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Simple Solar MPPT Circuit

Simple Solar MPPT Circuit

A simple yet effective solar panel MPPT charger circuit can be built using a couple of 555 ICs and a few other linear components. Let's learn the procedures.

MPPT Circuit Objective

An MPPT or Maximum Power Point Tracker for solar panels is a method which enables deriving maximum available current from a solar panel throughout the day without disturbing its specified voltage, thus allowing greatest efficiency from the panel.

As we all know, acquiring highest efficiency from any form of power supply becomes feasible if the procedure doesn't involve shunting the power supply voltage, meaning we want to acquire the particular required lower level of voltage, and maximum current for the load which is being operated without disturbing the source voltage level, and without generating  heat.

Briefly, a concerned MPPT should allow its output with maximum required current, any lower level of required voltage yet making sure the voltage level across the panel stays unaffected.

One method which is discussed here involves PWM technique which may be considered one of the optimal methods to date.

We should be thankful to this little genius called the IC 555 which makes all difficult concepts look so easy.

Using IC 555 for the PWM Conversion

In this concept too we incorporate, and heavily depend on a couple of IC 555s for implementing the MPPT effect.

Looking at the given solar mppt circuit using IC555 we see that the entire design is basically divided into two stages.

The upper voltage regulator stage and the lower PWM generator stage.

The upper stage consists of a p-channel mosfet which is positioned as a switch and responds to the applied PWM info at its gate.

The lower stage is a PWM generator stage. A couple of 555 ICs are configured for the proposed actions.

How the Circuit Functions

IC1 is responsible for producing the required square waves which is processed by the constant current triangle wave generator comprising T1 and the associated components.

This triangular wave is applied to IC2 for processing into the required PWMs.

However the PWM spacing from IC2 depends on the voltage level at its pin#5, which is derived from a resistive network across the panel via the 1K resistor and the 10K preset.

The voltage between this network is directly proportional to the varying panel volts.

During peak voltages the PWMs become wider and vice versa.

The above PWMs are applied to the mosfet gate which conducts and provides the required voltage to the connected battery.

As discussed previously, during peak sunshine the panel generates higher level of voltage, higher voltage means IC2 generating wider PWMs, which in turn keeps the mosfe switched OFF for longer periods or switched ON for relatively shorter periods, corresponding to an average voltage value that might be just around 14.4V across the battery terminals.

When the sun shine deteriorates, the PWMs get proportionately narrowly spaced allowing the mosfet to conduct more so that the average current and voltage across the battery tends to remain at the optimal values.

The 10K preset should be adjusted for getting around 14.4V across the output terminals under bright sunshine.

The results may be monitored under different sun light conditions.

The proposed MPPT circuit ensures a stable charging of the battery, without affecting or shunting the panel voltage which also results in lower heat generation.

Note: The connected soar panel should be able to generate 50% more voltage than the connected battery at peak sunshine. The current should be 1/5th of the battery AH rating.

How to Set up the Circuit

  1. It may be done in the following manner:
  2. Initially keep S1 switched OFF.
  3. Expose the panel to peak sunshine, and adjust the preset  to get the required optimal charging voltage across the mosfet drain diode output and ground.
  4. The circuit is all set now.
  5. Once this is done, switch ON S1, the battery will start getting charged in the MPPT mode.

Adding a Current Control Feature

A careful investigation of the above circuit shows that as the mosfet tries to compensate the falling panel voltage level, it allows the battery to draw more current from the panel, which affects the panel voltage dropping it further down inducing a run-away situation, this may be completely against the MPPT law.

A current control feature as shown in the following diagram takes care of this problem and prohibits the battery from drawing excessive current beyond the specified limits. This in turn helps to keep the panel voltage unaffected.

RX which is the current limiting resistor can be calculated with the help of the following formula:

RX = 0.6/I, where I is the specified minimum charging current for the connected battery

A crude but simpler version of the above explained design may be built as suggested by Mr. Dhyaksa using pin2 and pin6 threshold detection of the IC555, the entire diagram may be witnessed below:

No MPPT without a Buck Converter

The above first technically correct MPPT circuit designed by me presented a simple varying PWM concept which automatically adjusted the PWM of a 555 based circuit in response to the changing sun intensity.

Although the output from this circuit produces a self adjusting response in order to maintain a constant average voltage at the output, the peak voltage is never adjusted making it considerably dangerous for charging Li-ion or Lipo type batteries.

Moreover the above circuit is not equipped to convert the excess voltage from the panel into a proportional amount of current for the connected lower voltage rated load.

Adding a Buck Converter

I tried to rectify this condition by adding a buck converter stage to the above design, and could produce an MPPT that looked very near to a real MPPT. The entire article can be studied below:

Self Optimizing Solar PWM Charger Circuit with Buck Converter

However even with this improved MPPT circuit I could not be entirely convinced regarding whether or not the circuit was truly capable of producing a constant voltage with trimmed down peak level and a boosted current in response to the various sun intensity levels.

