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Basic Circuits and Circuit Building Blocks From Open Circuits Jump to: navigation, search These are circuits and parts of circuits that we see over and over again in larger projects. Understanding a complex circuit is much easier if you understand these building blocks. Operational amplifier are the basis for many circuit building blocks especially in the range of DC to 1 meg Hz. See OpAmp Links. 1 Introduction and Page Status.... 2 Amplifiers 3 Current Sense Resistor ( Shunt Resistance ) 4 Current Limit or Constant Current ( Transistor Based ) 5 Filter Capacitor / Decoupling Capacitor / Low Pass Filter 6 High Side Switch 7 Light Emitting Diode ( with current limiting resistor ) 8 Op amp Non Inverting Amplifier 9 Op amp Unity Gain Buffer 10 Parallel Circuit 11 Pull Up and Switch 11.1 ToDo 12 Pull Down and Switch 13 Relay with Diode Snubber 14 Three Terminal Regulator 15 Transistor Low Side Switch 16 Transistor High Side Switch 17 Transistor Emitter Follower 18 Transistor -- Push Pull Circuit 19 Transistors -- Darlington connected 20 Transistors -- Sziklai pair 21 RC Filter 22 Series Circuit 23 Seven segment LEDs 24 Schmitt Trigger 25 Oscillators 26 Power up low active reset circuit 27 ADC Voltage Protection Circuit 28 Voltage Divider 29 Voltage Divider using a Light Dependent Resistor 30 Wheatstone Bridge 31 Further Reading Introduction and Page Status.... ( Some of schematics have been drawn in Eagle and the screen captured, use other methods if you wish. Feel free to add your own circuits, as long as they are basic building blocks, there are lots of other places for project circuits. If you get into more advanced circuits, give them their own page and link to them. Some entries are not complete, if the explanation of the circuit does not match the diagram that is a good tip off. ) To Do Why not put alpha order? work on external links More circuits that would be good to add AC Coupling Capacitor / High Pass Filter Battery Lamp and Switch Diode Rectifier Current rating and full wave rectification LM35 Temperature Sensor 555 Timer astable oscillator diode for forward drop bias voltage row and collumn connection charge pump transformer voltage multiplier and voltage doubler diode logical or RC timer diode full wave bridge H Bridge An H bridge is an electronic circuit that causes current to flow in one direction or the other ( from a singel ended power supply ). Often used for motor control motor driver. It is an electronic double pole double throw switch. [1] See Section on H-Bridge Simple Oscillator circuits Current mirrors RF Mixers Tranistor Current Mirror Colpitts Oscillator Links to basic circuits: Donny's Learn Electrical Engineering for Beginners DC/AC Circuit Reference Educypedia A web site of links. Lots of material. Amplifiers An amplifier is any circuit which has a larger output than input, typically either larger voltage or larger current, or both. Generally larger power out than in. Several of the circuits here are amplifiers, but as these are only basic circuit, many types of amplifiers are omitted here. See the sections on: Op amp Non Inverting Amplifier, Op amp Unity Gain Buffer .... AmplifierSite.com Current Sense Resistor ( Shunt Resistance ) A current Sense Resistor is a low value of resistor that is placed in parallel with some other circuit. We can then measure the voltage across the resistor to compute the current. If the resistor has a low value compared to other components we can ignore the effect on the circuit. We use the word shunt when the voltage is measured by a device that has a fairly low resistance itself. We then have to do a more careful calculation of how the current is shared by the two devices. Circuit: Where R shunt resistor used to sense the current ( and divert it from the meter ). Usually much less in value than the internal resistance of the meter. METER meter or other device used to measure the voltage across the shunt resitor. Often the resistance of the meter is ignored ( if high ). BATTERY a battery or other voltage source. BULB an incandescent light bulb In the old days a sensitive meter, say 50 mv full scale, would be used with a set of shunt, some looking like metal bars, to measure a wide range of currents, up to and exceeding 50 amps. Sometimes a meter came with a set of shunts for measuring different currents. See links. A completely different way to measure currents is to use a hall effect sensor. Scienceshareware.com's How A Precision Resistor Is Used to Measure / Calculate Current and Power in an Electrical Circuit. High-Side Current-Sense Measurement: Circuits and Principles Shunt (electrical) From Wikipedia, the free encyclopedia Other ways to measure current: Motor_driver#current_sense [edit] Current Limit or Constant Current ( Transistor Based ) This is a modification of the emitter follower to limit the current output. So if your output stage is an emitter follower you can add current limiting to it. Or given enough input drive, say from a voltage divider it will act as a constant current source. Circuit: Current Limit or Constant CurrentWhere R1 base resistor to limit base current to transistor Q1. R2 current sense resistor used to sense the current and turn on transistor Q2. Q1 main transistor supplying the load current. Q2 current limiting transistor. Discussion: The idea here is that R2 is a current sense resistor. When the sense voltage across R2 reaches about .7 ( for silicon transistors ) Q2 begins to conduct and diverts the base drive from Q1 cutting its output current. So the max. current from the circuit is reached when I*R2 = .7. This circuit can be used to protect amplifiers ( including push pull amps. ), power supplies and other circuits; or it can be used as a constant current circuit. It is not a precision circuit, but it is cheap, simple, and effective circuit. Variable (Adjustable) Current Limiter Circuit This is a bit more complicated version using a transistor to drive a darlington transistor, with the limit being adjustable. Current Source for Resistance Measurement The Problem with Current Limit Discusses this circuit as applied to a power amplifier. Constant current LED-Tester Simple application of the circuit as an LED tester. Filter Capacitor / Decoupling Capacitor / Low Pass Filter Circuit: Where D2 is a diode, it lets current pass only in the direction of the arrow. R resistor Input a source of alternating current ( occasionally DC in which case the whole circuit serves only to protect against a reverse connection. C1 the first, main, filter capacitor. C2 the second filter capacitor. D
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