Some of the circuit designs and ideas presented in this blog may not be tested or confirmed practically. Though the author firmly believes that all the circuits would work and provide the intended results as proposed in the articles, the user must exercise caution while deciding what's appropriate.
The author cannot be held responsible for any issues or damages, may it be in the form of monetary or physical losses that might occur during the making of the listed circuit ideas in this blog, either due to negligence, ignorance or lack of proper knowledge about the subject. The user or the person who is involved with the building of the project her/himself will be solely responsible for the results, positive or negative, whatsoever.
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And please remember electricity can be dangerous if it is not used correctly. Therefore, by using this site we assume that you are completely aware of this and are well versed regarding how to use electricity correctly to avoid fatal accidents.


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gurpreet said…
Hi, mr swagatam i have a hard drive 3 phase bldc motor and want to power it and control its speed using any easy circuit not with esc controller or arduino because they are expensive. I have googled for a long time but none of my use, i have powered the motor using its original controller board but cant control its speed because it is very hard to understand the board for me, can you tell me how to take out components from that board which are required to run the motor or give me a circuit that will run and also control the speed of the motor.

Thanks and regards
Hi Gurpreet,

It's a complex circuit, but I'll to design it and post it if possible.

I have no idea about the control board, so will be difficult to say about the parts used.

The Knight said…
Dear Mr. Majumdar,

I stumbled upon this fantastic blog of yours while looking for some circuits online and I must say your work here is praiseworthy. I used to design circuits a long time ago when help was not readily available on the click of a button and you had to depend on some magazines to share your circuits with the world. That too if they chose to publish you. You, therefore, are doing a commendable job here; helping enthusiasts and hobbyists. As it appears you are devoting quality time here, not only publishing your circuits but also helping people construct them in addition to designing circuits requested by them, I think I could ask you to help me here as well. Could you suggest a way around so that an old Emergency Light Circuit meant for 9W CFL could be used with LEDs'?
Thank you very much Knight,

If your emergency light back-up is through a battery then probably you wouldn't require the CFL circuit, because LEDs can be illuminated directly with the battery... here it would be via a relay for the required switching actions.
The Knight said…
A quick response as expected! Thank you very much.

Of course you are right. I will tell you where I went wrong. I was of the opinion that the CFL circuit just needs to produce sufficient initial voltage to initiate the discharge and then the potential falls to a safe value. So doing away with that portion of the circuit would straighten out the things. It is at this point that I sought your help. What I overlooked here is that it would actually incorporate a step up circuit as well to take the value to roughly 230V to keep the discharge going and CFL illuminating. And you do not need 230V to light up LEDs'. It is much easier construct a simple circuit for auto switching and battery overcharge/deep discharge protection than to try and take out those stages mentioned earlier from an already built circuit.

P. S.: Where do you procure components for your circuits here in Mumbai from? Is it from Lamington Road?
You are welcome!

Here's one emergency lamp circuit which you can included in your existing design:


Yes, in Mumbai Lamington Road is the place where you can get all kinds of spare electronic components.
V1 = 12V

R2 = 150K
R3 = 10 Ohms
R4 = 10 Ohms
D1 = D2 = 1N4007
C3 =
T1 = 13-0-13 step up transformer
i have no transistors TIP41/42A
But i have mosfet 7805.
Can u you hlp me to build a inverter grom these components??
No, these won't be enough for an inverter
Mr. Swagatam
I hope you are in a good live.
Sir i need your help if it is possible for you.
I need a electronic circuit for that i will explain it.
I want circuit uesing transistor or ice 555.
When i press on the switch the circuit. Start counting for one minute after counting the relay turn on and stay on for 3 minutes after 3 min the relay turn off.
Remember the main switch is on.
If i switch it off and switch it on again the circuit start same cycle.
Hello Mohammad, if it's possible I'll try to publish it soon
Shayan Firoozi said…
Hi Swagatam ,

first i want to thank you for all supports you have done for me

i have a very simple automatic 12 volts battery charger which working very well

i myself draw its schematic from the real board,

i need some modifications , i would be glad if you help me and also share this circuit on your wonderful site

this is the schematic :


1- i need to add 2 LED's to this circuit , one for charging indicator and one for indicating battery full charge

