Hey don't feel bad at all. It's probably best that you get this confusion cleared up right now or it will haunt your circuits forever. What you are saying is still basically incorrect though. Voltage can (sort of) exist without current, but not without resistance. When you're reading a voltage off two pins, remember that they are effectively separated by an infinite resistance of air. Without this resistance, there could be no voltage. In Ohm's law, if R=infinity, then current drops to zero. Resistance can exist without either current or voltage (as in a resistor sitting there on your desk), but its arguable whether its actually resistance unless it is resisting something. Without a current to resist it's no better than a clod of dirt or something. Keep in mind exactly what current is... It's the flow of electrons, electricity in it's most fundamental form. Current exists in all electrical circuits. Without electrons flowing to the battery terminals, there would be no voltage on them. Without current flowing through a resistor, there would be no voltage. Current, in its most basic form, can (sort of) exist without any voltage. All you need is some organized flow of electrons through a negligible resistance. If you haven't considered the following analogy to fluid dynamics it might help your understanding. Think of voltage as a pressure in a system of pipes, current as the amount of water flowing, and resistance as a necking down of the pipe. Large resistance equate to large pipe-area reductions. It should now become clear that with an infinite resistance the pressure (voltage) assumes some constant state. For a pressure/voltage drop to occur there must be some resistance, since if there is no resistance the water/current will just flow freely. It would be silly to say that there is some pressure in an empty pipe, and likewise it would be silly to say that there is some voltage without a current backing it. Voltage is more the willingness of a current to overcome resistance than a measure of electricity. Every day you incur thousands of volts upon your body just walking around on the carpet, but obviously this does not really do anything (besides zap that expensive new chip you're working on.) I'm sure there's a better rendition of the analogy out there somewhere since I just pulled this out of my arse. Search on google if you think it will help. Jeeze I hope that helped some, surely there's gotta be something in there that sparks a lightbulb? ----- Original Message ----- From: "Rick Regan" To: Sent: Friday, April 16, 2004 7:47 PM Subject: Re: [EE]: Why isn't Ohm's Law written I=V/R? > > No. Like I said before, if your power supply contains bipolar > > transistors, then it's all BASED on current, since bipolar transistors > > are current-controlling devices. > > > > There's this big transistor on the back, probably on a heat sink. The > > power supply allows the base current of that transistor to rise > > (increasing the collector current as well, but the beta factor) until > > it senses that a reference voltage has reached a correct value. In CV > > mode, the reference voltage is just the output voltage In CC mode, the > > reference voltage is the voltage across some current-sensing resistor. > > Your linear regulators (7805, etc) work the same way. The internal > > components are controlling current, rather than voltage directly. > > > > A transistor is a fine example of a device that permits current to be > > controlled directly. Bipolar transistors are current-controlled, FETs > > are voltage controlled, but in each case it's the current that is being > > manipulated. (Come to think of it, tubes work this way too...) > > It's probably my fault for not being clear enough > about what I was asking, so I will make one more attempt > (I promise - this is my last post!). > > I am not saying the algebra is wrong. I am not saying > that at any given time it's not convenient to put any one > of the three variables on the left hand side of the > equation. I was just trying to understand how current > could be an entity in its own. This was my understanding > and I guess you're saying I'm wrong: > > - You can have V without I > - You can have R without I > - You CAN'T have I without V and R > > Thanks for the responses. (I will now unsubscribe from the [EE] tags and stick with [PIC] ;)). > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads