PWM LED dimmer question ( electronics )

[caretak3r]

more info on power draw of 5m strip - and an answer is provided besides splitting the lengths - instead feeding power to both ends:
http://electronics.stackexchange.com/a/19484

 

[lax123]

is this circuitry necessary?
If i remember correctly last time i tried to pwm those strips i used a unp -something multitransistor Array and a 3$ arduino micro clone. -ok besides that it could be fun to build it on ur own...
But strings must not be too Long, but as I just learned this would be desired anyway.

 

[stardustsailor]

is this circuitry necessary?
If i remember correctly last time i tried to pwm those strips i used a unp -something multitransistor Array and a 3$ arduino micro clone. -ok besides that it could be fun to build it on ur own...
But strings must not be too Long, but as I just learned this would be desired anyway.

This is a very efficient circuit to dim all 5 meters of one led strip..(36 Watt ) ...in fact it can dim 2x 5 meters led strings (total 72 Watt )...
A new better version ....

....

Very easy to make ..
'Very efficient ..
Dimming range : ~10% up to >95% ...
(With BAT42 Schottkey diodes it reaches ~ 99% ...)..

 

[caretak3r]

also, i found some hyper reds to test out -- they are 3528s instead of 5050s or 5630s, but it's the only deep/hyper red I could find:
http://www.ebay.com/itm/5M-16-4FT-3528-Bright-Hyper-Red-SMD-300-LEDs-Flexible-Strip-12V-ANon-Waterproof-/271413282448

I've got one on order - will take a photo for comparing color to one of my luxeon 660s when it comes in. Not sure how else to 'test' since I don't have a spectrometer laying around.

 

[stardustsailor]

I've got one on order - will take a photo for comparing color to one of my luxeon 660s when it comes in. Not sure how else to 'test' since I don't have a spectrometer laying around.

I'm waiting for your results (post'em here also ,@ this thread ,if you like ....)

Spectrometer ..?

$15 cost the DIY option ..
Plus online analyser plus open source software :

http://publiclab.org/wiki/spectrometer

http://publiclab.org/wiki/dsk

Arduino fan ?

http://www.thishollowearth.org/worlds-first-opensource-arduino-spectrometer/

 

[stardustsailor]

Stupid Simple Constant Current led driver .

Cost :~$1 ( Yes ..ca. one dollar ... )



(...)
When power is applied, the gate resistor R[SUB]G[/SUB] turns on the MOSFET. This allows current to run through the LED, the MOSFET and the sensing resistor R[SUB]S[/SUB]. As current increases, the voltage drop across R[SUB]S[/SUB] is increased as well. When this voltage drop reaches the base-emitter voltage of the transistor (V[SUB]BE[/SUB]=0.7V), the transistor is turned on. This will pull the MOSFET's gate to the ground turning it off. Therefore, the current through the LED is regulated to the one defined by the resistor R[SUB]S[/SUB].

The calculations for this circuit are very simple. To choose an R[SUB]S[/SUB] resistor you only need to solve this formula:

R[SUB]S[/SUB] = 0.7 / I[SUB]f_LED[/SUB]

The Voltage portion of the previous formula is always 0.7 Volts. This value is derived from the transistor's V[SUB]BE[/SUB] contact.
Like before, the power dissipation on the MOSFET is calculate by the voltage across the Drain-Source multiplied with the current. The voltage across the MOSFET is calculated with this formula:


V[SUB]M[/SUB] = V[SUB]DD[/SUB] - V[SUB]f_LED[/SUB] - V[SUB]RS[/SUB]


The voltage drop across the sensing resistor is always 0.7, because the BJT transistor will not let the voltage drop to go higher than the V[SUB]BE[/SUB]. Therefore, we can simplify the above formula to:


V[SUB]M[/SUB] = V[SUB]DD[/SUB] - V[SUB]f_LED[/SUB] - 0.7


The power dissipation on the MOSFET is:


[SUB]P[SUB]T[/SUB] = V[SUB]M[/SUB] x I[SUB]f_LED[/SUB][/SUB]


A few words about the Gate resistor R[SUB]G[/SUB]. Since MOSFETS are voltage components (unlike BJT transistors that are current components), this resistor is not very important to have an exact value. Make sure that it is big enough not to damage the transistor, but it is not too big. Roughly, the resistor can be calculated to provide about 0.8 to 1 mA of current.

RG=VDD / 0.001 (to 0.0008 )..

If e.g the supply voltage is 40 V then Rg = 40 / 0.001= 40000 = 40 K

(...)