In order to be entirely confident regarding the concept and to eliminate all the confusions I had to go through an exhaustive study regarding buck converters and the involved relation between the input/output voltages, current, and the PWM ratios (duty cycle), which inspired me to create the following related articles:

How Buck Converters Work

Calculating Voltage, Current in a Buck Inductor

The concluding formulas obtained from the above two articles helped to clarify all the doubts and finally I could be perfectly confident with my previously proposed MPPT circuit using a buck converter circuit.

Analyzing PWM Duty Cycle Condition for the Design

The fundamental formula which made things distinctly clear can be seen below:

Vout = DVin

Here V(in) is the input voltage which comes from the panel, Vout is the desired output voltage from the buck converter and D is the duty cycle.

From the equation it becomes evident that the Vout can be simply tailored by "either" controlling the duty cycle of the buck converter or the Vin....or in other words the Vin and the duty cycle parameters are directly proportionate and influence each others values linearly.

In fact the terms are extremely linear which makes the dimensioning of an MPPT circuit much easier using a buck converter circuit.

It implies that when Vin is much higher (@ peak sunshine) than the load specs, the MPPT processor can make the PWMs proportionately narrower (or broader for P-device) and influence the Vout to remain at the desired level, and conversely as the sun diminishes, the processor can broaden (or narrow for P-device) the PWMs again to ensure that the output voltage is maintained at the specified constant level.

Evaluating the PWM Implementation through a Practical Example

We can prove the above by solving the given formula:

Let's assume the peak panel voltage V(in) to be 24V

and the PWM to be consisting a 0.5 sec ON time, and 0.5sec OFF time

Duty cycle = Transistor On time / Pulse ON+OFF time = T(on) / 0.5 + 0.5 sec

Duty cycle = T(on) / 1

Therefore substituting the above in the below given formula we get,

V(out) = V(in) x T(on)

14 = 24 x T(on)

where 14 is the assumed required output voltage,


T(on) = 14/24 = 0.58 seconds

This gives us the transistor ON time which needs to be set for the MPPT circuit during peak sunshine for producing the required 14v at the output.

How it Works

Once the above is set, the rest could be left for the MPPT to process for the expected self-adjusting T(on) periods in response to the diminishing sunshine.

Now as the sunshine diminishes, the above ON time would be increased (or decreased for P-device) proportionately by the MPPT in a linear fashion for ensuring a constant 14V, until the panel voltage truly falls down to 14V, when the MPPT could just shut down the procedures.

The current (amp) parameter can be also assumed to be self adjusting, that is always trying to achieve the (VxI) product constant throughout the MPPT function. This is because a buck converter is always supposed to convert the high voltage input into a proportionately increased current level at the output.

Still if you are interested to be entirely confirmed regarding the results, you may refer to the following article for the relevant formulas:

Calculating Voltage, Current in a Buck Inductor

Now let's see how the final MPPT circuit designed by me looks like, from the following info:


As you can see in the above diagram, the basic diagram is identical to the earlier self optimizing solar charger circuit, except the inclusion of IC4 which is configured as a voltage follower and is replaced in place of the BC547 emitter follower stage. This is done in order to provide a better response for the IC2 pin#5 control pinout from the panel.

Summarizing the Basic Functioning of the MPPT

The functioning may be revised as given under:IC1 generates a square wave frequency at about 10kHz which could be increased to 20kHz by altering the value of C1.

This frequency is fed to pin2 of IC2 for manufacturing fast switching triangle waves at pin#7 with the help of T1/C3.

The panel voltage is suitably adjusted by P2 and fed to the IC4 voltage follower stage for feeding the pin#5 of the IC2.

This potential at pin#5 of IC2 from the panel is compared by pin#7 fast triangle waves for creating the correspondingly dimensioned PWM data at pin#3 of IC2.

At peak sun shine P2 is appropriately adjusted such that IC2 generates the broadest possible PWMs and as the sun shine begins diminishing, the PWMs proportionately gets narrower.

The above effect is fed to the base of a PNP BJT for inverting the response across the attached buck converter stage.

Implies that, at peak sunshine, the broader PWMs force the PNP device to conduct scantily {reduced T(on) time period}, causing narrower waveforms to reach the buck inductor...but since the panel voltage is high, the input voltage level {V(in)} reaching the buck inductor is equal to the panel voltage level.

Thus in this situation, the buck converter with the help of the correctly calculated T(on) and the V(in) is able to produce the correct required output voltage for the load, which could be much lower than the panel voltage, but at a proportionately boosted current (amp) level.

Now as the sun shine drops, the PWMs also become narrower, allowing the PNP T(on) to increase proportionately, which in turn helps the buck inductor to compensate for the diminishing sunshine by raising the output voltage proportionately...the current (amp) factor now gets reduced proportionately in the course of the action, making sure that the output consistency is perfectly maintained, by the buck converter.

