Understanding Circuit  - Page 1
Forum section: electronics / beginners

author: yashrk
author_rank: Frequent Contributor
timestamp: February 15, 2014, 09:34:43 pm
content: Hey guys I found this circuit online and I got how the voltage and current is measured and basic rectification in it but other than that nothing got in to my head.Please help me understand this circuit how it works.

author: Rerouter
author_rank: Super Contributor
timestamp: February 15, 2014, 09:42:27 pm
content: That is likely because it is a very poorly drawn schematic, not following the convention of inputs on the left and outputs on the rightbecause they did as such, lets begin from the right, you have an op amp acting as a voltage reference, using a zener diode, next along you have the op amp regulating voltage, it does so with the 3 transistors being a darlington pair with 2 high current transistors instead of the one,third op amp from the right is the current limit comparitor, when your current limit is exceeded it steals the drive to the npn's turning them off,and forth from the right is the current setpoint op amp, it offsets the voltage generated by the current measuring resistor to allow you to set the current limit,

author: Dave
author_rank: Super Contributor
timestamp: February 15, 2014, 10:45:51 pm
content: I've taken the liberty of annotating the schematic.The current regulation part might be slightly confusing, so I have marked four nodes in the circuit (A, B, C and D).The bottom left opamp keeps node D at the same potential as node A. Node C is one diode drop above node D. This gives a voltage of approx 0.7V across the current adjustment potentiometer, so you can set the potential of the wiper of the potentiometer to be anywhere from the potential of node A to node A + 0.7V. You then have a second opamp (current error amplifier), which compares the potential of node B against the wiper. If node B exceeds the potential of the wiper, the opamp output will go low, sucking current away from the series pass elements.If you are looking for a good power supply circuit, this is not it. I would be willing to bet this circuit would oscillate like crazy, if you actually decided to build it.

author: IanB
author_rank: Super Contributor
timestamp: February 16, 2014, 11:58:39 am
content: That circuit doesn't even show any output terminals, so the simplest assumption is that it "does nothing useful"

author: grumpydoc
author_rank: Super Contributor
timestamp: February 16, 2014, 12:34:11 pm
content: QuoteIt's the bit labelled "Dummy Output 500 ohm", but it took me about a minute of staring to find it.

author: lapm
author_rank: Frequent Contributor
timestamp: February 16, 2014, 01:10:21 pm
content: Quote from: grumpydoc on February 16, 2014, 12:34:11 pmNo wonder its difficult to understant. Non standard ways to present things...

author: yashrk
author_rank: Frequent Contributor
timestamp: February 16, 2014, 02:09:52 pm
content: Its seriously pain in the as* to readhey can any one be my friend on Facebook I have no friend who is interested in electronics.yash19041995@gmail.comWell thanx for your reply guys..

author: madires
author_rank: Super Contributor
timestamp: February 16, 2014, 03:07:16 pm
content: Quote from: Dave on February 15, 2014, 10:45:51 pmYep, and both 2N3055 should have an emitter resistor to share the load current equally.

author: megajocke
author_rank: Regular Contributor
timestamp: February 16, 2014, 07:58:20 pm
content: I'd say the first and biggest problem with that circuit is that the absolute maximum voltage rating will be exceeded for all semiconductor devices except the diodes with a 50 V transformer.At high line of +10% and light load, assuming 10% regulation for the transformer, the supply voltage could climb to above 80 V!