Hopla Chucho, is a step down source, they work with a lot of current, it is very difficult to achieve ... but do not get lost, you can replace with a module of these,
http://articulo.mercadolibre.com.ar/MLA-648645302-modulo-step-down-xl4005-convertidor-5a-fuente-08-a-24v-_JM
I am willing to help you with the installation
Successes
I add the application circuit of your integrated

the datasheet
https://www.semicon.sanken-ele.co.jp/sk_content/nr111d_ds_en.pdf