🔧 The Problem: Unstable or Incorrect Output from Your SMPS?

Switched-Mode Power Supplies (SMPS) rely on a voltage feedback loop to maintain a constant output. If this loop isn’t tuned correctly, your output voltage may fluctuate or drift—causing issues in sensitive electronics. This is a common challenge for hobbyists designing custom power supplies.

🛠️ The Solution: Adjust the Feedback Resistor Divider

Most SMPS circuits use a resistor divider to sense the output voltage and feed it back to the control IC. You can fine-tune the output by selecting the right values for these resistors. Always choose precision resistors for better regulation and stability.

🔍 Practical Example: Tuning a 12V Output to 5V

Let’s say you’re repurposing a 12V SMPS module to output 5V instead.

The feedback loop uses resistors R1 and R2:

Vout = Vref × (1 + R1/R2)
For Vref = 1.25V and Vout = 5V,
Solve: 5 = 1.25 × (1 + R1/R2)
R1/R2 = 3 → Choose R2 = 1kΩ, then R1 = 3kΩ.

 

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