A DC-DC Converter for 28 Volt SMA-Relais

Although there already exist many websites about such stuff, another simple DC-DC converter is described here.

eagle .sch file

Capacitors: 10 uF/25V, Diodes: 1N4148 (or any other general purpose diode). The IC is an ICL7662 which is rated to have a maximum output voltage of 38.6 V at 20 V input. The ICL7660A may also be used but can take only 13.5 V input voltage. The output voltage equals twice the input voltage minus the voltage drop across the diodes.

eagle .brd file

original size

The board is done with "Eagle" from "Cadsoft" - click here to download Eagle (fully functional trial version, only board size is limited to 8x5 cm). Click here to download the schematic file. Click here to download the board file.

settling time

The plot above shows the switch-on behaviour. When 13.8 Volt is applied (upper, grey trace) it takes about 2 ms until the output reaches 24 Volt (green trace).

I use this DC-DC converter on several SMA relais since about 2 years now, none has failed so far. As a test, I put one converter on a 10 Hz square wave generator and let it switch a 24 V relais on/off a whole week (abt 6 million cycles). It survived this treatment as well.

The picture below shows a DC-DC converter mounted on top of the SMA-relais which it is switching.


operational device