AC Electronic Load Circuit - Page 1
Forum section: electronics / projects

author: cooldesire
author_rank: Newbie
timestamp: April 30, 2012, 04:21:17 am
content: Hello all, I'm new here...Can anyone help me to find acircuitfor "ac electronic load"very important for me, it is my final year projectI have two months to finish it.

author: free_electron
author_rank: Super Contributor
timestamp: April 30, 2012, 04:32:38 am
content: Quote from: cooldesire on April 30, 2012, 04:21:17 amplenty of time to design one then i think...Since it's your final year project YOU need to do the work ...We can help.. but you need to show what you have found so far, what routes you have explored.What current range are we talking ? what voltage range ?What about burden voltage ?Take a look at how a programmable current load is made. There's plenty of schematics floating around. in its simplest form it is a power transistor , a current sense resistor and an opamp ...As for the AC problem : here is a hint : convert your AC problem to a DC problem ... and then the solution is easy. ( think of a rectifier )

author: BravoV
author_rank: Super Contributor
timestamp: April 30, 2012, 05:01:48 am
content: Its amazing you don't even bother to search at the net instead of asking people here to do it for you for your homework.Another crappy electronic engineer in making.

author: cooldesire
author_rank: Newbie
timestamp: April 30, 2012, 11:09:29 am
content: I tried to simulate a circuit is taken place IEEE paper about "study on ac active load simulator" and worked on over "dc electronic load" for ac operation, but I couldn't succeed... Finally I decided to ask someone and right now I'm here...project ratings: Minimum 1A(rms)/48V(rms), f:50-60Hzneed a full schematic, I fail to design a circuit by myself...in the attachment, worked on over "dc electronic load" schematic taken place...

author: Bloch
author_rank: Unknown
timestamp: April 30, 2012, 01:31:09 pm
content: Quote from: BravoV on April 30, 2012, 05:01:48 amLOLhttp://www.edaboard.com/thread249311.htmlIt is kind of sadbut i do agree with you.

author: Unknown
author_rank: Unknown
timestamp: April 30, 2012, 01:50:14 pm
content: Please tell me that this is for a high school science class, and not a BSEE final project.

author: cooldesire
author_rank: Newbie
timestamp: April 30, 2012, 02:06:04 pm
content: I shared the same topic many electronics forum sites to approach to solution quickly....I'm an undergraduate student, I should make the project as possible as simple way...

author: free_electron
author_rank: Super Contributor
timestamp: April 30, 2012, 02:32:26 pm
content: Your schematic contains serious errors.First of all get rid of the diodes..... They are put in the wrong way to begin with.Second, the lm339 is a comparator and not suitable for regulation. You need an opamp.Download ltspice from national and draw the schematic of the left half ( forget the right half for now. )Get that to work and show a couple of plots here. Then we'll go on.I'm still willing to help, but it is deplorable that a bsee has no clue how to make a simple current sink... 1 opamp, 1 resistor and one transistor is all you need.

author: Rufus
author_rank: Super Contributor
timestamp: April 30, 2012, 02:45:14 pm
content: Quote from: BravoV on April 30, 2012, 05:01:48 amGovernments universally think they need more smart people to compete in the modern world.They want to put an ever increasing proportion of the population through university education because universities turn dumb people into smart ones, the bits of paper they issue prove it.

author: amspire
author_rank: Super Contributor
timestamp: April 30, 2012, 03:16:24 pm
content: Quote from: free_electron on April 30, 2012, 02:32:26 pmThere is an error in that the L and N connections should be shorted and connected to L, and ground should be replaced by N.I think this is a switching circuit using the hysteresis of the LM339 and the time constants of C1 and C2, but I am not sure exactly how they intended it to work.I would start with a linear circuit and not a switching circuit, so I would forget this circuit.The idea of a DC current sink circuit combined with a full wave regulator is sort of OK in acting as a linear load, but AC loads often have to be able to simulate reactive loads which would eliminate that idea.A circuit like this can only simulate a resistive load, if that is what you want.If you need to be able to control the current phase, then you need a 4 quadrant circuit - a circuit that can source and sink current for both positive and negative cycles. Not a simple project.Richard.

author: free_electron
author_rank: Super Contributor
timestamp: April 30, 2012, 03:37:34 pm
content: @rufus: let's not have this topic degrade into another 'paper with shiny star' bashing. for once we have something where people can leran from.@amspire : you corrected the polarity of the diodes. the OP had those wrong.i would not use a mos but a darlington transistor. Bob peas has some really nice instruction video's on youtube on how to make reliable current sinks. ( there's one where he builds a 'trarlington' )reactive loads are out of reach for such a simple thing... you'd need to measure voltage and current and be able to inject a phase shift. reactive loads require hefty power supplies to inject current into the loop..simple passive load is what we go for.. OP has 2 months, and given his 'enthousiasm' and 'excitement' of having to do this task ... it'll be enough.

author: cooldesire
author_rank: Newbie
timestamp: April 30, 2012, 04:17:56 pm
content: How can I verify this circuit in realand what type of mos and opamp should I use...I have these---> IRFP250 and IRF9640and should I need to use a mosfet driver...

author: free_electron
author_rank: Super Contributor
timestamp: April 30, 2012, 05:03:48 pm
content: you are not even close to the 'real' ... step yet.first make a correct schematic. you don;t need a mosfet driver. nut , if you want this thing to have fast response you will need an opamp with some 'kick' ( output current capability ) as the mos is essentially a capacitor that needs charging and discharging.look at something like a video opamp. those can typically drive quite a bit of current.as for the mos : the steepness of the transient curve is important. you don't want a mos that is bang-on, bang-off... your system will only have a very small window of operation. look for a linear mos... typically mosfets used in analog audio amplifiers work very well for this kind of work.but i would let go of the mosfet altogether and switch to a bipolar transistor. you'll run into less problems.

author: krish2487
author_rank: Frequent Contributor
timestamp: May 01, 2012, 05:45:59 am
content: Heres a idea for thoughts...You ll come across many DC electronic loads on this website and net in general...Mate a DC electronic load with a active PFC front end...:-DYou ve got a AC electronic load...Only a idea.. but you HAVE to do the work yourself..No one here is obliged to do anything and hand over your project on a platter to you.Guiding you is the maximum anybody will do here.Not because they cant but there is only a finite amount of help and guidance anyone can give you over the net.Secondly what will you learn if someone else does all your work for you..

author: nctnico
author_rank: Super Contributor
timestamp: May 01, 2012, 09:36:02 am
content: I think this will work:- bridge rectifier with schottky diodes- N-channel MOSFET- potmeter- 5V power supplyThe MOSFET works as a variable resistor so the current will also be -more or less- sinusoidal. I'd recommend you simulate it first.PS: The diode across the Mosfet is the internal body diode. It is a good custom to always draw it as well. It helps to tell the source and drain apart