The following post of a full wave motorcycle shunt regulator circuit was requested by Mr.Michael. Let's learn the circuit functioning in details.
How a Shunt Regulator Works
Shunt regulator is a device which is used for regulating voltage to some fixed levels by means of shunting. Normally the process of shunting is done by grounding the excess voltage, just as zener diodes do in electronic circuits.
However one bad aspect with such regulators is the generation of unnecessary heat. The reason for heat generation is the principle of its operation where the excess voltage is short circuited to ground.
The above practice may be implemented by simpler and cheaper means, but cannot be considered efficient and advanced. The system is based on destroying or killing energy instead of eliminating or inhibiting it.
The circuit of a motorcycle shunt regulator discussed in this article takes a completely different approach and restricts the in-flow of excess voltage instead of "killing" energy and thus stops the generation of unnecessary heat.
Circuit Operation
The circuit functioning may be understood as under:
When the mobike is started, voltage enters across the P-channel mosfet source/drain pins due to the gate trigger that becomes available via R1.
The moment the high voltage reaches R3, which happens to be the sensing input of the opamp, pin#3 of the IC senses an increased voltage.
As per the set reference at puin#2, the instantaneously reacts to the situation and the result puts the output of the IC to a high logic level.
The immediate high logic pulse restricts the negative base trigger of the mosfet, switching it OFF at that particular instant.
The moment T1 switches OFF, voltage at the junction of R3/R4 reverts to the original condition, that is the voltage here now drops below the reference level......this instantly activates the opamp output with a low logic signal which in turn switches ON T1 back into action.
The process repeats at a very rapid speed, keeping the output voltage marked with +/- at a constant level determined by the setting of R2/Z1 and R3/R4.
The above principle utilizes voltage inhibition technique of the excess voltage instead of shunting it to ground, thus saves precious power and also helps to control global warming in some way.
Parts List
R1, BR2 = 10Amp bridge rectifier
R1 = 1K
D1 = 1N4007
C1 = 100uF/25V
IC1 = IC741
T1 = mosfet J162
R2/Z1, R3/R4 = as explained in this article
Shunting Excess Power to Ground is Recommended in Alternators
When it comes to alternators, the best way to restrict or limit excess voltage is to short the excess power or shunt the excess power to ground. This eliminates the rising current in the armature and protects the winding from heating up.
A voltage regulator using this method can be witnessed in the following examples:
Video Clip below shows an opamp based shunt regulator circuit, and its testing procedure
Parts List
R1, R2, R3 = 10K
R4 = 10K preset
Z1, Z2 = 3V zener 1/4 watt
C1 = 10uF/25V
T1 = TIP142 (on large heatsink)
IC1 = 741
D1 = 6A4 diode
D2 = 1N4148
Bridge rectifier = standard motorcycle bridge rectifier
How to Set up the Circuit
For a 12V system, apply a 18V from a DC power supply from the T1 side, and adjust R4 to precisely set 14.4V across the output terminals.
An even simpler motorcycle shunt regulator using the shunt regulator IC TL431 can be witnessed below, the 3k3 resistor can eb tweaked to chnage the output voltage to the most favorable level.
For single phase alternators, the 6 diode bridge rectifier could be replaced with a 4 diode bridge rectifier as shown in the following diagram:
Feedback and Update from an Avid reader Mr. Leonard Fons
I've come up with a bit more that needs to be considered.
I'm using a MOSFET (IXFK44N50P) for the clipper and series regulators. Never did much with FETs because when they first came out, the least little static charge would blow them out in a heartbeat. So this is actually my first attempt to use them.
I assumed that, like junction transistors, the more power they handle, the more power needed to drive them. NOT TRUE. In looking again at the datasheet, I see that Gate current is plus or minus 10 nano Amps.
That is ten trillionth of an amp. They do not require a TIP142 to drive them. A one watt, high gain darlington will do the job very nicely. And the entire circuit will fit on one board. I still need another regulator housing for the rectifier. But I'm about ready to put this all together and try it out.
Of course, I will try it out before I actually mount it into the housing, but I don't expect to make any modifications.
Realizing that these FETs use almost no gate current at all makes quite a difference. I'll find out just haw accurate my theory is for the current to ground when clipped at 60 volts, rather than shunting all current to ground.
A when I pot it into the I have to insure that the FETs have no gap to the housing. That was another issue with one of the others. A sixteenth inch space between the components and the housing,
With that gap filled with epoxy, it's not very efficient at dissipating the heat. By the time the housing starts getting warm, you'd burn your fingers on the components. One change I may make is the series diode in the monitor line. A green LED located where I can see it while riding will let me know if it's charging.
