1 Watt LED Emergency Lamp Using Li-Ion Battery

The post describes a simple 1 watt led emergency lamp circuit using li-ion battery. The design was requested by one of the keen readers of this blog, Mr. Haroon Khurshid.

Technical Specifications


Can you help me design a circuit to charge a
nokia 3.7 volt battery by using regular nokia cellphone charger circuit and utilize that battery for lighting 1watt leds connected in parallel there should be light indicator and also automatic on of system in case of power failure kindly you consider my idea and design one

kind Regards,

Haroon khurshid

The Design


The requested 1 watt led emergency lamp circuit using li-ion battery may be easily built with the help of the below given schematic:

 



 

Adding a Current Control for the LED

 



Rx = 0.7 / 0.3 = 2.3 ohm 1/4 watt

The voltage from the cell phone charger power supply is dropped to around 3.9V by adding diodes in the positive path of the supply. This should be confirmed with a DMM before connecting the cell.

The voltage should be limited to around 4V so that the cell is never allowed to cros the over charge limit.

 

Although the above voltage will not allow the cell to get charged fully and optimally, it will ensure the cell doesn't get damaged due to over charge.

The PNP transistor is held reversed biased as long as mains AC stays active, while the Li-Ion cell is charged gradually charged.

In case the mains AC fails, the transistor switches ON with the help of the 1K resistor and instantly illuminates the 1 watt LED connected across its collector and ground.

The above design can also be implemented using a transformerless power supply circuit. Let's the learn the complete design:

Before proceeding with the circuit details it should be noted that the following proposed design is not isolated from mains and therefore is extremely dangerous to touch, and it has not been verified practically. Build it only if you  personally feel sure about the design.

Moving on, the given 1 watt LED emergency light circuit using Li-Ion cell looks quite a straightforward design. Let's learn the functioning with the following points.

It's basically a regulated transformerless power supply circuit which can also be used  as a 1 watt LED driver circuit.

The present design perhaps becomes very reliable owing to the fact that the dangers normally associated with transformerless power supplies are effectively tackled here.

The 2uF capacitor along with the 4 in4007 diodes form a standard mains operated capacitive power supply stage.

Adding an Emitter Follower for Voltage Regulation


The preceding stage which consists of an emitter follower stage and the associated passive parts form a standard variable zener diode.

The main function of this emitter follower network is to restrict the available voltage to precise levels set by the preset.

Here it should be set at around 4.5V, which becomes the charging voltage for the Li-ion cell. The final voltage that reaches the cell is around 3.9V due to the presence of the series diode 1N4007.

The transistor 8550 acts like a switch which activates only in the absence of power through the capacitive stage, meaning when AC mains is not present.

During the presence of mains power the transistor is held reverse biased due to the direct positive from the bridge network to the base of the transistor.

Since the charging voltage is restricted at 3.9V keeps the battery just under the full charge limit and therefore the danger of over charging it is never reached.

In the absence of mains power, the transistor conducts and connects the cell voltage with the attached 1 watt LED across the collector and ground of the transistor, the 1watt LED illuminates brightly....when mains power restores, the LED is switched OFF immediately.

 



If you have further doubts or queries regarding the above 1 watt led emergency lamp circuit using li-ion battery, feel free to post them through your comments.

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Comments

hans said…
i have a 4v1/2 A battery , do you have a automatic charger schematic for that battery?
Swagatam said…
You can try the second circuit from this link:

https://homemade-circuits.com/2012/07/make-6v-4ah-automatic-battery-charger.html
prashant said…
Hi Swagatam,

Can I can add a diode from base of transistor to LED, so that LED is ON even with power from mains.
I want to keep LED glowing always, either from mains or battery.
Please let me know, if that is possible.