T2 along with the associated components form the current limiting stage or the error amplifier stage. It makes sure that the output load is never allowed to consume anything above the rated specs of the design, so that the system is never rattled and the solar panel performance is never allowed to divert from its high efficiency zone.

C5 is shown as a 100uF capacitor, however for an improved outcome this might be increased to 2200uF value, because higher values will ensure better ripple current control and smoother voltage for the load.

P1 is for adjusting/correcting the offset voltage of the opamp output, such that pin#5 is able to receive a perfect zero volts in the absence of a solar panel voltage or when the solar panel voltage is below the load voltage specs.

The L1 specification may be approximately determined with the help of the info provided in the following article:

How to Calculate Inductors in SMPS Circuits


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

199 thoughts on “Simple Solar MPPT Circuit”

  1. Thanks sir great teacher. To optimise the performance of this circuit I used different inductor sizes but no difference,

    1. Please easy way to get the appropriate inductor. I have read your articles
    2. The input current is 2.23amps while the output is 1.15amps, a great loss, how can I reduce this loss, I set the charging voltage to 14.2v

      • Hello sir, I read a manual of mppt charge controller that says it charges using mppt technology for 2hours then switch to normal charging system without using mppt and bulk converter Why the need ordinary charging system when mppt to help in fast charging

        • Hello Favor, MPPT works only when the sunshine is above a specified minimum strength…it it drops below it MPPT may not be effective.

          • Thanks Swag for your reply, please what could be the rationale for 2hours standard for the manufacturer why not longer hours, the battery can’t be 60% charged with 2hours

            • That will need to confirmed from the manufacturer, it can be difficult to judge without knowing how the unit is designed to function, and its limitations.

          • I have not fully understood how mppt works. I think bulk converting can still work when the battery voltage is at 13.8v and the converter output is set at 14.5v and the solar input voltage is at 18v. Am I correct sir

  2. Good day Mr. Swagatam

    From studying your design carefully and reading your explanations I get it that the circuit will just work when the panels voltage is at least 14.4 V or higher…am I correct? Pease do enlighten me.


    • Hi Cecil, that’s right because we have used a buck converter here which will transform voltages which are above a certain preset value.

    • Dear sir,

      Can we incorporate the buck boost circuit you have into this design? I also would like to ask how to scale this design to handle 100 amps? Thanking you very much in advance.

      • Dear Cecil,

        Either a buck or a boost converter can be used with this concept both cannot work and it won’t make sense.

        It can be scaled to higher current by using a flyback isolated converter and by appropriately dimensioning the inductor and the transistors.

  3. Please, for the boost converter, the diode ba159 was producing smoke, but the max reverse voltage is 1000V, Sir, what could be wrong, what can I do. Thanks.

  4. Thanks sir, I got both the buck and boost converter. The buck tested with bulb after several tweaking was able to charge the battery, but by 4pm with went to 12.2v. The boost got to 20.7v and corrected to 14.5v and was going down till the bulb went off by 6:35 pm Questions
    1. How to synchronise the two.
    2. How to stabilise the voltage to be constant, and self adjust in relation to the sun intensity.

    • Tolu, you will have to make an opamp based comparator which will toggle the converters depending on the voltage levels.

      However automatic optimization may be difficult.

    • first you must be able to build the two circuits successfully then we can discuss regarding how to switch them alternately

  5. that’s why anything lower than the set value will make the buck converter ineffective…you said

    Please, how can I make it automatic so that by 4-6pm it will still be effective.

    • you will have to make a buck-boost type of converter, or make the two separately and toggle the buck circuit off and boost circuit ON when the voltage goes below 14V

  6. Thanks sir, I didn’t not get above 2.60Amps charging current from the load and 0.1-0.2Amp gain over the input Vin from the Solar panel. However, my pwm charge controller is getting about 3.65Amps at the Vin and 3.43Amps at the load
    2. Couldn’t it be that the Rx calculated was limiting the current. Also,
    3. I could only set the charging voltage as 15.5V( nothing less) as against the Solar panel 18.5V, how can it be lowered to 14.4v

    • Hi Tolu, first of all I think for a 18V/3 amp input an MPPT is absolutely not required, and might not produce the best results. you can simply use a buck converter or a buck-boost converter and use it for your battery. an MPPT would be required only if the input voltage is significantly higher than the battery level, or lower than the battery voltage specs.

      However for the present situation, the current limiter could be causing the issue, you can remove it to verify the issue.

      • Hello Swagtagam, I have some questions,
        1. Does it also mean mppt is not essential for 48v solar panels for 48v nominal battery, because you said the panel voltage should be significantly higher.
        2. At 88 turns of gauge 25 for L1, the maximum output voltage I got was 12.7v not, how can I optimize this to 14.4v.
        3. Around 5pm, when the panel voltage dropped to 14v, the output voltage on the load goes to 10.5v, why is this so.

