I tend to use Digikey as a partys selector as their listed stock is good and their parametric search engine reasonable. YMMY. Digikey would have many suitable diodes. I understand the advice you were given to use a diode an an initial dropper. It's workable and easy, but it seems an unusual way to do it. IF you have a FET that can tolerate the required dissipation then you can operate it in linear mode to achieve the output voltage of your choice. Effectively you are producing an LDO with the FET as a pass element. MOSFETs are capable of as low on-state voltage drops =A0as you are liable t= o need. eg at 1 A a 0.1 volt drop =3D 0.1V/1A =3D 100 milliohn Rdson. This is a very modest Rdson. 25 milliohm will give you 25 milliVolt etc. Search Digikey or where-ever for a suitable FET. Required parameters include. - Rdson - see above. - Vgs low enough to provide the rated Rdson at available voltage. You have up to about 5 V available as gate drive. - Dissipation - relevant only if used in linear mode as an LDO as above. If used as on or off only, dissipation =3D I x Von =3D 1A x say 50 mohm =3D= 50 mW. If used as an LDO pass element then at 1A you need 100 mW dissipation capability for each 0.1V drop across the MOSFET when regulating. > Approximately=A0how much current is needed to drive a FET? You would benefit very great from some basic learning on key components, such as MOSFETS. Even some basic Gargoyling would produce dividends. The OFFICIAL intention of this list is that people should at least try to answer such questins themselves instead of just asking. Typing your exact query into Gargoyle (hey - even just into your browsers address bar in some systems) produces many relevant answers The very first answer is http://focus.ti.com/lit/ml/slup169/slup169.pdf which answers your query well. =A0=A0 Russell On 15 December 2010 23:49, V G wrote: > > Hi all, > > 1. I have selected a power diode to drop the voltage of the initial 5.8 > volts to something less than 5.5 volts. I was hoping to find a high curre= nt > Schottky or Germanium diode, but was unable to find one, so I ended up > selecting the following: > > http://www.futurlec.com/Diodes/6A01.shtml > > It's a 6 A power diode which h= as > a 0.6 - 0.7 volt drop at around 1 A. Should be suitable for my purposes. > > What are your opinions on this? > > 2. To switch the 4.4-5.8 V @ ~1 A, what type of FET should I use? I hear > that JFETs have lower output impedance and so I am tempted to using those= .. > > I'm looking at the transistors here: > http://www.futurlec.com/Transistors.shtml > > Also, what is the difference between all those "series"? > > 3. The comparator will need to be able to drive the FET(s). Approximately > how much current is needed to drive a FET? I'll need to select the > comparator based on that, or add some transisotrs. > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .