MC33262DR2

MC34262, MC33262 Power Factor Controllers The MC34262/MC33262 are active power factor controllers specifically designed for use as a preconverter in electronic ballast and in off−line power converter applications. These integrated circuits feature an internal startup timer for stand−alone applications, a one quadrant multiplier for near unity power factor, zero current detector to ensure critical conduction operation, transconductance error amplifier, quickstart circuit for enhanced startup, trimmed internal bandgap reference, current sensing comparator, and a totem pole output ideally suited for driving a power MOSFET. Also included are protective features consisting of an overvoltage comparator to eliminate runaway output voltage due to load removal, input undervoltage lockout with hysteresis, cycle−by−cycle current limiting, multiplier output clamp that limits maximum peak switch current, an RS latch for single pulse metering, and a drive output high state clamp for MOSFET gate protection. These devices are available in dual−in−line and surface mount plastic packages. http://onsemi.com POWER FACTOR CONTROLLERS MARKING DIAGRAMS 8 Features • • • • • • • • • • Overvoltage Comparator Eliminates Runaway Output Voltage Internal Startup Timer One Quadrant Multiplier Zero Current Detector Trimmed 2% Internal Bandgap Reference Totem Pole Output with High State Clamp Undervoltage Lockout with 6.0 V of Hysteresis Low Startup and Operating Current Supersedes Functionality of SG3561 and TDA4817 These are Pb−Free and Halide−Free Devices Zero Current Detector 5 2.5V Reference Undervoltage Lockout Zero Current Detect Input VCC PDIP−8 P SUFFIX CASE 626 8 MC3x262P AWL YYWWG 1 1 8 8 SOIC−8 D SUFFIX CASE 751 1 x A WL, L YY, Y WW, W G G 3x262 ALYW G 1 = 3 or 4 = Assembly Location = Wafer Lot = Year = Work Week = Pb−Free Package = Pb−Free Package 8 PIN CONNECTIONS Drive Output 7 Multiplier, Latch, PWM, Timer, & Logic Overvoltage Comparator + Error Amp Multiplier Input 3 4 Current Sense Input Voltage Feedback Input Compensation Multiplier Input Current Sense Input 1 8 VCC 2 7 Drive Output 6 GND 5 Zero Current Detect Input 3 4 (Top View) 1.08 Vref ORDERING INFORMATION + Vref Multiplier Voltage Feedback 1 Input See detailed ordering and shipping information in the package dimensions section on page 17 of this data sheet. Quickstart GND 6 Compensation 2 Figure 1. Simplified Block Diagram © Semiconductor Components Industries, LLC, 2013 August, 2013 − Rev. 14 1 Publication Order Number: MC34262/D MC34262, MC33262 MAXIMUM RATINGS Rating Symbol Value Unit (ICC + IZ) 30 mA Output Current, Source or Sink (Note 1) IO 500 mA Current Sense, Multiplier, and Voltage Feedback Inputs Vin −1.0 to +10 V Zero Current Detect Input High State Forward Current Low State Reverse Current Iin Total Power Supply and Zener Current Power Dissipation and Thermal Characteristics P Suffix, Plastic Package, Case 626 Maximum Power Dissipation @ TA = 70°C Thermal Resistance, Junction−to−Air D Suffix, Plastic Package, Case 751 Maximum Power Dissipation @ TA = 70°C Thermal Resistance, Junction−to−Air mA 50 −10 PD RqJA 800 100 mW °C/W PD RqJA 450 178 mW °C/W Operating Junction Temperature TJ +150 °C Operating Ambient Temperature (Note 4) MC34262 MC33262 TA Storage Temperature Tstg − 65 to +150 °C HBM MM CDM 2000 200 2000 V V V ESD Protection (Note 2) Human Body Model ESD Machine Model ESD Charged Device Model ESD 0 to + 85 − 40 to +105 °C Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect device reliability. 1. Maximum package power dissipation limits must be observed. 