Thanks
Prashant
Swagatam said…
Hi Prashant,

yes you can do it.
Mahesh said…
Can I use a higher capacity mobile battery (more mAh) for longer backup with the 1watt led? Any modification required ? Gr8 blog . Keep it up.
Swagatam said…
Thanks! yes it can be done, no modifications would be required except the series 10 ohms resistor which will need to be decreased for appropriate charging of the batt
nalini ranjan said…
Hi Swagatam

pls. tell can i use 3 x 1watt led in parallel with the first circuit? and how?

thanks
Swagatam said…
Hi Nalini,
use TIP127 for the transistor and a 3.7V/2ah li-ion battery
Hi Swagatam,
Is it possible to apply 2 identical batteries parallel instead of one battery to increase the capacity?
Swagatam said…
Hi asanka,

yes it's possible.
Jignesh said…
i have build this circuit with three 1W led in parallel with proper heat sink....and it really works good....and happy with this .....thank u Swagatam....i have been waiting for it so long
Swagatam said…
It's my pleasure Jignesh!
Heeran Manilal said…
Hi, I require a circuit that can work from 230Vac input, and the circuit must be able to charge a lithium ion 7.4v 2600mah battery pack as well as drive a micro controller that will power up one 3 watt led.
Swagatam said…
You will need a 9V 1amp smps adapter for charging the battery, the MC can be powered via a 7805 IC from this adapter.
Jignesh said…
Hi Dear,
Happy Holi....!
Hope u'll be fine....
i have a little problem, i have charged this lamp for over night. now if i am using the lamp, it works good but after 3 to 4 days when i am going to switch on the lamp, i found the battery drainout completely. again i charge this unit fully but i am facing same problem.....hope u understand this.......need solution
Swagatam said…
Hi, thanks!
Is this happening while plugged in to AC supply??
Saeed Abu said…
hi how much(ohms) resistance i have to use to connect 3pcs 1 watt LED with 3.7v mobile phone battery to get optimum brightness? I used 3.3ohms half watt but it becomes hot(resistance+LED)please help me.My Email:saeed_rony16@yahoo.com
Jignesh said…
no.....not at all. after completely charged i had disconnect the unit from charger. i am using nokia's small pin charger and also i have two cellphone batteries connected in parallel ( 800mAh and 1000mAh ).

Swagatam said…
in your email you notified that you are using 5 batts in parallel, so 3 leds would be ok with them.

use 3.3 ohms for each led separately...it will not become too hot...just warm.

actually it should be 1.6 ohms, but 3.3 ohms would be fine.

use sufficiently large heatsink for the leds.
Swagatam said…
if you disconnect it from the mains the LED would get switched ON, so I can't understand how you could keep it for 3/4 days in that way.

put a switch in series with the battery.... switch it off when the unit is not connected to mains, this would prevent the batt from getting discharged.
Saeed Abu said…
hi, thanks brother for ur reply.Above 2nd circuit i need auto battery charge cut off system and auto change over ac to dc when main fails.Also i need more simple version of this circuit.is this can be designed?
Swagatam said…
brother, a simple circuit cannot be made with so many features....you can try the following design which has all the required features but it uses a transformer:

https://homemade-circuits.com/2013/02/make-this-automatic-10-watt-to-1000.html
Jignesh said…
hi Swagatam
i have build this unit properly with brightness control switch, normally s/w is in off positon. and i have uploaded the image on google+, plz check it out....thanks
Swagatam said…
Hi Jignesh,

Yes it looks OK to me
Saeed Abu said…
thanks brother for ur response.For 1st circuit is there is any over charge protection system (auto full charge cutoff) for battery included? if not how can i add it?
Also can it run by Nokia standard cell phone charger?
Swagatam said…
bro you can use the first circuit from this link:

https://homemade-circuits.com/2011/12/how-to-make-simple-low-battery-voltage.html#uds-search-results

just connect its pin6 through a 1N4007 diode to the base of the transistor in the above circuit.

and also swap the pin3, pin2 with each other so that it functions like a high voltage cut off instead of low voltage cut off.
Swagatam said…
bro, sorry the above suggestion won't work, the cut off transistor will need to be configured in series with the batt positive.

the cut of transistor will be triggered via the opamp pin6.
Saeed Abu said…
Bro thanks for ur reply.Actually im Pharmacist(M.Pharm) & Electronics is my hobby.So i go through ur mentioned link & i dont understand ur suggestion to modify that diagram also about ur mentioned cut off transistor.So would u mind to send me the complete circuit diagram through my email(saeed_rony16@yahoo.com)? My requirement is:(1) Circuit is Operated by Nokia standard cell phone charger (2) Battery nokia 3.7 volt (3) Auto ac to dc changeover system when ac fail (4) Battery overcharge protection system(auto battery full charge cutoff) with LED indicator.I have tried many times to develop such type of circuit but i failed. So Please bro help me urgently. Please design it simple.
Swagatam said…
Bro, I understand and will try to do it, but it could take some time due to my busy schedule...kindly bear.
Y0f4N said…
it's great idea of circuit and smart cause add 2 diode , thanks for goofle found this link. for above circuit 10 ohm for current control ?
I just want design some "dream emergency LED" with spect as for battery charger is automatic, when running from battery and battery get low (3.2 Volt) then cut off so LED is off it will prevent damage from battery.so far I just build auto bat charger and LED driver
Saeed Abu said…
bro what about my specified circuit diagram what i am asking u to developed? R u still busy now?
Saeed Abu said…
bro what about my specified circuit diagram what i am asking u to developed? R u still busy now?
Swagatam said…
yes 10E is for battery charging curret limit.

