Controller for LLC resonant converter

[ronsimpson]

Commenting on the design in post #20: Set the two resistors on FB pin to get a Vout of 1/2 of Vin. (or about 1/2) This will force the duty cycle to 50%. Use Rt and a resistor from Micro-DAC to RT to change frequency.
Here is the bad part: Vin=4V, Vout=2V (add the LC not shown and full wave bridge then load) I think you can get 1V for the LEDs) A LLC is used when the input voltage is much higher than the output voltage.

 

[Mery96]

I will review what you said and get my teacher's opinion. Thank you so much for your help.

 

[opampsmoker]

OK so its a skool project...so i guess its a way to get into LLC cheaply and without the high voltages.
As well as Ron's and others' great advice, i'd look into like what you implied by saying about removing the transformer...because then you kind of get like a high frequency fluoresent ballast driver type thing.
So you just need the half bridge driver with hi and low side fet drives...and it will be 50:50 duty cycle and frequency variable to whatever degree you can manage...higher frequency for lighter load.

I think you will need to have first off, a bias boost supply, which boosts up the 3.7v batt voltage to some 10v or so so you can have something to work with. There are lots of wee boost controllers...eg from analog.com or ti.com or richco etc etc.

But it might be worth going back to your professor and reminding him that an LLC is a voltage outputting topology, and does not like to drive loads like LEDs which tend to clamp the output voltage to a fixed level...though if your vin and vout are always exactly the same then you can design it to suit this and you will be ok.

So we need to find you a 50:50 hi and low side driver and a wee boost controller for starters.

Actually ive just realised you will need the transformer because V(batt) min is 3V and your led voltage could be more than that.

 

[Mery96]

Actually this is going to be a senior project so my teacher wants me to do a little extra work. Last time I spoke, he said that isolation is not mandatory, so I can use class E dc-dc converter, if it is Class E, there will be only one switch control and since there will be no transformer, I will reduce the volume of my project. I think it seems more advantageous to use class E, but I don't have a clear information, I'm still researching. As a result, I have to use LLC or class E topology. I'll search a little more and choose one of the two.

I think you will need to have first off, a bias boost supply, which boosts up the 3.7v batt voltage to some 10v or so so you can have something to work with. There are lots of wee boost controllers...eg from analog.com or ti.com or richco etc etc.

Based on what you have said, can I increase my battery voltage with a boost converter integration and control Half-bridge LLC Resonant Converter with ICE2HS01G integration, which requires 13 volts for run?

 

[opampsmoker]

You cannot use Class E as it cannot boost. When i said use Booster, i meant just to provide a low power bias rail...not to boost the whole battery output up to higher voltage.

I suppose you can use ICE2HS01G. (there may be easier ways though)...its got the necessary 50/50 drive....Just give its Vcc pin 13v or whatever it wants.

 

[Mery96]

I asked for LLC

 

[opampsmoker]

OK, attached is your LLC converter, driving one LED at 1 Amp from a single Li ion cell.
It is in the free download LTspice simulator...just open the .asc file and hit the running man icon.

Now all that is needed is to flesh it out with the actual part numbers.

 

[opampsmoker]

It looks like ICE2HSO1G has an input which can be connected to an external opamp error amplifier to adjust the frequency......so this can be used in regulation.

 

[opampsmoker]

Here is a slight improvement...the Q factor is lowered by reducing the Lr and increasing Cr.....thus it has a less steep slope of Vout vs Frequency, and will be easier to regulate the current because small changes in frequency dont now result in such big changes in led current.

You could do worse than drive it with a micro...and start with the frequency very high...then gradually draw down the frequency until you get the led current that you want...(this is in fact how high frequency fluorescent ballast drivers work...its the same principle)

Does anybody know of a bootstarp Hi/Lo side driver IC that can be used here?.......eg drive it with a 50% square wave of variable frequency and it will produce the drive to the top and bottom fets of the sims provided here...ie driving top and bottom fets alternately as in an LLC driver.

I like the ICE2HSO1G but it seems a bit of overkill perhaps....you'd still need the bootstrap hi/lo side driver with the ICE.