2. ESD protection per JEDEC JESD22−A114−F for HBM, per JEDEC JESD22−A115−A for MM, and per JEDEC JESD22−C101D for CDM. This device contains latchup protection and exceeds 100 mA per JEDEC Standard JESD78. ELECTRICAL CHARACTERISTICS (VCC = 12 V (Note 3), for typical values TA = 25°C, for min/max values TA is the operating ambient temperature range that applies (Note 4), unless otherwise noted.) Min Typ Max 2.465 2.44 2.5 − 2.535 2.54 Regline − 1.0 10 mV Input Bias Current (VFB = 0 V) IIB − − 0.1 − 0.5 mA Transconductance (TA = 25°C) gm 80 100 130 mmho Output Current Source (VFB = 2.3 V) Sink (VFB = 2.7 V) IO − − 10 10 − − VOH(ea) VOL(ea) 5.8 − 6.4 1.7 − 2.4 VFB(OV) 1.065 VFB 1.08 VFB 1.095 VFB V IIB − − 0.1 − 0.5 mA Vth(M) 1.05 VOL(EA) 1.2 VOL(EA) − V Characteristic Symbol Unit ERROR AMPLIFIER Voltage Feedback Input Threshold TA = 25°C TA = Tlow to Thigh (VCC = 12 V to 28 V) VFB Line Regulation (VCC = 12 V to 28 V, TA = 25°C) Output Voltage Swing High State (VFB = 2.3 V) Low State (VFB = 2.7 V) V mA V OVERVOLTAGE COMPARATOR Voltage Feedback Input Threshold MULTIPLIER Input Bias Current, Pin 3 (VFB = 0 V) Input Threshold, Pin 2 3. Adjust VCC above the startup threshold before setting to 12 V. 4. Tlow = 0°C for MC34262 Thigh = +85°C for MC34262 = −40°C for MC33262 = +105°C for MC33262. http://onsemi.com 2 MC34262, MC33262 ELECTRICAL CHARACTERISTICS (continued) (VCC = 12 V (Note 6), for typical values TA = 25°C, for min/max values TA is the operating ambient temperature range that applies (Note 7), unless otherwise noted.) Symbol Min Typ Max VPin 3 VPin 2 0 to 2.5 Vth(M) to (Vth(M) + 1.0) 0 to 3.5 Vth(M) to (Vth(M) + 1.5) − − K 0.43 0.65 0.87 1/V Input Threshold Voltage (Vin Increasing) Vth 1.33 1.6 1.87 V Hysteresis (Vin Decreasing) VH 100 200 300 mV Input Clamp Voltage High State (IDET = + 3.0 mA) Low State (IDET = − 3.0 mA) VIH VIL 6.1 0.3 6.7 0.7 − 1.0 Input Bias Current (VPin 4 = 0 V) IIB − − 0.15 −1.0 mA Input Offset Voltage (VPin 2 = 1.1 V, VPin 3 = 0 V) VIO − 9.0 25 mV Vth(max) 1.3 1.5 1.8 V tPHL(in/out) − 200 400 ns VOL − − 9.8 7.8 0.3 2.4 10.3 8.4 0.8 3.3 − − 14 16 18 Characteristic Unit MULTIPLIER Dynamic Input Voltage Range Multiplier Input (Pin 3) Compensation (Pin 2) V Multiplier Gain (VPin 3 = 0.5 V, VPin 2 = Vth(M) + 1.0 V) (Note 8) ZERO CURRENT DETECTOR V CURRENT SENSE COMPARATOR Maximum Current Sense Input Threshold (Note 9) Delay to Output DRIVE OUTPUT Output Voltage (VCC = 12 V) Low State (ISink = 20 mA) Low State (ISink = 200 mA) High State (ISource = 20 mA) High State (ISource = 200 mA) V VOH Output Voltage (VCC = 30 V) High State (ISource = 20 mA, CL = 15 pF) VO(max) Output Voltage Rise Time (CL = 1.0 nF) tr − 50 120 ns Output Voltage Fall Time (CL = 1.0 nF) tf − 50 120 ns VO(UVLO) − 0.1 0.5 V tDLY 200 620 − ms Vth(on) 11.5 13 14.5 V VShutdown 7.0 8.0 9.0 V VH 3.8 5.0 6.2 V − − − 0.25 6.5 9.0 0.4 12 20 30 36 − Output Voltage with UVLO Activated (VCC = 7.0 V, ISink = 1.0 mA) V RESTART TIMER Restart Time Delay UNDERVOLTAGE LOCKOUT Startup Threshold (VCC Increasing) Minimum Operating Voltage After Turn−On (VCC Decreasing) Hysteresis TOTAL DEVICE Power Supply Current Startup (VCC = 7.0 V) Operating Dynamic Operating (50 kHz, CL = 1.0 nF) ICC Power Supply Zener Voltage (ICC = 25 mA) VZ 5. Maximum package power dissipation limits must be observed. 