The circuit presented here is for a DC-CDI which are used in motorcycles. A DC-CDI is the one in which the high voltage (200-400VDC) is converted from 12V supply voltage.
Researched and Submitted by: Abu-Hafss
Studying the circuit, we see that it has two parts i.e. the smps CDI unit, enclosed in the pink box and the remaining circuit on the left is high voltage converter.
The working of the CDI may be found in this article.
The circuit on left is a high voltage converter based on a blocking oscillator. The components Q1, C3, D3, R1, R2, R3 and transformer T1 forms the blocking oscillator.
L1 is the primary coil and L2 is the feedback coil. C1, C2 and D1 are DC voltage smoothing components.
How it Works
When the circuit is powered on, R3 provides forward bais to the base of Q1. This turns on Q1 and current starts flowing thru the primary coil L1 of the transformer.
This induces voltage in the secondary or the feedback coil L2.
The red (phase) dots in the transformer symbol indicates that the phase of the voltage induced in L2 (and L3) is shifted 180°.
Which means when the bottom side of L1 is going negative, the bottom side of L2 will be going positive.
The positive voltage of the L2 is fed back to the base of Q1 thru R1, D1, R2 and C3. This causes the Q1 to conduct more hence, more current flows thru L1 and ultimately more voltage is induced into L2.
This causes L1 to saturate very rapidly which means no more changes in magnetic flux and hence no more voltage is induced into L2.
Now, C3 starts discharging through R3 and finally Q1 is switched off. This stops the current flow in L1 and hence the voltage across L1 comes to zero.
The transistor is now said to be "blocked". As C3 gradually loses its stored charge, the voltage on the base of Q1 begins reverting to a forward-bias condition by means of R3 thus switching on Q1, and hence the cycle is repeated.
This switching of Q1 is very fast such that the circuit oscillate at quite high frequency. The primary coil L1 and secondary L3 forms a step-up transformer and thus a fairly high alternating voltage (more than 500V) is induced in L3.
To convert it to DC a fast recovery diode D2 is deployed.
The zeners, R5 and C4 forms the regulator network. The sum of the values of the zeners should be equal to required high voltage to charge the CDI's main capacitor (C6).
Or alternatively a single TVS diode with desired breakdown voltage may be used.
When the output at the anode of D2 reaches the breakdown voltage (sum of zener values), the base of Q2 receives the forward bais and hence Q2 switches on.
This action steals the forward bais of Q1 thus stopping the oscillator temporarily.
When the output is dropped below the breakdown voltage, Q2 switches off and hence the oscillation resumes. This action is repeated very rapidly that the output is maintained slightly below the breakdown voltage.
The positive trigger pulse at point (D) in the CDI unit is also fed to the base of Q2. This is important to pause the oscillation because SCR U1 demands the current across its MT1/MT2 to be zero to be able to self-disconnecting.
Moreover, this increases power economy as all power supplied during discharging is wasted otherwise.
A special request from Mr. Rama Diaz to have multi CDI sections sharing a common HV converter circuit. Some parts of his request is quoted below:
Ok most engines these days don't have distributors anymore, they have a coil for each spark plug or in many cases have a dual post coil that fires 2 spark plugs at the same time, this is called "wasted spark" since only one of the two sparks is actually getting used each ignition event the other one just fires into the empty cylinder at the end of the exhaust stroke, so in this configuration a 2 channel CDi will run a 4cyl and 3 channel for 6cyl and 2 x 2 channel for v8 etc...
Almost all 4 stroke engines have 2 cylinders that are paired so only 1 coil (connected to 2 spark plugs) will fire at a time the other one/s will fire at the alternate ignition events driven by a separate trigger signal, Yes aftermarket ECU's have up to 8 completely separate ignition trigger signals....
yes we could just have 2 or 3 totally separate units but i would like to have everything contained in one unit if possible, and im thinking there would be some way to share some of the circuitry...
...so im thinking you could have one heavier current step-up section to provide the ~400v then have two (or 3) separate CDI coil driver sections with a separate trigger signal for each one to drive the coils independently....possible??
That way i could use 2 (or 3) dual post coils attached to 4 (or 6) spark plugs and have then all fire at the correct time in wasted spark configuration 🙂
This is exactly the way we often do it now inductively using simple transistor based ignitors but the spark strength is often not strong enough for turbo and high performance applications.
