PWM LED dimmer question ( electronics )

stardustsailor

stardustsailor

Well-Known Member
Well ,I've designed -based on some diagrams,from all over the web ,one led dimmer
for one experiment regarding led strips (SMD 5050 ) .
It uses a 555 timer ,as a flip-flop ,with a pot selecting the Duty Cycle .
Frequency ain't so stable,but that doesn't matter so much ,as long it remains above ~200 Hz ,
in order for the leds not to 'flicker' ....

The output signal of the 555 will open the base of a BD711 npn transistor ...
Quite good npn for this case .
It can handle 12 A continuously (Collector -emitter Current ) and peaks of 18A ...
Up to 100 Volts .With a ( Switching )transition frequency of 3MHz ...More than enough ..
( PWM frequency :300-600 Hz )

555 led dimmer circ.jpg...


1) first question :The base's resistor what value should have ?
(for normal operation at 12V / 3-4 A ,and signal from 555 is ~12 Volts .Base has 5v max )
Im thinking somewhere in the range 470-1 K ....
Guod ?
Any ideas ?

2) Second question: This PWM dimmer can not be used after the output of a CC led driver ,right ?
Firstly ,because of the high voltage of the CC driver (in case of high power from leds in series )
and secondly ,because the CC driver will react ,to PWM ,trying to balance the current ..So ,I suspect serious voltage spikes ,there ...
Am I right ?



Here's the pcb ..
Most of the parts -resistors-caps-diodes - are SMD's ..
Only the 555 & the BD711 are through-hole..
(not drilled yet )


240971.jpg..


Guod...
Some help to an old friend ?
 
stardustsailor

stardustsailor

Well-Known Member
Oh yeah ...
I did not thought of that ...
So ,can i use a BC547 (all time classic !!! ) as a darligton pair with the BD 711 ?

Mosfets ....
Wait ...
I have two last ones I think ...
BS 108 and BS 170 are out of question I think ...

Well..
I have one IRF 9530 and one IRF 530 ..
Which one ?
If any of them will do .
I remember them being pricey ...
Never used them though...
 
stardustsailor

stardustsailor

Well-Known Member
A N-channel or a p channel ?
(kidding ..)

A N- channel ,with Gate connected through 1K res to pin 3 /( 'out' of 555 ) ,
Source at ground
and Drain to led strip (as ' - ' ) ?

Then it is IRF 530 ,I guess ....
 
stardustsailor

stardustsailor

Well-Known Member
I'm condemned to print,etch and throw away PCBs..
Thing is that I have a breadboard and all its 'parafernalia' ..
Never used it ,though...
Stupid ...
 
stardustsailor

stardustsailor

Well-Known Member
Last -stupid-question ....
The channel Source-Drain of the Mosfet ,will have 12 V ...
Doesn't the Gate need +5V more ,in order to 'open' ?

Or I 'm confused ?
(Dunno much about handling the power MOSFETs ..Yet ... )
 
stardustsailor

stardustsailor

Well-Known Member
IRF 530

Gate to Source Voltage . VGS ±20 V
Drain to Source Breakdown Voltage (Note 1) .VDS 100 V
Drain to Gate Voltage (RGS = 20kΩ) (Note 1) . VDGR 100 V
Continuous Drain Current .ID 14A
TC = 100oC .10A

Pulsed Drain Current (Note 3) IDM 56 A (Wow!!!)

Gate to Threshold Voltage VGS(TH) VGS = VDS, ID = 250μA : 2 - 4.0 V

14A, 100V, 0.160 Ohm, N-Channel Power
MOSFETs
These are N-Channel enhancement mode silicon gate
power field effect transistors. They are advanced power
MOSFETs designed, tested, and guaranteed to withstand a
specified level of energy in the breakdown avalanche mode
of operation. All of these power MOSFETs are designed for
applications such as switching regulators, switching
convertors, motor drivers, relay drivers, and drivers for high
power bipolar switching transistors requiring high speed and
low gate drive power. These types can be operated directly
from integrated circuits.


On-State Drain Current (Note 2) ID(ON) VDS > ID(ON) x rDS(ON) MAX, VGS = 10V :14 A


I think it will do ,but is way expensive mosfet ...
 
stardustsailor

stardustsailor

Well-Known Member
This is supposed to be a 5-90+ % power range dimmer ....

But something's wrong ...

I get only ~10,smthng - 11,smthng dimming ..
Less than a volt ....


240983.jpg
^^^ at max dimming with load ..
Not good pwm ...


240981.jpg
^^^ pot wiper half way ..(5K )
WTF ?


240984.jpg
240984.jpg

a) the pin 7 ,1K res should be larger ? 4.7 K ?

b ) the Gate res should be larger than 1K ( full open gate ? ) or smaller than 1 K (can't fully open gate ? )

c) the 555 is not working properly ..(i think it was one that kinda ..smoked ..a bit ...)

d) the 100n timing cap.. ? Nahhh..No... Set frequency seems correct ( 10K ,1K @pin 7 ,100n )..

