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FAN7930B -- Critical Conduction Mode PFC Controller
October 2010
FAN7930B Critical Conduction Mode PFC Controller
Features
Additional OVP Detection Pin Input Voltage Absent Detection Circuit Maximum Switching Frequency Limitation Internal Soft-Start and Overshoot-less Control Internal Total Harmonic Distortion (THD) Optimizer Precise Adjustable Output Over-Voltage Protection Open-Feedback Protection and Disable Function Zero Current Detector 150s Internal Startup Timer MOSFET Over-Current Protection Under-Voltage Lockout with 3.5V Hysteresis Low Startup and Operating Current Totem-Pole Output with High State Clamp +500/-800mA Peak Gate Drive Current 8-Pin Small Outline Package (SOP)
Description
The FAN7930B is an active power factor correction (PFC) controller for boost PFC applications that operate in critical conduction mode (CRM). It uses a voltage-mode PWM that compares an internal ramp signal with the error amplifier output to generate a MOSFET turn-off signal. Because the voltage-mode CRM PFC controller does not need rectified AC line voltage information, it saves the power loss of an input voltage sensing network necessary for a current-mode CRM PFC controller. FAN7930B provides over-voltage protection, openfeedback protection, over-current protection, inputvoltage-absent detection, and under-voltage lockout protection. The additional OVP pin can be used to shut down the boost power stage when output voltage exceeds OVP level due to the resistors that are connected at INV pin are damaged. The FAN7930B can be disabled if the INV pin voltage is lower than 0.45V and the operating current decreases to a very low level. Using a new variable on-time control method, THD is lower than the conventional CRM boost PFC ICs.
Applications
Adapter Ballast LCD TV, CRT TV SMPS
Related Resources
AN-8035 -- Design Consideration Conduction Mode PFC Using FAN7930 for Boundary
Ordering Information
Part Number
FAN7930BM -40 to +125C FAN7930BMX FAN7930B 8-Lead Small Outline Package (SOP) Tape & Reel
Operating Temperature Range
Top Mark
Package
Packing Method
Rail
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
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FAN7930B -- Critical Conduction Mode PFC Controller
Application Diagram
Figure 1.
Typical Boost PFC Application
Internal Block Diagram
Figure 2.
Functional Block Diagram
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
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FAN7930B -- Critical Conduction Mode PFC Controller
Pin Configuration
VCC OUT GND ZCD
FAN7930B
8-SOP
INV Figure 3.
OVP COMP
CS
Pin Configuration (Top View)
Pin Definitions
Pin #
1 2 3 4 5 6 7 8
Name Description
INV OVP COMP CS ZCD GND OUT VCC This pin is the inverting input of the error amplifier. The output voltage of the boost PFC converter should be resistively divided to 2.5V. This pin is used to detect PFC output over voltage when INV pin information is not correct. This pin is the output of the transconductance error amplifier. Components for the output voltage compensation should be connected between this pin and GND. This pin is the input of the over-current protection comparator. The MOSFET current is sensed using a sensing resistor and the resulting voltage is applied to this pin. An internal RC filter is included to filter switching noise. This pin is the input of the zero-current detection block. If the voltage of this pin goes higher than 1.5V, then goes lower than 1.4V, the MOSFET is turned on. This pin is used for the ground potential of all the pins. For proper operation, the signal ground and the power ground should be separated. This pin is the gate drive output. The peak sourcing and sinking current levels are +500mA and 800mA, respectively. For proper operation, the stray inductance in the gate driving path must be minimized. This is the IC supply pin. IC current and MOSFET drive current are supplied using this pin.
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
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FAN7930B -- Critical Conduction Mode PFC Controller
Absolute Maximum Ratings
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable above the recommended operating conditions and stressing the parts to these levels is not recommended. In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability. The absolute maximum ratings are stress ratings only.
Symbol
VCC IOH, IOL ICLAMP IDET VIN TJ TA TSTG ESD Supply Voltage Peak Drive Output Current
Parameter
Min.
-800 -10 -10
(1)
Max.
