The common problem with many low cost inverters is their incapability of adjusting the output voltage with respect to the load conditions. With such inverters the output voltage tends to increase with lower loads and falls with increasing loads. The circuit explained here can be added to any ordinary inverter for compensating its varying output voltage conditions in response to varying loads.
Introduction
The circuit was requested to me by one of my friends Mr.Sam, whose constant reminders prompted me to design this very useful concept for inverter applications.
The load independent/output corrected or output compensated inverter circuit explained here is quite on a concept level only and has not been practically tested by me, however the idea looks feasible because of its simple design.
Simulation and Working
If we look at the figure we see that the entire design is basically a simple PWM generator circuit built around the IC 555.
We know that in this standard 555 PWM design, the PWM pulses can be optimized by changing the ratio of R1/R2.
This fact has been appropriately exploited here for the load voltage correction application of an inverter.
An opto-coupler made by sealing an LED/LDR arrangement has been used, where the LDR of the opto- becomes one of the resistors in the PWM "arm" of the circuit.
The LED of the opto coupler is illuminated through the voltage from the inverter output or the load connections.
The mains voltage is suitably dropped using C3 and the associated components for feeding the opto LED.
After integrating the circuit to an inverter, when the system is powered (with suitable load connected), the RMS value may be measured at the output and the preset P1 may be adjusted to make the output voltage just suitable enough for the load.
How to Set Up
This setting is probably all that would be needed.
Now suppose if the load is increased, the voltage will tend to fall at the output which in turn will make the opto LED intensity decrease.
The decrease in the intensity of the LED will prompt the IC to optimize its PWM pulses such that the RMS of the output voltage rises, making the voltage level also rise up to the required mark, this initiation will also affect the intensity of the LED which will now go bright and thus finally reach an automatically optimized level which will correctly balance the system load voltage conditions at the output.
Here the mark ratio is primarily intended for controlling the required parameter, therefore the opto should be placed appropriately either to the left or the right arm of the shown PWM control section of the IC.
The circuit can be tried with the inverter design shown in this 500 watt inverter circuit
Parts List
R1 = 330K
R2 = 100K
R3, R4 = 100 Ohms
D1, D2 = 1N4148,
D3, D4 = 1N4007,
P1 = 22K
C1, C2 = 0.01uF
C3 = 0.33uF/400V
OptoCoupler = Homemade, by sealing an LED/LDR face to face inside a light proof container.
moses kaluya says
Hi swag i build inverter circuit using ic sg3525 successfully but only problem there is big delay when city power go off the inverter oscillator take time to switch on and this cause my computers to go off. How should solve this problem please swag!!!
Swag says
Hi Moses,
Please post this question under the same article which you are referring to, so that I can see the schematic and understand the issue you are facing at the moment…
Aminu Yahaya Ibrahim says
Good day Sir.
Sir could you help me with a timing alarm circuit.
I want the project to work as follow:
1st, to ring an alarm at 35minuts intarval for atleat 3 times.
2nd, to ring an alarm at 35minuts intarval for atleast 2 time.
3rd, to ring an alarm at 35minuts interval for atleast 2times.
Again, I want another one to work at 30 minuts interval with the above discriptions, that is 1st, 2nd and 3rd.
Thanks for the help Sir.
Swagatam says
Aminu, you can try the following concept and adjust the stages accordingly as per your need
https://homemade-circuits.com/2013/06/automatic-programmable-school-bell.html
limit the number of timer stages as per your need…..
Aminu Yahaya Ibrahim says
Thanks for the help Sir.
But I dont mean C3 of IC4093 of the shared link. I mean C3 of the above IC555.
Swagatam says
you can use 0.47uF also for C3.
Aminu Yahaya Ibrahim says
Sir, I built this circuit. But I did not used IC4047, as suggested, I used IC4093 as in this inverter:
http://www.homemade-circuits.com/2012/02/how-to-build-400watt-high-power.html?m=1.
And is it necessary to use C3 i.e 0.33uf 400v?