        • Hi Tolu, The full charge level for a 48V battery will be around 56V, therefore if your panel is rated at around 70V then you can avoid a complex MPPT, and work with a buck converter instead. Because by the time the 70V reaches 56V, your battery will be almost 70% charged.

          Calculating L1 with formulas can be a little complex, so you can go by some trial and error, and try increasing the number of turns of L1, or/and try varying the IC1 frequency by increasing R1 value, in order to increase the output voltage.

          The above discussed MPPT simulator uses a buck converter which will only optimize a higher voltage into a lower voltage level, it will not boost a low level voltage to a higher level, that’s why anything lower than the set value will make the buck converter ineffective.

          • Thanks sir, I got 14.3v after some tweaking from the output, but not charging. No current draw, no increase in battery voltage. What could be wrong.

            • Tolu, connect a 12V motorcycle bulb instead of the battery and then tweak it to 14.3V, the bulb must illuminate brightly. If not then perhaps your buck converter is not correctly built…

  7. Hi Swagtagam, thanks, questions
    1.the panel voltage was adjusted to 14v into ic4 follower stage Vout Gotten was 10v, when fed into pin#5, the voltage 10v changed to 0.55v. Is it OK.
    2. From the testing, the panel voltage adjusted at P2 does not have any effect on the output voltage to the battery, how does this p2 relevant to the mppt

    • Hi Tolu,
      P2 controls and sets the PWM from IC2 at its pin#3, IC4 is used as a buffer only so that sufficient current can be delivered at pin#5 of IC2.

      the above arrangement is used for adjusting the output from the buck converter. As solar panel voltage changes, the output from P2 will also change, which will in turn alter the PWMs at pin#3 of IC2 proportionately, finally this change in PWM will adjust the output of the buck converter so that the battery charging procedure remains unaffected.

      P1 can be removed as it does not much importance

  8. I want to use this circuit for input of transformer that provides 14v dc with 30 Amp also i will use it for solar power cell. How can Merge those two inputs with a relay that has the first priority for DC transformer ! Any help

    • transformer cannot used because the primary of the trafo will be rated at 220V, which will require the solar panel to be also rated at 220V…

  9. Please how can I make this circuit 48v charger to be able to charge any battery from 12v to 48v and convert the voltage, amps accordingly as mppt. Thanks

      • I got the buck converter but the p2 in the mppt circuit does not adjust the panel voltage however the resistance value in line of p2 can be read at tip emitter when turned but has no effect to panel voltage. Is p2 for adjusting the panel voltage. Thanks

        • Happy Happy New Year , thanks for the good work, I checked resistance value of p1 without connecting anything the value was 0-234ohms for value of 10k resistor. All the 10k used gave 234ohms whereas p2 reading was in 10k range. Please why could p1 giving such value. Thanks

          • Happy New Year to you Tolu,

            If the preset is not connected with the circuit and still showing 234 ohms then the preset is surely faulty, or your meter may be malfunctioning….

            • then no problem…

              you should check and set the circuit stage wise.

              isolate the the IC1/IC2 stage and check it separately, then check the opamp stage separately, next check the buck stage separately and so no…

              make sure you learn everything regarding their functoinig while implementing the procedures..

            • check whether the PWM from pin#3 of IC 2 is correctly working in response to a varying voltage at pin#5 of IC2…apply a varying voltage externally from 0 to 12V through a variable power supply at pin#5 of IC2, and check the waveform at pin#3, if you don’t have a scope connect a transistor driver at pin#3 of IC and connect a motor with it and check whether the motor speed is varying in response to the varying voltage

          • I connected the positive of the 12v adaptor to the positive line of the ic2 and the negative to the pin #5 and varied the voltage and checked the changes at pin #3 in response.

            • that is not the right way to check…connect a fixed 12V supply to the circuit and add a 1 k preset across pin#5 and ground, then vary this 1K pot or preset and see if this alters the pin#3 proportionately or not

            • OK, now make the buck converter separately and feed the PWM at the base/gate of the power device and check the output of the buck whether the power output alters proportionately or not.

  10. can you please provide me circuit for automatic dimming solar circuit. Like if we have 5Ah Lithium battery and having 50 watts panel. now this 5Ah solar should run 9w Led for 12 hours. using a dimming circuit.

  11. Hi Swag, u are too wonderful, answering everyone infact great works, sir im John pls since i can not get the answer to this too difficult Maths [ f=1/1.453*rt*ct ] so please help me with the high amps 48v dc smmp solar circuit or to convert this 280v-300v to high amps 48v dc for charging batteries because im having a number of solar panels that is giving me about 280v-300v please help me for circuit to convert it to 48v to charge my 4 batteries thanks.

