Don't forget the temperatures. Since it is a small transformer the heat it = generates is probably rather high even when it isn't operating at full load= . = This has to be considered when it is going to be put in an enclosed space, = such = as an ordinary enclosure. The insulation materials are rated for a certain = maximum operating temperature which in turn gives a maximum operating = temperature for the transformer. This can normally be around 70C. This may = sound quite a lot but considering the temperature rise in an enclosed space= it = may mean that the operating temperature for the entire device may become as= low = as 40C or less. The heat generated when it is operating at worst case (short circuited or w= ith = a worst case load - power matching) may require you to put a fuse on the = secondary - even if it is a so called short circuit proof transformer. It a= ll = depends on the temperatures. You also have to consider the tolerances on th= e = input voltage. Also remember that an ordinary fuse for these purposes are = considered to let through 1.7 times its rated current for ever, without = blowing. = Also consider the current and voltage when building a full wave bridge = rectifier with filter capacitors. Sometimes it is good to use capacitors wi= th = higher ESR (or at least not use several connected in parallel) to keep the = peak = currents low. On the other hand low ESR decreases the temperature rise in t= he = capacitors (higher temperature is bad for capacitor lifetime). Note that th= e = transformer currents may need to be as high as 1.6-1.8 times the output DC = current. And of course, the voltage after the bridge is close to 1.4 times = the = AC rms output voltage. It can be even higher for small transformers that is = running on very low load. Some useful links: = /Ruben > Hi all, > = > Looking for advice on any pitfalls or recommendations for putting an > AC transformer (pretty small - 110VAC primary, 9VAC secondary, 2.8KVA) > onto a PCB design. > = > Post transformer, I'll do the classic rectifier make of diodes > (1N4004s)/LM7805 equivalent/bypass caps. > = > Any pointers appreciated! > = > -marc > = =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D Ruben J=F6nsson AB Liros Electronic Box 9124, 200 39 Malm=F6, Sweden TEL INT +46 40142078 FAX INT +46 40947388 ruben@pp.sbbs.se =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist