moderate power offline applications, monolithic circuit, such NCP101X

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moderate power offline applications, monolithic circuit, such NCP101X

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AND8134/D Designing Converters with NCP101X Family
moderate power offline applications, monolithic circuit, such NCP101X series, represents pertinent choice engineers looking design speed ease implementation. Incorporating everything needed build reliable safe Switch-Mode Power Supplies (SMPS), NCP101X combines current-mode controller power MOSFET. Semiconductor proprietary high-voltage technology, device directly supplies itself from rectified mains and, numerous cases, does need auxiliary winding operate. This application note details internal circuit operation gives tricks make your design successful. Specs Glance NCP101X capitalizes successful NCP1200 series where words compactness flexibility could both applied qualify controller philosophy. this particular version, controller looks very similar that 1200 lateral MOSFET been added part. Let's quickly browse features: Need Auxiliary Winding: Semiconductor's Very High Voltage Integrated Circuit technology lets supply directly from high-voltage rail. call Dynamic Self-Supply (DSS) already implemented 1200 series. This solution simplifies transformer design ensures better control SMPS difficult output conditions, e.g. constant current operations overload. However, improved standby performance, auxiliary winding connected disable operation. Short-Circuit Protection: permanently monitoring feedback line activity, able detect presence short-circuit, immediately reducing output power total system protection. Once short disappeared, controller resumes goes back normal operation.
Fail-Safe Optocoupler OVP: When auxiliary
winding connected pin, device stops internal Dynamic Self-Supply takes operating power from auxiliary winding. active clamp connected between ground. case current injected this clamp exceeds level around typ., controller immediately latches stays this position until user cycle down (e.g. unplugging converter from wall). adjusting limiting resistor series with terminal, becomes possible implement over voltage protection function, latching circuit case broken optocoupler feedback loop problems. Standby-Power: SMPS naturally exhibit good efficiency nominal load, they begin less efficient when output power demand diminishes. skipping unneeded switching cycles, NCP101X drastically reduces power wasted during light load conditions. auxiliary winding further help decreasing standby power extremely levels invalidating operation. that case, experience shows that standby power below achievable. Acoustic Noise While Operating: Instead skipping cycles high peak currents, NCP101X waits until peak current demand falls below fixed maximum limit. result, cycle skipping take place without having singing transformer. thus select cheap magnetic components free noise problems. SPICE Model: dedicated model transient cycle-by-cycle simulations available also averaged version help closing loop. Ready-to-use templates downloaded OrCAD's PSpice, INTUSOFT's IsSpice4 from Semiconductor's site, NCP101X related section.
Semiconductor Components Industries, LLC, 2003
October, 2003 Rev.
Publication Order Number: AND8134/D
AND8134/D
Dynamic Self-Supply Dynamic Self-Supply (DSS) offers easy means provide power control section, without using auxiliary winding. consists current source connected swinging high-voltage drain, operated depending level: below given value, source rises When reached desired value, source turns off, longer consumes power. This system self-regulated works
From Bulk
hysteretic regulator: consumption increases, current source will stay longer period will shorten. result, being connected drain, average current taken from that path, reflects average current drawn from (neglecting operation losses). Figure depicts implemented Figure portrays typical operating signals.
Drain
Start-Up Time
9.00
Avg.
Current Source
7.00
Error Flag Test Here 5.00 Source Source 3.00
Current Reading
1.00
16.6m
49.9m
83.2m
116m
150m
Figure internal supply implementation
Figure typical operating signals, like ripple.
down slopes internally used timers eventually detect error condition, e.g. overload event. When feedback level pushed maximum, active clamp starts operate limits current, cycle cycle. This active clamp nothing else than usual "zener" find NCP120X series, except that clamping level smaller NCP101X series. soon this clamp activated, asserts digital flag, testifying overload condition loss feedback signal. When logic senses that reached that error flag asserted, logic stops pulses enters safe, auto-recovery, burst mode. soon error goes away, SMPS resumes operation.