  12. dear Swagatam Majumdar, i have a problem that in may country i cant find a 36V solar controller, i need to charge 36v 350 am battery's


  13. Hi Swagatam, I appreciate all the help you've been giving me lately. You're a great resource for my senior project.

    I'm trying to make sure I understand the functionality of the circuit correctly:

    It takes an input from the solar panel, which can vary depending on the sunlight. The circuit then adjusts the PWM's to the battery depending on the solar panel voltage. (Wider pulse for lower sunlight, thinner pulse for more sunlight). In order to keep the average voltage in the optimal charging range. Is this correct? Or am I missing something?

    Thank you!

    • Hi Austin,

      yes that's correct, however since a P-mosfet is used for processing the output results, we need the PWMs to follow the sunshine by decreasing the PWM width as the sun goes down and vice versa, so that the response is inverted by the p-mosfet for implementing the required opposite effect across the output.

  14. You are welcome!

    And yea, i have read all of your blog and the one you made with 4047 and 3 sets 555 ic , i preferred this one, cuz of review from other hobbyists you uploaded in the blog.

    Now i want to know if i can use General purpose NE555 ic insteed of 7555 ic . cuz 7555 ics are not found in the local market arrount the place i live. I have Ne555 available.

    Please reply.

    And another question, can i use this above MPPT circuit to make pwm charger by changing the solar pannel of 20 voltage with 24 volt 5 Amp bulk transformer to charge 12 volt 20 AH battery? Please tell me your openion.

    Waiting 4 your reply

    • any 555 variant can be used, that's not critical…all and any type of 555 will work.

      yes the above design can be used in the way you want, however since the peak voltage of the PWM pulse will be always equal to input voltage (24V) so I am not sure what consequence this may have for the battery in the long term.

  15. Thank you very much for your kind reply. I was also thinking like you. Cuz i need ad much efficiency i can get. I have modified an auto cut circuit for this pannel. I will connect it for full charging auto cut.

    Sir, i read you blog frequently since 2012. But it was my first comment on here. I need a 100% pure sine wave (similler to AC) inverter of good efficiency by Bulk type transformer (12-0-12/10A) and analog IC's. could you please design it for me. I have read all your blog but i would like to build a inverter like microcontroller inverter output (sine wave).

    I am seeking your help.

    • thank you KM,

      I have plenty of sine wave inverter designs in this blog, however none of them will produce an exact replica of the actual grid sine-waveform and it is not required also…all my designs are PWM based and can be safely used as sinewave equivalent inverters.

      just type sinewave in the search box given on the top of the page…and you'll be redirected to the relevant pages, from where you can choose the one you prefer.

  16. Sir my solar pannel output voltage is 17v. Will this circuit work correctly on this output voltage? I am planning to build it. Please reply asap.

    • KM, if your battery is 12V, then you won't require the above circuit, you can simply connect the panel through some diodes in series with your battery for getting maximum efficiency

  17. Question Mr Swagatam would it be a good idea to use a buck boost converter circuit as u explained in one of ur post in our mppt design sir. Alex

    • If your requirement is a stepped down voltage with correspondingly increased current, then it's better to opt for a buck converter…..buck boost circuit can be employed but the process might require a lot of optimization and inconvenience.

  18. The 555 supply derived from battery if battery is 11V the charger will not start

    should nt the 7812 be given supplu from panel with a dropper ???

    • the 555 output implements the adjustments by supplying a varying PWM, not by a varying voltage….therefore 11V will not affect the procedures….

  19. Hi Mr.Swagatam, i want to ask you about that PWM like MPPT circuit. there is a 2.7V zener series with 470 Ohm after 12V regulator. is that make all of Vcc to be 2.7V or it's just for the IC1 (Wave generator) only? i'm afraid it can work as well. because the IC was running on 4v minimal i think. so thank you for your explanation.
    i want to make this one for my off grid 20Wp PV and 45AH 12V Battery.
    regard. Dhyaksa Hada.

    • okay i have tried to make this one yesterday, but i simulate the input from 16,5V Power Supply to 45AH Battery. but i think there is a malfunction on my circuit. now i try to make a simple one. just ordinary NE555 Fix frequency PWM and the Output from Pin 3 is drive a Gate mosfet (P-Mosfet) with series 100 Ohm resistor. try to turn it on, and it's charge the Battery. but i had my Mosfet and Blocking Diode was very HOT (like 70'C and up with my analog thermometer). how i can make the right one without any HOT devices?
      thanks a lot Mr.Swagatam.

    • which mosfet did you use? don't use a mosfet because mosfets are critical devices and require strict parameters….use a BJT instead…you can try a TIP122 but it may too require a large heatsink.

    • I use P-Channel MOSFET IRF-9540N for high switch… i don't know where is the problem. Ordinary NE555 that use 10k & 2.2nF for the Rt&Ct. Vin from Solar panel (I simulate it from Adj. Power Supply) 16.50V and Schottky diode + 100uF/25V Caps after Drain pin of Mosfet. or can you suggest me a simple one that completely working without any HOT mosfet? i'm very confuse with DC-DC Converter before. i have tried to built a lot but i still can't make it work well..

      thank for the advice Mr.Swagatam…

    • Dhyaska, I'll design the circuit as per your requirement and post it soon, and let you know, it will be similar to the above but a bit simpler.