VZ +500 +10 +10 8.0 6 +150 +125 +150 2.5 2.0
Unit
V mA mA mA V C C C kV
Driver Output Clamping Diodes VO>VCC or VO<-0.3V Detector Clamping Diodes Error Amplifier Input, Output, OVP Input, ZCD and OVP Pin CS Input Voltage
(2)
-0.3 -10 -40 -65
Operating Junction Temperature Operating Temperature Range Storage Temperature Range Electrostatic Discharge Capability Human Body Model, JESD22-A114 Charged Device Model, JESD22-C101
Notes: 1. When this pin is supplied by external power sources by accident, its maximum allowable current is 50mA. 2. In case of DC input, acceptable input range is -0.3V~6V: within 100ns -10V~6V is acceptable, but electrical specifications are not guaranteed during such a short time.
Thermal Impedance
Symbol
JA
Parameter
Thermal Resistance, Junction-to-Ambient
(3)
Min.
150
Max.
Unit
C/W
Note: 3. Regarding the test environment and PCB type, please refer to JESD51-2 and JESD51-10.
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
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FAN7930B -- Critical Conduction Mode PFC Controller
Electrical Characteristics
VCC = 14V, TA = -40C~+125C, unless otherwise specified.
Symbol
VCC Section VSTART VSTOP HYUVLO VZ VOP ISTART IOP IDOP IOPDIS VREF1 VREF1 VREF2 IEA,BS IEAS,SR IEAS,SK VEAH VEAZ gm tON,MAX1 tON,MAX2
Parameter
Start Threshold Voltage Stop Threshold Voltage UVLO Hysteresis Zener Voltage Recommended Operating Range Startup Supply Current Operating Supply Current Operating Current at Disable
Conditions
VCC Increasing VCC Decreasing ICC=20mA
Min.
11 7.5 3.0 20 13
Typ.
12 8.5 3.5 22
Max.
13 9.5 4.0 24 20
Units
V V V V V A mA mA A V mV mV A A A
Supply Current Section VCC=VSTART-0.2V Output Not Switching VINV=0V 90 2.465 120 1.5 2.5 160 2.500 0.1 20 VINV=1V~4V VINV=VREF -0.1V VINV=VREF +0.1V VINV=1V, VCS=0V 6.0 0.9 90 35.5 11.2 -0.5 -12 12 6.5 1.0 115 41.5 13.0 7.0 1.1 140 47.5 14.8 0.5 190 3.0 4.0 230 2.535 10.0
Dynamic Operating Supply Current 50kHZ, CI=1nF
Error Amplifier Section Voltage Feedback Input Threshold1 TA=25C Line Regulation Temperature Stability of VREF1 Input Bias Current Output Source Current Output Sink Current Output Upper Clamp Voltage Zero Duty Cycle Output Voltage Transconductance
(4) (4)
VCC=14V~20V
V V mho s s
Maximum On-Time Section Maximum On-Time Programming 1 TA=25C, VZCD=1V Maximum On-Time Programming 2 TA=25C, IZCD=0.469mA
Current-Sense Section VCS ICS,BS tCS,D Current Sense Input Threshold Voltage Limit Input Bias Current Current Sense Delay to Output
(4)
0.7 VCS=0V~1V dV/dt=1V/100ns, from 0V to 5V -1.0
0.8 -0.1 350
0.9 1.0 500
V A ns
Continued on the following page...
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
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FAN7930B -- Critical Conduction Mode PFC Controller
Electrical Characteristics
VCC = 14V, TA = -40C~+125C, unless otherwise specified.
Symbol
VZCD HYZCD VCLAMPH VCLAMPL IZCD,BS IZCD,SR IZCD,SK tZCD,D
Parameter
Input Voltage Threshold Detect Hysteresis
(4) (4)
Conditions
Min.
1.35 0.05
Typ.
1.50 0.10 6.2 0.65 -0.1
Max.