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Hello… I made a 75 watt led light for my motorcycle… When i connected it to motorcycle the voltage dropped significantly because the rectifier was only rated at 100 watts and shunted the excess power… So i decided to make a powerful rectifier… I made the last design given by “lens fons” and unfortunately it blew up!!! It was working fine until i opened the throttle up a bit and then the mosfet that was shunting the voltage above 60 volts got destroyed… The other two are fine… I used 500v, 40a mosfets and tip50 instead of bsr51… I think the problem is that the gate of the first mosfet is not protected… Lets say if there is a 90 volt spike then in that case 90 volts minus the 60 volts of the zener is 30 volts at the gate… Which is the max tolerance of the gate!!! That voltage was not shunted yet and it reached the gate!!! I’m gonna use a TL431 instead of the 60 volt zener to shunt the excess power because at least it guarantees that i will get no more than 10v at the gate… And i think that the resistors from the gate to the ground should also be of 1K ohm… Please respond if you get my point and FOR GOODNESS SAKE MAKE THESE CHANGES IN THE CIRCUIT PROPOSED BY LENS FONS!!!
The gate of all the MOSFETs are fully protected up to the zener voltage. How can the spike reach 90V when the MOSFET itself is configured to shunt the entire supply at the gate zener voltage. For example If the gate zener is 15 V then the MOSfET will start conducting at 15V and will shunt any excess voltage above 15V to ground.
For reverse spike protection you can add reverse diodes across the MOSFEt drain/source…..your MOSFET could be blowing due to avalanche current.
So… You mean to say that i can use IRFP150n to regulate 500v down to 60v??? When its datasheet says that the maximum source-drain voltage should not exceed 100v??? Because according to you the voltage will never exceed 60v so why is lens fons putting in a 500v mosfet??? Isnt tl431 a solution??? And if avalanche current is the problem then should i a add 1000v – 6a schottky diode to the drain-source???
500V MOSFET is used for ultimate protection to the MOSFET, but it is an understood fact that the output voltage will never exceed the zener value.
tl431 is just a zener diode with temperature stability feature and adjustable output facility.
schottky diode is not necessary, ordinary diode will do, since the alternator frequency may never exceed 200 Hz.
Bro… Just tell me can i use IRFP150n as the shunt MOSFET??? Cuz i have several of those lying around… And you are telling me to use a diode on the drain-source of the MOSFET… Please tell me the specifications of that diode… And do you recommend anything else???
You can use that MOSFET, diodes across the drain source can be 1N5408
I am assuming the voltage to be shunted is 24 V max, because 24 V is enough for most motor cycle electrical.
Bro… I will make a new one with new components… Because i just checked and alomost all the components have burned up… But i have a question… I discussed this with my father and brother and they said that it is HIGHLY UNLIKELY that back EMF can pass through the three parallel 5010 bridge rectifiers connected to the 3 phases coming from the stator… Your comments on this???
Sure bro, I would recommend using power BJTs Like TIP3055, TIP35 etc instead of MOSFETs, because MOSFETs can be very unpredictable….spikes can enter anywhere, anytime, no matter how many stages of electronics you have.
Hello, I was led here via an answer on one of your other pages.Thank you. Reference using the above circuits with a DC generator. I can readily see that I can omit the bridge rectifier and replace with a single diode, also the need for an extra diode in the out-put to prevent battery discharge through resistors R3 & R4. Would Schottky diodes be preferable here given their lower forward voltage drop? As I wish to use a 6Volt system would I need to change the values of R3 & R4 or possibly make one of them a trim-able so as to give a little room for adjustment?
Hi, your assumptions are correct. You can use Schottky diodes for decreasing the drop, and you will have to change the R3/R4 values until the required 6 V gets shunted across the supply lines. Yes, the ground side resistor could be made trimmable for facilitating easy and quick adjustments..
Will installing a mosfet regulator to a motorcycle with a permanent magnet rotor and single phase stator create any improvements with respect to heating of the stator? I only ever read that the regulator runs cooler but nothing mentions effects on the stator. My thoughts are that the mosfet reg would have little or no impact on the stator.
It may not prevent the heating up of the stator winding, but the shunt regulator will definitely prevent high voltage build up on the stator winding and safeguard it from burning.
sorry … I need 28vdc 40ah … why install a 15v zener diode … is it possible to install a 28v zener diode?