Overload events always happen during start-up sequence where controller strives grow Vout. During that time, loop pushes peak current maximum (hence clamp activation) waits until Vout reaches target. time given controller supply build-up Vout corresponds first downslope (see Figure error flag still high first event, then controller activates burst. result, important check with oscilloscope that device regulates before first event. This done monitoring (pin4) (pin1). Figure indicates, proper dimensioning CVcc implies release before downslope.
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Pulses Start
Error Check
Feedback Power released before check. error
Figure release before first event indicates that supply enough time start-up.
Jittering Using ripple excursion that notice internally used modulate switching frequency controller. Typically, 3.3% deviation observed
sweep between VccON VccOFF, e.g. 62.8 67.2% typically reference. This so-called frequency jittering lowers peaks following harmonics.
Without Jittering With Jittering
L1avg L2avg
Figure Frequency Jittering Spreads Energy Content Lowers Discrete Peaks
jittering actually performs so-called spread spectrum modulation which "spreads" energy adjacent frequencies rather than inside single ray. When receiver opens it's narrow filter window given frequency accumulated (averaged) energy
reduced frequency modulation. result, less efforts needed input filter design. Connecting auxiliary winding disables frequency modulation since ripple fades away.
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AND8134/D
Duty-Cycle NCP101X series, current source connected drain node, unlike 120X family where tied bulk rail. result, current source "sees" swinging node affected large dV/dt with voltage excursions from almost ground (MOSFET nearly (MOSFET OFF). This situation sometimes affect behavior, especially duty-cycle exceeds 45%. that case, voltage necessary operate source available current cannot refuel capacitor. Why, since average voltage across being null, current source should face similar situation when connected bulk? reality, pulse frequency makes situation difficult current source, high-voltage MOSFET, that needs quickly turn-on during time only. certain point, duty-cycle large, voltage starts bend before stopping hysteretic regulation. Figure portrays typical curves where duty-cycle expands toward engenders bending. Should duty-cycle further increase, would stop (the simply flattens) would still continue operate.
Duty-Cycle
Duty-Cycle
Bends
Figure When duty-cycle exceeds 45%, starts bend, indicating beginning limit DSS.
take full benefit DSS, here some recommendations that need understood successful design: Design steady-state duty-cycle smaller than minimum input voltage maximum load. problem that transient duty-cycles exceed that limit, e.g. during load variations. NCP101X work both without problem.
necessary, grow-up bulk capacitor reduce
ripple line thus increase available rectified voltage worse input case. sure test your final design right ambient temperature while observing ripple. slightly bent ripple Figure problem observed high ambient temperatures.
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AND8134/D
Auxiliary Winding? being directly connected drain node, power dissipation sometimes affect remaining heat dissipation room MOSFET power budget high. Since average voltage across transformer primary inductance null steady-state, average power taken supply controller Vbulk ICC1, neglecting switching losses. Vbulk ICC1 roughly then power already Suppose package dissipate 50°C TAMBIENT, then room left MOSFET only 930m-370m naturally hampering power capability considered device. Also, no-load standby power cannot lowered below these high line since always operating. solution improve situation could disable auxiliary winding reduce power drawn controller almost nothing. This improves no-load standby power barrier sight. Also, package power dissipation becomes entirely dedicated MOSFET alone, considerably raising power capability considered device. when using auxiliary winding Dynamic Self-Supply? need extremely standby power: auxiliary winding design power converter okay filtering sensitive issue, need jittering: want pass maximum power from NCP101X member: auxiliary winding precise short-circuit protection must: Safety motivates open-loop protection: auxiliary winding NCP101X features active clamp pin: when voltage presents this exceeds VccOFF typical, zener-like circuitry starts activate prevents voltage from going further course, mode, this circuit unactive since current source stops excursion VccOFF. circuit permanently monitors current flowing this zener circuit. When this current reaches certain value (7.4 typical), comparator permanently latches-off controller user must cycle down reset latch. result, when connect auxiliary winding, MUST limit current flowing into otherwise have risks destroy active zener injected current exceeds will latch your converter state soon starts-up.
Internal Rlimit
VccOFF Permanent Latch CVcc Aux. Winding
Figure active clamp limits voltage excursion triggers latch injected current high.