1.65 0.15 7.5 1.00 1.0 -4 10
Units
V V V V A mA mA ns
Zero-Current Detect Section
Input High Clamp Voltage Input Low Clamp Voltage Input Bias Current Source Current Capability Sink Current Capability
(4) (4)
IDET=3mA IDET= -3mA VZCD=1V~5V TA=25C TA=25C dV/dt=-1V/100ns, from 5V to 0V IO=-100mA, TA=25C IO=200mA, TA=25C CIN=1nF CIN=1nF VCC=20V, IO=100A VCC=5V, IO=100A
5.5 0 -1.0
Maximum Delay From ZCD to Output (4) Turn-On Output Voltage High Output Voltage Low Rising Time
(4) (4)
100
200
Output Section VOH VOL tRISE tFALL VO,MAX VO,UVLO tRST fMAX tSS VOVP,INV 9.2 11.0 1.0 50 50 11.5 13.0 12.8 2.5 100 100 14.5 1 50
(4)
V V ns ns V V s kHz ms V V V V V V C C
Falling Time
Maximum Output Voltage Output Voltage with UVLO Activated Restart Timer Delay Maximum Switching Frequency Internal Soft-Soft
(4)
Restart / Maximum Switching Frequency Limit Section 150 300 5 2.675 0.175 2.845 0.345 0.40 0.05
(4)
300 350 7 2.730 0.230 2.960 0.50 0.15 155
250 3 TA=25C TA=25C TA=25C TA=25C 2.620 0.120 2.740
Soft-Start Timer Section Protections OVP Threshold Voltage at INV pin HYOVP,INV OVP Hysteresis at INV pin VOVP,OVP OVP Threshold Voltage at OVP pin HYOVP,OVP OVP Hysteresis at OVP pin VEN HYEN TSD THYS Enable Threshold Voltage Enable Hysteresis Thermal Shutdown Temperature Hysteresis Temperature of TSD
(4)
0.45 0.10 140 60
125
Note: 4. These parameters, although guaranteed by design, are not production tested.
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
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FAN7930B -- Critical Conduction Mode PFC Controller
Comparison between FAN7530 and FAN7930B
Function
OVP Pin
FAN7530
None
FAN7930B
Integrated
FAN7930B Advantages
No External Circuit for additional OVP Reduction of Power Loss and BOM Cost Caused by additional OVP Circuit Abnormal CCM Operation Prohibited Abnormal Inductor Current Accumulation can be Prohibited Increase System Reliability with AC On-Off Test Guarantee Stable Operation at Short Electric Power Failure Reduce Voltage and Current Stress at Startup Eliminate Audible Noise due to Unwanted OVP Triggering Can Avoid Burst Operation at Light Load and High Input Voltage Reduce Probability of Audible Noise Due to the Burst Operation No External Resistor is Needed Stable and Reliable TSD Operation Converter Temperature Range Limited Range
Frequency Limit
None
Integrated
AC Absent Detection Soft-Start and Startup without Overshoot Control Range Compensation THD Optimizer TSD
None
Integrated
None
Integrated
None
Integrated
External None
Internal 140C with 60C Hysteresis
Comparison between FAN7930 and FAN7930B
Function
RDY Pin OVP Pin Control Range Compensation
FAN7930
Integrated None None
FAN7930B
None Integrated Integrated
FAN7930B Remark
User Choice for the Use of Number #2 Pin
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
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FAN7930B -- Critical Conduction Mode PFC Controller
Typical Performance Characteristics
Figure 4.
Voltage Feedback Input Threshold 1 (VREF1) vs. TA
Figure 5.
Start Threshold Voltage (VSTART) vs. TA
Figure 6.
Stop Threshold Voltage (VSTOP) vs. TA
Figure 7.
Startup Supply Current (ISTART) vs. TA
Figure 8.
Operating Supply Current (IOP) vs. TA
Figure 9.
Output Upper Clamp Voltage (VEAH) vs. TA
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
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FAN7930B -- Critical Conduction Mode PFC Controller
Typical Performance Characteristics
Figure 10. Zero Duty Cycle Output Voltage (VEAZ) vs. TA
Figure 11.
Maximum On-Time Program 1 (tON,MAX1) vs. TA
Figure 12.Maximum On-Time Program 2 (tON,MAX2) vs. TA
Figure 13.
Current Sense Input Threshold Voltage Limit (VCS) vs. TA
Figure 14. Input High Clamp Voltage (VCLAMPH) vs. TA
Figure 15.
Input Low Clamp Voltage (VCLAMPL) vs. TA
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
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FAN7930B -- Critical Conduction Mode PFC Controller
Typical Performance Characteristics
Figure 16.
Output Voltage High (VOH) vs. TA
Figure 17.
Output Voltage Low (VOL) vs. TA
Figure 18.
Restart Timer Delay (tRST) vs. TA
Figure 19.
OVP Threshold at OVP Pin (VOVP,OVP) vs. TA
Figure 20.
Output Saturation Voltage (VRDY,SAT) vs. TA
Figure 21.
