Miscellaneous Devices

Miscellaneous Devices:

Thermistor Operation : The word thermistor is a combination of thermal and resistor. A thermistor is a resistor with definite thermal characteristics. Most thermistors have a negative temperature coefficient (NTC), but positive temperature coefficient (PTC) devices are also available. Thermistor Operation are widely applied for measurement and control of temperature, liquid, level, gas flow, etc. Silicon and germanium are not normally used for thermistor manufacture, because larger and more predictable temperature coefficients are available with metallic oxides. Various mixtures of manganese, nickel, cobalt, copper, iron, and uranium are pressed into desired shapes and sintered (or baked) at high temperature to form thermistors. Electrical …


Tunnel Diode Operation and Characteristics : Tunnel Diode Operation – A tunnel diode (sometimes called an Esaki diode after its inventor, Leo Esaki) is a two-terminal negative resistance device that can be employed as an amplifier, an oscillator, or a switch. Recall from earlier topics that the width of the depletion region at a pn-junction depends upon the doping density of the semi-conductor material. Lightly doped material has a wide depletion region, while heavily doped material has a narrow region. A Tunnel Diode Operation uses very heavily doped semiconductor material, so the depletion region is extremely narrow. This is illustrated in Fig. 21-12 …


Tunnel Diode Parallel Amplifier Circuit : For operation as an amplifier, a tunnel diode must be biased to the center of its negative resistance region. Figure 21-17(a) shows the basic circuit of a Tunnel Diode Parallel Amplifier Circuit. Load resistor RL is connected in parallel with diode D1 and supplied with current from voltage source EB and signal source es. Figure 21-17(b) uses the tunnel diode piecewise linear characteristics to show the dc conditions of the diode when the signal voltage is zero (es = 0), and when es = ±100 mV. The current gain equation for a Tunnel Diode Parallel Amplifier Circuit can …


Voltage Variable Capacitors : VVC Operation – Voltage Variable Capacitors diodes (VVCs) are also known as vari­caps, varactors, and as tuning diodes. Basically, a Voltage Variable Capacitors is a reverse biased diode, and its capacitance is the junction capacitance. Recall that the width of the depletion region at a pn-junction depends upon the reverse bias voltage, (Fig. 21-1). A large reverse bias produces a wide depletion region, and a small reverse bias gives a narrow depletion region. The depletion region acts as a dielectric between two conducting plates, so the junction behaves as a capacitor. The depletion layer capacitance (Cpn) is proportional to …


Updated: May 1, 2020 — 1:15 pm