(...)We can adjust the circuit to provide about 300mA for a high brightness LED.
The sense resistor is set to 2.5 Ohms (combination of 1 Ohm resistors)

ADVANTAGES:

The sense resistor dissipates less power due to the low voltage (0.7V) The current is kept stable regardless of the voltage supply The MOSFET can deliver more current with less I[SUP]2[/SUP]R losses The system has much higher efficiency since the gate resistor needs to deliver only a small current More stable in temperature changes DISADVANTAGES: Not very efficient since a lot of power is lost across the MOSFET

Example : Drive 10 leds of total Vf = 35 V at 1000mA
Supply voltage Vdd : 38V

Rs=0.7/ 1= 0.7 Ohm ....(2x 1.4 in parallel )
Vm= 38-35-.7=2.3 V

Power dis. @ Mosfet : 2.3 x 1 =2.3 Watts (=> mosfet needs small passive heatsink )
Efficiency : ~92.1 %
( ~1.8 % lost as heat at resistor Rs,~ 7.1% at mosfet..Theoretically ,at least ...)

The closer is Supply voltage (Vdd) to Total Vf of leds ,the more efficient the driver ...

 

[Positivity]

Simple to a select few..lol. Guess simple matters your perspective

Maybe u can sell them? Peeps always looking for dimmers

 

[stardustsailor]

Simple to a select few..lol. Guess simple matters your perspective

Maybe u can sell them? Peeps always looking for dimmers

I bet ya ...
If you spend the small amount of money needed ,to buy the parts ...
I 'm sure you will be amazed ...
All it takes ,is to make the 'start' ...
Take the first steps ...

(It might become a long journey ...You never know ... )

 

[Positivity]

So if you were to open a meanwell or inventronics dim driver would that be what's in there?

is this design limited to those types of stringed leds or would it work on all types?

where does powering the dimmer come into play? Like the mean wells need for a seperate 10v source or inventronics built in power source?

sorry for all the questions, just trying to understand what you've built

 

[stardustsailor]

So if you were to open a meanwell or inventronics dim driver would that be what's in there?

Oh ,way complicated 'things' inside there !!!

is this design limited to those types of stringed leds or would it work on all types?

Only to led strings driven with Constant Voltage supply ,like 12 Volt leds string,yes.
It can not be used with CC led drivers ,as the switch-on & switch off of the PWM dimmer ,will 'confuse the CC driver,
which will try to supply a constant current ,while sensing on/off states... (sudden resistive changes),That will cause spikes and damage the leds,the dimmer circuit and possibly the CC driver itself ...
Total destruction !

where does powering the dimmer come into play? Like the mean wells need for a seperate 10v source or inventronics built in power source?

Dimmer powers up from the same 12 V DC supply of the leds .(Common Anode connected ,they have the + 'line' connected ...
PWM switchg happens in the -/'ground line'...
(N channel Mosfet means the current flows channel negative ...
It is a drain of current (the - /cathode out for the leds )-as it comes from + / anode
and a 'source' of current to ground ..( the - /cathode of supply )..
Switch /'Valve ' (gate ) opens when voltage is applied (>4 Volt ) ,and current flows from drain to source ....
(Like a N-P-N BJT transistor ...Only ,transistor needs low voltage at "base "and some current pass through to emitter ,
as transistor 'opens' /switches on /'saturates'

Transistor pins vs Mosfet pins

Base=Gate
Emitter = Source
Collector =Drain

sorry for all the questions, just trying to understand what you've built

I'think you 'll like electronics ...
It's a great 'hobby' ...


[/QUOTE]

 

[stardustsailor]

I'm thinking of having led strips , attached ,at each side-of four- of my grow tent...
So it takes 4 meters ( 1x1 m tent ) for a 'full wrap' ..

I want to have NW 5000K -WW 3000K -blue 460/470 -green 540/550 -amber 600/610 - red 620/630 and deep red 640/660 ..
Each with it's own 12 V PWM power mosfet dimming channel ....
For small scale experimental grows ..( aka spectrum optimisation research...)

This circuit operates REALLY smooth and linear ,regarding dimming ,from 0% up to ~99% ..

I need to make seven channels ..
Seven of these tiny and awesome PWM dimmers ..
In one box with seven dedicated output Ampere meters ..(to check on the leds ... )

They can be also used for dimming many things except leds .
Even motors /fans ..With more than great efficiency and wide dimming range .

In such case of dimming fans/motors/or any other conductive load(containing coils ) ,a 1N400x diode should be connected across output terminals .
( Cathode - (mark/line)of diode at +12 V ,anode+ of diode at Mosfet 's Drain (led /motor /load ' - 'output ) ,for protection from inductive 'kickback' spikes )

 

[stardustsailor]

Mosfet ....
Load 12 V / 4 A ,( 48 Watt ) for half hour operation ,up till now .
Temperature: Cold as ice .
No cooling required .

 

[TheHazeyMan]

Linear Tech. makes a good part, the part number is LT3791...... http://www.linear.com/product/LT3791

I have used this for many LED designs, full PWM control and a ton of power output for such a small part, don't use a 555 timer at 500KHz. Just build a discrete driver circuit.

Can you specify the details of exactly what you are trying to drive.... Voltage, current, and dimming requirements?

CREE also makes and LMD300 LED driver that outputs 40V @ 900mA constant current source with 0-100% dimming. They are meant to be paired with CREE's LMH2 LED module, but I would assume it could be used on anything.


