Category: Builds

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– Built with discrete components by design (no ICs), and deliberately kept simple to make it suitable for DIY. – It is a simple, open-loop, non-synchronous buck converter. It uses a 20 kHz, 50% duty-cycle astable multivibrator as the PWM signal source, a discrete transistor push-pull gate driver and a P-channel as the high-side switch.…

Understand MOSFET gate driving by building one with transistors

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Investigating how basic components work is my guiding principle in this part of the DIY buck converter project, too. The circuit is built around a push-pull output stage, with several refinements and some essential supporting components. * Q2 and Q3 – Push-pull stage: Q2 sources current to charge the MOSFET gate; Q3 sinks current to…

DIY shunt resistor for current measurement – how accurate is it?

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in Builds, DIY

I needed a shunt to measure current, but only had two 0.082 Ω, 3W resistors. Luckily, I found them in a scrapped PSU. Two resistors in parallel: 0.082 Ω || 0.082 Ω = 0.041 Ω, 6W total But how accurate is the result? And does it matter if the voltmeter connects through sense terminals about…

No signal generator? – Build a variable astable multivibrator

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This one is intended to provide the ~20 kHz switching signal for our future buck converter. The AMV (astable multivibrator) gives us the signal, but we’re not quite ready to drive the MOSFET yet. We still need a gate driver between the AMV and the MOSFET to turn the 6 V logic-level signal into a…

10 MHz Crystal Oscillator – Schematic and Build

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The circuit has been built and tested on the bench. Below are some measurements from testing different component values and operating conditions. R5 – Emitter Resistor R5 = 30 Ω 4.74 Vpp 5.90 V min 10.64 V max R5 = 200 Ω 2.17 Vpp 7.63 V min 9.80 V max Interestingly, the lower-amplitude waveform looks…

How well can a current mirror made from ordinary discrete transistors perform?…

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in Builds, DIY, Engineering Education, Schematic

– Only 11 µA difference between the reference current and the output current – – that is what I measured with a symmetric Wilson current source mirror built from ordinary, unmatched 2N3906 PNP transistors. For the experiment, I used: * 4 randomly selected 2N3906 PNP transistors * 2 randomly selected 18 Ω resistors * Both…

BJT Monostable Multivibrator – Schematic and Build

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– and a Design Detail You Might Have Missed – When the trigger pulls the base of the second transistor low, the first transistor switches on and its collector falls rapidly from nearly Vcc to almost 0 V. BUT: The timing capacitor between the collector of Q1 and the base of Q2 cannot change its…

Triggered Bistable Multivibrator – Schematic and Build

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PDF for downloading

Schematic for a Simple 218 Hz Astable Multivibrator

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Designed for the Transistor Multivibrator Experimentation Board, this circuit is a great introduction to transistor-based oscillators and multivibrator operation. BOM (Bill of materials) C1, C2: 100 nF (2x) JP1, JP2, Out-D1: Bridged (1x/3x) Q1, Q2: 2N3904 (2x) R1, R2: 2.2 kΩ (2x) R3, R4: 33 kΩ (2x) Version 2 of the PCB is coming this…

Testing v8.1 of the BJT Transistor Experimentation Board…

Jul 13, 2026

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