Author: John Mulindi
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DC Motor Power Op-amp Speed Controller
Let’s consider the functional diagram below: The D/A converter outputs a voltage directly related to the potentiometer position. However, the D/A converter’s output current is limited and not enough to drive a motor. A power operational amplifier (op-amp) circuit, configured as a noninverting amplifier can drive the motor at the higher currents required. In effect,…
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Power MOSFET Motor Control
Because of the very high input gate resistance of MOSFETs, MOSFET’s fast switching speeds, and the ease at which they can be driven makes them ideal to interface with op-amps or standard logic gates. Nevertheless, care must be taken to ensure that the gate-source input voltage is correctly chosen because when using the MOSFET as…
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Metal Oxide Semiconductor FET (MOSFET)
The Metal oxide semiconductor FET (MOSFET) also known as the insulated-gate FET (IGFET) is similar to JFET but exhibits even larger resistive input impedance due to the thin layer of silicon dioxide that is used to insulate the gate from the semiconductor channel. This insulating layer forms a capacitive coupling between the gate and the…
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The Junction Field Effect Transistors (JFET)
The bipolar transistor has several disadvantages: it has low input impedance because of forward biased emitter junction, it has small high-frequency gain, it has considerable noise level and it is non-linear when |VCE| < 2V. Although low input impedance problem may be improved by careful design and use or more than one transistor, even so…
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Bipolar Junction Transistors (BJT)
By placing two PN junctions together we can create a bipolar junction transistor. In a PNP transistor the majority charger carriers are holes and typically germanium is favored for these devices. In NPN transistors the majority charger carriers are electrons; for this case, silicon is typically used. The thin and lightly doped central region is…
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Multiplexers and Demultiplexers in Digital Circuits
Multiplexers and demultiplexers are devices that route signals. A multiplexer also called a data selector takes one of several inputs and connects it to a single output. The input line that is connected is determined by the binary applied to the address lines. The diagram below shows a multiplexer with four input lines: The two…
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Basic Features of Power Semiconductor Controlled Drives
Power electronics deals with the applications of solid state electronics for the control and conversion of electric power. The conversion systems require switching power semiconductor devices on and off. The key components of an electric drive controlled by a power semiconductor converter are illustrated in the figure below: The converter regulates the flow of power…
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How to calibrate a dc voltmeter
An instrument may be calibrated by comparing its reading with that of a more accurate instrument when both are measuring the same quantity. The more accurate instrument is used as a standard for comparison purposes. The figure below illustrates the method for calibrating a dc voltmeter. An appropriate dc voltage level is applied from the…
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How to calibrate a dc ammeter
The figure below shows two dc ammeters connected in series, so that they are both measuring the same current. An ammeter may be calibrated by comparing it to a more accurate (standard) ammeter measuring the same quantity. The accuracy of the standard instrument should be at least four times better than the instrument to be…
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What are PLC-Based Water Treatment Plants?
Most of the water treatment plants in the previous decade were manually operated. However, they were automated to a certain degree using relays or electrical control panels but the system was not reliable and required a lot of space. In this modern era, water treatment facilities are automatically operated using PLC or Programmable Logic Controllers…