This DC-to-DC converter can generate up to 36 watts of power with an impressive 90% efficiency. It utilizes common and affordable components, including a modern FET and a Schottky diode. Despite its simple and cost-effective design, the converter boasts outstanding specifications.
Efficiency: approx 90%
Ripple voltage: max. 10 mV
Output current: max. 1.5 A
Switching frequency: 40 kHz
Input voltage: 12 V
Output voltage: 24 V regulated
Switching Element and Turn-off Speed Enhancement
The core switching component in this system is a fast power FET (T8). This FET possesses a relatively high input capacitance and undergoes activation and deactivation through a push/pull stage consisting of two RF transistors (T5/T6). To further augment the turn-off speed, Schottky-diode D2 is employed, a critical measure due to the pursuit of achieving utmost efficiency.
Generation of Switching Signal and Voltage Regulation
The generation of the switching signal is facilitated by a straightforward multivibrator, constructed using two RF-transistors (T1/T2). Additionally, a difference amplifier (T3/T4) has been integrated into the circuit to ensure a stable and regulated output voltage of 24 V.
Off-the-Shelf Components and Heat Dissipation
L2 serves as an off-the-shelf 5 A suppressor choke with a self-inductance of 65 µH. In contrast, L1 functions within the output filter, aimed at eliminating RF noise. L1 is an air-cored coil that can be easily crafted by winding 25 turns of 0.5 mm diameter enameled copper wire around a 10 mm diameter drill. Due to the high efficiency of the system, T8 dissipates less than 3.6 W of power, making a modest heatsink with a rating of approximately 10 K/W sufficient. For added safety, it is recommended to incorporate a fast fuse rated at around 3.5 A in the 12 V input supply.
Efficiency Optimization and Component Flexibility
Recognizing the significant impact of duty cycle on efficiency, an additional capacitor (C3) has been introduced in parallel with C2. The ideal configuration can be determined by adjusting this supplementary capacitor.
The rest of the components do not require strict specifications. Any 5 A suppressor choke can be employed for L2, any 5 A Schottky-diode for D3, and virtually any power MOSFET, such as BUZ10, BUZ20, or BUZ100, for T8.