Nifty Fifty

 

1 Resistor divider to measure high voltage

A resistor divider uses two series resistors to scale down a high input voltage to a lower level proportional to the resistor values. This is commonly used to inter- face high-voltage DC signals with the low-voltage Analog-to-Digital Converter (ADC) pins of microcontrollers.

2 Shunt resistor to measure current

A shunt resistor is a low-resistance component placed in the path of a current to create a small, measurable voltage drop according to Ohm’s Law. This allows for precise current monitoring in battery management systems and power meters.

3 Linear hall sensor to measure AC/DC current

By placing a wire near a linear Hall effect sensor, the magnetic field generated by the current flow is converted into a proportional voltage. This provides a non- contact, isolated method for measuring both AC and DC currents in industrial motor controllers.

4 Bridge rectifier

A bridge rectifier uses four diodes in a bridge configuration to convert alternating current (AC) into direct current (DC) by redirecting both halves of the AC cycle. It is the fundamental component in most AC-to-DC power supplies.

5 Half-wave rectifier with peak voltage detector

This circuit uses a single diode to allow only one half of the AC waveform to pass, followed by a capacitor that stores the peak voltage value. It is often used in signal processing to detect the envelope of an AM radio signal. 

6 Precision rectifier

A precision rectifier combines an operational amplifier with diodes to elimi- nate the standard 0.7V diode drop, allowing for the rectification of very small millivolt-level signals. It is widely used in high-fidelity audio equipment and instrumentation.

7 Filter capacitors and chokes

Filter capacitors smooth out voltage ripples by storing charge, while chokes (inductors) oppose changes in current to block high-frequency noise. These are essential in power supply stages to provide clean DC power to sensitive electronics.

8 Current limiter circuit

A current limiter uses active components like transistors to restrict the output current to a maximum safe level, preventing damage during a short circuit. It is a standard protection feature in laboratory power supplies.

9 Over voltage protection circuit (crowbar)

A crowbar circuit uses a Zener diode and a Silicon Controlled Rectifier (SCR) to quickly short-circuit the power supply line if the voltage exceeds a threshold, blowing a fuse to protect the load. This is used in high-reliability systems to prevent catastrophic over-voltage failure.

10 Current source

A current source provides a constant flow of current regardless of the load resis- tance or supply voltage variations. It is used to bias transistors or drive LEDs at a constant brightness.

11 Current sink

A current sink is the complement to a current source, drawing a constant current from a load to ground. It is frequently used in the output stages of integrated circuits to ensure stable operation.

 

12 Current mirror

A current mirror uses a pair of matched transistors to ”copy” the current flowing through one branch into another branch. This is a fundamental building block in the design of operational amplifiers and integrated circuits.

13 Op-amp inverting, non-inverting, and differ- ential amplifiers

These circuits use operational amplifiers with feedback to amplify signals with specific gains and phase relationships. They are the workhorses of analog signal processing, used in everything from pre-amplifiers to sensor signal conditioning.

14 Op-amp current to voltage converter

Also known as a transimpedance amplifier, this circuit converts a small input current (often from a photodiode) into a proportional output voltage. It is used in optical communications and light-sensing applications.

15 Transistor as a switch

By operating a transistor in saturation and cutoff modes, it can act as an elec- tronic switch to turn high-power loads on and off using low-power control signals. Low-side switches connect the load to ground, while high-side switches connect it to the positive supply.

16 H-bridge circuit

An H-bridge consists of four switches (transistors) arranged in an ”H” shape to allow voltage to be applied across a load in either direction. This is the standard circuit for controlling the direction and speed of DC motors.

17 BJT emitter follower

The emitter follower, or common collector amplifier, provides high input impedance and low output impedance with a voltage gain of approximately one. It is used as a buffer to prevent a signal source from being loaded down by a subsequent stage.

18 Darlington pair and Sziklai pair

The Darlington pair connects two transistors to achieve extremely high current gain, while the Sziklai pair offers similar gain with improved thermal stability. These are used to drive high-current loads like solenoids or large speakers from low-power logic.

19 Push-pull amplifier

A push-pull amplifier uses a pair of complementary transistors to amplify both halves of a signal efficiently. This configuration is standard in class-B and class- AB audio power amplifiers to minimize heat and distortion.

20 Pull-up and Pull-down resistors

These resistors ensure that digital logic inputs settle at a known ”high” or ”low” state when no active signal is present. They are critical for interfacing switches and open-collector outputs to microcontrollers.

21 Transistor as dynamic load

Using a transistor instead of a resistor as a load provides high incremental resis- tance while allowing for a specific DC bias. This technique is used in integrated circuits to achieve very high gain in small spaces.

22 Integrator and differentiator

An integrator produces an output proportional to the integral of the input signal (acting as a low-pass filter), while a differentiator produces an output proportional to the rate of change (acting as a high-pass filter). These are used in analog computers and control systems.

23 Single supply Op-amp AC voltage amplifier

This circuit uses a voltage divider to bias an op-amp at half the supply voltage, allowing it to amplify AC signals using only a single positive power source. It is common in battery-powered portable audio devices.

24 Precision voltage reference circuits

These circuits produce a highly stable and accurate DC voltage that remains constant despite temperature changes or supply fluctuations. They are used as reference points for ADCs and DACs to ensure measurement accuracy.

25 Zener power supply

A Zener diode used in reverse-bias mode provides a simple method of voltage regulation by maintaining a constant voltage across itself. It is used for low- current voltage stabilization in simple electronic devices.