6. Adjust VCC above the startup threshold before setting to 12 V. 7. Tlow = 0°C for MC34262 Thigh = +85°C for MC34262 = −40°C for MC33262 = +105°C for MC33262. Pin 4 Threshold 8. K + VPin 3 (VPin2 * Vth(M)) 9. This parameter is measured with VFB = 0 V, and VPin 3 = 3.0 V. http://onsemi.com 3 mA V VCS, CURRENT SENSE PIN 4 THRESHOLD (V) 1.6 VCC = 12 V TA = 25°C 1.4 1.2 VPin 2 = 3.75 V VPin 2 = 3.5 V 1.0 VPin 2 = 2.75 V VPin 2 = 3.25 V 0.8 VPin 2 = 2.5 V VPin 2 = 3.0 V 0.6 VPin 2 = 2.25 V 0.4 0.2 VPin 2 = 2.0 V 0 -0.2 0.6 1.4 2.2 3.0 3.8 0.08 VPin 2 = 3.75 V VPin 2 = 3.5 V VPin 2 = 3.25 V 0.06 VPin 2 = 3.0 V 0.05 VPin 2 = 2.75 V 0.07 0.02 DVFB(OV), OVERVOLTAGE INPUT THRESHOLD (%VFB) DVFB, VOLTAGE FEEDBACK THRESHOLD CHANGE (mV) VCC = 12 V Pins 1 to 2 0 -4.0 -8.0 -12 25 50 75 100 125 TA, AMBIENT TEMPERATURE (°C) 0 -0.12 0.24 VCC = 12 V 109 108 107 106 -55 -25 0 25 50 75 100 125 TA, AMBIENT TEMPERATURE (°C) Figure 5. Overvoltage Comparator Input Threshold versus Temperature 0 Transconductance 80 VCC = 12 V VO = 2.5 V to 3.5 V RL = 100 k to 3.0 V CL = 2.0 pF TA = 25°C 4.00 V 30 60 60 90 40 120 20 150 0 3.0 k 10 k 30 k 100 k 300 k f, FREQUENCY (Hz) 3.25 V 2.50 V 180 3.0 M 1.0 M VCC = 12 V RL = 100 k CL = 2.0 pF TA = 25°C 0 Phase q, EXCESS PHASE (DEGREES) 120 gm, TRANSCONDUCTANCE (mmho) -0.06 0 0.06 0.12 0.18 VM, MULTIPLIER PIN 3 INPUT VOLTAGE (V) 110 Figure 4. Voltage Feedback Input Threshold Change versus Temperature 100 VPin 2 = 2.0 V 0.01 Figure 3. Current Sense Input Threshold versus Multiplier Input, Expanded View 4.0 0 VPin 2 = 2.25 V 0.03 Figure 2. Current Sense Input Threshold versus Multiplier Input -25 VPin 2 = 2.5 V 0.04 VM, MULTIPLIER PIN 3 INPUT VOLTAGE (V) -16 -55 VCC = 12 V TA = 25°C V/DIV VCS, CURRENT SENSE PIN 4 THRESHOLD (V) MC34262, MC33262 Figure 6. Error Amp Transconductance and Phase versus Frequency 5.0 ms/DIV Figure 7. Error Amp Transient Response http://onsemi.com 4 1.76 800 1.72 700 Voltage Current 600 1.68 1.64 -55 -25 0 25 50 75 TA, AMBIENT TEMPERATURE (°C) 500 125 100 800 VCC = 12 V 700 600 500 400 -55 Figure 8. Quickstart Charge Current versus Temperature Vsat, OUTPUT SATURATION VOLTAGE (V) Vth, THRESHOLD VOLTAGE (V) VCC = 12 V 1.6 1.5 1.4 Lower Threshold (Vin, Decreasing) 1.3 -55 -25 0 25 50 75 TA, AMBIENT TEMPERATURE (°C) 100 125 0 VCC 100 125 VCC = 12 V 80 ms Pulsed Load 120 Hz Rate -2.0 Source Saturation (Load to Ground) -4.0 -6.0 4.0 Sink Saturation (Load to VCC) 2.0 0 GND 0 80 160 240 320 IO, OUTPUT LOAD CURRENT (mA) Figure 11. Output Saturation Voltage versus Load Current VO , OUTPUT VOLTAGE Figure 10. Zero Current Detector Input Threshold Voltage versus Temperature VCC = 12 V CL = 15 pF TA = 25°C 10% 100 ns/DIV Figure 12. Drive Output Waveform 100 mA/DIV I CC , SUPPLY CURRENT VCC = 12 V CL = 1.0 nF TA = 25°C 90% 0 25 50 75 TA, AMBIENT TEMPERATURE (°C) Figure 9. Restart Timer Delay versus Temperature 1.7 Upper Threshold (Vin, Increasing) -25 100 ns/DIV Figure 13. Drive Output Cross Conduction http://onsemi.com 5 5.0 V/DIV Vchg, QUICKSTART CHARGE VOLTAGE (V) VCC = 12 V tDLY, RESTART TIME DELAY (ms) 900 1.80 Ichg, QUICKSTART CHARGE CURRENT (mA) MC34262, MC33262 MC34262, MC33262 14 VCC , SUPPLY VOLTAGE (V) I CC , SUPPLY CURRENT (mA) 16 12 8.0 VFB = 0 V Current Sense = 0 V Multiplier = 0 V CL = 1.0 nF f = 50 kHz TA = 25°C 4.0 0 0 10 20 30 VCC, SUPPLY VOLTAGE (V) 13 Startup Threshold (VCC Increasing) 12 11 10 9.0 Minimum Operating Threshold (VCC Decreasing) 8.0 7.0 -55 40 Figure 14. Supply Current versus Supply Voltage -25 0 25 50 75 TA, AMBIENT TEMPERATURE (°C) 100 125 Figure 15. Undervoltage Lockout Thresholds versus Temperature FUNCTIONAL DESCRIPTION Introduction frequency switching converter for the power processing, with the boost converter being the most popular topology, Figure 18. Since active input circuits operate at a frequency much higher than that of the ac line, they are smaller, lighter in weight, and more efficient than a passive circuit that yields similar results. With proper control of the preconverter, almost any complex load can be made to appear resistive to the ac line, thus significantly reducing