeling diodes, are wired in parallel with individual solar cells or panels, to provide a current path around them in the event that a cell or panel becomes faulty or open-circuited. This allows a series (called a string) of connected cells or panels to continue supplying power at a reduced voltage rather than no power at all.
When used as an AC signal amplifier, the transistors Base biasing voltage is applied in such a way that it always operates within its “active” region, that is the linear part of the output characteristics curves are used. However, both the NPN & PNP type bipolar transistors can be made to operate as “ON/OFF” type solid state switches by biasing the transistors base differently to that of a signal amplifier.
A free, easy-to-use computer-aided design software package for Windows platform, that lets you design printed circuit boards of professional quality very quickly
Now that we know what is an LED, we need some way of controlling it by switching it “ON” and “OFF”. The output stages of both TTL and CMOS logic gates can both source and sink useful amounts of current therefore can be used to drive an LED. Normal integrated circuits (ICs) have an output drive current of up to 50mA in the sink mode configuration, but have an internally limited output current of about 30mA in the source mode configuration.
Although a 7-segment LED display can be thought of as a single display, it is still seven individual LEDs within a single package and as such these LEDs need protection from over current. LEDs produce light only when it is forward biased with the amount of light emitted being proportional to the forward current.
An Optocoupler or opto-isolator as it is also called, is a single electronic device that consists of a light emitting diode combined with either a photo-diode, photo-transistor or photo-triac to provide an optical signal path between an input connection and an output connection while maintaining electrical isolation between two circuits.