I'll soon try to present the required circuit in my blog, do keep in touch.
Swagatam said…
bro, due to some busy schedule I am not able to do it immediately, rest assured the first article that comes next in my blog will be yours.
Saeed Abu said…
Bro what about my specified circuit diagram what i am asking u to developed? R u still busy now?My requirement is:(1) Circuit is Operated by Nokia standard cell phone charger (2) Battery nokia 3.7 volt (3) Auto ac to dc changeover system when ac fail (4) Battery overcharge protection system(auto battery full charge cutoff) with LED indicator.I have tried many times to develop such type of circuit but i failed. So Please bro help me urgently. Please design it simple.
Swagatam said…
Bro, please find it here:

https://homemade-circuits.com/2014/04/li-ion-emergency-light-circuit-with.html
ravindra metri said…
Sir .plz givr pitout BT136 in data sheet there showd M1 M2 G i cant unstand. 2Uf/400v mrans 205/400v ? In our city 100uf/225v not avlible 100uf/160v use
ravindra metri said…
Above ac circuit can i use 9v rechargable battery and 1 watt 2 LED use what chage made for circuit
Swagatam said…
Ravindra, the right lead is always the gate, the center connects with the mains/load while the left terminal connects with the ground.

Are you referring to the above circuit? it's a difficult design, you can try other simpler ones.
Swagatam said…
9V PP3 won't support 1 watt LEDs.
ravindra metri said…
In our city 100uf/225v not avlible 100uf/160v can i use
Swagatam said…
yes it will do, even 10uF/400V will also do.

Please ignore the previous commenrt in the other article.....
ravindra metri said…
2uf/400v not available can i use 2.2uf/400v
ravindra metri said…
Sir. I want circuit design for 3 phase submarshible motor control like single phase priventor, dry run ,auto start few seconds
Swagatam said…
I'll try to design if possible, although my knowledge regarding 3-phase systems is not so good.
ravindra metri said…
Sir. I have LED driver its output is 6-12v and 300 MA i want to 1 watt led 3 to 6 which resister i use how much watt. I connect 1 WATT 3 LED series with 10 ohm 1 watt resistor but LED & RESISTER going hot
Swagatam said…
Ravindra, 3 LeDs in series is correct (@12V), but use 6 ohm 1 watt resistor for optimum brightness.

The LED will become HOT, you will need to mount it on a suitable aluminum heatsink otherwise it will get damaged within seconds.
ravindra metri said…
Sir. Any circuit for AC to 1watt LEDx 10 no led connect
ravindra metri said…
above 2nd circuit 1K 1watt hot then blow
arun kumar said…
please tell me 2 circuit output voltage/amps?
Swagatam said…
use 1K/2 watt, and use 105/400V for the input capacitor
Swagatam said…
Ravindra, use the second circuit from above....add all the 10 leds in series directly across the emitter of BD139 and ground, remove the 8550, 1k, 1N4007 associated parts these are not required.

now adjust the preset slowly to get full illumination over the connected LEDs.
Swagatam said…
capacitive power supplies become inefficient with their amps when used for low voltage applications, the second circuit will not give more than 100mA output if 2uF/400V is used as the input cap
arun kumar said…
second circuit battery 3.7/800ma to 3.7/ ?ma any modify circuit please tell
me
arun kumar said…
hai sir 2circuit battery used 3.7v /800ma to 3.7v /?ma any modify in circuit please send me sir
arun kumar said…
hai sir 2 circuit battery used 3.7v/800ma to 3.7v / ?ma any modify 2 circuit please tell me sir
Swagatam said…
not more than 800mAH, it's the maximum value
Hi Sir! I have successfully installed and used this circuit with 5led x 1w, I'm very happy for it. It's all thanks to Sir, I thank you very much Sir! Sir I want to ask is this circuit can be fitted LDR is not? If they must establish how? Sir reply me on my email: memory1gb@yahoo.com. Again thank you very much Sir!
Swagatam said…
Hi Truong, thanks!

