A bench power supply is the first tool most electronics labs build. This one uses an LM2596HV buck regulator fed from a sealed 36 V DC adapter — so there is no mains wiring inside the box — and gives a front-panel adjustable output from 1.2 V to 30 V at up to 2 A continuous, with a volt/amp meter on the front.
What you'll build
| Target spec | Value |
|---|---|
| Input | 36 V DC from an external adapter (≥ 2.5 A) |
| Output voltage | 1.23 V – 30 V, set with a 10-turn pot |
| Output current | 2 A continuous (3 A peak, the LM2596's rating) |
| Efficiency | Roughly 75–90 % depending on output voltage (to be measured) |
| Display | Panel volt/amp meter |
| Protection | Input fuse; the LM2596's built-in current limit and thermal shutdown |
How it works
A buck converter switches its input on and off about 150 000 times per second and smooths the result with an inductor and capacitor, so the output is roughly the input times the fraction of time the switch is on. The LM2596 contains the switch, the oscillator and the control loop; you add the diode, inductor, capacitors and the feedback divider that sets the voltage. If you haven't read it yet, How a Buck Converter Actually Works explains every part of this circuit.
Schematic
The calculations
Output voltage range
With R1 = 820 Ω and a 20 kΩ pot: RV = 0 gives 1.23 V; RV = 20 kΩ gives 1.23 × (1 + 24.4) ≈ 31 V. In practice the regulator needs a couple of volts of headroom, so 30 V is the usable top end from 36 V in. The voltage divider tool lets you try other resistor pairs.
Inductor
Ripple current is largest when the output is half the input (D = 0.5). At 36 V → 18 V, 150 kHz, 68 µH:
At 2 A load the peak current is about 2 + 0.88/2 ≈ 2.4 A, so choose an inductor with a saturation rating of 4–5 A.
Voltage and current ratings
- LM2596HV — the HV version is rated to 60 V input; the standard LM2596 (40 V max) is too close to 36 V.
- C1 100 µF, 63 V low-ESR (≥ 1.5 × the input voltage).
- C2 470 µF, 50 V low-ESR (≥ 1.5 × the 31 V maximum output).
- D1 SB560 Schottky, 60 V 5 A: it carries the full load current while the switch is off.
- CFF (optional): the datasheet recommends a small feed-forward capacitor across the upper feedback resistor at higher output voltages. Take the value from its component table (a few nF), and leave it out for the first power-up.
- Fuse 3 A: at 30 V × 2 A out, the input draws about 60 W ÷ 36 V ÷ 0.9 ≈ 1.9 A.
Heat
At 5 V and 2 A (10 W out) with ~80 % efficiency, about 2.5 W turns into heat — mostly in the regulator and the diode. Use the power dissipation calculator to size the heatsink: the TO-220 version needs a small clip-on heatsink at full current.
Parts list
| Qty | Part | Notes |
|---|---|---|
| 1 | 36 V DC adapter, ≥ 2.5 A | Sealed, certified brick with a barrel or XT60 output. |
| 1 | LM2596HVT-ADJ (TO-220-5) | Plus heatsink and insulating pad if the tab touches metal. |
| 1 | 68 µH power inductor, ≥ 4 A saturation | Toroid or shielded drum. |
| 1 | SB560 Schottky diode | 60 V, 5 A. |
| 1 + 1 | 100 µF 63 V and 470 µF 50 V low-ESR electrolytics | "Low ESR / switching" types. |
| 1 | 20 kΩ 10-turn potentiometer + knob | Fine adjustment across the full range. |
| 1 | 820 Ω resistor, 1 % | R1. |
| 1 | 4.7 kΩ ½ W resistor | Bleeder across the output, so the voltage falls quickly when turned down. |
| 1 | Panel volt/amp meter (0–100 V, 10 A, with shunt) | Check its supply range — see build step 4. |
| 1 | Small LM2596HV module set to 12 V | Auxiliary rail for the meter (and an optional fan). |
| 1 each | Fuse holder + 3 A fuse, rocker switch, DC input jack, binding posts | Red/black 4 mm posts. |
| — | Enclosure, perfboard, 18 AWG wire for the power path | Thin jumper wire for the feedback only. |
Build steps
- Plan the layout. Keep C1, the LM2596, D1 and the ground connection between them as tight as possible — that loop carries the fast switching current. Keep the feedback wire (pin 4) short and away from the inductor.
- Build the regulator on perfboard with a fixed resistor in place of the pot first (for example 3.3 kΩ ≈ 6.2 V). Power it from a current-limited source or through the fuse, and measure.
- Fit the pot. Wire it as a variable resistor (wiper + one end). Check the full range with a multimeter before connecting anything else.
- Add the meter. Many panel meters accept only 4.5–30 V on their supply wire, so power it from the 12 V auxiliary module rather than the 36 V input. The shunt goes in the negative output lead.
- Box it. Input jack → fuse → switch on the back; pot, meter and binding posts on the front. Mount the regulator's heatsink with airflow, and add the bleeder resistor across the output posts.
Testing checklist
- No load: the output adjusts smoothly from ~1.23 V to ~30 V.
- Meter voltage agrees with a multimeter to within ±0.1 V.
- Load test with power resistors (for example 10 Ω, 25 W at 10 V = 1 A): note the voltage drop and the regulator temperature after 10 minutes.
- Output ripple on an oscilloscope at 1 A (AC-coupled, 20 MHz bandwidth limit).
- Efficiency at 5 V, 12 V and 24 V: Pout ÷ Pin.
- Short the output briefly: the LM2596 should current-limit, not blow up.
Results
Status: planned. Measured range, ripple, efficiency table, thermal photos and the video will be added after the build.
Ideas for version 2
- Adjustable current limit (constant-current mode) with a shunt, an op-amp and a second pot — essential for charging batteries and testing LEDs.
- Down to 0 V by injecting a small negative offset into the feedback node.
- Linear post-regulator for low-noise output on analog projects.
- Digital control: an ESP32 with a DAC or digital pot to set and log the voltage.