CIRCUIT DESIGN:
The entire circuit shown above can be used. The CDI unit enclosed in pink box can be used to drive one dual post ignition coil. For 4- cylinder engine, 2 CDI units; for 6-cyl, 3 CDI units can be used. When using multi CDI units, the diode D5 (encircled in blue) has to be introduced to isolate the C6 of each section.
TRANSFORMER SPECIFICATIONS:
Since the frequency of the oscillation is fairly (more than 150kHz), ferrite core transformers are used. A tiny 13mm EE core transformer can perfectly do the job but, handling such a small component might not be easy. A little bigger may be selected. Enameled copper wire 0.33 - 0.38mm for the primary (L1) and 0.20 - 0.25mm for the secondary L2 & L3.
The picture shows the bobbin's top view.
For primary winding, start from pin no. 6, wind 22 neat turns in the direction shown and end at pin no. 4.
Cover this winding with a transformer tape and then start the secondary winding. Starting from pin no. 1, wind 140 turns (in the same direction as that for primary) and make a tap at pin no. 2 and then continue another 27 turns and end at pin no. 3.
Cover the winding with tape and then assemble the 2 EEs. It is advisable to make an air gap between the 2 EEs. For this a tiny paper packing may be used. Finally use the tape to keep the 2 EEs united.
Questions & Answers
Swagatam,
What would be the maximum voltage output of this circuit with the given 140:22 transformer ratio?
Hi Pete,
It could reach 200V too 300V according to me…
Hi, can you advise typical current I would expect at both non trigger and at 2000rpm
Regards
Neville
New Zealand
At non-trigger (standby with the ignition on but engine not running), the circuit will draw a very low standby current, usually between 50 mA and 150 mA. This is because the circuit quickly charges the capacitor and then pauses.
At 2000 RPM, the current will increase noticeably to around 0.5 Amps to 1.5 Amps. At this speed, the circuit has to constantly and rapidly recharge the capacitor after every spark which pulls more steady power from your 12V battery.
Big thanks for the typical current draw. I plan on making circuit with my constructed arduino nano that is providing auto advance curve with trigger at 50degrees before TDC. I had play with simple circuit and had the issue of SCR latching on. Keen to try this circuit, I will develop pcb with nano and cdi, will share files and software when completed. This project will be for my 1951 Royal Enfield motorcycle.
Glad to hear the current draw details helped you! Your project for the 1951 Royal Enfield motorcycle using an Arduino Nano for the 50-degree auto advance curve sounds absolutely superb.
Regarding your previous issue where the SCR was latching on, this specific circuit diagram has a very special feature to fix exactly that. The trigger pulse coming to the SCR is also connected to the base of the transistor Q2. When the trigger pulse arrives, it instantly stops the high-voltage oscillator from running. This drops the charging current going into the SCR to zero for a millisecond, which breaks the latching loop and forces the SCR to successfully reset and turn off every single time.
So hopefully this layout will completely solve your latching problem when you build your new PCB. Please go ahead and design the board, and definitely share the Gerber PCB files and Nano software code here when you complete it so other builders can also benefit.
Seems like the air gap on the transformer is critical. Do you have a recommended thickness? Also should the air gap be on all 3 legs of the EE core? Once I acquire a few components I’ll give it a try.
Thanks Again
That’s right, air gap is critical, however it can be implemented simply inserting a piece of paper or a layer of insulation tape between the center limb of the E core, or between the two outer limbs of the E core….more info is given here:
https://www.homemade-circuits.com/how-to-create-air-gap-in-a-ferrite-core-transformer/
Thanks that’s the information that I needed. One more question, what frequency should Q1 be switching at? My current setup is switching at 3MHz, is that too fast?
Thanks, glad it helped, however i have no idea about the frequency, I guess it should be in kHz, maybe many 10s of kHz.
Yes, 3MHz looks too fast.
I’ll get a video once I finalize my testing and modifications. I’m seeing a drop in voltage at high RPMs and would like to try to push it higher. Mind you right now it is performing good since I am pushing 11,000 RPMs using wasted spark for a two stroke, that’s a spark every 2.5ms.
This is all bench testing and not on the engine yet.
Thanks again and hopefully I can get it to where I need it to be.
