[introduction] in numerous and syntonic converter, LLC syntonic converter is having the high power is the most commonly used develop in density application to attack structure. The design note of the syntonic converter of half bridge LLC that we had introduced to use NCP4390 before, the specification that includes principle of job of concerned LLC syntonic converter among them, transformer is harmonious brace up the design of the network, and the choice of component. Before we will introduce those who design a program today 9 measure deserve to design give typical examples will try to explain, help you complete the design of LLC syntonic converter.

Design a program

The article introduced to use a figure the design program that 12 medium circuit graphs regard reference as, among them syntonic inductance is implementation of the feeling that use leakage. Design specifications is shown as follows:

● Nominal input voltage: 396 VDC (PFC class is outputted)

● Output: 24 V/12 A (288 W)

● Maintain the demand of time: 20 Ms

● The dc link capacitance that PFC outputs: F of 330 μ

[Measure – 1] defines systematic norms

As the first pace, define information of the following norms please.

Estimate efficiency (E_Ff) : Estimation power changes efficiency, give the biggest power input below power of the biggest output in order to calculate. The basis estimates efficiency, the biggest power input is:

Input? Voltage limits: Voltage of the biggest input will be nominal PFC outputs voltage.

Although section of PFC preliminary adjustments implement can adjust input voltage, but it is in maintain also can drop inside time. Be needed to maintain the voltage of the smallest input inside time to be:

Among them V_O.PFC It is nominal PFC outputs voltage, T_HLD It is to hold time, and C_BLK It is capacitance of dc link high capacity.

Design give typical examples

Hypothesis efficiency is 96% ,

The maintenance to 20 Ms time, can get voltage of the smallest input is

To acquire larger abundant amount, setting of voltage of the smallest input is 300V.

[Measure? 2] defines the voltage gain scope of syntonic network

Once decided LLC is syntonic of converter the smallest with voltage of the biggest input, we can define the smallest gain of LLC converter and the biggest gain.

Nominal input voltage needs the smallest gain. Reduce switch frequency variation for the oldest rate, it is to let LLC syntonic converter work around syntonic frequency normally. The voltage gain below syntonic frequency is:

During holding time, PFC outputs voltage (the input voltage of LLC syntonic converter) drop, because this needs taller gain,will adjust output voltage. Gain of the biggest voltage is:

We can use a lesser M value to score taller peak value gain; However, if M value is too little, can bring about transformer coupling not beautiful and loss of efficiency. It is M cost too small setting is controlled in 3~7 normally.

Design give typical examples

L_P With L_R The rate between (M) chooses 5.69. The smallest gain obtains by next type:

The smallest gain below voltage of the biggest input chooses 1.13. Next, the biggest gain that can get tension of the smallest input is

Graph 13: The biggest gain / the smallest gain

[Measure? 3] decides transformer circles number is compared (N=N_P/ N_SS

Use measure? 2 in acquisition the smallest gain (M^Min) , we can calculate transformer circles number compares as follows:

Design give typical examples

Because SR is used at outputting rectifier, low to having R_DS.ON SR MOSFET, V_FIt is 0V suppose. From this, can get transformer circles number comparing is

[Measure? Resistor of load of 4] computation equivalent

Use from formula (the transformer that 16) obtains circles number is compared, we can be calculated equivalent and laden resistor.

Design give typical examples

[Measure? 5] designs syntonic network

In measure? 2 be chosen after choose M is worth, from the graph 10 medium peak value are read in gain trace take proper Q cost, in order to score a needed the biggest gain. Because peak value gain trace is to use base wave is similar those who generate, because this is syntonic,the real gain below should be compared use base wave is similar forecast a value to make an appointment with 10~15% high.

Once decided Q is worth, we can gain following syntonic weight:

Design give typical examples

According to measure? 2 medium computation, M^MaxFor 1.49. In measure? 2 in, m is worth a choice 5.69. From the graph in 14 medium peak value gain trace, can get the biggest Q is worth for 0.37.

Graph 14: Gain of use peak value (can amount to gain most) syntonic network design

Through will syntonic frequency the choice is 95kHz, syntonic heft is as follows certainly:

When compose builds transformer, actual parameter will be adjusted as follows, in order to get used to C_R = 48 NF, L_R = 58 H, L_P = 330 H and F_O The standard below condition of = 95 KHz divides value of a quantity.

Use base the gain trace that the final and syntonic network with similar wave designs is as follows.

