AliExpress Gem of the Month - January 2025

Today, I am starting a new series where I will make a confession and seek forgiveness for past mistakes—especially for the numerous valuable Patreon euros I spent on low-quality Chinese stuff. But as always, when digging, you might find a lump of coal or perhaps a diamond. In this series I want to share one Diamond I found every month! Lets get started:

LM2596 DC-DC Step-down Power Supply Module

Most DIY enthusiasts are familiar with buck converters, but for those who aren't:

The LM2596 is an affordable and widely used circuit for reducing higher voltages to lower levels. It handles input voltages from 4V to 40V and efficiently delivers up to 1A of current without excessive heating. The output voltage is adjustable, allowing it to be set to approximately 95% of the input voltage.

Whether you're powering microcontrollers, LED lights, or other electronics, the LM2596 provides a reliable and cost-effective solution for voltage regulation in your projects. You can purchase a pack of 10 units for just 6 EUR, with free shipping included.

But today, I want to share an alternative way to utilize buck converters. Many of you are familiar with the frustration of howling fans, particularly the GDSTime fans, which are notorious when it comes to 2-pin fans driven by a PWM fan controller. This is where a little buck converter comes into play. I connect the buck converter between the output of the fan's MOSFET and the fan itself. Here's the schematic of the circuit:

By fully adjusting the potentiometer, I reduce the 24V input to a 23.2V output, causing the fan to run slightly slower compared to its operation without the circuit.

The fan MOSFET outputs square wave pulses that we aim to convert into a smooth DC current through multiple steps. First, the square wave is transformed into a sawtooth waveform using the C1 capacitor. To achieve an even sawtooth, it’s essential to select a PWM cycle time that matches the characteristics of the capacitor. I obtained optimal results by driving the circuit at 20 Hz.

In the next step, the LM2596S voltage regulator converts the sawtooth waveform into a DC voltage, though this introduces a bit of jitter at the output. Finally, an LC filter removes this jitter, resulting in a stable DC output with less than 50 mV of fluctuation which eliminates any audible PWM noise from the fan.

Isn't an RC Filter the Easier Solution?

While the traditional 51 Ohm / 220µF RC filter works effectively for smaller fans, such as the 5015 model that draws around 1W of power, it becomes inadequate for larger fans like the 12032, which consume approximately 12W. In these higher-power applications, using an RC filter leads to significant power loss to the fan or causes excessive heat buildup in the resistor. This inefficiency makes RC filters unsuitable for more demanding fan models. Consequently, alternative solutions with a voltage regulator are necessary to ensure optimal performance and minimize heat loss.

However, as with any solution, there is a caveat. Operating the circuit at 20 Hz means that the C1 capacitor is charged and discharged 20 times per second, resulting in a high current draw from the fan's MOSFET. If your board manufacturer has cheaped on using quality MOSFETs, this increased stress can lead to their burnout when using such a circuit. Therefore, it's crucial to double-check the specifications and quality of your MOSFETs before implementing this setup. Below is the schematic of my BTT Kraken Fan MOSFET for reference:

As you can see, the fans are controlled by an ES3400 MOSFET, and there is a 24V / 1A fuse on the fan output. The fuse is not an issue for our application because any current exceeding 1A is drawn only momentarily. Fuses are designed to burn out only if the current surpasses their rating for an extended period. Therefore, even current spikes of 3-4A would not hurt the fuse since it's frequency is high enough so that we remain on the safe side

When it comes to the MOSFET we have to check it's data sheet:

The key specifications to consider are the continuous drain current and pulsed drain current. For my ES3400 MOSFET, the continuous drain current is rated at 4.6A at 70°C, which represents the worst-case scenario. Additionally, it can handle up to 30A for short pulses. These values are well beyond what the LM2596 would ever require so it's save to say that the LM2596 is not able to damage my MOSFET.

So, if you're tired of your fans howling and want to eliminate PWM noise, this 60 cent gadget is the perfect solution.

For my T250 I use 4 of them:

• 1x Left Side Blower

• 1x Right Side Blower

• 1x for all 4 60x20 Motor Fans

• 1x for the 2 60x20 Electric Fans

There are dozens of different buck converters available on the market. I used this specific one, but others should also work; you might need to adjust the PWM frequency depending on the converter you choose. Check it out here.