Perfect! thanks for updating the results, appreciate it a lot….let us know how it goes…
My circuit is working now, my problem was the polarity on the primary winding. Open circuit I’m able to get 550vdc and switch frequency is around 48KHz.
Thanks Again
That’s great, If possible please send me a 10 second video of its working, I will post it on youtube with your credentials on it…
Hi Mr Swagatam could you assist, i want to build my own CDI unit for a bombardier ds 650.
I need a circuit and the components to buy and built.Your assisstance is highly appreciated.
Regards,
gert.
Sure Gert, Do you have a pickup coil in your bike, if you do, then you can simply assemble the circuit as explained in the following article, and use it in your bike:
https://www.homemade-circuits.com/how-to-make-capacitive-discharge/
Hello Mr. Swagatman.
Let me introduce myself, I’m Eko from Indonesia. I’m interested in this and would like to try assembling and installing it on a 1984 Kawasaki KZ250R.
I think I’ll have difficulty determining the ignition timing. Is there a guide for this DC CDI? I mean, how to determine the ignition timing, including the length of the pickup pulser.
Thanks Eko,
The ignition timing is controlled by the pickup coil attached with the crank shaft of the engine…so you just need to configure the CDI trigger input with this pickup coil output for controlling the timing of the ignition firing…
Hello sir, I would like to have the schematic for a CDI unit for an engine with automatic advance or retard for a moped with a pulse coil. I’ve seen that they use a potentiometer to change the spark timing. I would like to have a diagram of it and the parts to assemble it. Greetings from Uruguay.
Hi Carlos, I will design it soon for you, however remember for this simple idea to work, you will have to first physically advance the pickup coil mechanically on the engine. You set the physical position of the sensor so that it triggers at the maximum possible advance the engine would ever need at highest RPM (for example, 30 degrees before top dead center), after this we can introduce an adjustable RC delay circuit which can be adjusted anywhere between this maximum advance or lowest minimum retard…
Hello, please recommend a DC CDI for a two-stroke engine.
Hi, you can try the circuits presented in the following article:
https://www.homemade-circuits.com/make-this-enhanced-capacitive-discharge/
Good evening Mr. Swagatam. I noticed in my CDI circuit that from around 5000 RPM onwards, the spark power decreases significantly. I assembled the circuit according to the description provided in this article. However, I am using a 1.5uF/400V polyester capacitor and the coil is from an inductive system. Could this be the problem?
Good evening Tony,
yes, both the capacitor value and the coil type could be the reason for the loss of spark energy above 5000 RPM. Try optimizing the capacitor with lower uF values and higher voltage variants, MKT type, and make sure the coil you are using is designed for CDI systems only and not for conventional inductive ignition systems
Good Mr. Swagatam, I made the circuit and it worked perfectly with lost double spark coil, then I remembered that I need a rpm limiter with two step for start.a simple analog circuit maybe with adjustment potentiometer. Does Mr have any suggestions?
That’s great news Tony! Glad you could make it work for you! For a RPM limiter, you can consider trying the following circuits, let me know if you have any further doubts:
https://www.homemade-circuits.com/frequency-to-voltage-converter-circuit/
Good day, sir. Swagatam and the rest. Returning only to inform the success of assembly and operation of the proposed circuit. I had some problems with the inverter but after solved it worked perfectly. I would like to send a video showing, but here it was not possible.
Thank you Tony, I am so glad the circuit worked for you.
Yes, it would be really great if you could sed me the video of the working unit.
Please send it to my email ID:
homemadecircuits
@gmail.com
Bom dia novamente Sr. Swagatam. Só mais uma pergunta apenas.
Qual a voltagem dos capacitores C1, C2, C3, C4 E C5 respectivamente que posso utilizar???
Hi Tony, all those capacitors can be rated at 50V minimum, or higher.
Boa noite Sr. Swagatam. Primeiramente gostaria de agradecer por disponibilizar o diagrama deste circuito (CDI DC) achei muito interessante e pretendo usa-lo em meu projeto. O projeto em questão é meu carro, um (VW Gol 1995 “Brasil”) com motor 4 cilindros turbo que eu mesmo montei o qual vou instalar uma injeção “SPEEDUINO”. Eu consigo usar este circuito para funcionar em conjunto com a injeção, coletando os sinais de ignição e utilizar sistema de centelha perdida ???
