LLC converter stand for [Solved]

Last updated : Sept 5, 2022

How do LLC conversions work?

A regular LLC resonant half bridge converter works a combination mode of a voltage divider and amplifier of resonant inductor voltage of the resonant tank. At the resonant frequency, impedance of resonant tank is zero, which means the input voltage is 100% applied on the load.

What is LCC resonant converter?

LCC series–parallel resonant converter (LCC-SPRC) is the preferred high voltage DC power supply (HVPS) topology for medical X-ray imaging generator applications, due to its advantage in wide operating ranges, and full-range soft switching capability.

What is full bridge LLC?

"Full Bridge" means that four MOSFETs are used, as opposed to two in "Half Bridge". MOSFET is the abbreviation of "Metal Oxide Semiconductor Field-Effect Transistor" - and the main task of this transistor is to generate high-frequency alternating voltage.

What is CLLC converter?

The CLLC resonant converter is widely used as a DC transformer to interlink the AC/DC to DC bus, because of its advantages of high power density and the capacity of bi-directional power transfer.

What is LLC topology?

An LLC power stage is sown in Figure 2.1. The circuit has two full bridge circuits separated by an isolation transformer. The transformer ratio is set for nominal operating voltage. The resonant tank gain is function of resonant elements (Lm, Lr and Cr), load and switching frequency.

What is ZVS resonant converter?

Typically in ZVS converters a resonance capacitor which is placed in parallel with the semiconductor switch, is used to resonant the voltage across the switch to zero at turn-on. The two basic quasi-resonant and multiresonant topologies are shown in Figs. 7.54 and 7.55, respectively.

What is the use of resonant converter?

Circulating current in a resonant converter is used to charge or discharge the parasitic capacitors of the switching elements (e.g. MOSFET) during the switching dead-time, a period that all the switches are turned off.

What is the major difference between a full bridge and a phase shifted full bridge controller?

The short circuit is the key difference between the phase-shifted full-bridge and the hard-switched full-bridge. The short circuit prevents the primary currents from decaying to 0. And the result is that energy is available to drive ZVS transitions.

Is LLC bidirectional?

CLLLC, with its symmetric tank, is capable of bidirectional operation. The problem with using an LLC structure for bidirectional use is that the switching frequency, when operating in the reverse power flow mode, is governed by the transformer winding capacitance and the leakage inductance.

Where are LLC converters used?

As an advantageous topology with electrically isolated features, a soft-switching function, high energy density, and high-frequency operation potential, the LLC resonant converters are widely used in EV charging stations, LED lighting drivers, photovoltaic systems, LCD TV power supplies, and other practical products.

What is buck converter and its working?

A buck converter (step-down converter) is a DC-to-DC power converter which steps down voltage (while stepping up current) from its input (supply) to its output (load).

What is ZVS operation?

ZVS enables the voltage regulator to engage “soft switching”, avoiding the switching losses that are typically incurred during conventional PWM operation and timing.

What is meant by ZVS and ZCS?

ZCS operates with constant on-time control, while ZVS operates with constant off-time control. With a wide input and load range, both techniques have to operate with a wide switching frequency range, making it not easy to design resonant converters optimally.

What is meant by zero voltage switching?

ZVS (Zero Voltage Switching) means switching the 110/230VAC output when the immediate voltage is zero. ZVS (Zero Voltage Switching) is easier to implement than ZCS (Zero Current Switching). ZVS is a good solution for switching on/off devices such as switching power supplies.

What is the zero voltage switch used for?

In simple terms, zero-voltage switching can be described as the power to the device is turned off or on only when the output voltage is zero volts. This technique functions on pulse width modulation-based (PWM) operations like most other contemporary switching voltage regulators.

What are the advantages of parallel resonant inverter?

Resonant inverters have been widely used in consumer electronics, telecom power supplies, and electronic ballasts. Compared with the PWM converters, it has many advantages, such as low EMI, low switching loss, and high power density.

What is soft switching in converters?

Soft switching means that one or more power switches in a dc-dc converter have either the turn-on or turn-off switching losses eliminated. This is in contrast to hard switching, where both turn-on and turnoff of the power switches are done at high current and high voltage levels.

What is SMPS circuit?

A switched-mode power supply (SMPS) is an electronic circuit that converts power using switching devices that are turned on and off at high frequencies, and storage components such as inductors or capacitors to supply power when the switching device is in its non-conduction state.

What is phase shift PWM?

Phase shift PWM scheme is used on the input-side to accomplish the zero voltage turn-on on power switches and improve the converter efficiency. Three-level diode-clamp circuit topology is adopted in the presented circuit to lessen the voltage ratings on active devices for high voltage applications.

Why is it called a buck converter?

The buck converter is so named because the inductor always “bucks” or acts against the input voltage. The output voltage of an ideal buck converter is equal to the product of the switching duty cycle and the supply voltage.