Graph 15: Design the gain trace of give typical examples

When because be in,working under resonance, base wave is similar generated peak value gain wants lower than gain of real peak value 10~15% , accordingly we undertook SIMPLIS is emulated in order to examine real gain. Emulation result makes clear, below 75kHz, 300V input can score a needed the biggest gain. Emulation result still makes clear, in nominal input voltage and the switch frequency that are fully loaded with a condition to fall are 105kHz.

Graph 16: The emulation below condition of Vin = 300 V, Fs = 69.55 KHz, Po = 288 W

Graph 17: The emulation below condition of Vin = 396 V, Fs = 105 KHz, Po = 288 W

[Measure? 6] designs transformer

Graph the excitation electric current of the 18 transformer in showing LLC syntonic converter. In the limit of of primary side winding makes B of density of the biggest magnetic flux_Max Wants the smallest v/LIT all over the ground number obtains by next type:

Among them the cross section that Ae is transformer magnetism core is accumulated (the unit is M²) , and Bmax is amplitude of density of the biggest magnetic flux (the unit is tesla) , if pursue,18 are shown. If do not have referenced data, use B_Max= 0.2~0.3 T will reduce magnetism core loss. Ask an attention, the fictitious gain MV that causes by feeling of sub side leakage appeared in formula, (refer to a graph 7) .

Graph 18: Amplitude of magnetic flux density

Select appropriate v/LIT all over the ground number for sub side, make primary side v/LIT all over the ground thereby N of several prep above_P^Min.

The wire gauge of primary side and sub side winding should the basis is nominal electric current of RMS of input report depressive is affirmatory, give out by next type

Design give typical examples

Transformer chooses SRV5018 magnetism core (Ae = 189.2 Mm2) . Bmax chooses 0.1T, in order to reduce the magnetism core loss of transformer. The smallest primary side of transformer circles number is

N_SChoose 3; Np chooses 28.

Nominal below input voltage, can get the RMS electric current of transformer winding is

[Measure? 7] chooses syntonic capacitance

Graph the 19 primary side electric current that showed different job requirement falls (syntonic capacitance electric current) undee. When choosing syntonic capacitance, should consider rated electric current, because can have a large number of electricity,had shed capacitor. In nominal the RMS electricity that syntonic capacitance carries below input voltage already was in formulary (obtain in 23) .

Nominal the voltage of the largest syntonic electric capacity below input voltage and nominal and laden condition gives out by next type:

The biggest voltage that the rated voltage of syntonic capacitance should issue according to every horn condition is affirmatory.

Nominal the voltage of the largest syntonic electric capacity that inputs voltage and output to shed a condition to fall too gives out by next type:

The voltage of the largest syntonic electric capacity below voltage of the smallest input and nominal and laden condition gives out by next type:

Ask an attention, to the circumstance of complete bridge LLC, should delete formula (25) ? (The VIN / 2 in 27) .

Graph 19: The primary side electric current that LLC syntonic converter issues in different job mode is undee

Design give typical examples

In measure? 6 in, the RMS galvanometer of syntonic capacitance calculates as follows:

Nominal the voltage of the largest syntonic electric capacity below input voltage and nominal and laden condition obtains by next type:

Through be OCP n setting 13A, can get nominal the voltage of the largest syntonic electric capacity that inputs voltage and output to shed a condition to fall too is

Through the will smallest frequency the setting is 65 KHz, can get the voltage of the largest syntonic electric capacity below voltage of the smallest input and nominal and laden condition is

[Measure? 8] commutator network is designed

When transformer sub side uses winding of central take a percentage of a deal when, double diode voltage stress is output voltage.

The RMS value of the electric current that has shed every commutate diode gives out by next type:

In the meantime, the ripple electric current that has shed output electric capacity gives out by next type:

The voltage ripple on output electric capacity is

Design give typical examples

The voltage stress of rectification diode and voltaic stress are:

The tension that causes considering stray inductance is too strong, choose 75 V? POWERTRENCH of 4.5 M Ω^? MOSFET serves as synchronous commutator. The conduction on every MOSFET loss is 0.47W.

The RMS electricity that exports capacitance is:

Paralell connection of output electric capacity uses electric capacity of F of μ of 4 1200. The rated electric current of every capacitance and ESR are 2.77 ARMS and 15 M Ω respectively.

Ripple of output electric capacity is calculated as follows

[Measure? 9] electric current detects circuit configuration

Graph 20: Typical electric current detects configuration

NCP4390 will detect the integral of instantaneous switch electric current and switch electric current, if pursue,20 are shown. Because NCP4390 is located in sub side, because this should use voltaic transformer,detect primary side electric current. When PROUT1 is low n, is in-house restoration switch met ICS? Qian of the voltage that cite a base in 0 V. Conversely, when PROUT1 is tall n, ICS cites a base not Qian, integral capacitance (C_ICS) charge all right by the electric inpour that sheds classics RICS resistor and discharge.