the harmonic current content. With the goal of exceeding the requirements of legislation on line−current harmonic content, there is an ever increasing demand for an economical method of obtaining a unity power factor. This data sheet describes a monolithic control IC that was specifically designed for power factor control with minimal external components. It offers the designer a simple, cost−effective solution to obtain the benefits of active power factor correction. Most electronic ballasts and switching power supplies use a bridge rectifier and a bulk storage capacitor to derive raw dc voltage from the utility ac line, Figure 16. Rectifiers Vpk Rectified DC Converter AC Line 0 + Bulk Storage Capacitor Line Sag Load AC Line Voltage Figure 16. Uncorrected Power Factor Circuit 0 This simple rectifying circuit draws power from the line when the instantaneous ac voltage exceeds the capacitor voltage. This occurs near the line voltage peak and results in a high charge current spike, Figure 17. Since power is only taken near the line voltage peaks, the resulting spikes of current are extremely nonsinusoidal with a high content of harmonics. This results in a poor power factor condition where the apparent input power is much higher than the real power. Power factor ratios of 0.5 to 0.7 are common. Power factor correction can be achieved with the use of either a passive or an active input circuit. Passive circuits usually contain a combination of large capacitors, inductors, and rectifiers that operate at the ac line frequency. Active circuits incorporate some form of a high AC Line Current Figure 17. Uncorrected Power Factor Input Waveforms The MC34262, MC33262 are high performance, critical conduction, current−mode power factor controllers specifically designed for use in off−line active preconverters. These devices provide the necessary features required to significantly enhance poor power factor loads by keeping the ac line current sinusoidal and in phase with the line voltage. http://onsemi.com 6 MC34262, MC33262 Operating Description UC3842 series. Referring to the block diagrams in Figures 20, 21, and 22 note that a multiplier has been added to the current sense loop and that this device does not contain an oscillator. The reasons for these differences will become apparent in the following discussion. A description of each of the functional blocks is given below. The MC34262, MC33262 contain many of the building blocks and protection features that are employed in modern high performance current mode power supply controllers. There are, however, two areas where there is a major difference when compared to popular devices such as the Rectifiers PFC Preconverter AC Line + High Frequency Bypass Capacitor Converter + MC34362 Bulk Storage Capacitor Load Figure 18. Active Power Factor Correction Preconverter Error Amplifier can occur during initial startup, sudden load removal, or during output arcing and is the result of the low bandwidth that must be used in the Error Amplifier control loop. The Overvoltage Comparator monitors the peak output voltage of the converter, and when exceeded, immediately terminates MOSFET switching. The comparator threshold is internally set to 1.08 Vref. In order to prevent false tripping during normal operation, the value of the output filter capacitor C3 must be large enough to keep the peak−to−peak ripple less than 16% of the average dc output. The Overvoltage Comparator input to Drive Output turn−off propagation delay is typically 400 ns. A comparison of startup overshoot without and with the Overvoltage Comparator circuit is shown in Figure 24. An Error Amplifier with access to the