A phototransistor is an electronic switching and current amplification component that relies on exposure to light to operate, much like how normal transistors rely on electricity to operate. When light falls on the junction of a phototransistor, reverse current flows in proportion to the luminance of the light. This makes phototransistors excellent at detecting light pulses and converting them into digital electrical signals. Unlike normal transistors, they are operated by light rather than electric current, and provides a large amount of utility for a low cost.

Phototransistors work in a similar manner to photoresistors, but can produce both current and voltage, whereas photoresistors only produce current due to the change in resistance. Phototransistors have their base terminal exposed, and instead of sending current to the base, the photons of striking light activate the transistor. This is because a phototransistor is a bipolar semiconductor with its base region exposed to illumination, which focuses the energy that passes through it. Since they are used in almost every electronic device that depends on light. Phototransistors are frequently used in security systems and punch card readers, encoders, IR photodetectors, computer logic circuitry, lighting control, and relays.

Phototransistors come in several different configurations, including common emitter, common collector, and common base, with common emitter being the most frequently used. Compared to conventional transistors, it has more base and collector areas, and is made from gallium and arsenide for high efficiency. The base is the lead responsible for activating the transistor, and is the gate controller device for the electrical supply. The collector serves as the positive lead, and the emitter is the negative lead and the outlet for the larger electrical supply.

The advantages of phototransistors is that they produce a higher current than photo diodes, are relatively inexpensive to manufacture, simple to use, and small enough to fit several of them onto a single integrated computer chip. They are also very fast and can produce nearly instantaneous output (they operate literally at the speed of light, after all), and they produce a voltage, something that photoresistors cannot do. However, because phototransistors are made from silicon, they cannot handle voltages of over 1,000 volts, are more vulnerable to surges and spikes of electricity, and do not allow electrons to move as freely as other devices do, such as electron tubes.

At ASAP NSN Hub owned and operated by ASAP Semiconductor, we can help you find all the phototransistor systems and parts for the aerospace, civil aviation, and defense industries. For a quick and competitive quote, email us at sales@asapnsnhub.com or call us at 1-920-785-6790.


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Field effect transistors (FETs) are used to amplify weak signals, mostly wireless signals. This is useful for aircraft, that often operate dozens if not hundreds of miles away from the signal’s source. A field effect transistor is a type of transistor that alters the electrical behavior of a device using an electric field effect to control the electrical conductivity of a channel. FETs are classified into JFET (Junction Field Effect Transistor) and MOSFET( Metal Oxide Semiconductor Field Effect Transistor). Both are mainly used in integrated circuits, and are similar in operating principles, but different in composition.

JFET is the simplest type of field effect transistor in which the current can pass either from source to drain or drain to source. Unlike bipolar junction transistors, JFET uses the voltage applied to the gate terminal to control the current flowing through the channel between the drain and source terminals which results in output current being proportional to the input voltage. Featuring a reverse-biased gate terminal, JFETs are three-terminal unipolar semiconductor devices used in electronic switches, resistors, and amplifiers. JFETs are more stable than bipolar junction transistors and control the amount of current by the voltage signal. JFETs are broken down into two basic configurations

  • N-Channel JFET: the current flowing through the channel between the drain and source is negative in the form of electrons. It has lower resistance than P-Channel types.
  • P-Channel JFET- the current flowing through the channel is positive and has higher resistance than N-Channel JFETs.

MOSFET is a four-terminal semiconductor field effect transistor fabricated by the controlled oxidation of silicon and where the applied voltage determines the electrical conductivity of a device. In a MOSFET, the gate located between the source and drain channels is electrically insulated from the channel by a thin layer of metal oxide to control the voltage and current flow between the source and drain channels. MOSFETs are used in integrated circuits because of their high input impedance. They are mostly used in power amplifiers and switches, and in embedded system designs.

MOSFETs come in two configurations:

  • Depletion Mode MOSFET: the device is normally ON when the gate-to-source voltage is zero. The application voltage is lower than the drain-to-source voltage.
  • Enhancement Mode MOSFET- the device is normally OFF when the gate-to-source voltage is zero.

Comparing the two, JFETs are easier to manufacture and are less expensive. They are also less susceptible to damage because of their high input capacitance. MOSFETs are able to operate in high noise applications, and can operate in both depletion and enhancement mode, and have a higher input impedance.               

At ASAP NSN Hub, owned and operated by ASAP Semiconductor, we can help you find all the electrical transistors for the aerospace, civil aviation, and defense industries. For a quick and competitive quote, email us at sales@asapnsnhub.com or call us at 1-920-785-6790.


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Multiple instruments inside an aircraft’s cockpit are dependent on AC transducers. Transducers include synchros, resolvers, and linear/rotary variable differential transformers (LVDTs/RVDTs) and are used in numerous applications including navigation reference units, automatic direction finders, distance measurement equipment, and landing gear position and control. Synchros have been used in both commercial and military purposes; they are the transducer of choice when reliability is important and environment conditions are unforgiving.

Synchros and resolvers are essentially transformers in that they have primary winding and secondary winding. Just like a transformer, their primary winding is driven by an AC signal. Synchros, however, have a primary winding and three secondary windings, with each secondary winding mechanically oriented 120 degrees apart. A resolver has two primary windings and two secondary windings, spaced 90 degrees from each other. While electrically similar to transformers, they are mechanically more like motors, where the primary winding in a synchro or resolver can be rotated with respect to the secondary windings. For this reason, primary windings are also called rotors, while secondary windings are referred to as stators, due to their fixed position. In an automatic direction finder (ADF), the resolver or synchro is used to drive an indicator. As the aircraft turns the amount of coupling in the transducer changes proportionally, thus indicating for the pilot just how far their aircraft has actually turned.

Synchros are used to track the rotary output angle of a closed-loop system, which uses  feedback to achieve accuracy and repeatability. A synchro can be turned continuously, and since its secondary winding outputs are analog signals, provide infinite resolution output. As the shaft of a synchro turns, the angular position of its rotor winding changes in comparison to the secondary (stator) windings. The relative amplitude of the resulting AC output signals from the secondary windings indicates the rotary position of the synchro’s shaft.

The analog output signals that synchros generate must then be converted into digital form by a synchro-to-digital converter. Conventional analog-to-digital converters do not work well in this task, as synchros have inductive characteristics that affect such readings, synchro output signals can be distorted due to nonlinearities in the synchro and phase-shift the transducer, and synchro output signals typically contain lots of electric noise due to their working environment. Therefore, a synchro-to-digital converter must use transformer-isolated inputs and outputs.

At ASAP NSN Hub, owned and operated by ASAP Semiconductor, we can help you find all the synchros, resolvers, and transducers systems and parts for the aerospace, civil aviation, and defense industries. For a quick and competitive quote, email us at sales@asapnsnhub.com or call us at 1-920-785-6790.


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