2-when main fails or unplug (for long time) battery current comes back to the circuit and it will drain the battery , we can not use diode because circuit cant detect battery voltage so automatic behavior of the circuit wouldn't work

thank you for you time and help
Hi Shayan,

first of all this is NOT an automatic battery charger

Adding LEDs for full charge and discharge is not possible in this circuit, you will need an opamp circuit for that, without a opamp it is not possible to get an automatic operation and the indications..

as shown here:


diode can be added at the output of your circuit, no problem with that, the circuit will still detect the discharge levels, because the moment you connect the battery it will pull down the LM338 output supply to the same level, through the diode.
Shayan Firoozi said…
But I'm using this circuit from 2 year to now without any problem and it's detecting full battery and doesn't charge it,also its manufacturer said it's automatic and I,ve test it
It is working for you because you are removing the battery from the supply manually. If you keep it connected permanently then slowly your battery will get damaged with this charger, because the circuit does not have the cut-off facility or an automatic changeover from high current to a lower current level when the battery gets fully charged

Shayan Firoozi said…
Thank you swagatam,
With all respects manufacturer said this is trickled mode charger and you can leave you battery permanently under charger !!
Also I myself leave a 12 4.5ah with this charger for months!! How can I be sure about this subject?
Shayan, if it' a trickle charger then automatic function becomes irrelevant, and anyhow the circuit does not have an auto-cut off and it is not required if it is a trickle charger. But a trickle charger will not have the ability to charge a battery if it's discharged below its optimum level...and a trickle charge current is supposed to be at least 10 to 30 times less than the battery normal charging current, so in your diagram the circuit is designed to provide 1.3 amps...that implies your battery should be at least 100AH to be trickle charged with this charger safely.
applying 1.3 amp to a 4.5 ah is suicidal, I am not sure how your battery is surviving for months connected to this charger.

OK I think I got, it's because your charger is set at 13.75V which is much less than the optimal 14.3V....so by keeping your battery undercharged you are able to carry on with this inefficient charger... for months :)

Shayan Firoozi said…
I used 220 to 16 volts 600 milli ampere transformer,but if this charger is not automatic why stop charging after battery reaches 13.6 ?!! So strange
when a battery gets fully charged it stops accepting further charge, that's why it seems the charging has stopped.

In that case you can simply use a supply from 14V rectified source, no need of 317 and the remaining circuit, you will still find the battery cutting off at 14V.

automatic charger will completely cut-off (switch off) the output supply to the battery through a relay or a transistor on full charge which your circuit is not equipped to do.
Shayan Firoozi said…
Thank you,so I wanted to this charger for a battery backup setup,it means I should leave my battery permanently plugged to this charger,in this situation you think my battery will be damaged even with low amperage transformer?? If yes,so please help about a simplest automatic 12 volts battery charger ,besides I have to use 16 volts transformer,
Thank you again swagatam for all your supports
You are welcome shayan!

You can try the first circuit from this example article:


since yours is a 12V battery, you can eliminate all the 22k resistors and the zener diode connected with pin#7 of the IC.

Rest can be used as indicated in the diagram. This circuit will always cut off the supply to the battery whenever it's fully charged and resume as soon as it drops below that level.

yes it is not safe to connect a battery continuously with a source which may be above 1/10th of its AH value....you can use the above linked circuit with your LM317 circuit to ensure a constant 14V from the 16V source.
Shayan Firoozi said…
Thank you , for a SLA battery what charging voltage is common ?

in normal temperature(20C to 40C) 13.7 is goood ? the battery is standby and it's not on load
14V is good and will keep the battery almost fully charged, at 13.7V the battery will be only 70% charged
Shayan Firoozi said…
But in my battery datasheet said :
Standby use : 13.5-13.8 volts
Cycle use : 14.4-15.0 volts

is 14v safe for standby use ??
If you are not using the battery frequently then 13.8V will be better
Singonet Ir said…
Hi Swagatam
I'm designing a mini DC UPS , so i need to detect main failure
i need an simple circuit which switch a MOSFET ON/OFF whenever main Fails or when get back !
it should be fast enough to protect my Loads from interruption
Hi Singonet,

you can try the following concept:

Singonet Ir said…
Mr Swagatam,
thank you very much
but i need something like this :

actually i need a very simple 220 volts indicator with LED , then i wanna replace LED with a mosfet to make a electronic switch

thank you again
Mr Singonet, you can do it in the following manner:

replace the LED points with the transistor gate(base) and source(emitter)....

gate(base) will connect with the C1/D1 junction.