    • oh thank you so much for your help to me. 🙂 because in my region now was very unpredictable for the mains supply. i'm afraid that can make a lot of electricity doing malfunction (like notebook,refrigrator, etc.) once again thank you so much..
      you can notify me by email or social networking like FB with my email account.

      thanks from Indonesia. 🙂

    • Hello Dhyaksa, yes it seems it will work, you can carry on with this circuit in the meantime until I finish designing the proposed more sophisticated one.

  20. Great job, yet again. SO I hven't been able to build your inverter from the other circuit because these transformers aren't popular in my area still looking though. But I went and got a 500 watt inverter for $20 works well, i power everything, downside it's modified sinewave so my sensitive appliances hum 🙁 so I don't use it on them just incase.

    my question for this circuit is the wiring, if the tracks are joining to another track is that what the big black joins are for and some tracks have gaps to indicate not touching passing tracks but the tracks that pass and dont have the big black dots are they still joining when they crossover another track? like the 2 IC555 and the 4 capacitors see that track that just comes straight through them to the zener diode. also what voltage are the 4 capacitors?

    • Yes in the diagram enclosed above, the lower section indicates the black dots as the joints while the plain intersection as "not connected" meaning only the intersections that have black dots are joint other are NOT.

      In the upper section, the "not connected" intersections are simply shown as broken line intersections.

      As a rule of thumb capacitors should have a voltage rating that may be twice of the supply voltage, if it's greater there's no harm.

  21. Hello sir,
    Please tell me the changes needed in this circuit to charge a 48v battery ( 2x24v Batteries connected0. What will be the specification of solar panel for the new circuit?

    • Hello Akshay, the basic design will not change, only the 7812 will need to be replaced with an ordinary 22K resistor/zener diode network in order to supply the ICs with the required safe operating voltage….the zener could be a 12V zener diode

  22. Sir me bhanu
    1)Sir why 2.7v zenor is connected to base of the transistor and again why the transistor is used there. I know that pin 7 is discharge pin why the transistor is used in IC2 only.
    2)why sir the transistor is used between mosfet and the diode of solar panel..
    3)Why the 14v zenor is used in the output of pin5 only in IC2.
    4)What are the functions of ceramic capacitor in the circuit…….
    Please sir help me ‘’Thank you’’

    • BC557 and 2.7v zener are for current limiting so that the 555 pwms do not falter during voltage fluctuations.
      pin5 zener is for restricting the voltage within the 555 supply voltage otherwise the pwms will get clipped.

      capacitors are for determining relevant frequencies.

  23. amps handling capacity is solely dependent on the mosfet…no other component is involved with amps and load.
    so it's all about modifying the mosfet as per the required output specs

  24. Yes sir thanks …. me bhanu
    1) but sir got a good circuit from your site it is used for charging battery form solar panel where LM338 or LM317 is used link is (homemadecircuitsandschematics).
    From this circuit i can get a variable DC supply which will be helpful for me… is it be possible for me….
    2) First i will generate 24 volt from LM338 & then this 24v i will connect to the input of solar MPPT charger for getting required voltage for charging battery….is it possible….

    3) You have given a formula for calculating resistance value that is 0.6/charging current ,, in the place of charging current can i use this formula to get the the resistance value easily i.e 1/10th of battery Ah value. the battery is 7Ah so 7/10=0.7 Amp then 0.6/0.7= 0.857 Ohm 0.857*1000= 857 kohmbut is this correct formula…or I will use simply 0.6/battery Ah
    4)Sir i am previously i have about color code of 14v zenor diode,, according to your suggestion i have searched online but i could not get a satisfied answer so can i use 15v zenor in place of 14v zenor
    I am doing this in my project i have assembled all the components have some doubt …Thank u sir…

  25. 3) You have given a formula for calculating resistance value that is 0.6/charging current ,, in the place of charging current can i use this formula to get the the resistance value easily i.e 1/10th of battery Ah value. the battery is 7Ah so 7/10=0.07ohm then 0.07*1000=70 kohm is this correct formula…
    4)Sir i am previously i have about color code of 14v zenor diode,, according to your suggestion i have searched online but i could not get a satisfied answer so can i use 15v zenor in place of 14v zenor
    Thank u sir….me "bhanu"

  26. Thank u sir for helping me …i am planing to connect a 12v DC to 24DC converter for charging the battery of 12v 7.5ah. Sir is it possible…
    First i will connect 12v solar panel to converter circuit then the output will be 24v , again this 24v i will connect it to battery of 12v…. sir is it possible
    Thank u sir…me bhanu

  27. Thank u sir ….i have still having some problem in solar MPPT charger…
    1)sir the 1uf ceramic capacitor is not available but 1uf 400v ceramic is available can i use this here.
    2)There is a formula used (0.6×RX) it is for resistance calculation but sir why 0.6 is used.
    3) I got a zenor diode of 14v but there is a color code in it is it a zenor or not???… the color code is 1st band is yellow & 2nd band is brown….
    4)Here 20v solar panel is used but i want to connect 12v solar panel for charging the battery of 12v 7Ah… it is a UPS battery….sir can it be possible
    Please sir help me ….Thanks..