you can add an LDR feature by doing the following steps:

take a BC557 transistor, connect it's emitter to battery positive, collector to base of 2N2907
and connect the base of BC557 to LDR's one lead, the other lead of the LDR will connect with the negative of the battery.
also connect a 1M pot across the base of BC557 and the positive of battery.

adjust the pot to get the required results.
I got the email of Sir. Thank you very much Sir!
basit momin said…
Sir wat will be the changes for the circuit if I want to run 3 leds of 1 watt in series
Swagatam said…
basit, put all the three in parallel with a 1 ohm series resistor with each LED
basit momin said…
Which watt resistor
basit momin said…
For first circuit where I can fix a preset
basit momin said…
Sir wat is 2n 2907 in 1st circuit
basit momin said…
And in first circuit 1k resistor is 1watt or 1/2watt
Swagatam said…
preset for what??
Swagatam said…
it's a transistor
Swagatam said…
a 1/2 watt will do
basit momin said…
Preset as light Dimmer for leds
Swagatam said…
use a 10k preset and connect it across base and emitter of the transistor for dimming purpose
basit momin said…
Sir instead of preset can I use on of switching if yes then where can I fix it and where is light indicator for first circuit
Swagatam said…
you can fix a resistor via a switch in series with the LED, use a 22 ohm 1/2 watt resistor for this
Swagatam said…
you can connect an indicator LED across the junction of the two input diodes and ground with a series 1K resistor
Muhammad Nafees said…
Hi Genious
What will be the changes in first circuit for 4v 1.2A battery
Swagatam said…
No changes will be required, you can it as shown.
kamlesh_sexy said…
HI friend,
I have a issue with this circuit,
also one friend having the same issue, (@Jignesh)
<<>

My Issue is similar to jignesh issue.
I build this circuit, added 3.7(18650 2000ma battery Original Samsung).
when i connect the fully charged battery to this circuit, the led glow much batter and last up to 4 to 6hrs. when battery got low, i connect mobile charger to charge the battery to this circuit as per u show, the mobile charger output is 5v 800ma Nokia, i charged over night (approx 7 to 9 hrs), in morning i checked whether battery is heat or not, or any components are get heat or not, but nothing happen, nothing get heat. alright its fine, i switch on the led but the led glow dimm and last not more then 1hrs, less then 1hr. again i disconnect the battery and charged by other charger (18650 battery charger) and again i connect to this circuit, its last 4 to 6 hrs).
please solve this.. Thank u in advance :)
Swagatam said…
Hi Kamlesh,

you mean to say that you tried the first circuit, the LED emergency lamp action works fine with a fully charged battery, but once discharged the battery does not get charged fully, right?

in that case you can try replacing the 10 ohm resistor with a 1 ohm resistor and see if that helps.
kamlesh_sexy said…
Ok, I will replace the 10ohm resistor with 1ohm and I will check whether the battery charge full or not, and thank you very much for your reply.
ok so your 10ohm resistor is 2w, so what watt resistor for 1ohm I need? the same 2w or another?
kamlesh_sexy said…
Oh I have to ask you one more thing,
if input (mobile charger) value is 5v 800ma to 2a, so I can use 1ohm resistor?
I am mean I told u that I am using now 5v 800ma and u told me to replace 10ohm resistor with 1ohm, if I use 5v 1a or 5v 1.5a or 5v 2a, so I have to use 1ohm resistor for more then 800ma charger(input power from mobile charger)?
Swagatam said…
the watt will need to be judged by touching the resistor, if it gets too hot, then you can think of increasing the wattage.