OVP Threshold Voltage (VOVP) vs. TA
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
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FAN7930B -- Critical Conduction Mode PFC Controller
Applications Information
1. Startup: Normally, supply voltage (VCC) of a PFC block is fed from the additional power supply, which can be called standby power. Without this standby power, auxiliary winding to detect zero current detection can be used as a supply source. Once the supply voltage of the PFC block exceeds 12V, internal operation is enabled until the voltage drops to 8.5V. If VCC exceeds VZ, 20mA current is sinking from VCC.
Figure 23.
Circuit Around INV Pin
Figure 22.
Startup Circuit
2. INV Block: Scaled-down voltage from the output is the input for the INV pin. Many functions are embedded based on the INV pin: transconductance amplifier, output OVP comparator and disable comparator. For the output voltage control, a transconductance amplifier is used instead of the conventional voltage amplifier. The transconductance amplifier (voltagecontrolled current source) aids the implementation of OVP and disables function. The output current of the amplifier changes according to the voltage difference of the inverting and non-inverting input of the amplifier. To cancel down the line input voltage effect on power factor correction, effective control response of PFC block should be slower than the line frequency and these conflicts with the transient response of controller. Twopole one-zero type compensation may be used to meet both requirements. The OVP comparator shuts down the output drive block when the voltage of the INV pin is higher than 2.675V and there is 0.175V hysteresis. The disable comparator disables the operation when the voltage of the inverting input is lower than 0.35V and there is 100mV hysteresis. An external small-signal MOSFET can be used to disable the IC. The IC operating current decreases to reduce power consumption if the IC is disabled. 0 is the timing chart of the internal circuit near the INV pin when rated PFC output voltage is assumed at 390VDC and VCC supply voltage is 15V.
Figure 24.
Timing Chart for INV Block
3. OVP Pin: Over-Voltage Protection (OVP) is embedded by the information at the INV pin. That information comes from the output through the voltage dividing resistors. To scale down from high voltage to low one, high resistance normally used with low resistance. In cases the resistor of high resistance get a damage and resistance is changed to high, though INV pin information is normal output voltage exceeds its rated output. Once this happen, output electrolytic capacitor may be exploded. To prevent such a catastrophe additional OVP pin is assigned to double check output voltage. Thus additional OVP may be nd st called 2 OVP while INV pin OVP can be called 1 OVP.
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
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FAN7930B -- Critical Conduction Mode PFC Controller
Since the two OVP conditions are quite different, protection recovering mode is different. Once the first OVP triggers, switching stops immediately and recovers switching when the output voltage is decreased with a hysteresis. When the second OVP triggers, switching can be recovered only when the VCC supply voltage falls below VSTOP and builds up higher than VSTART again and VOVP should be lower than hysteresis. If the second OVP is not used, the OVP pin must be connected to the INV pin or to the ground.
where, VAUX is the auxiliary winding voltage, TIND and TAUX are boost inductor turns and auxiliary winding turns respectively, VAC is input voltage for PFC converter and VOUT_PFC is output voltage from the PFC converter.
Figure 26.
Circuit Near ZCD
Figure 25.
Comparison of 1 and 2 Recovering Mode
st
nd
OVP
Because auxiliary winding voltage can swing from negative voltage to positive voltage, the internal block in ZCD pin has both positive and negative voltage clamping circuits. When the auxiliary voltage is negative, internal circuit clamps the negative voltage at the ZCD pin around 0.65V by sourcing current to the serial resistor between the ZCD pin and the auxiliary winding. When the auxiliary voltage is higher than 6.5V, current is sinked through a resistor from the auxiliary winding to the ZCD pin.
4. Control Range Compensation: On time is controlled by the output voltage compensator with FAN7930B. Due to this when input voltage is high and load is light, control range become narrow compared when input voltage is low. That control range decrease is antiproportional to the double square of the input voltage. Thus at high line unwanted burst operation easily happens at light load and audible noise may be generated from the boost inductor or inductor at input filter. Different from the other converters, burst operation in PFC block is not needed because PFC block itself is normally disabled during standby mode. To improve this kind of unwanted burst operation at light load, internal control range compensation function is implemented and approximately shows no burst operation until 5% load at high line. 5. Zero-Current Detection: Zero-current detection (ZCD) generates the turn-on signal of the MOSFET when the boost inductor current reaches zero using an auxiliary winding coupled with the inductor. When the power switch turns on, negative voltage is induced at the auxiliary winding due to the opposite winding direction (see Equation 1) and positive voltage is induced (see Equation 2) when the power switch turns off.