    • 1) yes 1uF/400v can be used.
      2) 0.6 is the trasistors minimum biasing voltage
      3) I'm not sure about the color codes, you'll may take the help of any online zener color code chart.
      4) a 12V source will never charge a 12V batt…you will need at least 14 to 15V for charging a 12V batt.

  28. Hello sir… i have already assembled the elements of solar MPPT charger but i cant understand the rating of the diode 6A4 ×5….. please sir help me….

  29. Hello sir me Bhanu ….. can you please tell me the specification of Mosfet used in MPPT solar charger circuit..
    Thank you sir…..

  30. Dear Sir,
    thank you very much for your support for us.. we are looking forward for your simple mppt controller with I/V tracker system.. thank you very much sir

  31. hello Mr Swagatam we look forward for u designing a more efficient mppt controler as u discuss one that uses smps and transformer thank u

  32. Yes, the above circuit does not track the I/V of the panel so in true sense it's not an MPPT, rather it's a solar panel optimizer circuit, I'll try to update the above with an I/V tracker system soon, so that it justifies its name.

  33. Thank you for this… I am trying to power a resistive load (heat coil). Using the CREE-CMF20120D-N CH, SIC PWR MOSFET, 1200V, 33A . VOUT can vary greatly, simply to convert PV energy to heat.

    Any advice would be much appreciated.

  34. Thank u Mr Swagatamfor ur refrence to the motor driver circuit. i will use a different fet and see the results and let u know because this is the best described mppt controler I see that looks pratical. Thanks for ur support

    • Thanks Alex,
      Actually the above circuit is an MPPT simulator not exactly an MPPT because it does not track the IV curve of the panel…you can say it's kind of a solar panel optimizer.

    • I am trying to understand your explanation here about a mppt simulator.So the devider network does not work as a data colletor to tell the circuit what to do.Could u explain more clearer.Than u Sir

    • thank u Mr Swagatam I am folowing all ur post on mppt controllers becaue I want to build a working one. I changed my fet and used the irf9540 I am getting the maximum panel volt out now at the output of the diode but the problem is when I adjust the pot the voltage does not vary. It varies the voltage at the gate of the fet yes but not at the output could u help me here. Thank u.Now I see ur new circuit I dont know which one to build ???? sir

    • It can be a little tricky, you will have to check, and set by comparing the input voltage, the voltage at pin#5 and the drain voltage through some trial and error. Check how the drain voltage responds to the other two voltages and then try to figure out the most optimal relation between these three such that when the panel voltages dips, the drain voltage rises (opposite response)

    • Mr Swagatam I am having problem with this circuit and I see some other guy is having the same problem . The voltage at the output drain of the fet is not changing with the setting of the pot. even if u disconect the gate of the fet the voltage is there passing from the panels. Please recheck to see if something is wrong somewhere. The voltage at pin 5 change as u say it should and the frequency is somewhere in the hz so i think the two ics are working correctly but the controling of the voltage at he output not able to be adjusted. Please help us here this guy posted his coment on the 28 of august. Thank u for ur help

    • Mr Alex, I am always helpful to the readers here, but it's the responsibility of the readers also that they understand the presented concept from the core and only then proceed with the construction, because otherwise it would become very difficult for them to troubleshoot even with my help.

      Anyway, in the above circuit the response of the mosfet will be opposite to the response at pin#5 or at pin#3 of the IC2, meaning as the voltage drops, the conduction at the drain of the mosfet would increase.

      You are saying that even if you disconnect the gate, the mosfet conducts…. it simply suggests that your mosfet may be faulty, do one thing use a TIP127 transistor in place of mosfet and check, because transistors are easier to handle than mosfets.

      Apply an equivalent solar peak voltage and adjust the preset to produce about 15V at the collector of TIP127, now as you reduce the input voltage, the collector voltage should try to compensate by maintaining its collector voltage to around 14/15V.

  35. Hello Mr. Swagatam! You've been doing a great job by helping the electronics hobbyists. Please I have massive interest in this circuit, but i like to ask if a heatsink should be placed on the mosfet.
    Thank you sir.

  36. Good day Mr. Swagatam.

    I am am currently building your circuit to charge a 12V, 31Ah deep cycle battery via a 80W, 21.8V polycrystalline panel.

    According to the battery specifications the recommended charge current should not exceed 7A max, and the panel can supply around 5A in peak conditions. I was just wondering if the 5x6A diodes will not be overkill for my configuration, I am also using an IRF9540n mosfet able to drain -23A@-10V. Any other suggestions will be appreciated.