inverting input and output is provided. The amplifier is a transconductance type, meaning that it has high output impedance with controlled voltage−to−current gain. The amplifier features a typical gm of 100 mmhos (Figure 6). The noninverting input is internally biased at 2.5 V ± 2.0% and is not pinned out. The output voltage of the power factor converter is typically divided down and monitored by the inverting input. The maximum input bias current is − 0.5 mA, which can cause an output voltage error that is equal to the product of the input bias current and the value of the upper divider resistor R2. The Error Amp output is internally connected to the Multiplier and is pinned out (Pin 2) for external loop compensation. Typically, the bandwidth is set below 20 Hz, so that the amplifier’s output voltage is relatively constant over a given ac line cycle. In effect, the error amp monitors the average output voltage of the converter over several line cycles. The Error Amp output stage was designed to have a relatively constant transconductance over temperature. This allows the designer to define the compensated bandwidth over the intended operating temperature range. The output stage can sink and source 10 mA of current and is capable of swinging from 1.7 V to 6.4 V, assuring that the Multiplier can be driven over its entire dynamic range. A key feature to using a transconductance type amplifier, is that the input is allowed to move independently with respect to the output, since the compensation capacitor is connected to ground. This allows dual usage of of the Voltage Feedback Input pin by the Error Amplifier and by the Overvoltage Comparator. Multiplier A single quadrant, two input multiplier is the critical element that enables this device to control power factor. The ac full wave rectified haversines are monitored at Pin 3 with respect to ground while the Error Amp output at Pin 2 is monitored with respect to the Voltage Feedback Input threshold. The Multiplier is designed to have an extremely linear transfer curve over a wide dynamic range, 0 V to 3.2 V for Pin 3, and 2.0 V to 3.75 V for Pin 2, Figures 2 and 3. The Multiplier output controls the Current Sense Comparator threshold as the ac voltage traverses sinusoidally from zero to peak line, Figure 18. This has the effect of forcing the MOSFET on−time to track the input line voltage, resulting in a fixed Drive Output on−time, thus making the preconverter load appear to be resistive to the ac line. An approximation of the Current Sense Comparator threshold can be calculated from the following equation. This equation is accurate only under the given test condition stated in the electrical table. Overvoltage Comparator An Overvoltage Comparator is incorporated to eliminate the possibility of runaway output voltage. This condition VCS, Pin 4 Threshold ≈ 0.65 (VPin 2 − Vth(M)) VPin 3 http://onsemi.com 7 MC34262, MC33262 Current Sense Comparator and RS Latch A significant reduction in line current distortion can be attained by forcing the preconverter to switch as the ac line voltage crosses through zero. The forced switching is achieved by adding a controlled amount of offset to the Multiplier and Current Sense Comparator circuits. The equation shown below accounts for the built−in offsets and is accurate to within ten percent. Let Vth(M) = 1.991 V The Current Sense Comparator RS Latch configuration used ensures that only a single pulse appears at the Drive Output during a given cycle. The inductor current is converted to a voltage by inserting a ground−referenced sense resistor R7 in series with the source of output switch Q1. This voltage is monitored by the