DIY Bench Power Supply LM2596

There is a ton of material on the internet about DIY bench power supplies based on TI LM2576 [1], TI LM2587 [2] and TI LM2596 [3] buck/boost converters.

I used [4], [5] and [6] as a starting point for my own design.

Repository structure

/software/      Bare-metal firmware implementation with OOP approach (PlatformIO project)
/hardware/      Circuit schematics and simulations as documentation
/mechanics/     Housing design files
/misc/          Material of built version

Features

• Two channels with on/off LED and button per channel
• Adjustable voltage (CV)
• Settable and adjustable current limit (CC)
• LED indicators for enabled current limit and reached limit
• LCD showing measured voltages, currents and current limits per channel
• Buzzer feedback (acoustic button feedback, current limit warning)

Design / Components

• Arduino Pro Mini as controller (mainly because of the 8 analog pins)
• LM2596 buck converter boards [7]
• HP notebook 90W power supply brick (19V, max. 4.74A)

Simulation

Texas Instruments does provide SPICE models for the LM2596 3.3, 5 and 12 volt version. But not for the ADJ version. Simple LTspice simulations with a modified SPICE model are located here: /hardware/ltspice/.

Modified lines to edit out the internal voltage divider (see file LM2596_5P0_TRANS.LIB).

Original lines:

...
E_U1_E5         U1_N16912605 0 VALUE { V(FB_INT, GND) }
...
R_RFB2         FB FB_INT  7.63k TC=0,0
R_RFB1         GND FB_INT  2.5k TC=0,0
...

New lines:

...
E_U1_E5         U1_N16912605 0 VALUE { V(FB, GND) }
...
*R_RFB2         FB FB_INT  7.63k TC=0,0
*R_RFB1         GND FB_INT  2.5k TC=0,0
...

Added simulations are:

• lm2596-modified-3_3v-load-3_3-ohm-transient-10ms.asc with results
• lm2596-modified-3_3v-load-33-ohm-transient-10ms.asc with results
• lm2596-modified-5v-load-5-ohm-transient-10ms.asc with results
• lm2596-modified-5v-load-50-ohm-transient-10ms.asc with results
• lm2596-modified-17v-load-17-ohm-transient-10ms.asc with results
• lm2596-modified-17v-load-50-ohm-transient-10ms.asc with results

Special simulation with added current limiter (not sure about results):

• lm2596-modified-5v-load-5-ohm-transient-10ms-with-current-limiter.asc with results

Schematic

The schematic can be found at EasyEDA. I did no PCB (perfboard design is enough).

Performance of LM2596

For a detailed performance review of the LM2596 see [8].

References

• [1] Website TI LM2576: https://www.ti.com/product/LM2576
• [2] Website TI LM2587: https://www.ti.com/product/LM2587
• [3] Website TI LM2596: https://www.ti.com/product/LM2596
• [4] GreatScottLab LM2587 modification project: https://www.instructables.com/id/Adding-a-Current-Limit-Feature-to-a-BuckBoost-Conv/
• [5] Youtube Video LM2576 design: https://www.youtube.com/watch?v=EVL7TzCde8I
• [6] Website article LM2576 design: https://www.smbaker.com/lm2576-constant-voltage-constant-current-switching-power-supply
• [7] Converter from ebay Germany: https://www.ebay.de/itm/3x-LM2596-DC-Step-Down-Spannungswandler-Arduino-Modul-Regler-LM2596S/252785167788
• [8] Performance test and review of 20W DC-DC Step Down Voltage Regulator: https://lygte-info.dk/review/Power%20Adjustable%20buck%20converter%20LM2596%20UK.html