    Thank you very much

    • Good Day Christiaan,

      The diodes would be in parallel theerfore would drop just 0.6V, you can remove them if you want as they are only placed to safeguard accidental reverse polarity connections. The diode at the mosfet drain may also be removed.

      The mosfet is fine, it's capable of handling -23A @ -100V to be precise.

    • Thank you very much sir, I thought the diodes was solely for reverse polarity protection, I didn't realize the paralleling results in a much needed lower voltage drop than adding only a single diode -basics! Yes that is -23A @ -100V for the mosfet sorry.

      Thanks for your reply

    • You are welcome!

      Actually a rectifier diode will drop 0.6 volts doesn't matter whether a single is in the line or many in parallel, but will add up if they are in series.

  37. Hello Mr Swagatam I am trying to build this circuit . I want to know at what frequency this circuit operates and which parts of the circuit deal with the frequency settings and which ic deals with the pulse width pulse . Thank u

    • Hi Alex,
      The frequency is not critical, although it is determined by R1/C1.

      IC2 is responsible for the PWMs, I have explained everything in the article.

    • Hello Mr Swagatam I built the circuit but I am having some problems with it . Should I be able to adjust the output voltage from 0 to the maximum panel voltAGE. If so I have 40 v coming in from the panel to charge a 24v bank but when I adjust I get from 0 to 22v only could u tell me where I could check for possible causes.

    • Hello Alex,

      Since the mosfet conduction depends on the duty cycle from the IC, means the mosfet output should become adjustable right from zero to max panel voltage, or almost near to max.

      However the 22V would have damaged the ICs in your case, because the ICs won't tolerate more than 18V.

      I would suggest you to replace the ICs and connect a 7812 with the new ICs for protecting them from the high voltage….and then check afresh.

    • Hello Mr. Swagatam I want to modify this controller to handle 60 amps. If I parellel three IRF9540n and diodes would this work or do you recomend a different mosfet and diode arrangement

    • hello Mr Swagatam thank u for ur usual quick support. I have a regulator already in the circuit for the ic thats ok but I was just wondering I am not able to adjust to maximum voltage could this be the fet I am using because the maximum 40v is at the source of the fet but not at the drain could this be my devider not right for the 40v panel voltage.. Thanks for ur support

    • Hello winston,

      Your idea would also work, just make sure to connect 0.22 ohm 1 watt resistors in series with the source of each mosfet and also include separate gate resistors for them.

    • Hello Alex,

      Please refer to the following snippet, the PWM at pin#3 of IC2 controls the mosfet output, so according to me the output must vary from zero to max:


    • Thanks Mr.Swagatam,
      I will try this modification,but the wattage of the resistors in series with the source ( 1 watt) seems low if each mosfet is to handle 20 amps.

  38. Check the voltage at pin#3 of IC2, it should change in accordance with the preset, if not would mean something's not correct within the IC1/IC2 stages.

  39. Hi Swagtam, nice circuit !! I just wanted to ask if it was possible to insert a visual monitor of what's happening on this circuit during operation, (LED or LCD) , if yes how and where on this circuit should that be inserted? Thank you

    • Hi Marika,

      A couple of LED voltage indicators can be made using LM3915 IC, one can be set for measuring the panel voltage while the other the pin#3 voltage of IC2.

      The displays would then clearly indicate the tracking procedures comparing the response of the two inputs.

    • Dear Swagtam, I have built the circuit including the LM3915 IC, but I'm stuck on the type of MOSFET , here's what I have available for use : a solar panel 150W/12V and a 65AH/12V battery (that I will upgrade to 100AH soon) , what is your advice on the mosfet ? will an IRF540 work? Thanks.

  40. I think you have made a valid point, in your case that is for inputs and outputs greater than 15V the iC supply must be protected with a resistor/zener network.

    The 14V zener should be included as shown, however the reset/supply pins4/8 should be connected via a 10K resistor and clamped with a 15V zener.

    After this you would be able to continue with the procedures as explained in the article.

  41. thank u Mr Swagatam for ue reply on the divider but I was trying to say I am charging a 48v battery bank so if i would still use a 14v zener . My panel volts is about 80v coming in awaiting ur reply

  42. yes surely the buck boost stage can be inserted after the mosfet in the above diagram. The current output simply depends on the mosfet and the solar panel rating

  43. try using an online potential divider calculator and find the values of the resistor/pot which determine the potential at pin5 of IC2. This adjustments should be equal to the charging voltage 14.4V at optimal sun light that is 80V, once this is adjusted the zener can be kept as given.

  44. please Mr Swagatam u said the network resstors are 10k and 22k but in the drawing it is 1k and 10 k please make it cllear here thank u Sir I also looked at the buckboost circuit u designed I was wondering if u incorporate this in the stage between the fet and diode if this would work and increASE the current also. Please look into this . Thank u

  45. I have just tried to imitate the actual version through a simpler concept, I have not tested the results so cannot confirm regarding its efficiency.

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