Driving a 10W High Power LED with CC/CV with PWM???

Che0063

Newly Enlightened
Joined
Aug 14, 2017
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Hi everybody!

I am planning on building my own high power 10W portable lamp, powered by lithium ion batteries. To regulate the power, I will be using this Constant Voltage Constant Current regulator

http://www.ebay.com.au/itm/5A-PWM-D...847080?hash=item282afbf4a8:g:ON0AAOSwnHZYme5D

As you can see from the picture, it has one single pin for the PWM signal - How would I create this PWM signal?

If somebody could direct me to a schematic that shows how to generate a signal on one wire, that would be great. Presumably the PWM IC would have its own power source and simply generates a PWM output. Essentially what I want is a PWM CPU Fan controller, but only with the yellow wire (Which I believe sends the PWM signal)


All of the other PWM signal generators basically interrupt the entire circuit. This is now what I want as I've heard using PWM externally of a CC Source can make it extremely unstable.
 

DIWdiver

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Jan 27, 2010
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Hi, and welcome to the forum!

First of all, it's not really just one wire. There has to be a reference (usually ground, or IN-) as well. You also likely need a wire to power the PWM circuit. I'm not being flippant, I actually had a customer who thought that the Dallas (now Maxim) "1-Wire" devices could actually be used with only one connection.

If you are into making your own, google "555 astable" and you will find many schematics, how-to vids, etc. The '555 timer is available in many flavors from many manufacturers. Many will run directly off the battery up to 16V, some even higher. Be aware that some of them are low power (CMOS) and some are not and would gradually drain the battery if left connected. Probably the best way to do it is with two '555s (or one '556, which is a dual '555). Use the first one to generate the frequency (in astable mode) and the second, triggered by the first, to generate the pulse width (in monostable mode).

If you have something in mind that you'd like to use but don't think it would work, it might be adaptable pretty easily. Post what it is and I'll make some suggestions if nobody beats me to it. I agree that using PWM to turn the power on and off to the CVCC regulator is not a good idea, but most of those controllers can be connected to the PWM pin of your regulator with a pullup resistor, and it would work fine.
 

Che0063

Newly Enlightened
Joined
Aug 14, 2017
Messages
2
Hi, and welcome to the forum!

First of all, it's not really just one wire. There has to be a reference (usually ground, or IN-) as well. You also likely need a wire to power the PWM circuit. I'm not being flippant, I actually had a customer who thought that the Dallas (now Maxim) "1-Wire" devices could actually be used with only one connection.

If you are into making your own, google "555 astable" and you will find many schematics, how-to vids, etc. The '555 timer is available in many flavors from many manufacturers. Many will run directly off the battery up to 16V, some even higher. Be aware that some of them are low power (CMOS) and some are not and would gradually drain the battery if left connected. Probably the best way to do it is with two '555s (or one '556, which is a dual '555). Use the first one to generate the frequency (in astable mode) and the second, triggered by the first, to generate the pulse width (in monostable mode).

If you have something in mind that you'd like to use but don't think it would work, it might be adaptable pretty easily. Post what it is and I'll make some suggestions if nobody beats me to it. I agree that using PWM to turn the power on and off to the CVCC regulator is not a good idea, but most of those controllers can be connected to the PWM pin of your regulator with a pullup resistor, and it would work fine.

Thank you for your prompt respon
Yes, I realise that I was stupid, and that there was a ground pin on the Buck Converter for the exact purpose. I've settled on this board:

http://www.ebay.com.au/itm/LED-Tube...108451?hash=item2cb2c97623:g:LYQAAOSwYIxX5MWl

It has two PWM outputs, but I will only be wiring the PWM and Ground Pins together. Will this work? Of course, this will require its own power source, which I will be hooking up directly to my 4S 14.8v Li ion power source. I was ignorant of that as well before


One thing that is extremely interesting is the setup between the 4 pin CPU fan connector. If I simply connect the positive (Red) and ground (black) wires together to my 12v wall wart adapter, the fan wil run at full speed. But if I connect the PWM wire (Yellow) to the ground wire, the fan will slow down to its minimum speed. It keeps spinning, but at a much lower RPM rate. I would therefore presume that the PWM ground pin is also shared with the power ground pin?
 

DIWdiver

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Messages
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Location
Connecticut, USA
That looks like a fine board for your project.

I certainly never intended to call you stupid, and I think you know that. You've clearly got a good handle on what you know and what you don't know, and that's an excellent place to start! You also seem willing to experiment and learn from the results. No better student can be had. There are also people reading this who are very new, and still trying to figure things out, and I generally try to write for them too. I wouldn't call them stupid either. Just uneducated. The difference is you can't fix stupid (thank you Ron White!). Uneducated I can deal with. I can't cotton to stupid.

Throughout most of the world nearly all components with a single DC voltage supply are designed with the reference point at the low voltage side of the supply. Often this is referred to as 'ground', though this is often not strictly accurate. Many other names are also used, including common (com), Vss, Vee, V-, return, chassis, etc.

Anyways, it is a very safe bet to assume that the reference point for the PWM signal is the negative supply connection (I'm going to start calling this 'ground'), on both the regulator and the PWM board. I myself would always make this assumption unless the circuit was coming from Russia, or perhaps a former Soviet Block country.

So you connect all the grounds together - PWM board, regulator, battery (or batteries), etc. Then you connect PWM pin from one board to PWM pin of the other board and it should work. In this case, that's probably all you need. In some cases, you might need a resistor from PWM to V+, or to some other voltage. Depending on the circuits, you could need something else too, but with these components I think you are fine with just a direct connection. You can have different batteries running the regulator and the PWM board, or they can be the same. As long as all the grounds are tied together, you should be good.
 
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