T VAUX = - AUX VAC TIND T VAUX = AUX (VPFCOUT - VAC ) TIND
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
Figure 27. Auxiliary Voltage Depends on MOSFET Switching To check the boost inductor current zero instance, auxiliary winding voltage is used. When boost inductor current becomes zero, there is a resonance between boost inductor and all capacitors at MOSFET drain pin, including COSS of the MOSFET; an external capacitor at the D-S pin to reduce the voltage rising and falling slope of the MOSFET; a parasitic capacitor at inductor; and so on to improve performance. Resonated voltage is reflected to the auxiliary winding and can be used as detecting zero current of boost inductor and valley position of MOSFET voltage stress. For valley detection, a minor delay by the resistor and capacitor is needed. A capacitor increases the noise immunity at the ZCD pin. If ZCD voltage is higher than 1.5V, an internal ZCD comparator output becomes HIGH and LOW when the ZCD goes below 1.4V. At the falling edge of comparator output, internal logic turns on the MOSFET.
(1) (2)
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FAN7930B -- Critical Conduction Mode PFC Controller
Figure 30.
Maximum Switching Frequency Limit Operation
6. Control: The scaled output is compared with the internal reference voltage and sinking or sourcing current is generated from the COMP pin by the transconductance amplifier. The error amplifier output is compared with the internal sawtooth waveform to give proper turn-on time based on the controller.
Figure 28.
Auxiliary Voltage Threshold
When no ZCD signal is available, the PFC controller cannot turn on MOSFET, so the controller checks every switching off time and forces MOSFET turn on when the off time is longer than 150s. It is called restart timer. Restart timer triggers MOSFET turn on at startup and may be used at the input voltage zero cross period.
Figure 31.
Control Circuit
150s
Figure 29.
Restart Timer at Startup
Because the MOSFET turn on depends on the ZCD input, switching frequency may increase to higher than several megahertz due to the miss-triggering or noise on the nearby ZCD pin. If the switching frequency is higher than needed for critical conduction mode (CRM), operation mode shifts to continuous conduction mode (CCM). In CCM, unlike CRM where the boost inductor current is reset to zero at the next switch on; inductor current builds up at every switching cycle and can be raised to very high current, that exceeds the current rating of the power switch or diode. This can seriously damage the power switch and result in burn down. To avoid this, maximum switching frequency limitation is embedded. If ZCD signal is applied again within 3.3s after the previous rising edge of gate signal, this signal is ignored internally and FAN7930B waits for another ZCD signal. This slightly degrades the power factor performance at light load and high input voltage.
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2 13
Unlike a conventional voltage-mode PWM controller, FAN7930B turns on the MOSFET at the falling edge of ZCD signal. On instance is decided by the external signal and the turn-on time lasts until the error amplifier output (VCOMP) and sawtooth waveform meet. When load is heavy, output voltage decreases, scaled output decreases, COMP voltage increases to compensate low output, turn-on time lengthens to give more inductor turn-on time, and increased inductor current raises the output voltage. This is how PFC negative feedback controller regulates output. The maximum of VCOMP is limited to 6.5V, which dictates the maximum turn-on time, and switching stops when VCOMP is lower than 1.0V.
0.155 V / s
Figure 32.
Turn-On Time Determination
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FAN7930B -- Critical Conduction Mode PFC Controller
The roles of PFC controller are regulating output voltage and input current shaping to increase power factor. Duty control based on the output voltage should be fast enough to compensate output voltage dip or overshoot. For the power factor, however, the control loop must not react to the fluctuating AC input voltage. These two requirements conflict; therefore, when designing a feedback loop, the feedback loop should be least 10 times slower than AC line frequency. That slow response is made by C1 at compensator. R1 makes gain boost around operation region and C2 attenuates gain at higher frequency. Boost gain by R1 helps raise the response time and improves phase margin.
VCC
VSTART=12V
VREFSS 5ms
VREFEND=2.5V
VINV=0.4V gM
ISOURCECOMP
(VREFSS-VINV)
gM=ISOURCECOMP
VCOMP
ISOURCECOMP
RCOMP=VCOMP
FAN7930 Rev.00
t
Figure 33.
Compensators Gain Curve
Figure 35.
Soft-Start Sequence
For the transconductance error amplifier side, gain changes based on differential input. When the error is large, gain is large to make the output dip or peak to suppress quickly. When the error is small, low gain is used to improve power factor performance.