The 15V zener is for protecting the MOSFET gate…….the 28V should be set by modifying the 3k3, 4k7 resistors appropriately.
You can use IR9540 MOSFET
what is the mosfet part number?
I need a 40AH output …… Input 0-60VAC 40AH and output 28VDC 40AH ….. thanks
If it is from an alternator then you can use the following concept:
https://homemade-circuits.com/wp-content/uploads/2012/10/shunt-3.png
You can replace the transistor with a MOSFET, and make sure to connect a 15v zener diode across source/gate of the MOSFET
Hi
can you help me make a 3phase wiring rectifier with input voltage 0-60VAC … and output 28VDC ..
thank you
Yayan Suryana
Hi, what is the current output needed?
I have a question about the shunt controller circuit with LM431 using a single diode bridge.
If the battery is permanently connected to the shunt controller, the battery will slowly drain. When the zener voltage in this circuit is set to 7.0V, the zener will already draw current from about 5V.
So if the circuit remains coupled to the battery, it will drain to about 5V.
Is there a solution for this?
Thx
The battery can drain through the 3k3/4k7 resistor not through the IC,, because IC is adjusted to conducted at 14 V.
The solution is to add a rectifier diode at the battery positive, cathode of the diode will go to the battery positive.
Thanks for the reply. The circuit still consumes power because a small base current already flows at 6V. At the zener voltage (set @ 7.2V), the transitor is fully conductive.
I can summarize that the switch point should be steeper (smaller margin between off and on).
The extra diode in the circuit can indeed be a solution so that the current can’t flow back from the battery to the circuit.
It will have to be a big power diode. All consumers (lights, indicators, horn, …) are directly on the battery.
The necessary current for this will therefore have to pass through the diode.
(?) …wouldn’t it be better to place the shunt function in the AC part?
Thx
Sorry I am having difficulty in understanding how the transistor would keep conducting below 14 v? The TL431 resistor must be adjusted so that it conducts only at 14V. The resistive divider values shown in the diagram may not be correctly adjusted, they are arbitrarily chosen.
So according to me the transistor will be completely switched off until the voltage from the dynamo exceeds 14 V, otherwise the whole idea of voltage regulation will fail.
Using the shunt at the AC side would mean using 3 separate SCRs which can be even costlier than using a high wattage diode?
I am using a single phase alternator (full signal) and calculated the resistance divider (zener voltage setting TL431) for a 6V system.
Can I post an electrical diagram of my test circuit?
For a 6 V battery, the full charge limit should be 7 V. So the principle is the same, the 6 V battery cannot discharge through the transistor below the full charge 7 V level. You can post the image to any free image hosting site and provide the link here…
https://photos.app.goo.gl/YRj4aBpxd5A8YH5S7
I hope, you can open the link.
It looks OK to me, the battery can never discharge through the transistor under normal circumstances. The R1/R2 should be adjusted such that the transistor conducts only at 7 V
Hello, I was wondering if this circuit also works when one side of the light coil is connected to ground.
dear sir could you help me to modify your circuit ( made with tl431 and tip 147) to put n-mosfet thanks
Hello aytac, you can try the folowing design:
dear sir many thanks… i did this circuit as same as in shematic but rarely i have fixit 3.5volts
but without circuit i can reach in same rpm of wind turbine around 36volts
Hi Aytac, you must adjust the resistor values to get the correct desired shunting threshold. Please specify what is your desired regulation voltage output, if possible I’ll solve it for you.
That is a simple source-follower voltage regulator, plenty of such circuits are already present in this website. You wanted a shunt regulator so i suggested shunt regulator design. Shunt regulator is the recommended circuit for alternators, other standard regulator may burn the alternator winding at high voltages.
dear friend many thanks for your shares i would like to ask your advice …
i am trying to make simle wind turbine with printer step motor ( it has 3 bobines so i put diodes i have continuously dc voltages) then i tried your eash zero drop mosfet schematic but i used irf630 and not worked for me so i have n channel mosfet i would like to use mosfet like this shematic
instead of TIP142…
my electric generator has around 32v .
i want to fix output 12v
my op-amp is lm339p
many thanks
Hi, the op amp shunt regulator will also work with an N channel, just make sure the op amp output turns ON at around 12 V. You can put an LED/1k across pin6 and ground to confirm the results.