There are much better ways to acheive optimal results than using a 1970's IC and a fet and transistor. Check out the datasheet on both the LMD300 or the LT3791.

I am an electrical engineer and work with LED lighting systems everyday and the driver circuitry associated, kind of my area of expertise.

Edit : Actually after looking back, the LT3791 might not be able to handle the current draw you were speaking of in the first post, let me do some digging because I know they have them out there, and you will get true PWM dimming and a much higher efficiency, do you have any experience with ORCad or Eagle Cad? For PCB design? I have a quick turn board factory that will have me protos in 2 weeks flat, great quality.

 

[stardustsailor]

Linear Tech. makes a good part, the part number is LT3791...... http://www.linear.com/product/LT3791

I have used this for many LED designs, full PWM control and a ton of power output for such a small part, don't use a 555 timer at 500KHz. Just build a discrete driver circuit.

Can you specify the details of exactly what you are trying to drive.... Voltage, current, and dimming requirements?

CREE also makes and LMD300 LED driver that outputs 40V @ 900mA constant current source with 0-100% dimming. They are meant to be paired with CREE's LMH2 LED module, but I would assume it could be used on anything.

There are much better ways to acheive optimal results than using a 1970's IC and a fet and transistor. Check out the datasheet on both the LMD300 or the LT3791.

I am an electrical engineer and work with LED lighting systems everyday and the driver circuitry associated, kind of my area of expertise.

It's a simple 300Hz PWM ,power Mosfet dimmer ,for Constant Voltage applications.
Such as fan dimming and led strips dimming (which are driven with CV PSU's at 12 ,24 or more rarely at 48 Volts DC .

Simple enough .

For CC led driving ,I 've used the A6210 ...

( 3A ,2MHz,Buck-regulating led driver ,tiny ,needs good reflow skills )

But ,right now ,I'm interested on dimming simply 12 volt DC led strips ...
...
Rather not so complicated things,I may say so ...

 

[TheHazeyMan]

http://www.irf.com/product-info/datasheets/data/irfp4668pbf.pdf

IRFP4668
^ Check out this N CH HEXFET, I have used them multiple times and they are straight beasts. I have a few laying around but they are incredible.

Also worth looking into CREE's new silicon carbide Z-fets. They are insane, crazy fast switching, and high efficiency. Not cheap at all, about $40 per FET, but I was able to get a sample of one and got to evaluate it, and I was stunned at the switching times low OnResistance, mad very impressive parts.

http://www.cree.com/Power/Products/MOSFETs/TO247/C2M0025120D

 

[TheHazeyMan]

Yah I hear that brother, well if you would like to in the future I would like to help you with coming up with a nice fabricated PCB for driving these kinds of applications, this is what I do at work all day so I'm a little over enthusiastic lol.

 

[only1realhigh]

To new to LED's to figure all this out, but I see sds is knowledgeable about things.
Here is the link to one of my drivers.
http://www.inventronics-co.com/upload/EUC-036SxxxDT(ST)_2013041202583970311.PDF
2nd to last page will show the dimming circuit, at least what they show.

I used 10k pot's on all my driver's, yes 5 of them required large sized pots which I have ordered.
I have 5 driver's that the data sheet shows the same diagram as above link shows.
The 10k pot did work, just not 0 to 100% as I want with my LED's.
HELP, if anyone can help me.....

 

[Positivity]

Not my thread but I'll give it a go. Hopefully sds or anyone familiar with this can lend a hand..

But I did get a mini lesson on this..see if I'm on the right track or not.

Implementation 1 on the datasheet uses a slide dimmer. Well slide dimmers are apparently really expensive so I'd rule that out.

Implementation 3 uses a resistor. I'm not exactly sure what to make of the graph. 100% dimming at less than 1k? Not sure how to put that together. Looks like you could use a 10k pot and a 1/4 resistor following the wire schematic.

But..implementation 2. Also a resistor. In a similar format to the one I just ran across. The only difference is it seems to need a 1k (1/4w) resistor between the vaux line and dim + line. Then from there to either end of a 2.5k potentiometer. The dim - wire to the wiper (middle connect) of pot.

I'd try that..or the implementation 3 first since you already have the 10k pot and both scenarios will need the 1/4w resistor. The parts are only a few dollars each. When I run into these type problems I tend to just keep trying till I get it.

 

[only1realhigh]

I wonder what I did, the data sheet I downloaded originally only showed the slide dimmer, diagram 1. This same diagram is listed in the other driver's data sheet.
Maybe things got updated and I will check each driver's data again.
I do say my head is spinning, around and around, but it has to stop some where, LOL.
I can do this, maybe I just need to slow down and attack this issue only until it is done and not worry so much about the wife's "to do" list.

 

[only1realhigh]

now that my downloads are complete, and I study them, I would go with implementation 3, but I still see that the wiper contact of the pot being the Dim + ?
#3 graph shows when pot turned total counter clockwise you are at 100% and when you rotate clockwise you decrease (dimming) led brightness. Like you said Pos, just try and see which way is doing what and note the results.