Can I used any of 0.39uf 400v or 0.47uf 400v or any other one?
Thanks Sir.
Swagatam says
Aminu, C3, and R7 are responsible for generating the basic 50Hz frequency, you can replace C3 with any other capacitor but then you will have to also change R7 value proportionately so that the 50Hz frequency is not disturbed.
Aminu Yahaya Ibrahim says
Sir, I have bought the components of this circuit to give it try with the suggested circuit of IC4047 and I will update you on it very soon.
Thanks for your effort to help us Sir.
Swagatam says
Aminu, I hope you have understood the working of the circuit and will be able to optimize the results correctly…otherwise it could be difficult to get the intended output.
Wish you all the best
Wade Benjamin says
Hi Swagatam, have you tested this circuit?
Swagatam says
Hi Wade, I have not yet tested it.
ainsworth lynch says
I can just buy any optocoupler and place in this circuit right
Swagatam says
no, it's a homemade LED/LDR opto, not the regular ones that are available in the market
vishwas poojary k says
sir how to implement this circuit in ic4017 modified sine wave inverter??
Swagatam says
the above circuit is quite crude, i won't recommend it.
vishwas poojary k says
ok..
sebinpaul2007 says
Hello Sir,
am an btech final year student . for us the project dates came.and we are planning a project in which a small inverter have to be used. and we got accompany with a ready made inverter using KA3525A and it found it to be working. but the main factor is that we dont have its designs and all. only the circuit and the component list. but our project guide tols us to provide its design for that inverter. so for the design parameters we seems to be helpless.we got the data sheet. but no use for us as we are unaware of that particular IC..so please help me out…
Swagatam says
Hello Sebin,
You may refer to the following articles:
https://homemade-circuits.com/2013/01/understanding-sg3525-ic-pin-outs.html
https://homemade-circuits.com/2013/01/modified-sine-wave-inverter-circuit.html
Swagatam says
yes R1 is in parallel to the LDR…..
Swagatam says
yes any standard 5mm led will do….
Swagatam says
Hi Roger,
LDR are identified with their resistance values at certain fixed ambient light, different types may have different values….it's never constant.
Anonymous says
Hi Swagatam
I think that something is wrong with blogspot as it requires a number of 'PUBLISH' clicks before it finally submits a comment and now it is even stranger that my last comment never appeared however here I am again.
Appreciate your approach towards your readers and your passion with electronics.
I have observed that majority of readers are interested to use FET's in output stage of inverter and as such SG3525 is a good candidate as it, by design, supports FETs however we have no understanding how to use it. If time permits that please do write an article about its all capabilities as an inverter or switch mode power supply. Another reason is that said IC is very cheap and easily available in markets. I think that this IC can provide almost all features and will be build successfully even by novice users so would be a nice addition to your site. I have already collected some material about It and am afraid that its all I can do since I have no such expertise as you do, if you need it I can email it to you.
Thanks and regards
Sam
Anonymous says
Hi Swagatam
A lot of thanks for your prompt responses, as ever. I am surely interested only in discrete related circuit diagrams as it helps to learn more and have a feel of 'independence' to it.
Recently during a visit to my local electronics market I have found assembled kits of sg3524/sg3525 but only as a square wave output. I have already made several requests at sites having these circuit diagrams but no response till date. You are the first and only one who posted a discrete sort of solution for a load independent MODIFIED SQUARE WAVE inverter. Majority of other sites have just square wave inverter circuits.
I only asked to confirm as I also though that sg3524/25 can do much more. I understand that it is hard to full fill each and every request (you are having a lot in these days) and am afraid that it may wear out our precious source :).
Thanks again for answering all our queries to the best of your knowledge.
Regards
Sam
Anonymous says
Hi Swagatam
Thank you so much for designing and providing requested circuit. I think it is a very usefull concept and is not just limited to above usage.
Thanks again.
Sam
Anonymous says
pls do u knw hw i can modify a microwave oven transformer to be use in an inverter
f.m 9ja says
why don't u just use sg3524 ic