use Ohms law for determining the resistor value

R = (supply voltage - battery voltage)/mAH of battery



sivakumar said…
Dear firiends I want a help from this forum, my 14" crt tv showing EEPROM ERROR what to do ? I replaced the new EEPROM IC also, but still the EEPROM is showing please help me....
romeo gasilan said…
.sir can i use this circuit for 240 AC mains?.. Can u m0difY it for me using a relay when the battery is full. The relay is off and therfore the charging stops.im just ensuring the battery life. Thanks in advance
Swagatam said…
Romeo, you can try the following circuit for fulfilling your need:

https://homemade-circuits.com/2013/02/make-this-automatic-10-watt-to-1000.html
Rajkumar v said…
Dear sir,
I have a two 4 volt 0.5 mAh china Battery connect in parallel . I removed one DIODE of the series, go to the two DIODE. then Instead of using 10 OHMS to 1.3 OHMS 2watt . Well now loading the battery charge. please tell us your advice on this. Two diode in series. Why has been put here for?
Swagatam said…
Dear Rajkumar, normally cellphone charger will show around 7 to 8V when measured without load, therefore to correct this issue I connected the two diodes, but actually it's not necessary since on load the voltage automatically adjusts to the intended correct battery value
Rajkumar v said…
Thank you thank you so much. I clearly understand.
muchson chanafi said…
Hi Sir, I want to asked, diode after R 10 ohm, what diode Type?
Swagatam said…
Hi Muchson, you can use a 1N4007 diode there.
Pravin Chunekar said…
hi sir pls tell me 3.7 v /2080mah battery using led 1watt circuit disgrm
Swagatam said…
hi pravin, you can use the same circuits which are described above...
muchson chanafi said…
Hi Sir, in my area 2n2907 is nothing, what to replace them..
Swagatam said…
Hi Muchson, you can use BD140 or 8550 instead
Rajkumar v said…
Dear sir ,
Please help me I will have use a 4 V 2000mA or 1500 mA battery, then I use first circuit to power 2 numbers of 1 watt LED . may I use BD138/140 TRANSISTOR
If it's OK. What changes should I make it?

Thanks
Swagatam said…
Dear Rajkumar,

use a TIP127 instead for better power handling...the 1K could be replaced with a 10k resistor if TIP127 transistor is used
Thank you thank you so much.
Rajkumar v said…
Swagatam sir, In First circuit May I use brightness control.what will made this change?
Swagatam said…
Rajkumar, brightness control can be achieved crudely by inserting a 20 ohm 1 watt pot in series with the LED, or you can use a couple of series diodes with the LED and switch these diodes using a rotary switch for increasing or decreasing brightness.
Sidhesh dessai said…
Hi sir ,

I have 12v and 7ah battery , I want simple circuit , my requirements is 12v 9 watt DC led bulb like this 3 bulbs must work for 14 hours , or any other option by which I will have bright light in my room each 20 sq meters area (e.g 9 watt everreaday bulb which work on ac that much bright ) but itshould work on battery for 14 hours on 12v 7 ah battery
Swag said…
Hi Sidhesh, dividing 9 by 12 gives 750mA, 3 times makes of this gives 2.2 amps, which will not allow more than 2 to 3 hours of back from the battery, 14 hours will not be possible...
Sunil said…
Hello sir,18650 3.7v ×2 in parallel,1 watt led × 3 in parallel,does the same circuit work?
Swag said…
yes it will work just replace the 2N2907 with TIP127
Sunil said…
Hello sir,That was good,but brightness is dull.And charging battery is below 3.85v,what can i do to achieve more brightness and fully charging battery..
Swag said…
Hello sunil, replace the transistors with a TI127 to increase LED brightness, and allow charging of the battery for at least 10 hours.

make sure to connect a 4V zener diode across the battery terminal.
Sunil said…
Thank u sir for kind response,
I'm confused,in the schematic,is that zener diode or led indicator after 10 ohm resistor to the emitter?
Can i have rough schematic using tip127 plz?
Email:slamakasang@gmail.com
Swag said…
Sunil, it is a 1N4007 rectifier diode.

the schematic will be the same, just replace the 2N2907 with TIP127 with correct pin configurations.
aabhishek sharma said…
Hi sir ,can i post my article of emergency usb rechargeable lamp here on your website ,please check the link here ... ,its instructable for that project.
Swag said…
Hi Aabhishek, you can post articles in my site with images, but it should be original. Since you have already posted it in another site I cannot publish it again in my site.