Ok Sr. Swagatam, vou estudar e construir o circuito. quando funcionar voltarei aqui para relatar sobre. Muito obrigado 👍
No problem, Tony! All the best to you!
Perfect, if you allow me, I have some more doubts.
The signal I want to use is the coil firing command coming from the Speeduino ignition output. This is a square wave 0–5V pulse, already with dwell time included (about 4 ms).
Can I feed this signal directly into point D of your circuit?
Also, does point E go to the + terminal of the ignition coil’s primary winding?
Then, where do I connect the – terminal of the coil? Because your circuit does not show a connection for that.
Yes, you can feed the square wave pulses to point D.
Point E should be connected to the primary coil of the ignition coil, which is probably + in a car ignition coil.
The ground of the CDI circuit will connect with the ground of your vehicle.
You can also consider try the following enhanced version of the circuit:
https://www.homemade-circuits.com/universal-multi-spark-enhanced-cdi/
Thank you Tony,
Yes you can use the above CDI circuit with battery and trigger it via Speeduino sync pulses.
To implement wasted spark, select a coil setup that supports it and ensure the CDI capacitor and SCR are strong enough.
Build carefully, checking voltage, timing and component ratings, especially for a car engine.
Hi Mr. Swagatam. Thank you for sharing this detailed guide! I followed your instructions and built the circuit exactly as described with the exception of couple of capacitors but very close to your spec. However, I noticed that the output from the UF4007 diode was only 38V DC. Is this the expected voltage, or could there be an issue with my setup or what do you think I missed? I’d appreciate any insights you might have. Thanks again for your valuable contribution!
i had the same problem in the zener diodes I had the error zener diodes how many volts you used should be about 300 v
there is only one problem that at high revs the voltage in c6 drops to 50 v, in short, the circuit does not work for demonstration purposes
Hey Sinan. I just wanted to take a moment to thank you for sharing your experience with the circuit. It really means a lot. Knowing that someone else has been through the same challenge makes the learning process feel a little less daunting! Yes, you are right! I looked at the specs of the Zener diodes I used and they were only 12V. Unfortunately I do not have any other Zener with higher ratings, but I take your word for it that it can’t maintain charge at higher RPMs.
I have an old Kawasaki mule that has a bad cdi and it has been discontinued. A second hand from ebay cost >$500. I may keep looking for other options. Thank you.
Hello Mr. Nestor, actually this circuit wase designed and tested by a different author, who is quite reliable as far as I know him. However since it is not designed by me, I am not sure about the results of this circuit, mostly because it involves an SMPS transformer. However, if your input DC is 12V then 38V is not bad if nothing is heating up. The output voltage from the smps transformer will depend on the switching frequency and also the turns ratio…
I appreciate your very prompt response. Thank you.
Hello Swagatam,
Thank you for sharing your expertise.
I am trying to inspect/repair an old DC CDI unit for a single cylinder, 4-cycle 250cc bike.
I am having a terrible time trying to remove the OEM’s protective gel, which is mixed with many small white stones (silica?).
Do you know what is the right solvent for quickly and effectively removing this junk? I was not able to find any useful info on the net.
Thanks.
Hello Dustin,
I guess you are referring to the hard epoxy which is put into the CDI box to hide its details by the manufacturer. Unfortunately, there’s no solvent or chemical available which can dissolve this epoxy. The only way is perhaps to slowly and carefully break it bit by bit, until the circuit board is sufficiently retrieved.
Hello, I have built the circuit according to the diagram.
However, instead of a 3.3nF capacitor, I used a 3.9nF capacitor, and instead of an 18nF capacitor, I used a 15nF capacitor.and for C2 I use 470uf 16 volt electrolytes capacitor, I also built the transformer according to the formula.For building the transformer, I used enameled wire from a miniature relay and an small armature…
But the circuit doesn’t work. I’ve checked it multiple times, and everything seems correct. However, when I connect the input voltage, the TIP31 transistor gets very hot. I replaced it with a TIP41 transistor, but it still gets hot, and the capacitor doesn’t charge…
Is it possible that some of the components are faulty?
What do you think could be the issue? Please guide me; I would appreciate your help.