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hi everyone welcome to the mps now lab my name is thomas and this is radio and we're applications engineers at the mps office in barcelona so today we're going to be talking about llc converters so let's move on to the presentation besides myself today we're accompanied by prasad and jim who are field applications engineers for the us and they will be also available to answer any questions that you may have at the end so let's have a look at what we're going to talk about in this webinar today well first we're going to go over the llc converters applications and the motivation behind using this converter topology then we're going to go into understanding the llc converter's basic operation before delving into the specific design constraints that these converters have such as the gain the load the frequency and the inductance then we're going to show you a tool that we've developed to help you design your converter and then offer you a live demonstration of how these converters work in the lab and finally we're going to have our q a session so llc resonant converters are switched mode dc dc power converters that are often used in higher power high efficiency applications the reason for this is that lc converters offer high switching frequencies and lower switching losses this makes them ideal for high power applications where efficiency is key such as high quality psu for gaming and pcs and high power battery charging for applications such as electric vehicles mps currently offers several llc controllers the newest of which are the hr 1210 family which will be discussed during this presentation designers can choose any of these controllers depending on applications and cost performance requirements yes after explaining the details of the llc operation we're going to discuss a real design case such as a 600 watt psu with an efficiency above 90 percent and multiple outputs to serve different supply voltage levels for different loads what makes lc converters so attractive for such an application is that firstly llc converters are fully resonant and therefore produce less cmi they also allow soft switching in both the primary and the secondary zero voltage switching in the mosfets and zero current switching in the diode the range at which they can produce this soft switching is very wide which means that this this efficiency is not lost light loads and there's no inductor at the output which means that all the inductors can be more easily integrated into a single magnetic structure again saving area and cost and finally because of their low losses llc converters are suitable for a wide range of applications up to very high power so now let's move on to understanding how the llc converter works well the llc converter is made up of four blocks first there's the power switches which convert the input dc voltage into a high frequency square wave they can be implemented either in a half bridge or a full bridge topology depending on the application then we have a resonant tank whose job is to filter the input square wave and eliminate the harmonics outputting a sine wave of the fundamental frequency which goes into the transformer this is responsible for scaling the voltage down to an appropriate level through the scaling ratio n and isolating the input and the output of the converter then finally we have the rectifier which converts the reduced sine wave back into a dc signal for the output the total gain of this circuit therefore is defined by the transformer and the resonant tank gain let's uh go into the power switches as i mentioned previously the power switches can be implemented in a half bridge or a full bridge topology and the main difference is that the full bridge topology generates a square wave with no dc offset and the amplitude is the same as the input voltage whereas the half bridge topology emits a square wave that is offset by half the input voltage and has an amplitude of also half the input voltage so half that of the full bridge wave the another difference is that having few transistors the half bridge is cheaper but fewer transistors also means more current flowing through each of the transistors which therefore increases conduction loss the full bridge divides the current over more transistors but the changes in voltage are higher which results in increased switching losses the resonant tank is made up of a capacitor and two inductors called the resonant inductor in series and the magnetizing inductor in parallel its role as i said before is filtering out the harmonics of the square wave the tank's gain response is dependent on three main parameters the load which is expressed through the quality factor q the normalized frequency which is the ratio between the switching frequency of the mosfets and the tank's resonant frequency and the normalized inductance which is defined as the relationship between the resonant and magnetizing inductors it's important to mention that these calculations have been made using the first harmonic analysis this is applicable in this case because the resonant tank filters these uh input square wave only leaving the resonant frequency and we use this to greatly simplify our equations you may be asking yourself why there are two inductors in this converter well this is understood by observing the tank's response to heavy and light loads depending on the inductor present in the circuit with only the series inductor there's a clear resonant peak at the tank's resonant frequency for the heavy load whereas with the light load there is a much larger bandwidth on the other hand with only the magnetizing inductor the heavy load does not peak and the light load has a large gain at the magnetizing resonant frequency by joining both these inductors what we get is a frequency response that will adequately respond to a much larger range of loads and will enable stable control for all operation conditions so now let's go on to analyzing the three parameters so the load the frequency and the inductor and how they affect our converters operation to begin with we'll focus on the gain now as i said previously the gain the converters gain is the addition of two blocks the resonant tank and the transformer now the resonant tanks gain is variable depending on the load the frequency and the inductance whereas the transformers is fixed and depends on the ratio between the primary and the secondary coils ideally the tank should not amplify or dampen the signal it should simply filter out the harmonics and the transformer should be the only responsible element of changing the voltage level therefore the nominal gain of our resonant tank should be one however there are bound to be variations in the input voltage and because the transformers gain is fixed in order to obtain a constant output voltage the tank is going to have to compensate therefore when the input voltage is below the nominal value the tank will have to slightly amplify the signal producing the maximum resonant tank gain if the input voltage is above the nominal value then the minimum gain will have to ensure that the voltage at the primary of the trans