250 mho
115 mho
8. Startup without Overshoot: Feedback control speed of PFC is quite slow. Due to the slow response, there is a gap between output voltage and feedback control. That is why over-voltage protection (OVP) is critical at the PFC controller and voltage dip caused by fast load changes from light to heavy is diminished by a bulk capacitor. OVP is easily triggered at startup phase. Operation on and off by OVP at startup may cause audible noise and can increase voltage stress at startup, which is normally higher than in normal operation. This operation is better when soft-start time is very long. However, too long startup time enlarges the output voltage building time at light load. FAN7930B has "overshoot-less" control at startup. During startup, the feedback loop is controlled by an internal proportional gain controller and when the output voltage reaches the rated value, it switches to an external compensator after a transition time of 30ms. In short, an internal proportional gain controller eliminates overshoot at startup and an external conventional compensator takes over successfully afterward.
Figure 34.
Gain Characteristic
7. Soft-Start: When VCC touches VSTART, internal reference voltage is increased like a stair step for 5ms. As a result, VCOMP is also raised gradually and MOSFET turn-on time increases smoothly. This reduces voltage and current stress on the power switch during startup.
Figure 36.
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Overshoot-less Startup Control
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FAN7930B -- Critical Conduction Mode PFC Controller
9. THD Optimization: Total harmonic distortion (THD) is the factor that dictates how closely input current shape matches sinusoidal form. The turn-on time of the PFC controller is almost constant over one AC line period due to the extremely low feedback control response. The turn-off time is decided by the current decrease slope of the boost inductor made by the input voltage and output voltage. Once inductor current becomes zero, resonance between COSS and the boost inductor makes oscillating waveforms at the drain pin and auxiliary winding. By checking the auxiliary winding voltage through the ZCD pin, the controller can check the zero current of boost inductor. At the same time, a minor delay time is inserted to determine the valley position of drain voltage. The input and output voltage difference is at its maximum at the zero cross point of AC input voltage. The current decrease slope is steep near the zero cross region and more negative inductor current flows during a drain voltage valley detection time. Such a negative inductor current cancels down the positive current flows and input current becomes zero, called "zero-cross distortion" in PFC.
To improve this, lengthened turn-on time near the zero cross region is a well-known technique, though the method may be different from company to company and may be proprietary. FAN7930B embodies this by sourcing current through the ZCD pin. Auxiliary winding voltage becomes negative when the MOSFET turns on and is proportional to input voltage. The negative clamping circuit of ZCD outputs the current to maintain the ZCD voltage at a fixed value. The sourcing current from the ZCD is directly proportional to the input voltage. Some portion of this current is applied to the internal sawtooth generator together with a fixed-current source. Theoretically, the fixed-current source and the capacitor at sawtooth generator decide the maximum turn-on time when no current is sourcing at ZCD clamp circuit and available turn-on time gets shorter proportional to the ZCD sourcing current.
Figure 37.
Input and Output Current Near Input Voltage Peak
Figure 39.
Circuit of THD Optimizer
Figure 40.
Effect of THD Optimizer
Figure 38.
Input and Output Current Near Input Voltage Peak Zero Cross
15
By THD optimizer, turn-on time over one AC line period is proportionally changed, depending on input voltage. Near zero cross, lengthened turn-on time improves THD performance.
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(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
FAN7930B -- Critical Conduction Mode PFC Controller
10. Input Voltage Absent Detection: To save power loss caused by input voltage sensing resistors and to optimize THD easily, the FAN7930B omits AC input voltage detection. Therefore, no information about AC input is available from the internal controller. In many cases, the VCC of PFC controller is supplied by an independent power source like standby power. In this scheme, some mismatch may exist. For example, when the electric power is suddenly interrupted during two or three AC line periods; VCC is still alive during that time, but output voltage drops because there is no input power source. Consequently, the control loop tries to compensate for the output voltage drop and VCOMP reaches its maximum. This lasts until AC input voltage is live again. When AC input voltage is live again, high VCOMP allows high switching current and more stress is put on the MOSFET and diode. To protect against this, FAN7930B internally checks if the input AC voltage exists. If input does not exist, soft-start is reset and waits until AC input is live again. Soft-start manages the turn-on time for smooth operation when it detects AC input is applied again and applies less voltage and current stress on startup.
VOUT VIN
Though VIN is eliminated, operation of controller is normal due to the large bypass capacitor.
