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Transistor Circuits
Transistors:  #'s - C    D - I     J - O     P - S     T - Z

Last Updated: November 22, 2021 03:00 PM

Circuits Designed by Dave Johnson, P.E. :

Temperature Sensor MOSFET -   Recently I was asked by a company to discover why one of their products failed to operate properly in cold temperatures.  Two n-channel MOSFETs and a few resistors are wired to form a flip/flop latch circuit.  Each time the pushbutton switch is pressed, the circuit changes state and remains in that state until another activation of the switch.   . . . Dave Johnson, Lubbock TX (December 1, 2010)-DC Magazine - Issue 14 Dec 2010


Capacitance Proximity Switch
Draws very low power - Ideal for battery-powered applications
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Links to electronic circuits, electronic schematics and designs for engineers, hobbyists, students & inventors:

Temperature Sensor MOSFET -  Recently I was asked by a company to discover why one of their products failed to operate properly in cold temperatures.  Two n-channel MOSFETs and a few resistors are wired to form a flip/flop latch circuit.  Each time the pushbutton switch is pressed, the circuit changes state and remains in that state until another activation of the switch.. . . Circuit by David Johnson P.E.-December, 2010

Three Transistor Audio Amp 50 Milliwatt -  Here is a little audio Amplifier similar to what you might find in a small transistor radio __ Designed by Bill Bowden

Three Transistor FM Radio Bug -  My FM Wireless Microphone has been a very popular project with beginners and experienced constructors alike.  it has been used inside guitars and as the basis of a remote control system.   __ Designed by Harry Lythall-SM0VPO

Three-transistor current source covers wide range -  05/31/14  EDN Design Ideas:  This Design idea is a two-wire current regulator that strikes a good balance between performance and parts count.  Employing three transistors, three resistors, and one LED, it achieves good regulation (better than 1% over most of the voltage range) , lower operating voltage (1.2V typical) , and better tempco (0.07%/K) than other circuits of similar complexity.  it is designed to operate in a range of currents from tens of milliamperes to several amps.  it does not use any hard to find parts; for example: an LM10 can be used to make an even higher performance circuit, but this IC is not multi-sourced and is likely to be discontinued.   Design by Einar Abell0

Touch Switch using Transistors -  Schematic & notes only there no circuit description.   __ Designed by Tony van Roon  VA3AVR

Transistor & FVCs Make Linear Anemometer -  09/26/96 EDN Design Ideas:  The basic operation of this front-end sensor is identical to that of the earlier circuit.  Q1 is the self-heated airflow sensor; Q2 senses ambient temperature.  Zero-adjust resistor R2 sets the zero-airflow quiescen Design by W Stephen Woodward, University of North Carolina, Chapel Hill, NC

Transistor Amplifier Design -  Good stability and sufficient amplification in Transistor based circuits depends on the proper selection of components and their layout.  Gain of the transistor used as well as the current and voltage through it are the most important aspect in the working of a transistor amplifier.  Here explains the design parameters of an one __ Designed by D Mohankumar

Transistor Audio PreAmplifier -  This easy circuit provides good gain to week audio signals.    Use it in front of an RF oscillator to make an RF transmitter that is very sensitive to sound.   __ Designed by Tony van Roon  VA3AVR

Transistor Boosts Regulator Current -  11/04/10 EDN Design Ideas:  Use a common voltage regulator to make a current source Design by Yngve Linder, Örsundsbro, Sweden

Transistor Diode IC outlines -  Schematic only __ Designed by Bill Bowden

Transistor Forms RS-232C Digital Thermometer -  05/09/96 EDN Design Ideas:  An ordinary transistor can serve as an uncalibrated temperature sensor (Figure 1) for an accurate, PC-compatible thermometer.  Unadjusted accuracy is more than0.5°:C over the -50 to +50°C range, and the only limitation on resolution is the time devoted to measurement acquisition Design by WS Woodward, University of North Carolina—Chapel Hill

Transistor junctions monitor temperature zones -  12/31/69 EDN Design Ideas:   A simple circuit uses transistor junctions to monitor multiple temperature zones.  The temperature sensors are ordinary, general-purpose, low-cost, diode-connected transistors.  The well-known diode equation VBE = (kT/q) 'ln (IC  /iS) shows that there is a temperature dependency of approximately 2.2 mV/°C for a base-emitter junction.   Design by Matt Smith, Analog Devices, Limerick, Ireland

