Current flow in my circuit! - Page 1
Forum section: electronics / projects

author: Things
author_rank: Regular Contributor
timestamp: December 16, 2012, 01:43:49 pm
content: Hey guys, I'm having a bit of a dilemma here regarding conventional vs electron flow in my circuit design.Basically, the OUT connector here is going to a motor controller. Said motor controller also supports regenerative braking, sending power back up the same lines.What I'm trying to do, is to only allow the regen power to charge the batteries after passing through the CHARGE FET.Conventional flow says this would work:However, electron flow says it wouldn't? :(Ignore the 2 useless misplaced arrows)Is this what I actually need?This has me totally stumped!Dan

author: Unknown
author_rank: Unknown
timestamp: December 16, 2012, 04:47:42 pm
content: Are you confused by the diode symbol? A diode conducts if the voltage at the anode is ~ 0.7 V higher than the voltage at the cathode. The arrow symbol just indicates the forward direction of conventional current flow, so electron flow would go against this arrow. I don't see the point of mixing them both, this will just confuse you. Just pick one (>99% of the world picked conventional flow) and stick with it.

author: Things
author_rank: Regular Contributor
timestamp: December 16, 2012, 04:55:51 pm
content: Well not the diode symbol in particular, but whether my plan would even work in that config? As it seemed to be it would depend on either conventional or election current flow? because in the last screenshot, it makes sense from an electron flow point of view, but no sense in conventional current.

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: December 16, 2012, 07:26:46 pm
content: Quote from: ThingsYes

author: IanB
author_rank: Super Contributor
timestamp: December 16, 2012, 07:37:52 pm
content: Quote from: Things on December 16, 2012, 04:55:51 pmNothing depends on conventional flow or electron flow. Both are equivalent and all calculations work just as well as one way or another.However, since the whole world has standardized on conventional flow, you should ignore electron flow and pretend you have never heard of electrons. It will just confuse you (as it apparently is doing).Follow the device data sheets, use normal circuit symbols, and design using the standard formulas given in textbooks and on data sheets. Don't try and muddle things up by doing things differently from the way they are taught.

author: Things
author_rank: Regular Contributor
timestamp: December 17, 2012, 12:23:41 am
content: OK, thanksJust for clarification, will that last circuit actually only allow current flowing in to the out connector to pass through the CHG FET? Or will it still pass through the DSG one too?

author: PuterGeek
author_rank: Regular Contributor
timestamp: December 17, 2012, 12:35:19 am
content: In part it is going to depend on the actual FETs used and the gate voltages.With the correct components it is possible to make the discharge FET block reverse battery.A good way to learn would be manual circuit analysis and/or simulating the circuit in LTSpice.

author: Things
author_rank: Regular Contributor
timestamp: December 17, 2012, 12:39:03 am
content: Oh, so FET's actually allow the current to flow both ways?Charging:Discharging:Would it be possible to put a diode between that DSG(-) port and the Discharge FET to prevent it from allowing current backwards?Just put it into the Java circuit sim and it seems to do what I want with the 2 diodes like that:Dan

author: PuterGeek
author_rank: Regular Contributor
timestamp: December 17, 2012, 10:33:51 pm
content: Two diodes is one way to get there.Remember each diode has a voltage drop (0.7V typically) and they have to be able to handle the current. A standard 1N4007 diode can handle 1A so it will dissipate 0.7W as heat.So not only do you end up with a lower voltage, you are losing energy on both discharge and regeneration.