VAUX
MOSFET Gate
DMAX fMIN
fMIN
DMIN
NewVCOMP Input Voltage Absent Detected
IDS
Smooth SoftStart
FAN7930 Rev.00
t
Figure 42. Operation with Input Voltage Absent Circuit 11. Current Sense: The MOSFET current is sensed using an external sensing resistor for the over-current protection. If the CS pin voltage is higher than 0.8V, the over-current protection comparator generates a protection signal. An internal RC filter of 40k and 8pF is included to filter switching noise. 12. Gate Driver Output: FAN7930B contains a single totem-pole output stage designed for a direct drive of the power MOSFET. The drive output is capable of up to +500/-800mA peak current with a typical rise and fall time of 50ns with 1nF load. The output voltage is clamped to 13V to protect the MOSFET gate even if the VCC voltage is higher than 13V.
Figure 41.
Operation without Input Voltage Absent Circuit
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
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FAN7930B -- Critical Conduction Mode PFC Controller
PCB Layout Guide
PFC block normally handles high switching current and the voltage low energy signal path can be affected by the high energy path. Cautious PCB layout is mandatory for stable operation. 1. The gate drive path should be as short as possible. The closed-loop that starts from the gate driver, MOSFET gate, and MOSFET source to ground of PFC controller is recommended as close as possible. This is also crossing point between power ground and signal ground. Power ground path from the bridge diode to the output bulk capacitor should be short and wide. The sharing position between power ground and signal ground should be only at one position to avoid ground loop noise. Signal path of PFC controller should be short and wide for external components to contact. PFC output voltage sensing resistor is normally high to reduce current consumption. This path can be affected by external noise. To reduce noise possibility at the INV pin, a shorter path for output sensing is recommended. If a shorter path is not possible, place some dividing resistors between PFC output and the INV pin -- closer to the INV pin is better. Relative high voltage close to the INV pin can be helpful. ZCD path is recommended close to auxiliary winding from boost inductor and to the ZCD pin. If that is difficult, place a small capacitor (below 50pF) to reduce noise. Switching current sense path should not share with another path to avoid interference. Some additional components may be needed to reduce the noise level applied to the CS pin. 5. A stabilizing capacitor for VCC is recommended as close as possible to the VCC and ground pins. If it is difficult, place the SMD capacitor as close to the corresponding pins as possible.
2.
3.
Figure 43.
Recommended PCB Layout
4.
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
www.fairchildsemi.com 17
FAN7930 -- Critical Conduction Mode PFC Controller
Typical Application Circuit
Application
LCD TV Power Supply
Device
FAN7930B
Input Voltage Range
90-265VAC
Rated Output Power
195W
Output Voltage (Maximum Current)
390V (0.5A)
Features
Average efficiency of 25%, 50%, 75%, and 100% load conditions is higher than 95% at universal input. Power factor at rated load is higher than 0.98 at universal input. Total Harmonic Distortion (THD) at rated load is lower than 15% at universal input.
Key Design Notes
When auxiliary VCC supply is not available, VCC power can be supplied through Zero Current Detect (ZCD) winding. The power consumption of R103 is quite high, so its power rating needs checking. Because the input bias current of INV pin is almost zero, output voltage sensing resistors (R112~R115) as high as possible. However, too-high resistance makes the node easily affected by noise. Thus values need to strike a balance between power consumption and noise immunity. Quick charge diode (D106) can be eliminated if output diode inrush current capability is enough. Thought D106, system operation is normal due to the controller's highly reliable protection features.
1. Schematic
C1030,68 F ,630Vdc TH101, 5D15 LF101, 23mH
R112 3.9M
R116 3.9M
R102, 330k D101,1N4746 R104, 30k C105, 100nF C107, 33 F D104,1N4148 R111 0.08, 5W R110,10k R107, C108, 10k 220nF C112,470pF C110,1nF C109, 47nF
R113 3.9M R114 3.9M R115 75k C116,1nF
R117 3.9M R118 3.9M R119 75k C111 220 F, 450V
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
FS101, 250V,5A
Figure 44.
Demonstration Circuit
www.fairchildsemi.com 18
FAN7930 -- Critical Conduction Mode PFC Controller
2. Transformer
Figure 45.