This protective feature used protect load converter case broken optocoupler instance. Calculating Rlimit resistor easy long understands particularity converter featuring extremely standby power. Self-supplying controllers very standby applications often puzzles designer. Actually, SMPS operated nominal load deliver auxiliary voltage arbitrary (Vnom), this voltage drop below (Vstby) when entering standby. This because recurrence switching pulses expands much that frequency re-fueling rate capacitor enough keep proper auxiliary voltage. care must taken when calculating Rlimit trigger over current latch injecting (minimum spec) into active clamp) normal operation drop much voltage over Rlimit when entering standby. Otherwise could kept deactivated standby performance would degrade. thus able bound Rlimit between equations.
Vnom Rlimit Vstby VccON (eq. Itrip ICC1
Where: Vnom auxiliary voltage nominal load. Vstdby auxiliary voltage when standby entered.
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AND8134/D
Itrip current corresponding nominal operation. thus must selected well below avoid false tripping overshoot conditions. minimum value spec cover distribution cases from NCP101X lots lots. ICC1 controller consumption skip mode. This number slightly decreases compared ICC1 from spec since part standby does almost switch. VccON level which Vauxiliary must maintained keep mode. good shoot above order offer adequate design margin, instance Also, shall trigger active clamp much otherwise consumption will increase standby power quickly degrades. When pass barrier, every single milliwatt counts! Since Rlimit shall bother controller standby, e.g. keep Vauxiliary above selected above), purposely select Vnom well above this value. explained before, experience shows that decrease seen auxiliary windings from nominal operation down standby mode. Let's select nominal auxiliary winding offer sufficient margin regarding when standby (Rlimit also drops voltage standby). that case, current flowing through Rlimit will ICC1 (the supply controller) Iclamp, Iclamp circulating activated zener diode. select NCP1013 operating kHz, ICC1 Selecting clamp current Itrip below min. trip point) leads total current Applying equation gives:
Rlimit Rlimit
design power supply, then ratio between auxiliary power must 12/20 0.6. latch will activate when clamp current exceeds minimum spec. Theoretically predicting auxiliary drop from nominal standby almost impossible exercise since many parameters involved, including
converter time constants. fine tuning Rlimit thus requires iterations experiments breadboard check Vauxiliary variations. Once properly adjusted, fail-safe protection will preclude lethal voltage runaways case problem would occur feedback loop. fine tune Rlimit, please follow steps: Select highest Rlimit value, e.g. given equation Remove output load. Connect scope probe cathode auxiliary diode while observing output voltage another channel. Select shot operation scope, with positive trigger monitoring Vaux. Power converter with maximum input voltage short optocoupler LED: Vaux grows-up until latches-off. Capture one-shot graph Figure note Vout Vaux max. Vout gone, controller latched. not, reduce Rlimit retry step until latches-off. quickly reset controller, brief short between ground. Stop converter, make sure Vout back zero. Now, detailed step capture fresh start-up sequence note Vaux Figure have sufficient margin between auxiliary level overshooting start-up case) level which latches-off example), then have safe design. necessary, there room reduce Rlimit thus decrease latching voltage. Check standby power voltage during no-load maximum input voltage. Vpin1 really close no-load conditions, there chances that clamp activates increase consumption. pass barrier, increase Rlimit drop Vpin1 slightly below check that watt-meter passes barrier). Re-do step through check correct latch-off trigger.
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Circuit Latches Here Vout Vaux
Figure circuit latches when Vaux grows-up which corresponds Vout
Latching Level Margin Vaux Vout
Figure selected resistor gives sufficient margin when Vout naturally overshoots start-up.
Please note that this protective option more protect converter load from broken feedback loop
operation rather than precisely clamp output voltage with precision hundred milli-volts.
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AND8134/D
Design Procedure with NCP101X, Universal Mains Design, with application note "Evaluating Power Capability NCP101X Members", have picked-up right device, corresponding power level want reach with your supply. Suppose NCP1013P06 been selected from Table e.g. device plan build V-12 adapter, operating 50°C ambient, featuring DSS, operated European mains (230 15%): rectified bulk voltage will VinDC (230 15%) 1.414 VDC, VinDC (230 15%) 1.414 VDC. detailed data sheet, possible reflect Flyback voltage greater than Vin, avoid forward biasing MOSFET body-diode. Also, care must taken grow drain voltage above breakdown value, Therefore, turn-ratio will bounded between equations, first being BVdss, second limiting reflected voltage forward bias MOSFET body diode:
(Vout VinDC Vleak (Vout VinDC
(eq. (eq.