Create original projects and submit it to me, I'll pay you Rs.600/- for each project which must have minimum 500 words and a few images
Aabhishek Sharma said…
OK sir, so what's process for creating and submitting, can you explain procedure,
Thanks.
Swag said…
you must first tell me which topic you want to submit the article on, I'll tell you whether you can go ahead with it or not... if I say yes then you can start the work by creating a suitable description of the circuit with your natural explanation, without copying any sentence word to word from anywhere, and send the article to me with schematics and pics drawn by you, and if possible with a video...
Sparjan said…
Sir I don't understand what the use of bd139 transistor
Swag said…
Sparjan, It is configured as a voltage regulator, to stabilize the voltage at the adjusted preset level.
Hilman said…
hi bro...
i have li ion 18650 2800mAh and i have a lot of 3 Watt Led, if i need to backup for emergency as long as 10hours. how many led should i used to this circuit as paralel, and which component must be to changed?
Hilman said…
hi sir..
i have SLA Battery 6V 7,2Ah and 3 Watt HPL Led.. could i use this schematic for emergency Led as transformerless? and how many 3 watt led for backing up 15hours long life full brightness? which one the component to be changed?
Swag said…
Hi Hilman, yes you can use it, just make sure the input voltage is fixed at exactly 7V, and has a current not exceeding 0.5 amps
Swag said…
I would recommend a transformer based power supply or a SMPS based
Swag said…
Hi Hilman, with a single 18650 battery I would not recommend a 3 watt LED, because its back up won't be above 1.5 hour or 2 hours at the most
hilman said…
thanks for quick answer.. so how many 18650 cell for HPL led3watt and could to backup minimum 6hours life?
i am interesting in emergency led transformerless power supply.. i think total power 10 watt is quite enough for my lighting
hilman said…
oh okay..is that just preset potensio to get 7volt input battery right?
and how many HPL 3Watt led in series or paralel to load that enough for 15hours driving from battery?
hilman said…
i am a beginner in electronics, just learn by reading by my self... i'm not experience in smps psu and also minimum knowledge of transistor or transformer building.. so it will difficult for me... hehehe.. i don't have teacher..
Swag said…
Considering a 3.3V/1 amp LED like yours, a single cell would roughly provide a back up of around 2.6/3 = 0.86 hours in ideal conditions, but practically you can except it to be 0.86 x 0.6 = 0.5 hours.

therefore for getting 6 hours backup you may need 6/0.5 = 12 such cells
Swag said…
yes the potentiometer can be used for setting the 7V output, but the circuit is not isolated from mains so be extremely careful.

