Buck-Boost Bench Supply
A 0–30V adjustable bench supply with active current limiting, built around a buck-boost stage so it can regulate above or below the input rail.
Overview
A simple buck converter can only step voltage down, and a boost converter can only step it up. A buck-boost stage does both from the same unregulated input rail, which is what lets this supply sweep the full 0–30V range from a single 24–36V input instead of needing multiple supply rails.
Two feedback loops run at once: a voltage loop that holds the output at the set point, and a current loop that clamps output current the moment it hits the user-set limit, switching the converter from constant-voltage to constant-current mode automatically — the same behaviour you'd expect from a commercial bench supply.
Block Diagram
Key Components
- Power MOSFETs rated for the switching frequency and current used
- Inductor sized for the ripple current target
- Output capacitor bank for ripple filtering
- Precision current-sense resistor with an instrumentation amplifier
- PWM controller / MCU running the voltage and current loops
- Rotary encoders and an OLED display for set-point control
- Heatsink and airflow for the switching devices
Bill of Materials
| Ref | Part / Value | Rating | Package |
|---|---|---|---|
| U1 | LTC3789 — synchronous buck-boost controller | 4.5–38V input | QFN-32 |
| Q1–Q4 | IRF540N — power MOSFET | 100V, 33A | TO-220 |
| L1 | Power inductor, 47µH | 10A saturation | Shielded, 12×12mm |
| C1 | Input capacitor, 220µF electrolytic | 50V | Radial, ⌀10×20mm |
| C2, C3 | Output capacitor, 330µF electrolytic | 50V | Radial, ⌀10×25mm |
| R1 | Current-sense shunt, 5mΩ | 2W | 2512 |
| U2 | INA219 — current/power monitor, I2C | 0–26V bus | SOT23-8 |
| U3 | ATmega328P — control loop MCU | 1.8–5.5V, 20MHz | TQFP-32 |
| U4 | SSD1306 — 0.96" OLED display | I2C, 3.3V | Module |
Build Requirements
- Working knowledge of switching converter topologies and loop compensation
- A PCB layout with proper copper pour and thermal relief for the power stage
- A calibrated multimeter and electronic load for tuning and verifying regulation
- An isolated bench supply or transformer/rectifier front end to feed the DC input