Transistor latch improves on/offry -  11/23/00 EDN Design Ideas:  Figure 1 shows an example of on/off circuitry commonly used in battery-operated devices.  The p-channel MOSFET, Q1, serves as a power switch.  When you push the On button, S1, Q1's gate goes low.  Q1 turns on and supplies battery voltage to the DC/DC converter.  Depending on the battery voltage in the device, the DC/DC converter might convert the voltage either up or down Design by Eugene Palatnik, SIMS-BCI, Waukesha, WI

Transistor linearly digitizes airflow -  09/19/02 EDN Design Ideas:  A sensitive and reliable way to measure airflow is to take advantage of the predictable relationship between heat dissipation and air speed.  The principle of thermal anemometry relies on King's Law, which dictates that the power required to maintain a fixed differential between the surface of a heated sensor and the ambient air temperature increases as the square root of air speed Design by Steve Woodward, University of North Carolina, Chapel Hill, NC

Transistor Organ -  This simple circuit can provide hours of enjoyment as you learn tunes, play duets or just make some really weird sounds by pushing all the buttons at once.  You have probably seen this circuit before, it is fairly common.  I have seen it in several __ Designed by Aaron Cake

Transistor paIR lowers PWM IC's start-up current  -  03/18/99 EDN Design Ideas:  An auxiliary winding usually provide as power for the popular  UC384X-based offline switch-mode power supplies (SMPSs).  This winding feeds  the main PWM controller.   PDF contains multiple circuits, scroll to find this circuit.    Design by Christophe Basso, Motorola Semiconductor, Toulouse, France

Transistor quickly wakes sleeping LDO -  09/01/98 EDN Design Ideas:  NOTE:     FILE
has many circuits, scroll down.  Portable systems, such as telephone handsets, make extensive use of low-dropout (LDO) regulators.  These components provide noise-sensitive parts with a stable power-supply line.  When a telephone enters standby mode, most of the circuits go to sleep by disabling the LDO's outputs.  Operating current thus drops to a minimal level.  When a user starts to dial a number, the LDO receives an enable signal and immediately delivers the nominal operating voltage.  Unfortunately, most low-noise LDOs use a bypass capacitor that briefly loads the internal reference voltage upon wake-up. Design by Christophe Basso, Motorola Semiconductor, Toulouse, France

Transistor Schmitt Trigger Oscillator -  The Schmitt Trigger oscillator below employs 3 transistors, 6 resistors and a capacitor to generate a square waveform.  Pulse waveforms can be generated with an additional diode and resistor (R6).  Q1 and Q2 are connected with a common emitter resistor (R1) so that the conduction of one transistor causes the other to turn off.  Q3 is controlled.   __ Designed by Bill Bowden

Transistor Spot Checker -  The simple transistor spot checker is one of the most handy gadgets on the experimenter's workbench, especially if said experimenter has numerous surplus transistors with unknown histories or mysterious "in-house" part numbers.  A quick check can confirm that the problem lies elsewhere when a new circuit fails to function properly or help jog the memory on whether a 2N2905 is NPN or PNP without a trip to the data book.  The following schematic is of a tester I made about 30 years ago. (Yes, they had transistors back then.)  __  Contact:  Charles Wenzel of Wenzel Associates, Inc.

Transistor tester fits into your pocket -  20-Dec-01 EDN Design Ideas:  it can be heLPFul to rapidly and easily determine the polarity (npn or pnp] and function of a transistor.  The pocket-transistor tester in Figure 1 is ideal for quickly testing without regard to such parameters as gain and frequency response.  You connect the transistor, or device under test, between the collectors, T, of an astable multivibrator Design by Jean-Bernard Guiot, DCS AG, Allschwil, Switzerland

Transistor Tester Identifies Terminals -  03/17/11  EDN Design Ideas:  it also lets you determine if a transistor is an NPN or PNP type.   Design by Raju R Baddi, Tata Institute of Fundamental Research, Maharashtra, India

Transistor Trio Makes Vector Anemometer -  09/01/97 EDN Design Ideas:  A previously published Design idea (Reference 1] uses a heated transistor as an airspeed-to-frequency converter.  Because it uses only one transistor, the circuit cannot determine the direction of airflow.  Alternatively,  Design by W Stephen Woodward, Chemistry Department, University of North Carolina--Chapel Hill

Transistors offer overload Delay -  16-Sep-04 EDN Design Ideas:  Although an SMPS (switch-mode power supply] can protect itself against permanent short circuits, it sometimes has problems when dealing with transient overloads.  Transient overloads are not short circuits but can push the power supply above its nominal load value.  This scenario occurs with typical loads such as printer heads and small motors Design by Christophe Basso, On Semiconductor, Toulouse, France