With secondary diode forward drop (0.5 Schottky case), Vleak leakage excursion (safely clamped network) turn ratio Np/Ns. take leakage excursion (safety margin), then equation gives turn ratio whereas equation gives turn-ratio will chose value reflecting 12.5 during MOSFET time. This respects equation (MOSFET BVdss reached) also ensures
that valley Vds(t) will below ground during time ringing. Taking ratio will guide select right secondary diode. Peak Inverse Voltage (PIV) defined (VinDC max/N) Vout (eq. This leads maximum reverse voltage (374/20) 30.7 applied when primary MOSFET V/3.0 Schottky diode will perfectly design, e.g. MBRA340. explained text, will strive keep converter Discontinuous Conduction Mode (DCM) with duty-cycle less than VinDC offer comfortable operation. would DSS, could freely select duty-cycle choice long respect maximum value stated data-sheet. Keeping supply good practice since, that case, turn-on losses almost zero, neglect capacitive losses. will need equations determine primary inductance method will slightly differ from what used write. Here, several parameters bounding design such available peak current duty-cycle. Therefore, following below lines will know original design parameters (power voltage) part compatible end-up with working converter: From application note "Evaluating Power Capability NCP101X Members" Table know that available peak current actually minimum specification, that Ip_selected case, peak current simply given minimum data sheet, rounded mA).
Calculate critical inductance exceed order stay given design parameters:
Lpcritical (VinDCmin Vr)2 [Pout (Vr2 VinDCmin VinDCmin2)]
(eq.
critical
Then evaluate maximum value primary inductance since bounded duty-cycle (maxDC 40%) peak current:
Lpmax DCmax VinDCmin Ip_selected
(eq.
check Lpmax critical given This okay. check maximum power with Lpmax Ip_selected: Pout 13.6 okay, greater than needed.
Pout Lpmax Ip_selected2
(eq.
calculate clamping network, assuming leakage inductance (5.3 Since reflect will clamp limiting drain excursion BVdss. peak current worse case maximum specification, therefore apply formulae element calculations:
Rclamp
Vclamp (Vclamp-Vout Lleak Ipmax2
(eq.
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Cclamp Vclamp (eq. with Vripple Rclamp
Vripple Cclamp diode MUR160, ultra-fast diode. Checking Design with Spice Spice simulator offers check design assumptions they deliver expected results.
model made available under both Intusoft's IsSpice OrCAD's PSpice. Flyback template appears Figure with values plugged into models. secondary network TL431 whose bandwidth been rolled-off capacitor. Please note presence leakage inductance calculated clamp. missed right values this network, library will blow, this nice thing with simulation.
Iout
Xfmr 200m RATIO -0.05
MBR340 Vint
2.2mH
Vout Vout
Iprim 22nF Rclp
5.3mH
Isec Iripple1 470mF
100m
300m
Rload
Iclamp
MUR160
LLeak 106mH
100mF
Vdrain IDrain
Vline NCP1013P06
Vint
Vout
IVcc 33mF
100nF
Figure IsSpice Simulation Template Check Design Validity
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AND8134/D
13.5 8.80
12.5
8.40
Vout
Plot1
11.5
8.00
10.5
7.60
volts) Vout
7.20 volts) 2.42 5.21 8.01 10.8 13.6
Idrain
Plot2
-200
-400 amperes) Idrain
-100 volts) Vdrain 14.926 14.943 14.959 14.975 14.992
Figure Results Check Parameter Compliance
From Figure that line confirms duty-cycle (Pout discontinuous operation. Different waveforms would reveal good safety margin between Vds(t) BVdss.
Conclusion This application note describes design methodology NCP101X devices whose various features bring ease speed design. following steps, becomes simple develop test with Spice, power supply tailored your needs.
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moderate power offline applications, monolithic circuit, such NCP101X

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