Varying current

[Gregory]

Flyback
Yes I am not that experienced with LEDs or any thing relating to this application But I do a lot of reading to try to understand That is why I have asked the Forman as there is a mountain of knowledge out there Which I very much apperiated
If I understand you I am to increase the voltage to 50 volts or +
Require a Buck convertor
Require a over voltage protection.
What would you suggest to control the current.
Does the buck convertor control the current to 6 or 7 Amps or do I use a
HV9910B is an open loop, current mode, control LED

 

[Flyback]

With the HV9910B you would vary the current by putting a pot into the LD pin...and varying the voltage at the LD pin...that would dim your current for you.

Your max current is 6 amps I thought?
You set up the hv9910b to regulate at 6 amps, and then you dim it down from there with the pot as discussed.
Best to use overvoltage protection in case you turn it on and THEN attach the load.
If you remember to attach the load before you turn it on then you don't need the overvoltage protection.
Yes you need battery voltage to be 50v or more

 

[tvtech]

Wow Flyback. Nice to see you sharing and helping and not just asking questions. I really don't know if all your advise is correct....because I am unfamiliar with the parts concerned.

But I give you an A for effort and a rep for trying

Good to see this at last

Regards,
tvtech

 

[Flyback]

I have attached a excel sheet for the constant off time buck led driver using HV9910B.
This is for Vin = 50V and assumed vout max = 36v and iout max = 6 amps
(just give us a shout if your vin etc is different as its just a case of throwing the numbers in)

The components come out as follows....
Inductor = 100uH (ferrite core).....must not saturate with 8 amps, will have 6 amps rms current in it.
Off time resistor = 68k
(this gives fswitch = 73khz at 6 amps output)
I got you a sense resistor of 33 milliohms......this is the nearest E24 value to the required.
It needs to be at least 2 watts rated, and non inductive as possible.
Ensure to kelvin connect it back to the hv9910b
I would use about 330nF (no more than that) at the output. 1210 size up and at least 50V rated. This way you can get away without the overvoltage protection.
Put a about 100k resistor across this cap to discharge it when you turn off.
Make sure the cap is near the power diode, rather than near the load connector.
Try and keep to power diode, fet and inductor and hv9910b fairly close.

I think you will need a PCB .
You could use the free eagle package.
Your diode will carry 1.6 amps average and needs to be at least 70v rated.
Make it a schottky diode, to220 + heatsink
Make the mosfet at least 70v rated and to220. (try to get something with low rds(on) and low Qg)
Put a about 47k resistor from gate to source of the fet
Use at least 20uF at the input. (make sure these are close to the fet)
The input capacitance must be good for at least 2 amps of ripple current at 73KHz.

Eagle pcb is very easy to learn there are lots of tutorials on youtube etc. Including tangentsoft.net does a good eagle tutorial.
Start the layout be getting the hv9910b and the sense resistor as close as possible....and the RT resistor should also be near the hv9910b....as well as the cap on the hv9910b vcc pin.

The pot on the LD pin will have to set LD to 0.221v for iled = 6 amps...this has to be so becususe you wont find a 37 milliohm, 2 watt sense resistor so I had to make it 33milliohm.
...just turn the pot to get lower LD pin voltages for lower led current as you choose.

You may not be able to find that size inductor off the shelf.....you could put several shielded ones in series though to get the overall value.....or make one yourself using eg epcos ETD core. Or get a winder to do it for you...eg agw.co.uk.
Having said that its actually easy to do it yourself.....just find the cores AL value from datasheet and work it from there...AL = {L(nanohenry)}/N^2.
N = your number of turns. (MUST BE enamelled copper wire)
Remember you have 6 amps of rms inductor current.
Actually ETD core may not be big enough, but ePCOS tdk have others.

 

[tvtech]

Flyback

You know stuff. I believe now that you are not stressed in an impossible working environment...you are more relaxed. Holidays
You have time to share. And knowledge too.

You opening up here will get you far. I promise

Regards,
tvtech

 

[tvtech]

And I know you edited your post above mine....you want the post to be perfect. You see giving is hard..it's all or nothing. You worried that somebody will try and shoot you down in a Technical way...fact is you have bared all. And you know your stuff.

You have my greatest respect and support. At last you are sharing. Takes balls to do that

No matter if you are wrong or right.

Regards,
tvtech

 

[Flyback]

Here is a simulation of it with vin=50v, vout=36v, iled=6amps, and constant off time (3.6us of time).
The sim uses lt1243 'hacked' to be in constant off time, as I didn't have a model of hv9910b
Just download the free ltspice from linear.com....open the file and hit the running man icon.
rem to delete the waveform file afterwards.

 

[Gregory]

Flyback
I have tried to down load the Buck Led driver file but cannot could you repost it in another format
Thank you

 

[Flyback]

it is an .asc file and it is what opens in the ltspice program....you could also download it as a .txt file, and then save it as a .asc file. (it is basically a text file).
Anyway, I have uploaded it here as a .txt file.
Did you manage to download and install the ltspice simulator?
Cheers TvTech, but to be truthful, this is all easy-to-give info, just glad if it helps.

 

[ronv]

Sorry to come so late. Maybe you could post the data sheet for your LEDs? 36 volts divided by 8 LEDs is 4.5 volts each. This is an unusual voltage for an LED.

I am driving 10 strings of 8 LEDs require 36 volt 7 Amps I do not want to adjust the voltage. I require to dim the LEDs

Maybe you meant 8 strings of 10?