Transistors offer thermal protection for controller -  07/19/01 EDN Design Ideas:  When a switch-mode power-supply controller, such as On Semiconductor's NCP1200, operates at a high ambient temperature, you should protect the entire power supply against lethal thermal runaway.  The NCP1200 operates directly from the power mains without an auxiliary winding; therefore, the die in the IC dissipates power (Figure 1)  Design by Christopher Basso, On Semiconductor, Toulouse, France

Transistors tame peRFIDious leakage inductance -  09/27/01 EDN Design Ideas:  in flyback converters that use primary regulation, the loose coupling between the power secondary and the primary auxiliary windings often results in poor cross-regulation.  This situation arises mainly from the leakage inductance but also comes from the level of the primary clamp voltage.  Figure 1 shows a typical application schematic using On Semiconductor's (www Design by Christophe Basso, On Semiconductor, Toulouse, France

Two transistor FM transmitter / FM bug -  VOYAGER is a super-sensitive FM Radio microphone developed by Talking  Electronics.  The components are all common types of resistors, capacitors and transistors matched so well in this circuit that  amazing  sensitivity and  distance  are obtained.  The name VOYAGER was given to it "because it  goes so far".  We have re-designed the Board and further matched some components  to  suit  the  needs  of  the  classroom.  The result is a superb bug which is compact but powerful, and quite easy to build__ CdS Electronic

Two Transistor LED Flasher -  This circuit will flash a bright red LED as an attention getting device or fake care alarm. __ Designed by Bill Bowden

Two Transistor LED Flasher 1 -  Circuit Only __ Designed by Tony van Roon  VA3AVR

Two Transistor LED Flasher 2 -  This circuit will flash a super-bright LED (5000+ mcd).  Good for fake car alarm or other attention getting device.  Component values are not critical, try anything else first from your junkbox.  Obviously, the 470 ohm resistor (R3) determines the LEDs brightness and limits the current flow to about 20mA.390 ohm can also be used as a save value.  if you decide to go with a green or yellow led, which draw more current, you may want to replace the 470 ohm with an appropriate value.  Flash rate is determined by R2 and C1 __ Designed by Tony van Roon  VA3AVR

Two transistor lights LEDs -  04/09/09  EDN Design Ideas:  A previous Design ideas - describes a circuit that uses an astable multivibrator to drive an LED (Reference 1].  The circuit in Figure 1 uses a simpler alternative approach.  The circuit uses a 2N3904 NPN transistor and a 2N3906 PNP trans Design by Barry A Tigner, Michigan State University, East Lansing, MI

Two transistor replaces IC -  02/07/02  EDN Design Ideas:  Linear Technology's recently introduced LTC4300 chip buffers i2C clock and data lines to and from a hot-swappable card.  This task is difficult because the IC must work bidirectionally, meaning that you can simultaneously and active Design by Jim Hagerman, Hagerman Technology, Honolulu, HI

Two Transistors Form Bidirectional Level Translator -  11/07/96 EDN Design Ideas:  This example illustrates a translation from 5 to 3V, but it can accommodate almost any other voltage levels, provided the logic-low levels are equal (usually0V].  Translations from 1 to 100V are possible, albeit rather slow.  The key to this circuit is the unusual cross-coupling of the emitters Design by Jim Hagerman, Nokia Mobile Phones, San Diego, CA

Two transistors form high-precision, ac-mains ZCD -  7-Jun-07 EDN Design Ideas:  A simple two-transistor circuit can accurately detect the zero crossing of the ac mains voltage Design by Djessas Zoheir, Constantine, Algeria

Two-Transistor Atomic Frequency Standard -  Pretty ambitious title, wouldn't you say? Well, follow the reasoning: if you lower the voltage on the two-transistor flasher to 1.5 volts, the loop gain drops too low for sustained flashing. (See the circuit below.) But, the circuit is highly regenerative and only needs a very tiny push to get it going.  By adding a short wire, only a few inches, to the PNP base, the circuit will be triggered into oscillation by the AC electric field from the electrical power (50 or 60 Hz in most places)  __  Contact:  Charles Wenzel of Wenzel Associates, Inc.

Got Designs?
Please eMail
if you want me to link to and/or post your original design Thanks.

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Transistors:  #'s - C    D - I     J - O     P - S     T - Z

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