26 Op-amp based power supply

By using an operational amplifier to control a pass transistor, a power supply can achieve much higher precision and lower ripple than a simple Zener regulator. This is used in high-performance laboratory equipment.

27 3-terminal regulator

These integrated circuits (like the 7805) provide a complete, easy-to-use solution for voltage regulation with built-in thermal and current protection. They are the most common way to provide stable DC power to digital circuits.

28 Capacitive power supply

This circuit uses the reactance of a capacitor to drop AC mains voltage to a lower level without the bulk and heat of a transformer. It is used in very low-power, cost-sensitive applications like LED nightlights.

29 Comparator and comparator with hysteresis

A comparator compares two voltages and outputs a digital signal indicating which is higher. Adding hysteresis (a Schmitt trigger) prevents output chatter- ing caused by noise, which is vital for thermostat and level-sensing applications.

30 Window comparator

A window comparator uses two comparators to determine if a voltage falls within a specific range or ”window.” It is used for battery charge monitoring and in- dustrial process control limits. 

31 Counter circuits (Divide-by-N)

Counter circuits use flip-flops to divide the frequency of a clock signal by a specific integer. These are used in digital clocks and frequency synthesizers to generate specific timing intervals.

32 Crystal oscillator

A crystal oscillator uses the mechanical resonance of a vibrating crystal to create an electrical signal with a very precise frequency. This provides the stable ”heartbeat” or clock for microprocessors and radio transmitters.

33 RC-oscillator and Ring oscillator

RC-oscillators use resistors and capacitors to set frequency, while ring oscillators use an odd number of inverters in a loop. These are used for low-cost clock generation and on-chip timing in integrated circuits.

34 BJT and 555 based Multivibrators

These circuits can be astable (oscillating) or monostable (one-shot). They are used for generating pulses, PWM signals, and timing delays in various electronic control applications.

35 Basic gates with diodes and BJTs/MOSFETs

Logic gates like AND, OR, and NOT can be constructed using discrete diodes or transistors. This ”discrete logic” is useful for teaching basic Boolean algebra and for simple control tasks without a microcontroller.

36 Mux, Decoder, and digital comparator

These digital building blocks route signals (Multiplexer), translate binary codes to specific outputs (Decoder), or compare binary numbers. They are essential for memory addressing and data routing in computers.

37 Relay driver with snubber

A relay driver uses a transistor to energize a relay coil, while a snubber diode protects the transistor from the high-voltage flyback spike produced when the coil is turned off. This is used to control AC appliances from low-voltage logic.

 

38 ADC input over-voltage protection

This circuit uses clamping diodes or Zener diodes to ensure that the input voltage to an ADC never exceeds the power supply rails. It is a critical safeguard for preventing damage to microcontrollers from external sensor faults.

39 Wheatstone bridge

The Wheatstone bridge is a network of four resistors used to measure very small changes in resistance with high precision. It is the standard circuit for interfacing with strain gauges, load cells, and RTD temperature sensors.

40 PWM generator

A Pulse Width Modulation (PWM) generator varies the duty cycle of a square wave to control the average power delivered to a load. It is widely used for dimming LEDs and controlling the speed of DC motors.

41 LED as light sensor

An LED can act as a photodiode, generating a small current when exposed to light. This allows a single component to serve as both an indicator and a light sensor in low-cost ambient light detection circuits.

42 PWM DAC and R-2R DAC

A PWM DAC uses a low-pass filter to turn a digital pulse train into an analog voltage, while an R-2R ladder uses a network of resistors for faster conversion. These are used to generate audio or control voltages from digital systems.

43 Voltage doubler and inverter

These charge-pump circuits use diodes and capacitors to ”pump” charge to a higher voltage or to a negative potential. They are used to generate high voltages for displays or negative rails for op-amps from a single positive supply.

44 Joule thief

The Joule thief is a minimalist self-oscillating voltage booster that can drain nearly all energy from a single battery cell to light an LED. it is a popular circuit for emergency lighting and learning about switch-mode power conversion.

45 Wireless power transmitter and receiver

These circuits use inductive coupling between two coils to transfer energy across an air gap. This technology is the basis for Qi wireless phone charging and sealed waterproof appliances like electric toothbrushes.

46 Faraday power generator

Based on electromagnetic induction, this circuit generates electricity by moving a magnet through a coil of wire. It is used in ”shake-to-charge” flashlights and large-scale hydroelectric or wind turbines.

47 Quadrature phase circuits

These circuits generate two signals that are 90 degrees out of phase (sine and cosine). They are fundamental in modern communications for I/Q modulation and in motion control for sensing the direction of encoders.

48 Opto-coupler and opto-isolator

An opto-coupler uses an internal LED and phototransistor to transmit signals via light, providing total electrical isolation between two circuits. This protects sensitive low-voltage controllers from high-voltage transients on power lines.

49 BJT as zener diode

By utilizing the reverse breakdown of a BJT’s base-emitter junction, a transistor can act as a low-voltage Zener diode. This is often used as a makeshift voltage reference in hobbyist circuits when a specific Zener is unavailable.

50 Bidirectional logic level converter

This circuit uses MOSFETs to allow 3.3V and 5V logic devices to communicate safely in both directions. It is essential for connecting modern 3.3V sensors to older 5V microcontrollers like the Arduino Uno.

51 Bootstrapped ramp generator

A ramp generator creates a linear voltage rise over time, and ”bootstrapping” uses feedback to maintain a constant charging current through a capacitor. This provides a very linear sweep for applications like oscilloscope time-bases and PWM generation.