Claude Loullingen

Let no grass grow under your feet

Let no grass grow under your feet

Changing the output voltage of a Mean Well switching power supply

**Intro:**

I bought a switching power supply Mean Well DR-100-24 to supply some 24V LED stripes.
A nice to have feature is the adjustable output voltage. I wanted to dimm my stripes by this mean
in case they would be too bright.

In fact the stripes turned out to be slightly too light. Unfortunately the trimmer allowed rather
raising the voltage than reducing it (22-30V).

**Analysis:**

The trimmer was part of a voltage divider influencing the setpoint of the output voltage.
The OPAMP was connected such that it would adjust the output voltage U_{OUT} so that
U_{2} will be constantly equal to 2,5V. To the voltage divider applies the known rule
"The lowest voltage is applied on the lowest resistance.".
Reducing R_{1} will therefore reduce U_{1}.
As U_{2} is constant, the output voltage U_{OUT} must reduce too. U_{OUT}=U_{1}+2,5V.

**Strategy:**

The solution to reducing the minimal output voltage is thus to reduce the resistance of the resistor R_{1}.
As R_{1} is surface mounted I prefered to switch an aditional resistor R_{M} in parallel to R_{1}.
As known the equivalent resistor R_{1M} of a parallel circuit is always less than each individual resistance.

**Implementation:**

IN the following picture you can see how I implemented the additional resistor.
On the bottom side of the circuit board you will find many soldering points that are connected to +V_{CC}.

**Dimensioning:**

Unfortunately R_{M} cannot be easily dimensioned arithmetically as the voltage divider is loaded.
By trial & error I found a fitting value. With a value of 120kOhm the adjustable voltage range
is shifting to 16-24V.

**Warning:**

**The above discribed modification requires a qualification as electrician. I do not take over any warranty or responsability for any damage that might occur when following my instructions. You do this at your own risk.**

© by Claude Loullingen