Current Sense Input and compared to a level derived from the Multiplier output. The peak inductor current under normal operating conditions is controlled by the threshold voltage of Pin 4 where: VCS, Pin 4 Threshold = 0.544 (VPin 2 − Vth(M)) VPin 3 + 0.0417 (VPin 2 − Vth(M)) Zero Current Detector The MC34262 operates as a critical conduction current mode controller, whereby output switch conduction is initiated by the Zero Current Detector and terminated when the peak inductor current reaches the threshold level established by the Multiplier output. The Zero Current Detector initiates the next on−time by setting the RS Latch at the instant the inductor current reaches zero. This critical conduction mode of operation has two significant benefits. First, since the MOSFET cannot turn−on until the inductor current reaches zero, the output rectifier reverse recovery time becomes less critical, allowing the use of an inexpensive rectifier. Second, since there are no deadtime gaps between cycles, the ac line current is continuous, thus limiting the peak switch to twice the average input current. The Zero Current Detector indirectly senses the inductor current by monitoring when the auxiliary winding voltage falls below 1.4 V. To prevent false tripping, 200 mV of hysteresis is provided. Figure 10 shows that the thresholds are well−defined over temperature. The Zero Current Detector input is internally protected by two clamps. The upper 6.7 V clamp prevents input overvoltage breakdown while the lower 0.7 V clamp prevents substrate injection. Current limit protection of the lower clamp transistor is provided in the event that the input pin is accidentally shorted to ground. The Zero Current Detector input to Drive Output turn−on propagation delay is typically 320 ns. IL(pk ) = Pin 4 Threshold R7 Abnormal operating conditions occur during preconverter startup at extremely high line or if output voltage sensing is lost. Under these conditions, the Multiplier output and Current Sense threshold will be internally clamped to 1.5 V. Therefore, the maximum peak switch current is limited to: Ipk(max) = 1.5 V R7 An internal RC filter has been included to attenuate any high frequency noise that may be present on the current waveform. This filter helps reduce the ac line current distortion especially near the zero crossings. With the component values shown in Figure 21, the Current Sense Comparator threshold, at the peak of the haversine varies from 1.1 V at 90 Vac to 100 mV at 268 Vac. The Current Sense Input to Drive Output turn−off propagation delay is typically less than 200 ns. Timer A watchdog timer function was added to the IC to eliminate the need for an external oscillator when used in stand−alone applications. The Timer provides a means to automatically start or restart the preconverter if the Drive Output has been off for more than 620 ms after the inductor current reaches zero. The restart time delay versus temperature is shown in Figure 9. Peak Undervoltage Lockout and Quickstart Inductor Current An Undervoltage Lockout comparator has been incorporated to guarantee that the IC is fully functional before enabling the output stage. The positive power supply terminal (VCC) is monitored by the UVLO comparator with the upper threshold set at 13 V and the lower threshold at 8.0 V. In the stand−by mode, with VCC at 7.0 V, the required supply current is less than 0.4 mA. This large hysteresis and low startup current allow the implementation of efficient bootstrap startup techniques, making these devices ideally suited for wide input range off−line preconverter applications. An internal 36 V clamp has been added from VCC to ground