Build a professional 30V/5A programmable bench power supply with constant voltage/current modes, digital readout, and OVP/OCP protection.
Build a professional 30V/5A programmable bench power supply with constant voltage/current modes, digital readout, and OVP/OCP protection. This comprehensive guide covers everything from design through implementation, testing, and deployment.
Linear (series pass) regulator: transform AC → DC → regulate by dissipating excess voltage across pass transistor as heat. Extremely quiet (no switching noise), good for sensitive analog circuits. Efficiency: V_out/V_in — at 5V out from 35V in: 14% efficiency (86% wasted as heat). SMPS (Switching): buck converter switches at 100–500 kHz, duty cycle controls output voltage. Efficiency 85–95%. Some switching noise on output. For lab power supply: linear post-regulator reduces switching noise. This project: linear (toroidal + LT3080 parallel regulators) — clean output for analog/RF testing.
10 components required for this project.
| # | Component | Purpose | Qty |
|---|---|---|---|
| 1 | Toroidal transformer (35V, 10A secondary) | Mains isolation and step-down | x1 |
| 2 | LT3080 parallel linear regulator ICs | Low-dropout parallel regulation | x3 |
| 3 | 16-bit ADS1115 ADC | Precision voltage/current readout | x1 |
| 4 | STM32F103 MCU | Control loop, UI, calibration | x1 |
| 5 | Digital encoder × 2 | Voltage and current setpoint adjustment | x2 |
| 6 | 2.4" TFT display (SPI) | V/A/W readout display | x1 |
| 7 | Fan + temperature sensor (LM35) | Thermal management | x1 |
| 8 | Current sense resistor (0.01Ω, 10W) | Output current measurement | x1 |
| 9 | INA226 power monitor IC | Precision power measurement | x1 |
| 10 | Aluminum heatsink + chassis | Pass element thermal dissipation | x1 |
Follow these 5 steps carefully.
Linear (series pass) regulator: transform AC → DC → regulate by dissipating excess voltage across pass transistor as heat. Extremely quiet (no switching noise), good for sensitive analog circuits. Efficiency: V_out/V_in — at 5V out from 35V in: 14% efficiency (86% wasted as heat). SMPS (Switching): buck converter switches at 100–500 kHz, duty cycle controls output voltage. Efficiency 85–95%. Some switching noise on output. For lab power supply: linear post-regulator reduces switching noise. This project: linear (toroidal + LT3080 parallel regulators) — clean output for analog/RF testing.
CV mode: output voltage is regulated to setpoint, current varies with load (up to current limit). Used for most electronics testing. CC mode: when load tries to draw more current than setpoint → supply limits current, voltage drops. Used for: battery charging (constant current phase), LED testing, motor startup limiting. CV/CC transition: automatic. When in CC mode, LED indicator changes color. Setpoint: dual loop control — voltage control loop adjusts pass transistor base current to maintain V_set. Current sense resistor + INA226 measures output current. When I_out > I_limit: CC loop takes over.
LT3080 is a linear regulator designed for parallel operation. Each LT3080 has a SET pin that programs output voltage. Connect all SET pins together through equal resistors (10kΩ) → output voltage equals (single SET current) × R_total. Each LT3080 has an ILIM pin for current sharing: connect all ILIM pins together → automatic current sharing among all paralleled devices. Three LT3080 in parallel: 3 × 1.5A = 4.5A total output capability. Heat dissipation: spread across all three devices + heatsink. Benefit over single transistor: no matching required, inherent current sharing.
STM32 controls output voltage via DAC (16-bit, MCP4922) driving the LT3080 SET pin through a precision op-amp. Voltage setpoint: SET_current = V_desired / R_set. Read actual voltage/current via INA226 (I2C, 16-bit precision). PID control loop corrects for DAC nonlinearity. Calibration: apply known voltages (measured with calibrated DMM), record DAC codes, fit linear calibration equation (gain + offset). Store in internal flash. Temperature derating: reduce current limit as heatsink temperature rises (LM35 sensor + lookup table).
OVP (Over Voltage Protection): hardware comparator monitors output voltage — if > setpoint + 5%, instantly disconnects output relay (< 1µs response — protects DUT before MCU can react). OCP (Over Current Protection): CC mode inherently limits current. Hard OCP: if current > absolute maximum (5.5A), crowbar SCR clamp or disconnect relay. OTP (Over Temperature Protection): if heatsink > 70°C, reduce current limit or shut down. Reverse polarity protection: P-channel MOSFET or ideal diode controller protects from reverse connection. Soft-start: ramp voltage from 0 to setpoint on enable — prevents current surges into capacitive loads.
Core code for power_supply_ctrl.c:
// Programmable Lab Power Supply Controller // STM32F103, LT3080 parallel, INA226 measurement #include "stm32f1xx_hal.h" #include "ina226.h" #define DAC_MAX 65535 #define VOUT_MAX 30.0f // 30V max #define IOUT_MAX 5.0f // 5A max float v_setpoint = 5.0f; // V float i_setpoint = 1.0f; // A bool cc_mode = false; // INA226 readings float v_actual, i_actual, p_actual; // DAC output to LT3080 SET pin (via op-amp scaling) void set_voltage_dac(float voltage) { voltage = fmaxf(0, fminf(voltage, VOUT_MAX)); uint16_t dac_code = (uint16_t)(voltage / VOUT_MAX * DAC_MAX); // Write to MCP4922 SPI DAC MCP4922_Write(DAC_CHANNEL_A, dac_code); } void set_current_limit_dac(float current) { current = fmaxf(0, fminf(current, IOUT_MAX)); uint16_t dac_code = (uint16_t)(current / IOUT_MAX * DAC_MAX); MCP4922_Write(DAC_CHANNEL_B, dac_code); } void power_supply_update(void) { // Read measurements INA226_Read(&v_actual, &i_actual, &p_actual); // Determine CV or CC mode if (i_actual >= i_setpoint * 0.98f) { cc_mode = true; HAL_GPIO_WritePin(CC_LED_GPIO, CC_LED_PIN, GPIO_PIN_SET); } else { cc_mode = false; HAL_GPIO_WritePin(CC_LED_GPIO, CC_LED_PIN, GPIO_PIN_RESET); } // Over-temperature protection float heatsink_temp = read_lm35(); if (heatsink_temp > 75.0f) { float derating = 1.0f - (heatsink_temp - 75.0f) / 25.0f; set_current_limit_dac(i_setpoint * fmaxf(0.2f, derating)); if (heatsink_temp > 90.0f) { HAL_GPIO_WritePin(OUTPUT_RELAY_GPIO, OUTPUT_RELAY_PIN, GPIO_PIN_RESET); } } else { set_current_limit_dac(i_setpoint); } // Update display display_update(v_actual, i_actual, p_actual, v_setpoint, i_setpoint, cc_mode); }Test Programmable Lab Power Supply by verifying each subsystem individually before full integration.
Verify power voltages, check ground connections, use serial monitor for debug.
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