 

[Mery96]

Your posts were very informative for me, thank you.
I haven't used LTspice before. Are these LTspice files your designs? or is LTspice's own sample files?

Now all that is needed is to flesh it out with the actual part numbers.

What do you mean by the actual part numbers I want to ask here, I may have misunderstood, but is it the original component numbers to use?

Here is a slight improvement...the Q factor is lowered by reducing the Lr and increasing Cr.....thus it has a less steep slope of Vout vs Frequency, and will be easier to regulate the current because small changes in frequency dont now result in such big changes in led current.

I saw the difference in simulation, really good idea.

You coudl do worse than drive it with a micro...and start with the frequency very high...then gradually draw down the frequency until you get the led current that you want...(this is in fact how high frequency fluorescent ballast drivers work...its the same principle)

Is using ICE2HSO1G be worse than using micro?

A friend suggested I use the gate driver / controller to drive the mosfet and my PWM application for brightness level using stm32f103c8t6 via the gate driver / controller. I am looking for a gate driver / controller that I can use for LLC or Class E converters suitable for my input-output data. How do you think this idea?

 

[opampsmoker]

Well...attached is an easy way to do it.
But it would be good to be able to replace the LTC6990 with an oscillator that adds the dead time in for you....to avoid all the dead time circuitry shown.

These arent sample files, i did them. But as discussed.......still needs some circuit reduction really....hopefully other forum members will chime in with some suuggestions to tidy up the circuitry shown here.

Also, it really needs some output short circuit protection. Also, a circuit to provide a minimum oscillator frequency would be good to add in there....as you know, with LLC converters, there is a frequency below which you never want to go.

The AN-4151 app note by fairchildsemi.com tells of this.

Thinking about it...a micro could be good to provide the variable frequency oscillator instead of the LTC6990...but how would the micro provide the dead .
time?...Hmmm

Actually, youve got me thinking...yes...i suspect the ICE2HSO1G may be the way to go after all......since it has the dead time circuitry in it...and the variable frequency oscillator...and even has primary side overcurrent protection i think(?)

 

[opampsmoker]

brightness level using stm32f103c8t6 via the gate driver / controller.

If using the ICE2HSO1G then you would dim it by changing the frequency...use an opamp with a reference voltage set by the micro..and feed the opamp output into the relevant pin of the ICE2HSO1G...this will allow you to change the frequency via the ICE2HSO1G...as you know, you dim an LLC converter LED driver by increasing its frequency

 

[Mery96]

If using the ICE2HSO1G then you would dim it by changing the frequency

I plan to use ICE as a last resort, the switching frequency should be at least 1 MHz, I could not find a 1MHz or higher resonant controller other than ICE. I keep searching.

Actually, youve got me thinking...yes...i suspect the ICE2HSO1G may be the way to go after all......since it has the dead time circuitry in it...and the variable frequency oscillator...and even has primary side overcurrent protection i think(?)

These features you mentioned are available in ICE as far as I have reviewed datasheet. It will be a great advantage for me to have these features in a single integration.

Since I haven't practiced any, I just understand some things. This is how I summarized the parts I needed to confirm that I understood correctly; dead time control, variable frequency oscillator, minimum oscillator frequency, output short circuit protection, gate driver.

I have to design all these as separate circuits or find the IC that contains them.

When I review the LTC6990 Datasheet, it says 2.25V - 5.5V for V +. In the file, you have written "get this 5V here from linear regulator from the 10V rail" for LTC6990 OE and V + pins. I could not fully understand this.

 

[opampsmoker]

In the file, you have written "get this 5V here from linear regulator from the 10V rail" for LTC6990 OE and V + pins. I could not fully understand this.

You need a 5V rail..........i presumed you would have a 10V rail (for eg driving fets with and powering a controller IC), so i suggested deriving the 5V rail from the 10V rail.
Are you aware that you can use a linear regulator to get 5V from 10V?.....its often done if the power draw is very low, (which it would be, from the 5V rail)

 

[Mery96]

its often done if the power draw is very low, (which it would be, from the 5V rail)

I understand what you mean, thank you