Thank you, my friend. Best regards!
trafonun çıkışları şemaya uygun değil. dikkat etmemişler tasarım hatalı
ya trafoyu ters pinlerden saracaksınız yada şemayı ters çevireceksiniz
140 spir lik sargının çıkışı uf4007 diyotunun anot ucuna denk gelmesi lazım.
Hi, the above circuit was designed by a different author Mr. Abu Haffs, however it was tested by him to be OK.
Actually the transformer is the heart of the circuit and if the windings are not wrapped correctly or if the direction of the winding is not correct then the circuit will fail to oscillate and the transistor will start heating up.
You can try swapping the wire ends of either the primary winding or the secondary winding and check the response.
Hello, regarding capacitor C2, which type of capacitor should I use?
The capacitor is 470 microfarads, but I could only find electrolytic ones. However, the polarity is not specified in the circuit. What alternative value or type can I use instead?
Thank you for your response.
C2 capacitor can be an electrolytic, because it is fed from a rectifier diode, so electrolytic can be used.
The value can be anything above 220uF
Interesting project, I have to try it, I have almost all the components and I only need to make the transformer, the only component that I think I will not get on the market is the TVS since here in Guatemala it is difficult to locate these components and especially because the value of it.
I already designed the single-sided printed circuit board, it’s just for testing.
Greetings from Guatemala, Sergio Lorenzana.
Thank you Sergio, glad you found the project interesting.
Hope it works for you.
Let me know how it goes….
hello dear Swagatam thanks for sharing this project,
I want to make this but I’m having a little trouble
can you share PCB diagram and full part for me?
I appreciate it
Thank you David,
However, I am sorry, i do not have the PCB design for the above circuit. You may have to contact a professional PCB manufacturer for designing the PCB layout and for producing the sample PCBs.
Dear Swagatam, have a nice day!
I am making a friend a PCB according to your diagram for his 150cc motorcycle 1 cylinder.
For obvious reasons, the circuit is sensitive to the quality of the components.
Can I use the following parts?
BT151-800R as U1
BC547C as Q2
MJE13005 as Q1
SF18 as D2
SK56 3A rated SMD as D1
Please tell me whether it is possible to shift the ignition timing in this circuit using elements. To an earlier or later position. You may need to install a toggle switch
Regards
Q2-2n5551(bc546 does not work well in this circuit, the CE saturation voltage should be less than 0.6V, I used an optocoupler, it also works great)
Q1-KT805BM (any letter index) or any transistor from a computer power supply
BT151 any fit.
D1 I would put from 5A, not necessarily shots, any.
Thank you Sergey,
You can use the mentioned parts except MJE13005, which might not work well for a 12V application, instead you can use any other 50V or 100V 5 amp transistor.
I don’t think this circuit can be modified to shift and customize the ignition timing, I am not so sure about it.
Sir what are the first circuit capacitor voltage values.can you send parts list pls
PADMAHARSHA, The capacitor voltage values that are not specified in the diagram are all 50 V rated. Resistors are all 1/4Watt 1% MFR type.
Hi ,
Does motorcycle has a alternator as well. Please let me know.
Is thta not part of CDI circuit.
Thanks
Susanta’
Yes, all vehicles have an alternator. A voltage of around 100 to 200 V AC is fed to the CDI for generating the sparks
Hi
I made this circuit
The first problem for me was the number of turns of the transformer. When I reduced the number of primary turns to 10 and the number of feedback turns to 2 , the circuit was fixed.
Now it works properly but at low speed
When the rpm goes up to ~3000, the spark is very low
Can you tell me my problem?
(I changed the number of turns because the transistor was saturation)
Thank you
Hi,
I am glad you could make this circuit successfully.
At high speeds it seems the current entering the CDI coil cannot reach optimal value. I guess the C6 should be increased a bit, which might solve the problem, but I am not sure I am only guessing.
Try increasing the value of C6 from 1.5uF to 3 uF/600V and check the response
Hi Swagatam, Joop here from Holland. I made two dc cdi ignition and it Works 100% up to 350hz with a sparkdistance of 20mm with a quality Wilma mkp 1uf 630Volt condenser and a good coil. It draws 7-8 Watt at 14Volt With for 75 Volt zeners and a very small transformer.
Now my question: Can I use 18 or even 20Volt? I need 480hz. My bike is a triple cilinder, and it has one cdi with a strange distributor wich connects the ground off the 3 coils in turns to ground.