Replace D1 with a 12V 1 watt zener diode, connect the anode on the neutral side of the indicated mains input....remove R1 it is not required.

now connect the LED between the drain(collector) and the C1/D1 junction with a 1K resistor in series with the LED

Shayan Firoozi said…
Hi swagatam
Actually I,m interested in Mr Singonet circuits for my Dc ups,how to use this circuit to sense 220VAC and flow the current of a 12 volts battery to the load,I have to do it with mosfes,but my load is 12volt and I need to supply it whenever mains fails
My load is rated 8 amp.max,pleasr suggest me a mosfet model

Thank you again
Gajendra Mishra said…
Hi mr swagatam thanks for reply me, dear i have required a circuit of smps 500vAc to 12vdc 2A please help me
Hi Mr Swagatam, am constructing a power amplifier with a transformer of supply 85-0-85 VAC but I got certain circuits from Google where by when I constructed one of it, it failed to generate the signal to the power stage and the second one worked properly but there is one transistor which heats up whenever I give it the above supply after it's rectified& filtered & eventually the audio sound starts to change to abnormal, so really need your help because I've tried everything but I failed to notice the real cause of that problem.
"But this circuit which worked out was designed for 65-0-65 VDC but my transformer is of 85-0-85 VAC!"
Hi Kakooza, sorry I cannot find anything wrong in the circuit, not sure what may be causing the issue...may be the transistor is faulty or connected properly, or its base resistor is not OK.
Thanks sir, previously I didn't mention for you the transistor which is heating up but it's TR4 MJE340 but am using C4793 in place of it and Capacitors C4 & C7, am using 22uF/400V so I really don't know cause am stuck but still for transistor s TR1,TR2 & TR3 am using MJE350 respectively so which of those could be the route cause of transistor TR4 to be heating up, thanks.
Kakooza, C4793 is fine with its specifications and matches with MJE340, but it could be a duplicate one, so it's better you replace it with another one or even better if you could procure an MJE340....I am sure the problem is within this transistor or with the parts associated with its leads.
Hello sir well-done, since I began working with electronics, I only have one transistor amplifier I have ever constructed and worked out for me very well but it's a low voltage amplifier(35-0-35 VAC) that's why I never used it to design the other amplifier which has a supply of 85-0-85 VAC.
Therefore sir I just need your help on how to modify this circuit so that it can work on a high voltage supply and below is it's download link;
http://3.bp.blogspot.com/_B8Dh2WXNvg0/S7jlUBgY9yI/AAAAAAAAEPg/BekCF03Vwk8/s1600/Amplifier OCL 150 Watt.png
Hello Kakooza, you will have replace all the transistors with substitutes having voltage spec higher than 100V....also change the resistor values proportionately using the following relationship

35/85 = existing value/X

X = existing value x 85 divided by 35

X will be the new value which can be replaced for the existing value
Hello Sir, well done in all?
Am so great full for the above formula U gave me but I have two challenges in the above circuit I gave U where transistor TR3 heats up but its temperature starts slowly and increases with time and also resistor R4 heats up but its temperature tends to be constant.
But when I disconnect off the BASE of transistor TR3 from the COLLECTOR of transistor TR1, TR4 does not heat up any more, so what could be th problem sir, thanks.
Hello Kakooza, if you disconnect the base of any transistor then it will simply stop conducting which will mean the amplifier shutting down or start malfunctioning....so that's not the correct method of troubleshooting.

If you are not sure of this schematic then perhaps you can think of changing it with another more reliable one.

here's one design that was been tested by me, and I found it extremely good because it stated working instantly without any adjustments

But am making a transistor amplifier, can it be replaced with transistos instead of MOSFETS & give good results?
I think BJTs will also work in the referred diagram, you can try it out. But a PCB is a must in any case to avoid connection faults

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