Many thanks I will try then I will reply results…
Dear sir sorry for my ignorance
I just tried to make but I saw from diodes to battery + and – came directly electronic circuit connected like parallel so when I tested it I have same output voltage of diode ( I have around 24v side of diodes and battery) I am talking circuit builded with tl431
Hello aytac, it is a shunt regulator, meaning the excess voltage will be grounded by the MOSFET, so your 24V will grounded until it becomes 12 V, this will make the MOSFET very hot…you must use large heatsink on the mosfet. Make sure the mosfet amp rating is 3 to 4 times more than the input current
as I understand it, with shunting, the entire power of the generator will constantly be consumed(this is not good)
Isn’t PWM better?
In alternators shunting is the recommended way of tackling excess power, since it prevents the winding from getting subjected to excessive voltage and burning due to heat. PWM will not be able to prevent this situation.
Which was the best Battery Voltage regulator for single phase motorcycle generator. This is not an Alternator model.
for single phase use the last diagram
I think the heat can be lowered by an another rectifiing aproach. Oem parts are using half wave, and their bulky housing can handle the heat but here we want full wave without a wing-like stuff behind the seat.
I experienced on scooters that when you ride with burnt headlight bulb the oem regulator sometimes overheated and died. It is a general advice to always have your oem planned load on the generator so it won’t put lot of heat on the regulator.
I think most problems with heat is comes from full wave won’t used up, so what if you make a little addon and when the heatsink gets really hot (low alternator load) the rectifier falls back to half wave. And when it’s cooler again it starts to put out more power and hopefully it is used up by a seat heater or something like that and won’t burn the regulator.
Is there any point?
Heating is an integral part of a shunt regulator, if it’s not heating then it’s not working. So heating is good and this helps to keep the alternator in good shape.
Hi Swag Once again.
what to ask if there is a way to build this circuit with out the zener diodes
since it is not available where i buy parts
thxs
Hi Nitonito, that cannot be possible, zener will be required for a proper operation of the circuit
is the rectifier will experience extreme heating by the shunting process? passing high amount of current to laod also heats the rectifier thou
do i have to change R1 and Z2 value if I want to use IRF540, also if i wanted to use more than one mosfet, do i have to clone R1 and Z2 also?
yes obviously the rectifier will heat up and that's why it must either rated 3 times more than the max alternator current or mounted over a suitable heatsink.
adjust the preset such that mosfet gate receives around 9V at the desired trip point…for example if the regulation point is 14V, adjust the preset to produce 9V at the gate for the mentioned regulation limit, make sure to use a 8V zener in series with the mosfet gate, anode towards gate.
No need to change anything except the above suggestion.
is this for the first last diagram or the second one? as i see there is already a zener in series with the transistor base (i'm going to use mosfet instead of tip transistor)
the suggestion for the both the designs if mosfet is being used. I am referring to R4 in the first diagram and 4K7 resistor for the second diagram.
for the first design change the shown base zener to 9V zener if mosfet is used
which one is giving you the problem, please specify the diagram.
Hello Swagatam,
I need your advice again with this circuit, i'm having problem with the mosfet used in place of the bjt.
Problem is the mosfet gets killed 2s from the time the input voltage reaching 18v dc, that it is drain and source now always conducting no matter there is a signal or not on it's gate.
Tested the opamp circuit and it is working correctly, it's outputing 9v at the mosfet gate zener.
hello Ahmad, most Mosfets will not tolerate 18V at their gates and will get destroyed…you may have to modify the shown circuit and replace the shunt regulator IC with only resistors to form a potential divider at the gate of the mosfet.
This potential divider values then could be adjusted such that it produces around 9V at the mosfet gate when the alternator output is around 18V.
now I get confused, it is working as expected in this page https://homemade-circuits.com/2014/12/3-phase-motorcycle-voltage-regulator.html with input voltage easily swing to more than 100V with full engine rpm.
Why can't it work in this one with bench supply delivering not more than 20V 5A max. Is it because I connected the drain to input voltage by hand not making it fixed thus making some sparks which lead to damaged mosfet.