The applied circuit of NCP4390 uses RC filter to undertake allowing integral. To obtain accurate integral, electric current detects the design that resistor and voltaic transformer circle number is compared should ensure V_SENSE amplitude is in most time prep above V_ICS. Graph the 23 errors that showed accurate integral circuit are in PROUT1 (V_CM) drop how does the edge follow V_ICSPeak value voltage and V_SENSEThe rate between and change. Percentage is smaller, integral is more accurate.

When V_ICS Peak value voltage and V_CMThe rate between is less than 0.5 when, can obtain have acceptability error (about 10% ) accurate integral. As a result of the V when regular job_ICS Peak value voltage under 1.2V, accordingly we should choose R_CS1 With R_CS2, make thereby V_CM Prep above 2.4V.

Graph 21: ICS brings crural weaveform

Graph 22: V_ICS.IDEAL^PK With V_ICS.ACTUAL^PK definition

Graph 23: ICS brings crural voltage attenuation and V_ICS.IDEAL^PK/ V_CM

To obtain V_ICS peak value voltage, let us have a look at the ideal power input of LLC converter. Attack to develop of half bridge LLC structure, in guide PROUT1 the case that opens time definition to be T=0 falls, power input can express by next type:

Ask an attention, to the circumstance of complete bridge LLC, of equal-sign on the right side of should multiply with 2.

Hypothesis integral is ideal, the peak value voltage of ICS can express by next type:

Be united in wedlock (33) and (34) , voltage of ICS peak value but by estimation leaving type:

Cite the ability of switch of crural interior discharge considering ICS, C_ICS typical cost is 1 NF. For accurate integral, we suggest to use the electric capacity of 1% tolerance.

When V_ICS Peak value voltage and V_CM The rate between is insufficient hour, will pursue please 23 medium attenuation coefficient apply at formula (35) .

Electric current detects voltage (V_ICS) the average input electric current of syntonic converter of the LLC in integral peak value and switch cycle becomes direct ratio, if pursue,24 are shown. Accordingly, be restricted to be worth the per cent of the rated power of threshold value at inputting electric current according to correspondence, SR is enabled / the per cent that bans used laden condition to be to be fully loaded with a condition certainly. Normally, the rated load condition of 120% is used at shedding tripping operation point too, SR is in respectively 15% next enabling and ban with the rated load of 7.5% with. If pass the rated load requirement that sheds tripping operation point,be 140% , SR will be in of rated load 17.5% and 8.75% when enable and ban with.

Enable to increasing SR / ban the case that uses a site next acquisition taller shed limitation too, can bring the resistor RSLP between the foot to bring to bear on on VICS through ICS and 5VB additional slope. This technology is used at normally longer the circumstance that holds time. To given RSLP, cite crural tension for ICS additional the slope that bring to bear on gives out by next type:

Graph 24: Laden condition and ICS cite crural tension

Graph 25: Take slope compensatory electric current to detect configuration

Graph 26: The laden condition when increasing slope to compensate and ICS cite crural tension

Rated input voltage and the peak value of primary side electric current when be fully loaded with by estimation leaving type:

The rate between RCS1 and RCS2 should shed protection too according to primary side (point of OCP) tripping operation will decide, dot of this tripping operation should be less than IPR PK.

Design give typical examples

It is 44 (n to circling number is compared_CT) voltaic transformer, R_CS1 With R_CS2 The smallest proposal of the sum is worth between give out by next type:

Because power comsumption won’t be too tall, because this is OK R_CS1 + R_CS2 Install higher, so that be in V_ICS What ideal obtains on is integral. From this, we choose R_CS1 With R_CS2 The sum is 230 Ω .

Rated input voltage and the peak value of primary side electric current that are fully loaded with a condition to fall give out by next type:

Through n of OCP of will primary side the setting is 5A,

R_CS1 With R_CS2 Ω of individual choice 30 and 200 Ω .

This kind of design won’t bring a foot to bring to bear on to ICS additional slope.

C_ICSThe choice is 1 NF capacitance. The V when hypothesis 1.2 V_ICS attenuation coefficient is 1 (graph 23 in the reading when X=1.2/10.23) , be in nominal 13 A overload is offerred to protect below input voltage (I_O.OLP) corresponding RICS resistor is

RICS the choice is 30 K Ω .

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