I tryed it for a short time and it gives a stronger spark up to 530hz.
Thank You for schering you knowledge.
Regards Joop
Hi Joop,
You can use 18 to 20V, but make sure to increase the gate resistor value of the SCR to around 470 ohms 1/2 watt. The frequency of the sparks will depend on the RPM of the bike wheel. The wheel rotation will be converted to pulses from the pickup coil and sent to the CDI for triggering the ignition coil. As your bike moves faster the sparks will become faster and vice versa.
I would like to try construct the circuit for a half-bridge for a DC to DC inverter . I have a hope that for a large part of my desired application, you did a commendable job as if you are an alien from space. I shall try to make a minor modification or none at all.Thankfor your effort in arranging that the converter must operate with the fire semiconductor there are other areas that deserves technical appreciation, also I leave that to other. Thank you Homemade.
Alfred,
Malawi.
Thank you Alfred, glad you found the post helpful! Surely, you can construct it for your inverter project. Hope it works for you.
All the best to you!
Hi Swagatam,
I made this circuit but i’m not satisfied with final results because i’m facing these issues
Can you please help me, how can i overcome these issues?
Hamza.
Hi Hamza, try increasing the primary turns to 30 or 40 turns and check if that reduces the current consumption or not?
The transformer is the crucial part in this design, if it is not built correctly or the winding polarity is not correct, there could be problems. Make sure to put an paper gap between the E-core edges.
Hi, i been looking gor a good dc cdi drawing and think i found on, yours.
But it is for 4cyl car with distributor. This mean 2 ingnitions/rew. Do this construction manage to reload so fast. It Will be 8000r/min order 16000 unloads/min.
Tanken in advance.
Eric.
Hi, the above CDI circuits are for two wheeler and 3 wheeler application, not for 4 wheeler and is not suitable for 8000 RPM speeds.
Would it be possible to modificate it for 4 cyl with 8000 rpm? What is the week part, transformer or the ingnition capasitor?
Or other?
regards,
Eric
Sorry, I have no idea what type of CDI is required for operating a 4 cycle engine, so not sure how the above circuit can be modified?
The capacitor, SCR and the transformer are the 3 important parts of the circuit.
I have a 12VDC Car battery Source only. I am trying to make a CDI for my single sparkplug engine. I cannot find a way to make 200-300VDC without a very expensive transformer. Is there a cheap and simple way? Could I just buy an inverter from amazon 12vdc to European 220vac then a diode bridge to make DC? Please advise.
You can try the first concept from the following article. The transformer is an ordinary 0-12V/220V step down transformer connected the opposite way round for stepping up the 12V from the 555 oscillator into 220V AC for the ignition coil..
https://www.homemade-circuits.com/make-this-enhanced-capacitive-discharge/
What would a spark advance and rev limiter look like?
How high can it rev?
Do you etch your own circuit boards, can you recommend someone?
I do not know much about spark advance and rev limit.
I don’t etch PCBs I build them on strip boards through manually soldering the connections
regarding this circuit i have checked the trigger pulse with a occilloscope and got a reading of .8 v . do you think it will be high enough to opperate your circuit trigger ?
0.8V may not be enough for triggering the above explained circuits. Because D6 will itself drop about 0.6, and the remaining 0.2V will not be enough to trigger ON the Q2….a minimum of 2 V could be required for triggering Q2 and the SCR effectively…
Sir
What are the 3 zener diode specs for dc cdi
Padmaharsha, The zener diodes decide the voltage level that can be stored in the capacitor C6, which in turn decides how strong the CDI output voltage and the spark will be.
Be careful if you build this circuit. Capacitor C6 will hold it charge 400V even after power
has been removed. If you touch the back of the circuit board the capacitor will discharge giving you a mighty shock. The circuit packs a mighty punch. Treat with respect.
When running correctly the circuit will pull about 200ma at 12V and give out 400V.
Thanks Swagatam for posting this circuit.
Thanks for your feedback Alan, I hope the users will find it useful!
Hello
What are the necessary changes for this circuit to operate on 6V? In the primary winding of the transformer I put 11 turns but unfortunately I can not get more than 29v per output.
Thanks
Hello, The coil winding determines the output voltage so you may keep experimenting with the number of turns until the right output voltage is achieved. The idea was contributed by another author therefore I can’t suggest much on this.