 

[Flyback]

Good point.
In the post in #7 they look like Cree XP-G (?)
**broken link removed**
...Which is about 3.1V = Vf, so maybe the 36v is coming from it with the cable assembly?

 

[ronv]

Maybe life will get easier.

 

[Cicero]

A buck is definitely the most efficient solution, minimal power wastage in heat etc. But I'm concerned Gregory actually doesn't have the know-how or resources to do it? That's an smd PCB design and build - by Gregory who by his own admittance isn't too clued up with electronics.

EDIT: I just want to add that I mean no disrespect to anyone. We all want a workable solution at the end of the day.

 

[Gregory]

I have come across a step down buck . This is the speckes on the buck .
Having red a lot on buck convertor I believe this one will do the job.
Could you give me your opinion.
Output Type:
Single
Type:
DC/DC Converters
Brand Name:
DC Buck Converter
Size:
65 x 23.5 x 47 mm
Input Voltage:
DC 7-40V
Output Current:
8A
Output Voltage:
DC 1.2-35V continuously adjustable
Weight:
0.07 KG
Model Number:
Car Charger
Output Power:
300W
Module Properties::
non-isolated Buck CC CV Charging Module
Input voltage : :
DC 7-40V
Output voltage ::
DC 1.2-35V continuously adjustable
Output Current: :
8A
Constant current range ::
0.2-8A ( adjustable )
Output Power::
Maximum power is about 300W
Conversion efficiency ::
up to about 95%


Car Charger LED Driver Regulator DC 7-40V to DC 1.2-35V 8A 300W Buck CC-CV Adjustable Power Supply Laptop Charger #090009
Rated 5.0/5 based on 3customer reviews 100.0% of buyers enjoyed this product! (3 votes) 3 orders
Price:
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http://www.aliexpress.com/

 

[Flyback]

...that current charger you detail only goes up to 35v so no it wont be ok.
From your #7 post it does look like you have 8 strings of 10 in series, and that they are all cross connected, presumably for thermal coupling reasons.
I hope they are all matched leds.
Could you give the datasheet as Ronv said, so that we can see if the voltage limit of the above supply, is enough to drive your leds in worst case Vf. (having said that it does look like a cree xp-g)
The "binning and labelling" document for xp-g leds from cree says max vf is 3.75v at 350mA....Gregory you are running these at 750mA each, so your vf max will be around 3.9V lets say......that means your led bank voltage is 39V plus any cabling losses.
...that current charger you detail only goes up to 35v so no it wont be ok.

If you wanted to try the PCB , then the following "creating circuit boards with eagle" is a good guide to doing it, and the eagle layout program is free for boards which are double sided and less than 8cm by 10cm.
https://tangentsoft.net/elec/movies/
The hysteretic buck using hv9910b is the simplest form of led driver, and has few parts, so its a long shot, but might just be do-able. the gate drive is weak and so youll get a fairly less snappy dv/dt on the drain voltage , easing layout.....I would say just get all the power components reasonably tight and just go for it.

I am sure Gregory knows the structure of a pcb......if double sided , then its just a piece of fibreglass with copper tracks and pads on the top and bottom. The pads have solder resist around them to prevent shorting to other pads, and there is "silkscreen" lettering so that you know what the components go where. If connection to the bottom layer is required then you go through a via, which is a hole pated with copper.
Anybody who understands the basic structure of the pcb that they want, and who can use a windows pcb, can use eagle to lay out a pcb. Youtube has some good vids on it.
Eagle is that pcb layout package that really has no secrets and anyone can use it.

 

[JimB]

A few days ago, Alec_t asked:

Interesting. Is 'wet connector' a term of the art for that type?

In the subsea oil industry, the generic term which is generally used when avoiding company names or trademark names is "wet mateable electrical connector".

JimB

 

[Flyback]

i think if you are making electrical connections in the prescence of seawater, such that seawater traces may form a conductive trace between plus and minus of the connector, (and thus short them together) then a normal connector should not be used, but instead, an inductive coupler should be used. I can give you the website of a company that makes these if you wish? They make inductive couplers that come pre-connected to a lamp, then you simply clip the inductive coupler onto an insulated wire pair which carries 50khz AC. Its ideal for lighting because the wire pair carries 50khz ac which is current regulated, so no led driver circuit is needed beyond the inductive coupler.
Are you interested in this?

 

[Gregory]

The egal Cad download .
I have a IPad Air 5 Is there a app for Apple I Pad or software down load

 

[Flyback]

Eagle is a free download from cadsoft.de or cadsoftusa.
Sorry I dont know about those ipads but the help desk on the cadsoftusa website can help you.
So you cant find anything off the shelf for 36V and 6A?
not even multiple current source psu's in parallel to make it up to 6?

 

[Gregory]

This is specifications for the led
Quantity: 1pc

Chip Model: Cree XLamp XP-G R5

Lens Color: Water Clear

Emitted Color: White (Option: Warm White 3000K, please contact us if you want warm white)



Spatial Distribution
Parameter Min. Max. Unit
Luminous Intensity / 37040 LM
Viewing Angle 100 110 deg
Color Temperature 6000 6500 K
Wave Length / / nm
Forward Voltage 30.0 32.0 V
Forward Current 6 10 A


PCB Board Material: Copper

Dimensions: 82X66X1.6mm
**broken link removed**