Whaaaatttttttttt?
What the !@#$%^&*( is not working ?

:evil:

Guod ,any ideas ?

kiss-ass..
Please....
 
caretak3r

caretak3r

Well-Known Member
stardustsailor said:
Well ,I've designed -based on some diagrams,from all over the web ,one led dimmer
for one experiment regarding led strips (SMD 5050 ) .
It uses a 555 timer ,as a flip-flop ,with a pot selecting the Duty Cycle .
Frequency ain't so stable,but that doesn't matter so much ,as long it remains above ~200 Hz ,
in order for the leds not to 'flicker' ....
Click to expand...
I'm still playing with 5050s and 5630s - trying to find the best way to use them. Anyway, I wanted to dim a string the other day and i decided to just try a 12V pc fan dimmer and it did the job to some extent. i didn't do extensive testing, but the most i was able to get through the particular part I had was 25W.
 
stardustsailor

stardustsailor

Well-Known Member
I found it !
It works like cream !
Perfect ...
I used a 10 K res for the 530's Gate ..
And a 50 K pot ! ..
Great dimmin function !
Mosfet doesn't get warm at all !
Dimming range (approx) 10-95% ...
 
stardustsailor

stardustsailor

Well-Known Member
This led simple ,high efficiency,low cost PWM dimmer (~$5 ),will dim (or control ) a led channel of constant voltage drive (i.e. a 12 Volt 5050 smd led strip ).
Max load : 14 A x 12 V =168 Watt .
Max Voltage On IC : 15V

( If LM 555 Ic is powered by secondary psu ,then dimmer can handle up to ~100 Volts /14 A CV driven line [1400 Watt ] ).

Connections:
-Connect the 12 V + (red ) of CC Psu to leds .
-Also connect the 12V+ input of dimmer with the +12V CC psu (red )
-Connect ground of CC psu (black ) with GND of dimmer .
-connect Output - of dimmer to ground of led strip/series(black)
-Do not connect ground (-) of psu with ground of leds .This bypasses dimmer ,and leds operate at 100%.

Parts:

-1x LM 555 timer IC
-1x IRF 530 power MOSFET
-1x 1K resistor 1/4 Watt
-1x 10 K res 1/4 watt
-1x 50 K pot 1/4 watt
-2x Signal diodes 1N4148
-1x 10n ceramic cap
-1x 100n (0.1micro )ceramic cap
-1x 470microfarad ,25-35 Volt Electrolytic Cap

Total Cost :~$5-6 .


555 led dimmer circ final.jpg
Circuit diagram .

12 v led dimmer pcb.JPG
Single sided pcb with smd parts.(example)
(Only LM 555,IRF 530 & el.cap 470μ are through-hole parts ,installed top side )

(in the example ,the two ground planes /copper pours MUST be bridged with a small wire/bridge.
Other wise the 10n cap on pin 5 (Control Voltage ) has no ground,and lm 555 operates kinda unstable .)
 
stardustsailor

stardustsailor

Well-Known Member
Now,about 50smd led stripes .....

Each 5050 smd white led has three blue chips ,beneath it's phosphor layer ...
Each @20mA ...All three @60mA ...
Low driven chips=higher efficiency ....
But needs many ....
~ $15 for 36 Watts ( $0.41/Watt ) ,5 meters (15' ) long led strip ....
12 volts ,needs 3A ,per 5 meters ..

There's also another type of 72 Watts/5 meters (12 Volts -6 A ) ..

Great thing to 'lay ' around tent's walls !!!

I know that 5050 smd can grow mj ...
I've done that ,already ...

For ~0.41 /Watt ..
Great & pretty cheap supplemental led light ...to leds !!
And above all the rest ...It works great....
Tested and proven ...
 
caretak3r

caretak3r

Well-Known Member
SDS,

a thing or two about the SMD strips. I have some red 5050s and cool and warm white 5630s. I haven't yet gotten my hands on the newer 5730s. I've found that I can drive them as high as about 100W per 5M (60 LEDs/m) to where each individual led is drawing nearly .29-.33W. In order to do this, you have to split them into shorter strips - something about more resistance the longer the strip (I'll leave that to electronics experts like you to explain). I've also found that they put out a ton of heat when driven this hard, so it's not necessarily something too be desired, except for the fact that we'd want to drive all of the LEDs at similar power levels. For that reason, it's probably a good idea to split the 5M strips into 1M lengths at most.

I've been working mounting them on 3mm aluminum bar to more adequately disperse heat and that is going well so far. Based on your great work showing how well 1W LEDs can grow mj, I've been working under the assumption that there is a sweet spot (as far as how hard to drive these SMD strips) for driving these efficiently and having a nice low cost grow light. As you just mentioned, they absolutely should do a great job as supplemental lighting.
 
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