I liked this circuit very much as it only requires few component and I can make the mosfet share their load to handle more current easily.
in the other design the supply is coming through the IC 555 and therefore it's restricted to 12V at the gates of your mosfets, and the output is determined through the PWMs….. whereas in the last diagram above, the supply to the gate needs to be equal to the LM431 voltage, which directly determines the regulation voltage for the output, so to get 18V regulated you are perhaps adjusting the LM431 voltage to 18V at the gate…which is harming the mosfet.
if you have not adjusted the LM431 output at 18V then it could be strange…because the LM431 output at the gate will regulate the output at the same level….so if it's 9V at the gate, the output should be also approximately 9V regardless of the input.
or may be your power supply current is higher than the mosfet rating which could be damaging it.
it's the one with 741 circuit not the lm431, at 18V the the output from the 741 is the same as the input but after the gate zener it is now become 9v at 18v input which i'm using 8v zener for the gate mosfet.
according to the spec, gate voltage is +- 20V and maximum continuous drain current 30A. while my power supply is pretty much limited by the size of the transformer which is 5A and the voltage is set to 18V when the problem occures. or is it the 741 that subject to fail? could you point me to what to check to sort this problem out.
you are very big help
mosfets are sensitive devices and sometimes unpredictable, unless these are precisely handled in the circuit, you can get more details here:
https://homemade-circuits.com/2013/09/mosfet-protection-basics-explained-is.html
I would recommend you to try with a BJT first, such as TIP142 and see how it responds, if it responds well then the problem could be specifically with the mosfet.
and yes if the power device fails and stops shunting due to some reason then the IC 741 will be at risk and might get damaged due to unrestricted voltage..so I would recommend to provide some kind of protection to pin#7 of the IC, by using a regulator IC such as a 7812 or a 12V zener (through a limiting resistor)
I see, I will try with the suggested transistor then.
what parameters and formula do you use for calculating R1 value, is it
R = (Us – Vbe).Hfe / Load Current
R = (100 – 3.5).1000/10 = 9650 Ohm
I want to be able to calculate R1 value if I want to use another NPN transistor
the formula and the calculation is correct
however here we would want to allow the transistor to shunt maximum amount of current so that the regulation is effectively maintained, therefore any smaller value resistor can eb selected, it does not need to be calculated….and moreover since the TIP142 is a Darlington it will have a huge gain and any resistor between 1K and 50K will have almost the same results, therefore precision can be ignored
is the rectifier will experience extreme heating by the shunting process? passing high amount of current to laod also heats the rectifier thou
Mosfet design may harm Stator and rectifier, as Hayden pointed out
Second design may harm the rectifier
Simple design will blow up.
/Soren
sorry, your analysis is incorrect for the second and the last circuits
Soren
Would you please provide some explanations in favor of your remarks.
First design may harm your stator and rectifier. As pointed out by Hayden
Second design puts unneccesary stress on rectifier.
Simple design will blow up
the simple design works just great in fact, but with a huge heat sink needed, good thing i have the space.
thanks for updating the info, yes the heatsink has to be large to ensure proper functioning of the system.
Hi Swagatam Majumdar,
can you design and CDI which may theft control with a wireless key or something like sensor base,,,?
Hi Chito, yes it can be easily done by disabling one of the main CDI wires through the wireless relay.
If possible I'll try to present in my website soon.
I like the circuit design above because the simplicity. At the above diagram I replace 4k7 resistor with 2k7 and than 3k3 with 47k potentiometer to get 14.8 volt dc. It's all okay except of heat dissipation.
Hi Julian, I am glad it's working,
if the shunt regulator is controlling the voltage at the preferred level and also becoming hot, then that's a good sign, it means it's working as per its specifications.
No mater which circuit you try all will show equal amount of dissipation, because the dissipation is the equivalent of the excess power that's being generated by your bike alternator.
you can try adding a finned type heatsink to the transistor for enabling a better heat control, such as this:
diyaudioprojects.com/Testeq/Dummy-Speaker-Load/VHS-95-Heat-Sink.jpg
or you can also try replacing the TIP with a mosfet such as a IRF9540 and see the response.
Thank you sir for your explanation. I have checked and yes tl431 ic was broken. When i replace it with a new one the circuit is working properly. But one thing that anoying me… the heat dissipation of transistor. When i touch the allumunium body It's too hot. I put the cooling fan too but the result is the same. Between of motorcycle regulator diagram that you have posted in this page and than at https://homemade-circuits.com/2014/12/3-phase-motorcycle-voltage-regulator.html?m=1 and also https://homemade-circuits.com/2016/02/motorcycle-shunt-regulator-circuit.html?m=0.. which one can give the best of reduce heat dissipation? Thank you so much
I have made one using tl431 ic type. The problem is the output voltage of homemade regulator is increased also follow rpm rotation . Is the battery condition also affects the stability of the voltage at the output ? Need for help.
the regulator will regulate regardless of the battery condition, and not increase above the set value.
