ORIGINAL: JNorton
ORIGINAL: ckn
So to sum up, as voltage increases, the current can increase, be constant, or decrease, depending on whether it is a linear, non-linear, or highly non-linear devices respectively.
CKN
Absolute BULL PUCKY. Grab a scope at any point of time for any given load at that point of time if you increase the voltage across that load the current will increase. I don't care what the load is and I don't care at what frequency you are talking about. Ohms law is true - you cannot deny the math. Millions of engineering students each year try to inlabs all over the country - world. It holds true. With AC you have to take into acount inductive or capacitve loads - BUT Ohms law still holds true. I do not care if your load is constant is non linear.
John
EDIT -> I'm talking of external loads we use as hobbists. I'm not talking of internal loads within a switching regulator. I'm simply trying to get some basic principals taught so that most people can understand the relationship between volts, current, and resistance.
One of the most common misconception of Ohm's law by first year engineering students is that it applies to all loads. No. It is only true for linear devices such as resistors, inductors, capacitors etc. Strictly speaking even for these linear components Ohm's law still require that some physical conditions be met (such as constant temperature and pressure). Also for inductors the magnetic permeability of the core can introduce non-linearity. For capacitors the dielectric constant can introduce non-linearity.
For a linear device, Volt across device divided by current through device is a CONSTANT defined as the resistance (in case of DC) or impedance (in case of sinusoidal AC) in Ohms. You double the V and you will get double I.
For non-linear device, V divided by I will not be a constant. That is, doubling the V may not result in double I. In other words, the R seem to be changing with voltage.
Diodes and transistors are typical non-linear devices. Systems building out of them are even more non-linear.
So to sum up, it is not strictly correct to assume that when V increases across a load you will certainly have I increases as well. A typical example is the universal voltage adaptor that comes with the mobile phone. They are rated for a wide range of voltage to suit 90V to 260V ac. They are in fact a switching power supply. For that electronic system, as V increases, I actually decreases.
CKN