I just figured that if the 2 arrays were wired in series, that the main CC driver (HBG 160p) would adjust its V to compensate for the additional load when M1 was open.

Are you sure that the driver's rated maximum output voltage can cope with two LED arrays in series, and that its minimum rated output voltage is suitable for just one array?

 

Here's a sim of what I think you're getting at, but I see no way of adapting it to give independent individual dimming of both arrays.

M1 is on for the first 1 second, then off. Both arrays draw 2.6A.

 

@Alec_t Hopefully I'm a little bit clearer this time around, sorry for the miscommunication. Your sims are priceless. I'm tying to get the EAGLE simulator figured out, but its not as fluid as I'd like... Thanks again, lmk what you think

 

Here's a revised sim, closer to your latest idea. R1,Q1 bleed off current from Array1, without affecting the Array2 current. However, if you were to adjust the Array2 current then the currents through Array1, the zener diode and Q1 would all be affected too.
I still don't see how you will get independence for the current adjustments of both arrays.
Incidentally, the zener diode seems superfluous, as the voltage across Array1 will be determined largely by the LED forward voltage.

 

In my latest design, design #2

Couple of observations on that. (1) the zener would have to pass the full 2.6A continuously and dissipate over 13W, (2) with the FET switching the high side of Array2 the MCU would need to drive the FET gate at about 70V!

 

ie the 5.1v zener and 5Ω resistor would have to follow ohms law and limit current to 1A though array2, right?

No. Assuming you meant Array1 in my sim, the high current through the zener pushes the zener voltage up to about 6V, the forward voltage Vf of the array is only ~ 4.8V and the array current is ~200mA.

 

Why does zener pass 2.6A?

It doesn't. T1 would carry most of the current and dissipate a lot of power. My bad.

Would you mind showing the 70v gate drive calculation?

Vgs = 10V to turn FET fully on. When FET fully on, Vs ~ =Vd. Vd=60V, hence Vg = Vs + 10V = Vd + 10V = 70V.

How did you get 200mA?

That's what the sim shows when Q1 is allowed to bypass ~2A.

isn't 6v/5Ω still pretty close to 1A?

There isn't 6V across the resistor. Most of the voltage drop is across the LED array.

The chips I'm using for LED1 (my #2 pen drawing) are 5.0v.

That is their rated voltage when passing their rated current. At lower current their Vf is lower.

If the zener is @ 6v shouldn't the array be 6v too

No. The 5Ω resistor drops some of the voltage. LEDs are non-linear things, unlike pure resistors, so Ohms Law doesn't work with them.

 

You're saying that the R and the LED are splitting whatever zener V is being provided

Effectively, yes.

How would you recommend switching the LED1 array on & off. SSR?

I wouldn't. I'd recommend using two CC drivers . But, if you're determined ......
Connect LED1 on the low side of LED2 and use a low-side 'logic level' N-FET as in my sim. That avoids having to generate a high voltage to turn on the FET. You could replace the FET with an SSR.
When doing your calculations, note that Vf for your LED is rated as anywhere in the 5V to 8V range at 40mA.
Unless the LEDs in an array are closely matched for Vf, simply connecting them in parallel without individual current-limiting resistors, as you show, is not advised. It will result in non-balanced currents in the different LEDs. The one with the lowest Vf will hog most of the current and fry, followed rapidly by the LED with the next lowest Vf, and so on.
There is no information as to how Vf varies with current.

 

A constant resistor with a defined delta V being equal to a zener Rv range, or an Led Fv range, should have a current flow through it (through the R) reflectlive of those voltage ranges and constant R, right?

I'm not sure what you mean, but here's a sim showing the effect of changing the CC from 2.6A down to 1.3A :-

The drop in Array1 current isn't too severe.

 

Considering the hefty currents likely through Rs, the zener and T1, serious heatsinks for those components would be needed. I think by the time you factor in the costs of those, plus the costs of the components themselves, you could find an off-the-shelf second CC supply would actually be cheaper.

 

@Alec_t what is this line?..

 

It's the collector current of Q1 (your T1), i.e the bypass current.
The zener current, and hence the power dissipation, will depend on the gain of T1. I was erring on the safe side when suggesting heatsinking it.

 

Seeing the word "Heatsink" mentioned a few times, you are putting these big LED arrays on heatsinks aren't you?

 

Another thought, in automotive LED use they are usually connected as series parallel, meaning 3 or 4 (depending on the color)in series, then the sets of series connections in parallel, to keep them for going over the ~12VDC in the car circuit. Could you do this with the ones your using to keep from having a high voltage power supply? And it usually isn't good to run them at full amperage, many are used at 1/2 to 2/3 of the listed current, makes them last longer and doesn't lower the brightness that much.

 

Another thought, in automotive LED use they are usually connected as series parallel, meaning 3 or 4 (depending on the color)in series, then the sets of series connections in parallel, to keep them for going over the ~12VDC in the car circuit. Could you do this with the ones your using to keep from having a high voltage power supply? And it usually isn't good to run them at full amperage, many are used at 1/2 to 2/3 of the listed current, makes them last longer and doesn't lower the brightness that much.

All good points you bring up! Just so you are aware, LEDs is a minor area of expertise for me, I deal with these things on a daily basis. Rather it's the dimming cct I'm pretty noob at lol.

The problem with lowering your series strings is the increased current needed. Your limited in your design to how you can power them. For instance, in my case at 150w and 400 chips, 12v requires 100 parallel strings, -> 100 × 125mA, or 12.5A of current, that's going to be a difficult driver to find. Most drivers increase in effeciency closer to their max rated load, so the idea is to add enough chips so that you can blast your driver but minimize current per chip, which as you pointed out increases efficacy, in the same way managing heat does.

The lights are not wired straight series, they are evenly distributed between S: P

 

Well I stand corrected, I literally just found a 150w 12v driver lol... Now I need to check effeciencies.. Perhaps 12v is the way to go, ill check it out...

 

@shortbus
In my experience the bigger the V step down, the less the efficiency, the best 12V driver rated at 150w that I could find is 85% (Zuric magnetic driver). If you can find one higher than 93.5% I'll probably switch over as itd set me apart from the typical higher V drivers/lights...

 

Talking of efficiency, there's a lot of wasted energy with your latest circuit incarnation. T1, the series resistor on Array1 and the zener will all lower the overall efficiency. A second switch-mode CC driver would avoid that.

 

In my experience the bigger the V step down, the less the efficiency, the best 12V driver rated at 150w that I could find is 85% (Zuric magnetic driver). If you can find one higher than 93.5% I'll probably switch over as itd set me apart from the typical higher V drivers/lights...

I don't know about how those differences in efficiency will work out in the real world. But let me tell a story of two furnaces. 1 is an 85% efficient gas furnace that I put in my house, the other is a 95% furnace I put in a rental house. Guess which one has the lower gas usage? I chose the 85% on my own because that is what I was replacing. The 95% I let the salesman choose and believe it or not the 85% has a lower gas bill. and I keep it set at a warmer temp than the 95% house.

I know this has nothing to do with electrical or power supplies, but when ratings are that close together in my opinion they aren't that much different real world.

 

So, do you think my dimming cct will diminish overall effeciency more than adding a separate 90% ACDC or a 95% piggybacked DCDC?

Yes.

Can it be designed to have better effeciency

I don't think any analogue dimming will be as efficient as switch-mode dimming.