Circuit
Darlington Pair: Switch a 2 A Load with 0.24 mA of Base Current
A single transistor can switch a heavy load, but it asks for a heavy base current in return: a β of 100 means 2 A of collector current needs...
Amplifier
Inverting Op-Amp Amplifier: Design a Gain of −10 from a 0.5 V Signal
The inverting amplifier is the op-amp circuit that flips a signal upside down while making it bigger: a positive input comes out negative, a...
Circuit
Optocoupler Basics: Let a 5 V Microcontroller Switch 12 V Safely
An optocoupler lets a 5 V microcontroller control a 12 V circuit without any wire connecting the two sides. Inside one small chip, an LED ...
Diode
Half-Wave vs Full-Wave Rectifier: Which One Should You Build?
Both the half-wave and the full-wave rectifier turn AC into DC, and both use the same transformer — but one throws away half of every cycl...
Amplifier
Non-Inverting Op-Amp Amplifier: Design a Gain of 11 from a 0.5 V Sensor Signal
The non-inverting amplifier is the op-amp circuit you reach for when a small sensor signal needs to be made bigger without loading the sen...
555
555 Timer Astable Multivibrator: Design a Blinking LED Circuit
The 555 timer is the classic chip for making things blink, beep and switch on a schedule. Wired as an astable multivibrator it needs no tr...
Capacitor
Bridge Rectifier with a Capacitor Filter: Ripple Voltage and How to Size the Capacitor
A bridge rectifier turns AC into DC, but the output is still a long way from the smooth DC a circuit needs: it falls to zero 100 times eve...
Amplifier
Op-Amp Voltage Follower: A Buffer with a Gain of One That Saves Your Signal
A voltage follower is the strangest amplifier in electronics: its gain is exactly one — the output is just a copy of the input. So why use...
Capacitor
Capacitors in Series and Parallel: Equivalent Capacitance, Voltage Sharing and Stored Energy
Resistors in parallel add like conductances and in series like resistances — but capacitors do the exact opposite. Put capacitors in paral...
Circuit
Buck Converter Basics: How an Inductor Steps 12 V Down to 5 V
Nearly every phone charger and computer board has to turn a higher voltage into a lower one — 12 V down to 5 V, for example. A linear regu...
Circuit
Wheatstone Bridge: Find an Unknown Resistance from a Null Reading
An ohmmeter measures resistance by pushing a known current through it and reading the voltage — good enough for rough work, but its accuracy...
Biasing
BJT Voltage Divider Bias: A Stable Base Bias That Does Not Drift with Beta
A bipolar transistor only amplifies properly when its base is biased to the right operating point — the Q-point. The trouble is that a trans...
Capacitor
RC High-Pass Filter: Cutoff Frequency and Frequency Response Explained
The RC low-pass filter takes its output across the capacitor and passes the bass. Swap the parts — take the output across the resistor inste...
Efficiency
Transformer Turns Ratio and Efficiency: From 230 V to 12 V, Worked Example
A transformer changes AC voltage without any moving parts: the ratio of the voltages is the ratio of the turns. That one rule sizes everythi...
AC Circuit
Capacitive Reactance: How a Capacitor Behaves in an AC Circuit
A resistor opposes current the same way at every frequency. A capacitor does not: it blocks DC completely, lets high-frequency AC through ea...
Circuit
MOSFET as a Switch: Drive a 12 V Load from a 5 V Logic Signal
A microcontroller pin runs at 5 V and can supply only a few tens of milliamps — it cannot drive a 12 V, 2 A motor directly. The usual answ...