![]() ![]() Web site Copyright Lewis Loflin, All rights reserved. All NPN Transistor H-Bridge Motor Control.LM334 CCS Circuits with Thermistors, Photocells.Constant Current Circuits with the LM334.Simple Circuits for Testing MOSFET Transistors YouTube.Issues on Connecting MOSFETs in Parallel YouTube.Why Your MOSFET Transistors Get Hot YouTube.Issues on Connecting MOSFETs in Parallel.Test Power MOSFET Transistors, Observations.Build a High Power Transistor H-Bridge Motor Control.More Power MOSFET H-Bridge Circuit Examples.IGBT Based High Voltage H-Bridge DC Motor Control.Arduino Controlled IR2110 Based H-Bridge HV Motor Control. ![]() H-Bridge Motor Control with Power MOSFETs.N-Channel Power MOSFET Switching Tutorial.Understanding Bipolar Transistor Switches.Driving 2N3055-MJ2955 Darlington Transistors.Tutorial Using TIP120 and TIP125 Power Darlington Transistors.ULN2003A Darlington Transistor Array with Circuit Examples.Basic Electronics Learning and Projects.See Part 2: Opto-Isolated Transistor Drivers for Micro-Controllers. In fact we can even change the polarity of the higher voltage supplies without regards to the digital circuit's common negative ground. With opto-isolators we can sever this connection of the higher-voltage power supplies totally from the low-voltage digital circuits if desired. They all have a flaw of having to be electrically connected to low voltage digital circuits. In summery we have looked at a number of bipolar transistor and MOSFET driver circuits. When 5 volts is supplied Q1 switches on dropping the collector voltage to zero. The source terminal (S) is connected to the positive of the power supply and while Q1 is off (no 5 volts in) we have 12-volts on the collector (C) of Q1. In this example we use a P-channel power MOSFET. The only purpose of Rg (10K) is to bleed-off any remaining charge on gate terminal to shut the transistor off. An electrical charge (voltage) on the gate (G) relative to the source (S) will switch on the device. Unlike bipolar transistors MOSFETs are voltage operated devices, not current operated. Here is the basic driver using a N-channel MOSFET. The diodes are used to protect the transistors from surges created when switching magnetic loads. The internal circuits of the above two Darlingtons shows opposite electrical polarities. ![]() In the case of using 12-volts Rc and Rb should be 2200-ohms. (TIP125) When Q2 switches on current flows through Rc switching Q2 on. In the case of using a TIP120 R2 should be 1000-ohms. Here we would say the transistor "sinks" the current. If each transistor had a gain of 100, then to total gain would be 100 X 100 = 10,000. In reality they are two transistors with common collectors and emitter of one tied to the other's base. They have very high gain and require little base current. In this example we are using a NPN Darlington transistor. In many of these transistor circuits R1 ranges from 1000 to 2200 ohms for 5 volts. In this case it's only 100 mA limited by the light emitting diode. If Q1 has a gain of 50 and the base current through R1 is 5 mA, then the collector current will be 250 mA. In this example a digital "HIGH" on the input "sources" a current in the base/emitter of Q1 (limited by R1) which causes a larger current flow in the collector/emitter circuit and through the LED-resistor. The "HIGH" is switched to 5 volts inside the micro-controller "chip" while a "LOW" is switched to ground inside the "chip." Another digital state is known as floating that's as the name suggests is attached to nothing. Note a digital "HIGH" is 5 volts and a digital "LOW" is zero volts. We have a negative battery ground tied to digital ground. It consists of a NPN bipolar transistor controlling a high-power light emitting diode connected to a 12-volt battery. Illustrated above is the most common transistor driver circuit. All of the examples below assume a negative shared common. If we put the switch on the neutral side of the load, we say we "sink" the voltage. When a "switch" supplies a voltage (on the "hot" side) such as a household light switch, we say the switch "sources" the voltage. Also note the concept of sink/source as we go along. On this page we will look at transistor driver circuits using both bipolar transistors and power MOSFETs and will use them as electrical switches. Above illustrates a digital output driving a typical low-power light emitting diodes. Most electrical and electronic devices require voltages and currents that will destroy digital circuits, so we must rely on what I'll broadly call driver circuits. The output of most digital circuits and micro-processors is only five volts at most a few milli-amps. Bi-Polar MOSFET Transistor Driver Microcontroller Interfacing ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |