Higher Wattage 12v Card LED strobe unit

#1
Hi Forum,

I have created a 12v 4-6w LED strobe unit from a diagram- works good, however I need to hook up to 4 x 10 W LEDs on a 12v system (car). (Relay/ mofset?)


what is e best way to do this (note the LEDS are in separated by about 4-8ft)
 

Goeytex

Senior Member
#2
I would suggest using a MOSFET with very low On Resistance and Low Gate Charge. If strobing and/or using PWM I highly recommend using a MOSFET Gate Driver between the Picaxe and the MOSFET.
 
#3
understood, an thanks

so if i get this correct it would be 12v supply to the controller, use a
MOSFET to for extra wattage - pending wiring layout
each LED has a 12v 10W Driver - does this impact the strategy here
 

Goeytex

Senior Member
#4
You did not mention a "controller" before. I assumed that the LED was to be switched/driven by a Picaxe. Better give some more details so that the proper recommendations can be made.

Perhaps post a diagram of what you currently have.
 

Goeytex

Senior Member
#7
Attached is a example diagram of how I would do it. I have used Dual Mosfet drivers and low RDSOn FETS. This gives superior performance and efficiency.

However, if you only need to turn the LED's on and off occasionally then you can get by without the Mosfet drivers and can use Logic Level FETs driven directly from the Picaxe via a 330R resistor.

Example Circuit.png
 
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#9
Attached is a example diagram of how I would do it. I have used Dual Mosfet drivers and low RDSOn FETS. This gives superior performance and efficiency.

However, if you only need to turn the LED's on and off occasionally then you can get by without the Mosfet drivers and can use Logic Level FETs driven directly from the Picaxe via a 330R resistor.


View attachment 18818
Great thanks - I will (may) need for short bursts or extended periods of time, so the later is the best option
 

premelec

Senior Member
#10
With only on/off you can likely omit the drivers just use a resistor to gate and use logic level or better gate threshold MOSFETs... I agree with Goeytex - do be careful to not exceed gate voltages specified in data sheet...
 
#11
I think you need to give us more details of the LEDs. Can you give a part/model number or a URL to the LED or data sheet? Goeytex has drawn each of them as a simple, single LED in the diagram. They will definitely not be that simple at 10 watts each!

10 watt LEDs come in many varieties and some can require nearly 1 Amp. If they are a bare 10W LED emitter, you need to consider current limiting otherwise they will quickly overheat and destroy themselves.
 

Goeytex

Senior Member
#12
IWP is correct. There likely needs to be current limiting of some kind. How this is implemented depends upon the 10 Watt LED Arrays.

My assumption was that since the OP had previous success with 6 watt units, that the need for current limiting was understood. I will add a current limit block to the diagram to eliminate any confusion.

Warning: Automotive electrical systems can generate transients > 60V. In automotive applications it is good design practice to use automotive grade regulator(s)/ components and to provide transient suppression devices such as TVS Diodes to protect the Picaxe and other components from these transient voltage spikes. Failure to do so could lead to failed components.

Failure to provide proper current limiting to the LEDs will result in overheating and failure of the LEDs. The previously attached circuit will not provide a constant current to the LED's over the range of the automobiles +12V supply. (12v - 13.5v)

A much better solution would be to use a constant current source or a commercial LED controller for driving the LEDs.
 
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techElder

Well-known member
#13
I don't know why anyone would still be using a resistor to limit the current in an LED circuit.

I am a fan of these constant current gadgets, and have used them so many times.

I use this variety: http://www.mouser.com/ProductDetail...=sGAEpiMZZMsE420DPIasPsmbGP/Dsdbv7CfbaiDKVaw=

This is a listing of many ways these are available: http://www.mouser.com/Search/Refine.aspx?Keyword=cl2+constant

EDIT: Sorry, I forgot the OP was looking at 10W LEDs. However, while I have your attention, these constant current drivers can easily be put in parallel to multiply the total current they provide. :)
 
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premelec

Senior Member
#14
Look at the LM317 datasheet for how to wire a 317 as constant current with one resistor setting the current limit - note you may need a heat sinik on the 317 depending on voltages and currents...
 

Goeytex

Senior Member
#15
With a nominal supply (battery) voltage of 12.5v and the LM317s 3.0V drop out voltage, the LM317 can only supply about 9.5V to the load. This may not be enough for the LED's.

An LM1086 (better) has a typical dropout voltage of 1.3V and might get close enough. It all depends on the LED's forward voltage.
 
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