For your mentioned battery you can put 4 LEDs in series, but the maximum back up cannot be more than 5 to 6 hours
Swag said…
you can feel free to ask questions here, I'll try to help you learn the basics as much as possible
hilman said…
ok thank for helps... its time to test how long time to charge those 18650 cells.. i only have 8x 18650 may be whole day charging...
nice post here
Swag said…
You are welcome!
hilman said…
It's easy to get 7 volt but i found the strange how to control the amp to battery not exceeding 500 mAmp?
Swag said…
sorry, actually you will have to use a 6V/500mA transformer with bridge rectifier and filter capacitor for DC rectification. Transformerless might not help to charge the battery.
hilman said…
yes to get 7V ist easy to get without load the battery, but while loading the battery, transformerless wont to charge the SLA 6V 7.2 Ah Battery, and voltage getting drop.
i have small transformer get scrap from emergency lamp. its about 9volt, but i don't know what the capacity in amp.. because when adding bridge 1n4007 diode and then connected to the battery get drop voltage? its charging the battery? i doubt it. and how long get fully charged. the transformer get hot
Swag said…
hilman, the charging voltage will always drop and should drop upto the battery level when connected to a discharged battery, it is necessary no matter what type of charger is used, but a transformerless supply are generally designed to work at very low current, therefore these are not suitable for charging lead acid batteries.
your transformer should be able to produce 7V after rectification and around 500mA current only then it will be suitable for charging the mentioned battery, otherwise not.
abba said…
Hi Swagatam do you still recommend a transistor current sensor cct even if we can provide a resistor that will allow a fixed amount of current? like in the second cct if you remove the transistor with Rx and replace it with just a resistor that can allow the required current to the led as is usually done in led control cct.
thanks
Swag said…
Hi Abba, a resistor is a crude form of current limiter and may work well only for low dissipation application, for a 1 watt LeD the dissipation can be significantly high resulting in an inefficient current control and wastage of precious energy, therefore a transistor based current limiter may be more suitable here.
Naeem said…
Hi Swagatam,
For 2nd transformless cct,
I want to add 3000mAh li-ion samsung mobile battery.For that purpose is it ok to put 3 ac caps in parallel (205k*3pcs 400v),if so what further modifications need to be.
what is the function of 1k 1 watt resistor at the base of BD139.
can i use low voltage polar cap (say 50v 100uf) instead of 225v 100uf.
I also want to know is it safe circuit to left over long on AC mains like 24 hrs and led light would come on when there is mains off.
Regards,
Naeem.
Swag said…
Hi Naeem, I won't recommend it, because 3nos of 2uF capacitor would result in having 6uF capacitor which may generate a significant amount of switch ON surge current, damaging the transistor instantly, moreover the output will be floating with mains 220V, so all these factors can make the situation extremely dangerous and unfavorable
Naeem said…
Hi Swagatam,
Thankx for ur reply.Pls reply me for the rest of 3 queries:
what is the function of 1k 1 watt resistor at the base of BD139.
can i use low voltage polar cap (say 50v 100uf) instead of 225v 100uf.
I also want to know is it safe circuit to left over long on AC mains like 24 hrs and led light would come on when there is mains off.
Regards
NAeem
Swag said…
Hi Naeem,
1K is for biasing the BD139 transistor, without it the transistor won't conduct
you can use 100uF/50V at the emitter side of the BD139, not across the bridge. You can remove the bridge side capacitor, and use the 100uF/50V at the emitter side only.
The circuit may be safe for low current applications, and if the voltage is correctly adjusted for the battery...but mains voltage will be always floating across the whole circuit
Naeem said…
Hi Swagatam,
Thankx for reply.It mean that this circuit is not suitable for 24 hrs operation as AC mains always floating across the circuit
can i use D882 in place of BD139 as i already have it in my electronic parts.
Swag said…
Hi Naeem, the floating current is dangerous for the user not for the battery or the LED, if you enclose the circuit inside an insulated box then it would be fine. For the battery it would be safe if the current from the power supply is very low and used only as a trickle charger.
D882 will also work
Naeem said…
Hi Swagatam,
For testing purpose, I only constructed circuit excluding battery, LED and S8550(driver circuit). I measure voltage at cathode of battery protection diode ,unluckily voltage around 38v.I fully rotate preset on both way but no affect on output voltage.I also used
bleeder resistor 390k ohm instead 1Megohm ,
10uf 400v instead 225uf 400v,
D882 instead BD139.
Do u think its component mismatched fault which cause output steady high volts of 38v or half constructed circuit excluding driver circuit.
Regards
Naeem.
Swag said…
Hi Naeem, the BD139 is connected as an emitter follower, the voltage across its emitter will be around 0.6V less than its base voltage. For example if you set the base voltage at 12.6V using the preset, the the emitter voltage will be around 12V.
Make sure to connect a dummy load of around 1K resistor across emitter/ground side of the transistor and then take the measurement
Naeem said…
Hi Swagatam,
I attached 1k ohm dummy load as per ur suggestion but same result as previous no voltage control any other suggestion pls.
regards,
Naeem
Swag said…
Hi Naeem, check the base voltage of the transistor while adjusting the preset, if for example it shows 12V, and the emitter voltage shows 38V or some higher value then your transistor could be faulty, because for a good transistor in the emitter follower mode, its emitter voltage will be always roughly 1V less than its base voltage
Naeem said…
Hi Swagatam,
I tested input caps which i used in place of 2uf (155j+474j400v in parallel).Voltage adjustable with .47uf but difficult with both caps usage(155j n 474j)but both caps perfectly workable in other crcuits.
I also use 100 ohm variable which finely adjusted output volts but then led light not turn off by using switch at s8550 base resistor side.
Pls suggest me where to add a on/off switch and power on led indicator for the 2nd circuit
regards,
Naeem
Swag said…
Hi Naeem, the emitter voltage of BD139 must be slightly higher than the battery voltage, only then the LED will remain shut off otherwise the 8550 may keep conducting.
Naeem said…
Hi Swagatam,
There is a conflict b/t led driver and emitter follower circuit.Ied still glowing even base of 8550 through switch off.
Kindly suggest me little about npn led driver(s8050) connections.I want to use npn bjt with on/off switch
Regards,
Naeem.
Swag said…
Hi Naeem, please see the last circuit from this article,