Thanks for your comment Damion Woo, have a nice day.
- Shaunna Raza, Staff Member

hi I'm Sabine Yaakov this presentations entitled resonant LLC converter power states design the intuitive approach let me start off with a basic resonant Network here we have a source resonant inductor capacitor and a load this is the expression for the V out to V in ratio V out to be in ratio which is represented here in sort of a normalized way this is the ratio and this is frequency or normalized frequency where the Q is defined as the resonant times L r over r ec being a series resonant network or as Z over RC when RAC when Z in the square root of the inductor divided by the capacitor now I series resonant converter which is based on the series resonant network we have a no Morea transformer than a rectifier a load and a a filter capacitor and of course we have a drive in this case I'm showing a half bridge drive this is a nonlinear circuit and it is rather difficult to get a relationship like V out to V in and therefore it is customary and it's very convenient to sort of represent this network in the series resonant network that we can analyze by phasor analysis that is we don't have to do time domain analysis as we have to do here because we cannot linearize this circuit being a highly nonlinear circuit now the way to do this X has two parts to it first of all we want to replace the square wave here by a sinusoidal waveform this is the half bridge this is a full bridge in the idea is that this resonant network is actually a filter so when you feed in a square wave you maybe see the first harmonic say this is the switching frequency this is the switching frequency of this square wave and so you are actually fitting here the square wave and the current would be pretty much like a sinusoidal current depending of course on the Accu for very low Q it will not be the case but usually or run these converter at very high Q no too high too though and therefore you will see the first harmonics the major harmonics but then they hire our mornings this is like the breakdown general representation of the breakdown of the harmonics of the square wave like 3rd 5th etc would be pretty far away so yeah they're not not going to see it so the first step would be to replace the square wave that we have here by the first component first harmonics now as it turns out by Fourier analysis they relationship between the peak of the first harmonics to the height of the maximum value of the square wave is 4 over pi so this is the first step this is for a full bridge and if we have a half bridge we have only half the value so we have to divide it by 2 so this takes care of this sinusoidal waveform that now we can replace the square wave by this source and this would be the relationship between the square wave and this the source now what about the resistor it was shown by Professor Steigerwald that one way to do it is really to equate power dissipation that is if we have a nonlinear circuit like this this would be like the resonant converter we assume that there is a sinusoidal current here coming from the converter for the reason I've already said this is rectified we got this rectified current and the average of this rectified current goes into the load now equating the power means that if I have this equivalent circuit I'd like the power dissipated like this linear resistor now the equivalent our AC register this part to be equal to the power dissipated by this DC resistor so we have the relationship between the DC current here and the peak value of the sinusoidal current at the input and since power is I swear over RL this is for the DC here and the same thing goes for the AC and we have already the relationship between the AC and DC it comes out that the RAC is 8 over pi square RL is about point eight that is you can replace this whole thing by a linear representation our AC being eight over PI square this resistor now there's also of course a relationship between the voltage that you'll find here the DC voltage and the voltage that you'll find here and here is the relationship again I'm doing it my equating the power the power here is v square of DC over RL the power here is V AC of square over RAC and by equating this to we get with this relationship that the voltage the AC voltage this will be RMS voltage here is related to the DC voltage here by about 0.9 now in many cases we would have a transformer so we have to reflect they are AC calculated safe secondary to the primary and of course the reflection is done by multiplying it by n square and being the ratio between primary and secondary so by this we can now modify the RAC to be to take into account the transformer and therefore we can have now a AC equivalent linear circuit that can be analyzed by phasor analysis and in theis pspice ltspice or any other circuit simulator it can be run by AC analysis this cannot be run by AC analysis because AC analysis is proper for linear circuits and this is a nonlinear circuit so now let's go back to the converter itself this is again a series resonant converter and one thing we have to worry about is the gain we can get and the reason we need again is that no money we'd like to have a constant output and therefore if the input is changing then the ratio between input and output has to be controlled and this is of course done by the feedback such that when the voltage is deviating from the required value it will change the switching frequency in this case so as to bring it back so the first thing we have to worry about is the gain that we can get and let's say that we need the gain between point four point six just arbitrary as an example this would mean that for the plots that I have shown here you need if you'd like to go from q1 to about q5 then you'd need this span of frequency which is very high so this is the reason why this series is a nun converter it's not very popular as a voltage regulator that when you have to regulate the voltage it's very good by by the way for current sourcing but this isn't beyond the subject I'm discussing here another way to do it is to use a multi resonant converter which is for example the LLC LLC means that you have two inductors rather than one any capacitor the idea here is as follows you have now two inductors this is again the RIC the equivalent circuit is done exactly the same way I've shown before and in this case we have two inductors if our AC here is smaller much smaller than the impedance of this LM at the operating point on either President you might take then the impedance of L sub M doesn't play any role and you have actually a serious resonant converter and this will be the resonant frequency and the cube for this circuit you can define it as the Omega R this Omega R by these two elements and our AC however if our AC is much larger than Omega L M then LM of course will pay a role here and if LM is larger than L R you can sort of neglect its first approximation L R and you see that you have now a parallel circuit here parallel resonant circuit here the frequency again will be one over two pi now LM CR and of course the this frequency turns out to be at a lower frequency than the frequency we have seen before

Thanks Sebastian your participation is very much appreciated
- Shaunna Raza

About the author

Shaunna Raza

I've studied population biology at Wesleyan College in Macon and I am an expert in clinical neuropsychology. I usually feel blank. My previous job was baggage porters and bellhops I held this position for 5 years, I love talking about surfing and warli art. Huge fan of MrBeast I practice curling and collect artist trading cards.