Hi
What needs to be changed to run this off 48 volts?
Thank You!
Hi, nothing needs to be changed, you can use the circuit as is…however, the signal from the pick up must be 12V, and the CDI coil must be rated at 48V
Wahat is ZD1,ZD2 AND ZD3…..
zener diodes
Hi Swagatam,
Can you tell me what is the function of D4 (connect the base of Q1 to ground)?
If D4 has not, what is happening?
Thank you
Hi Trieu, it could be for protecting the transistor against reverse EMF transients
Hi Swagatam,
I see your detail your circuit and I have some questions:
– “The positive voltage of the L2 is fed back to the base of Q1 thru R1, D1, R2, and C3”. I think D3 instead of D1?
– Inverter circuit will work if it has not D1, C1, C2?
– I do your circuit with R3=4.7k, but it doesn’t work (the circuit doesn’t have a current). How the value of R3 I must change?
Thanks for your time.
Hi Trieu,
1) yes your first assumption is correct, it should be D3
2) yes it will work
3) It is an SMPS design and will need to be done with a lot of care, I cannot help much without practically checking the circuit, and moreover this design was submitted by an external author, and is not designed by me!
But in my circuitry its a bit different. I have made a different step up circuit using SG3525 pushpull with 3205 and a ferrite core. Output is stable 300v. And around 3uF of capacitors are applied at the output 300v. Im using mosfet instead of scr. Cause it is simple to use and it works well i have check it on breadboard. But the mosfet (or scr) also collapses 3uf(output stablizing) capacitor to ground along with the dump capacitor. Thats a big issue. Its like im short circuiting the output 300v. Kind of bad situation. Do you have any kind of solution what can i do for this. Im thinking to make a dual mosfet circuitry. Where P ch mosfet pull the 300 output voltage to charge cap at 300v. And N ch Mosfet ground the cap. For both gates votage signal would be same. So In normal condition p ch Mosfet will work when trigger would apply (+) N ch mosfet conducts Whereas p ch Mosfet stays off.
Ufffff Thats my imagination. I hope you have red to the end. And suggest me something valuable. Thanks
In your existing circuit you can put a P channel 400 V MOSFET in series with the line that connects the 300V with th SCR. Source will connect with the 300V line, dran with the SCR, and gate with the ground line via a 1K resistor. Attach the pick coil signal with the gate in such a way that it generats a minimum of +12V on the gate during each trigger. this will ensure, the MOSFET remains switched OFF during the triggering process and block the 300V line from the entering the SCR, while the SCR dumps the capacitor charge.
sir the availibilty of <100V p-ch mosfet or igbt is almost zero here. online are way to0 expensive. im using SG3525 ic in this Circuit. can i use shutdown pin as same time i trigger SCR in order to turn off the ic hence turning off the output while scr is doing its stuff. but im worried that how fast it turn off before the scr start to conduct. or there is another way to do it better
Harpreet, That looks like a much better idea, you can do that! The reaction time will be almost simultaneous, so there’s no need to worry about the timing
I have selected 1200V 50A n-ch IGBT for dumping the cap(it works similar like scr ). Could you suggest the P-channel Mosfet or P-channel IGBT. Cause p channel availibilty in market is quite less. And 5-10 ampere ( continuous ) would be fine i think. ???Please suggest some…..
Maybe you can try this
https://www.digikey.com/htmldatasheets/production/466566/0/0/1/ixt-k-x-40p50p.html
Hi there. i Have successfully made 12-300v stable circuit for cdi drive . now im facing a big problem just before finishing it. please read carefully
*1uF dump capacitor first terminal to 300v circuit and second terminal to ignition coil +ve terminal and coil -ve terminal to ground.
* scr MT1 is also connected to capacitor first terminal and MT2 to ground . when i trigger scr capacitor is grounded and ignition occur. but the incoming 300v Supply also grounded through scr. what should i do for that. i dont want to end up after finishing a major circuit just for this little one. if you need schematic then i can send just tell me about your email. and if you have solution please send schematic on my gmail. that would be greatly appreciated
Hello, It seems that is how the CDIs are designed to work, or may be while the SCR is being triggered the high voltage from the transformer is already collapsing towards the zero level.
I tried to attach the original trigger design with the above concept, and it also seems to do the same: