6 LEDs in Series

This reduces the current consumption from 2.5A to 20mA.

Its the same circuit like james ( messy one ;-) but with different component values. Leds just 20mA. Reference current much to low in uA range (james one much to high 200mA). So you both should find a compromise and agree on type of led 20mA or 700mA

I'm super confused now. So I need the diode opposite of the zener?

Removed diode giving more suitable current for Zener diode. Adjusted emitter resistor to make LED current approx. 20mA. Circuit now more tolerant of supply voltage fluctuations.

How can my LEDs operate at peak performance at 20mA? I think I need to read more on building circuits. You guys are sending stuff over my head. Lol

Sorry, we are confusing you. You don't need the diode. You do need to ensure base resistor is a value that puts sufficient current through the Zener such that the diode 'breaks down' to give the stable zener voltage. Look at my latest circuit and observe the voltage on the transistor base whilst varying the supply voltage either side of 24V. You will see the base (zener) voltage changes little. Finally, to my knowledge you cannot but LEDs that take anything like 700mA. I don't know how the ones you have in your circuit are 700mA since if you add one to the circuit and look at its characteristics you will see it's 20mA. I'm happy to clarify anything else if you need and sorry for confusing you.

'.... cannot BUY LEDs....

Robert, look at google, the world is much more then EC default settings.

hurz - you say 'decide on type of led 20mA or 700mA'. Where do you find 700mA LEDs and why would you choose them over similar brightness LEDs that use much less current?

James - can you tell me what type of LEDs you are intending to use? A part number, link to a data sheet or something?

Hurz - a quick look on internet finds many 700mA LED drivers but it's not so obvious what LEDs they are for driving :-) If the 'LED' is actually an array of LEDs in series/parallel combination then yes, I can imagine an 'LED' that consumes 700mA (but it is not an LED it's an LED array - perhaps still referred to as an LED though :-) James - don't read this, blast - too late!

Led World 10 PCS 3W Extreme Royal Blue Power LED 445-450nm Plant Grow with 20mm Star Base https://www.amazon.com/dp/B00MNB4LJU/ref=cm_sw_r_cp_awd_q9rbxb2F86AZG

This is one set I bought. So the If is not 700mA?

James I'm sorry to have confused you today. I had good intentions. When you said you were a noob I assumed you had somehow messed up the led characteristics. I wasn't aware LEDs with such high currents were available. I did know they were much, much brighter these days but assumed that was improved technology. Yes, the forward current is 700mA.

That's cool, you still explained not needing the diode so that helped.

Also any advice on building an LED pwm for dimming each array on its own.

OK, I'll have a think about that. Looking back at your Reef3 circuit, have you considered the power dissipation? The 2R resistor would need to be 2W, the 100R resistor 5 W, leds will be at least 2W each, transistor approx. 1.5W. Your power supply is providing 24V at 2.5A = 60W.

James, this may need a bit of adjustment but here we have 6 LED's taking approx. 700mA but switched on and off by a 555 PWM circuit to give you your dimming. The 1.2 Ohm resistor limits the current to the 700mA you wanted for your LED's. I notice you've moved up to more LED's and higher supply voltage but you may find this of interest.

I've been trying to build this but I can't get it to work. I've been using the 555 for pwm to no success. This will definitely help me. I stepped back down to 24v. So this is perfect!

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@LeButch will vefiry the above comment is garbage.