Transformer Schematic Diagram of FAN7930B
3. Winding Specification
Position No
Np
Pin (S F)
9, 10 7, 8
Wire
0.1x50
Turns
49
Winding Method
Solenoid Winding
Barrier Tape TOP BOT Ts
1
Bottom
Insulation: Polyester Tape t = 0.025mm, 3 Layers NAUX 24 0.3 6 Solenoid Winding
Top
Insulation: Polyester Tape t = 0.025mm, 4 Layers
4. Electrical Characteristics
Pin
Inductance 9, 10 7, 8
Specification
230H 7%
Remark
100kHz, 1V
5. Core & Bobbin
Core: EER3124, Samhwa (PL-7) (Ae=97.9mm ) Bobbin: EER3124
2
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
www.fairchildsemi.com 19
FAN7930 -- Critical Conduction Mode PFC Controller
6. Bill of Materials
Part #
R101 R102 R103 R104 R107 R108 R109 R110 R111 R112, 113, 114,116,117,118 R115,119 C101 C102 C103 C104 C105 C107 C108 C109 C110,116 C112 C111 C114 C115
Value
Resister 1M 330 k 10 k 30k 10k 4.7k 47k 10k 0.80k 3.9k 75k Capacitor 220nF/275VAC 680nF/275VAC 0.68F/630V 12nF/50V 100nF/50V 33F/50V 220nF/50V 47nF/50V 1nF/50V 47nF/50V 220F/450V 2.2nF/450V 2.2nF/450V
Note
1W 1/2W 1W 1/4W 1/4W 1/4W 1/4W 1/4W 5W 1/4W 1/4W
Part #
Q101 D101 D102 D103 D104 D105 D106
Value
Switch FCPF20N60 1N4746 UF4004 1N4148 1N4148
Note
20A, 600V, SuperFET 1W, 18V, Zener Diode 1A, 400V Glass Passivated High-Efficiency Rectifier 1A, 100V Small-Signal Diode 1A, 100V Small-Signal Diode 8A, 600V, General-Purpose Rectifier 3A, 600V, General-Purpose Rectifier
Diode
IC101
FAN7930B
CRM PFC Controller
Fuse Box Capacitor Box Capacitor Box Capacitor Ceramic Capacitor SMD (1206) Electrolytic Capacitor Ceramic Capacitor Ceramic Capacitor Ceramic Capacitor Ceramic Capacitor Electrolytic Capacitor Box Capacitor Box Capacitor ZNR101 10D471 T1 LF101 23mH Transformer EER3124 ZNR Ae=97.9mm
2
FS101 TH101 BD101
5A/250V NTC 5D-15 Bridge Diode 15A, 600V Line Filter
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
www.fairchildsemi.com 20
FAN7930 -- Critical Conduction Mode PFC Controller
Physical Dimensions
5.00 4.80 3.81
8 5
B
A
0.65
6.20 5.80
1.75 4.00 3.80 5.60
PIN ONE INDICATOR
1
4
1.27 0.25 0.25 0.10 CBA
(0.33)
1.27
LAND PATTERN RECOMMENDATION SEE DETAIL A
1.75 MAX 0.51 0.33 R0.10 R0.10
C
0.25 0.19 0.10 C
OPTION A - BEVEL EDGE
0.50 x 45 0.25
GAGE PLANE
0.36
OPTION B - NO BEVEL EDGE
NOTES: UNLESS OTHERWISE SPECIFIED A) THIS PACKAGE CONFORMS TO JEDEC MS-012, VARIATION AA, ISSUE C, B) ALL DIMENSIONS ARE IN MILLIMETERS. C) DIMENSIONS DO NOT INCLUDE MOLD FLASH OR BURRS. D) LANDPATTERN STANDARD: SOIC127P600X175-8M. E) DRAWING FILENAME: M08AREV13
8 0
0.90 0.40
SEATING PLANE
(1.04)
DETAIL A
SCALE: 2:1
Figure 46.
8-Lead Small Outline Package (SOP)
Package drawings are provided as a service to customers considering Fairchild components. Drawings may change in any manner without notice. Please note the revision and/or date on the drawing and contact a Fairchild Semiconductor representative to verify or obtain the most recent revision. Package specifications do not expand the terms of Fairchild's worldwide terms and conditions, specifically the warranty therein, which covers Fairchild products. Always visit Fairchild Semiconductor's online packaging area for the most recent package drawings: http://www.fairchildsemi.com/packaging/.
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
www.fairchildsemi.com 21
FAN7930 -- Critical Conduction Mode PFC Controller
(c) 2010 Fairchild Semiconductor Corporation FAN7930B * Rev. 1.0.2
www.fairchildsemi.com 22

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