Circuit: Single-Transistor Voltage Converter
December 23, 2024
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Curious how a solar-powered lamp powers an LED with just a single 1.2-V cell? In a 2012 edition, Elektor presented a clever single-transistor voltage converter circuit by Burkhard Kainka. Let's investigate.
Oscillating at around 500 kHz, the compact setup draws only 11 mA at 1.4 V while driving the LED with impressive brightness — and it keeps going even if the cell voltage drops to 0.8 V. Here’s how Kainka's design works: A coil and capacitor form a series resonant circuit, energized by the transistor’s collector. As the transistor alternates between conducting and blocking, the coil stores and releases energy. When the transistor switches off, the coil’s stored energy boosts the collector voltage to roughly double the cell voltage.
Using an oscilloscope, you’ll spot a 3 Vpp swing at the LED and a surprising 35 Vpp across the resonant capacitor. The circuit’s phase shifts — thanks to resonance and the transistor’s Miller capacitance — keep it humming smoothly.
But this circuit isn’t just for LEDs. Add a couple of diodes and capacitors, and it becomes a bipolar voltage converter. With ±4.5 V at 0.2 mA, it’s perfect for low-power op-amps. Simple and efficient, Kainka's design showcases the beauty of minimalist electronics engineering.
Editor's Note: The article was first published in a 2012 edition of ElektorMag. Some of the components, products, and/or links may no longer be available. Still, we feel the educational content remains valuable, and we think it will inspire you to start new projects of your own.
Oscillating at around 500 kHz, the compact setup draws only 11 mA at 1.4 V while driving the LED with impressive brightness — and it keeps going even if the cell voltage drops to 0.8 V. Here’s how Kainka's design works: A coil and capacitor form a series resonant circuit, energized by the transistor’s collector. As the transistor alternates between conducting and blocking, the coil stores and releases energy. When the transistor switches off, the coil’s stored energy boosts the collector voltage to roughly double the cell voltage.
Using an oscilloscope, you’ll spot a 3 Vpp swing at the LED and a surprising 35 Vpp across the resonant capacitor. The circuit’s phase shifts — thanks to resonance and the transistor’s Miller capacitance — keep it humming smoothly.
But this circuit isn’t just for LEDs. Add a couple of diodes and capacitors, and it becomes a bipolar voltage converter. With ±4.5 V at 0.2 mA, it’s perfect for low-power op-amps. Simple and efficient, Kainka's design showcases the beauty of minimalist electronics engineering.
The Original Voltage Converter Project
The article, “One-Transistor Voltage Converter,” appeared in Elektor July/August 2012. You can download the article for free during the two weeks following the publication of this news item. Enjoy!Editor's Note: The article was first published in a 2012 edition of ElektorMag. Some of the components, products, and/or links may no longer be available. Still, we feel the educational content remains valuable, and we think it will inspire you to start new projects of your own.
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