https://www.homemade-circuits.com/how-to-make-efficient-led-emergency/

you can replace the transformer power supply with a capacitive power supply and add the emitter follower between the supply output and the 1K resistor of the left side BC547
youngking said…
Hello sir, it been long. Sorry to quote you for using this circuit for variable power supply .
Ignore the 8550 transistor, the LED, and the IN4007 diode, and use the output which is available across the 1K resistor.
DO not use 2UF at the output instead use 0.33UF/400V.
Now my question is as follows:
1. According to the diagram you didn’t indicate the positive AND NEGATIVE therminal of 1 WATTS LED
2. I DON’T understand the 1M AT THE TOP OF 2UF/400V PLS CAN YOU Explain that
3. I bought other component except BD139, IS there any other transistor that can replace the 0.33UF/400V IS not my reach can I replace it with 0.3uf/400v if not what other values can I use pls sir l’m waiting for your response. Thanks GOD bless u
Swag said…
Hello Younking,
1) The negative of the LED will naturally connect with the negative line of the circuit, so the other terminal of the LED which is positive will naturally connect with the collector of the Transistor.
2) The 1M is for discharging the capacitor safely whenever it's unplugged
3) You can use TIP127.
4) You can try 474/400V or 0.47uF/400C capacitor
youngking said…
sir thanks for your response so far. next query how can i monitor the voltage while varing the preset since i can not buy muitlmeter
Swag said…
Youngking, I am sorry, I do not know how it may be possible to monitor voltage without a multimeter or voltmeter....
youngking said…
good day sir, please i went to market in search of voltmeter they told me they have two type ac and DC voltmeter so i'm confuse the one to choose but can voltmeter found in stabilizer be used and how can i connect this to your variable power supply circuit above ,although i have solder the component together but have not tested the circuit i'm waiting for your response. thanks
Swag said…
Good day Youngking, please post your question under the correct article, this article is not regarding stabilizer so i cannot answer it here.
youngking said…
hello sir, what i meant is that i have build the last circuit which i will use as variable power supply, now my question is as follows . 1. can i used a volt meter found in stabilizer to monitor the voltage while varying the preset of this variable power supply circuit. i hope is clear
Swag said…
Youngking, is your voltmeter maximum range matching the range for the power supply output? If it is matching then you can use it?
youngking said…
sir the voltmeter is 220volt can it work.
youngking said…
hello sir, i build this last circuit but it didn't work .when i touch the led with a tester it show tiny light. i also came across your circuit using LM317 for making variable power supply which you refer as the simplest. how can i modified it to 12v because you indicated voltage input as 28v pls sir responde to my query.
Swag said…
Hello Youngking, the above circuit is the simplest one, I'll make it soon and show you how to do it. which LM317 circuit are you referring to? Please show me the link.
Sherwin Baptista said…
Dear Sir,
I have plenty of standard 5mm 20mA cool white LEDs and what i want to know is that:

1. If i compensate them for a 1w LED then how many pieces of LEDs i would require to get 1w of optimum brightness for them?
I wish to use the 20mA LEDs since i wouldn't require to attach any heatsink for them (on the PCB)?

2. I have noticed that by comparing the 1w and 3w LEDs i found out:
The 1 watt LED is more power efficient, dissipating much lesser heat but giving a slight more than its rated 1w power i have noticed.

On the other hand the 3w LED does not produce 3 watts of equivalent brightness, dissipating a lot of heat and is not power efficient.
(I have used a proper heatsink for both cases).

3. I also want to use 3nos. 1w LEDs in series from 12v supply? is that energy efficient? or eqvilate the same 3w by using many pieces of 5mm 20mA LEDs in place of 1w LED?
Just asking for your suggestions>
Thanks
Swag said…
Dear Sherwin, using 1 watt LED instead of a single 3 watt may be more efficient in terms of light distribution and managing heat dissipation, but as far light intensity is concerned a 3 watt LeD will also efficiently emit the specified amount of light, because all these LEDs are tested using international standards by the manufacturer before assigning their specifications.

As far as 20mA LEDs are concerned they may be not as efficient as the high watt LEDs. However the SMD types are extremely efficient, and if an equivalent number of them are assembled can work more efficiently than the high watt counterparts, and moreover these do not require heatsink or current controller, making things even more desirable for the user.

You can use 3nos of 1 watt LEDs in series as described in the following article:

https://www.homemade-circuits.com/universal-high-watt-led-current-limiter/

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