Help me to design 12V to 12V 0.5A led driver circuit

[Rickooo]

Hi everyone.
I am working on designing led driver. The fact is, input volt is 12V and output volt is also 12V with constant current, constant volt with all protection at 0.5A output current.
Which IC do you recommended? I am unable to find suitable ic for the same. As input comes from SMPS supply of 12V. Thanks

 

[d123]

Hi,

Almost any DC-DC converter IC that does e.g. Buck-Boost usually can be configured for SEPIC (positive Vout = less than, equal to, and greater than Vin), and a lot seem to have a wide input voltage beyond 12V, check typical manufacturer's or retailers' webs. I couldn't recommend any specific one, 'though.

 

[KlausST]

Hi,

output volt is also 12V with constant current, constant volt

There usually is no constant current, constant voltage output for a LED driver .. either the one or the other....

CC/CV is often used at battery charging.

Klaus

 

[Rickooo]

Thanks for response. How about this https://www.analog.com/en/products/lt3999.html#product-evaluationkit @KlausST @d123

 

[d123]

Hi,

In principle, it looks suitable for your needs. Bear in mind what it says on page 11 in the 'Output voltage regulation' section. If you need a very stable 12Vout, consider making Vout 12.2V or 12.5V, etc. and following with an LDO - presumably not needed for constant current source.

Same page mentions application note AN70 that might be worth a read.

 

[KlausST]

Hi,

To me your requirements are not clear.
* is isolation needed
* about output voltage: constant, regulated, which range, which accuracy...
* the same for current

Thus I can't say whether the mentioned evaluationkit is suitable or not.
I even don't know if you want an evaluation kit...

Klaus

 

[Rickooo]

It's out of stock as of now. But, I wants to know, how Vin is 12V and Vout is 12V is possible. Like their should be a drop within. What do you suggest? @KlausST @d123

--- Updated Sep 24, 2020 ---

* is isolation needed
* about output voltage: constant, regulated, which range, which accuracy...
* the same for current

Yes, Isolation needed. Looking for mostly constant current. Range is up to 1A. As my requirement is 500mA and 750mA. Looking for the ic, so that I can make circuit and test with 6W 6V led of two in series.

 

[d123]

Hi,

My basic understanding is that with DC-DC converters, a 12V, 1A supply can output 12V <1A. Or, more volts is less current and more current means less volts. The circuit needs to get power from somewhere. Think of a seesaw or a sliding scale weighted at one end - what goes up at one end makes the other end go down, if that analogy makes sense. Someone else will have a more scientific explanation than mine.

Power Stage Designer by TI, it's free software, shows estimated input power needed for required output power with different DC-DC converter designs.

 

[Rickooo]

I have also look to this ic https://datasheets.maximintegrated.com/en/ds/MAX1771.pdf it's specially for 12V. How about this? I didn't found spice odel for the same. Not even maxim website. I found one thread, where one have used LT1619 which is similar to MAX1771. Well, I am not sure, if it is similar. Thanks

 

[KlausST]

Hi,

I'm still not sure what you need.

Maybe a flyback topology with current feedback (and just voltage limited, let's say to 15V).
There will be many flyback ICs that can be used. The most critical part is the transformer (I think) it has to be calculated/chosen properly. Usually the datasheet and application note tells you how.

Klaus

 

[d123]

Hi,

I have also look to this ic https://datasheets.maximintegrated.com/en/ds/MAX1771.pdf it's specially for 12V. How about this? I didn't found spice odel for the same. Not even maxim website. I found one thread, where one have used LT1619 which is similar to MAX1771. Well, I am not sure, if it is similar. Thanks

Maybe not suitable for your needs - it is not an isolated circuit. In other ways, from the graphs at least, it seems to cover 12V in and 12V out, 0.5 - 0.75A. You'd need to work out the power dissipation for the IC, as well.

Is there any particular reason not to parallel the two LEDs instead of placing them in series so Vout can be ~6V or a bit over, and halve the power dissipation in any MOSFETs, etc.? It would add flexibility to choosing your LED driver and could perhaps skip SMPS IC searches and focus on LED driver ICs - what you want in one package, but maybe they lack all isolation.

I still think that you're trying to squeeze maybe too much out of the LED supply/place Vout at its limit and would be leaving no space for compliance voltage/headroom - constant current usually means fluctuating output voltage to maintain the constant current, constant voltage means fluctuating output current to maintain a constant voltage. Sadly, we can't have our cake and eat it, in that sense. Glad to be corrected if I'm wrong about these ICs you are enquiring about. Maybe one of these ICs can do that, I have only had a quick read to get the gist of what they can do and am no SMPS expert at all...