Hi, This is a very good question you are asking and you are absolutely right that it is fundamental to any kind of electronics design. First of all, Ohm's Law is not a universal law but rather an observation about electrical conduction in metals and other good conductors. Their relationship between voltage and current is exceptionally linear over many orders of magnitude. This is not true of all materials or circuits. Semiconductor materials, conductive liquids, vacuum tubes, plasma (like in an electrical arc), etc. are all non-ohmic in behavior. You can also construct an active circuit using transistors which emulates any arbitrary V,I relationship. There is something fundamental going on here and that is that V and I are not independent. The V/I relationship is driven by both devices in your circuit (the power supply and the load). Think of it as two equations in two unknowns. V=3Df(I) is the relationship for the power supply and V=3Dg(I) is the relationship for the load. When you put them together, V and I must be the same for both so you end up with (usually) one well defined solution for what will happen (V and I take on values for which the two equations are satisfied or, more physically, V and I take on values where the power supply and load can "agree" to make them match) The V=3Df(I) function for an ideal constant current-constant voltage lab-type power supply is rectangular in shape. It is a horizontal line at the voltage setting from 0 Amps up to the current limit and then a vertical line at the current limit setting between 0 Volts and the voltage setting. In reality, the horizontal line is not quite horizontal and the vertical line not quite vertical so you end up with a true mathematical function with a very flat region and a very steep edge. Sean On Tue, Nov 23, 2010 at 3:44 PM, V G wrote: > Hi all, > > My understanding of analog electronics is next to nothing. But it > seems that to build a circuit of any sort, this knowledge is > essential. Well, to build a good circuit anyway. > > So I have a question. > > Let's say that there's a power source with variable voltage. Across > its terminals is a resistor of 10 Ohms. The power supply can only > supply a maximum of 1 Amp. > > If the voltage is gradually increased, to the point where I =3D V/R > 1 > Amp, what will happen? Will Ohm's "law" not be violated? > > In the case of the battery charger example: > > A NiMH battery should be trickle charged (assume constant current of a > few milliamps, rather than a high current pulse). The battery has a > relatively low internal resistance. How can the current supplied to > the battery be controlled precisely when the applied voltage is > relatively constant? > -- > 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 .