First test the results on a work bench using a 5 amp variable voltage supply…and confirm the voltage across the collector emitter of the regulator transistor which should be constant regardless of the voltage increase from the input.
make sure the transistor is mounted over a heatsink.
you can tweak the 3k3 resistor value to achieve the correct output
Thank you so much for the quick response sir. I have tip36 transistor and many 2SA1494 power transistor at home. Can i use them to replace tip142 or 147 transistor? Any solution to reduce heat dissipation of transistor to make it quiet cooler without a big heatsink. Cause when using a big heatsink will take more space on a bike.
Julian, you can try TIP36, although it's not a Darlington, it might work too since the base resistor is significantly low and the shunt IC is capable of providing sufficient current to its base.
heat generation is the hallmark sign of shunt regulators and it's ths attribute which actually safeguards the alternator….so this cannot be and should not be changed.
you can probably use an aluminum body and use it as the heatsink itself, but make sure it doesn't come in contact with the vehicle body
Just information on my motorcycle: battery 12v 9Ah, and the load is head lamp 12v 55watt 2 noss, stop lamp 12v 21 watt and klaxon as usually use on a car and many more. The problem is my battery is always no powerfull and i have to charge it manually. When i measure from the alternator is very powerfull at idle is 20 volt and then when running in full power is more than 50 volt but when i measure the original regulator output I'm surprise the voltage just about 12 volt no matter at idle or running on full power. That's why i want to build homemade motorcycle regulator from the above article that you have post. I hope the circuit design above solve my motorcycle problem. Thank you so much
the output from the regulator must be set at 14.4V for charging a 12V battery, so if your existing regulator is giving only 12V then that's not correct…
make sure to add a big heatsink with the shown TIP147 or the TIP142 transistors, otherwise the device could instantly get damaged
Thanks a lot Mr. Swagatam for the simpler design.. but if the output after rectifier in idle condition more than 25 volt dc, I think when the bike running will produce more voltage and current. I have tested the output rectifier without regulator when running is about 80 volt dc. The question is.. can the 3 phase motorcycle shunt regulator in the above article is able to handling the high voltage at the input of regulator and then stabilize the voltage too?
Hi Julian, yes, the last two designs are perfectly capable of controlling all voltages below 100V, which can be further upgraded simply by changing the power transistor rating.
Basically the designs are like higher power zener diodes, which will never allow the applied voltage to go higher than the specified rating.
here R4 in the second last diagram and 3k3 in the last diagram can be appropriately adjusted for setting up the circuits to any desired stabilized output within 20V
Sir, my motorcycle need 3 phase shunt motorcycle regulator. Could you help me to design that from the circuit above? Thank you.
Julian, I'll update a new design soon in the above article….the existing design might be incorrect.
I'll post shortly, which I have tested.
Julian, I have updated the new diagram in the article
.I appreciate your insight…thanks!
yes you are perhaps right, since a bridge is used here the emfs would also get transferred to the connected load…
'
I thought back EMF doesn't happen in this case since there is no current generated. So your design was very worthed.
Sorry for my bad English 🙁
….As for the second doubt, yes the p-channel will actually not switch OFF at all, but an NPN will certainly do, an N channel mosfet will switch off completely so the diagram needs a lot of corrections….
I have already addressed a similar issue in the following article, you may have a look at it:
https://homemade-circuits.com/2013/08/simple-zero-drop-solar-charger-circuit.html
Hi Abu-Hafss, I think you did not get haydens point, according to him automobile alternator output needs to be loaded in order to regulate (bring down) the line voltage, other means of regulation that does not load the alternator winding will cause harm to the particular winding,
The shunting of the excess voltage to ground satisfies the loading condition of the alternator and thus this method must be employed for regulating alternator outputs…. but I don't know whether this is true or not
But since the voltage from the rectifiers will be higher than 12V, I doubt the 12V output from the op-amp will not switch off the p-mosfet. Same will be the situation if n-mosfet is used. You need to optimize the configuration such that p-mosfet is completely switched off against 12V output from the op-amp or such that n-mosfet is completely switched on against 0V output from the op-amp.
Hi Swagatam
Your design is almost identical to this design
https://dl.dropboxusercontent.com/u/20969135/Voltage%20rectifier%20and%20regulator%20circuit%20for%20%20motorcycle..jpg
except that you have used a p-channel mosfet instead of those bulky transistors. If this transistorized circuit can work why can't it work with mosfet. I don't understand why Hayden123 has rejected your design.
Not yet, you can take the help of this design, it's similar and also correct:
https://homemade-circuits.com/2013/08/simple-zero-drop-solar-charger-circuit.html
I don't know much about alternator criticality so I won't comment until I research the whole thing….