to protect the IC and capacitor C4 from an overvoltage condition. This feature is desirable if external circuitry is used to delay the startup of the preconverter. The supply current, startup, and operating voltage characteristics are shown in Figures 14 and 15. Average 0 On MOSFET Q1 Off Figure 19. Inductor Current and MOSFET Gate Voltage Waveforms http://onsemi.com 8 MC34262, MC33262 MOSFETs. The Drive Output is capable of up to ±500 mA peak current with a typical rise and fall time of 50 ns with a 1.0 nF load. Additional internal circuitry has been added to keep the Drive Output in a sinking mode whenever the Undervoltage Lockout is active. This characteristic eliminates the need for an external gate pulldown resistor. The totem−pole output has been optimized to minimize cross−conduction current during high speed operation. The addition of two 10 W resistors, one in series with the source output transistor and one in series with the sink output transistor, helps to reduce the cross−conduction current and radiated noise by limiting the output rise and fall time. A 16 V clamp has been incorporated into the output stage to limit the high state VOH. This prevents rupture of the MOSFET gate when VCC exceeds 20 V. A Quickstart circuit has been incorporated to optimize converter startup. During initial startup, compensation capacitor C1 will be discharged, holding the error amp output below the Multiplier threshold. This will prevent Drive Output switching and delay bootstrapping of capacitor C4 by diode D6. If Pin 2 does not reach the multiplier threshold before C4 discharges below the lower UVLO threshold, the converter will “hiccup” and experience a significant startup delay. The Quickstart circuit is designed to precharge C1 to 1.7 V, Figure 8. This level is slightly below the Pin 2 Multiplier threshold, allowing immediate Drive Output switching and bootstrap operation when C4 crosses the upper UVLO threshold. Drive Output The MC34262/MC33262 contain a single totem−pole output stage specifically designed for direct drive of power APPLICATIONS INFORMATION 0.998 at nominal line. Figures 21 and 22 are universal input preconverter examples that operate over a continuous input voltage range of 90 Vac to 268 Vac. Figure 21 provides an output power of 175 W (400 V at 440 mA) while Figure 22 provides 450 W (400 V at 1.125 A). Both circuits have an observed worst−case power factor of approximately 0.989. The input current and voltage waveforms of Figure 21 are shown in Figure 23 with operation at 115 Vac and 230 Vac. The data for each of the applications was generated with the test set−up shown in Figure 25. The application circuits shown in Figures 20, 21 and 22 reveal that few external components are required for a complete power factor preconverter. Each circuit is a peak detecting current−mode boost converter that operates in critical conduction mode with a fixed on−time and variable off−time. A major benefit of critical conduction operation is that the current loop is inherently stable, thus eliminating the need for ramp compensation. The application in Figure 20 operates over an input voltage range of 90 Vac to 138 Vac and provides an output power of 80 W (230 V at 350 mA) with an associated power factor of approximately http://onsemi.com 9 MC34262, MC33262 Table 1. Design Equations Calculation Formula Calculate the maximum required output power. Notes Required Converter Output Power PO = VO IO Calculated at the minimum required ac line voltage for output regulation. Let the efficiency h = 0.92 for low line operation. Peak Inductor Current Let the switching cycle t = 40 ms for universal input (85 to 265 Vac) operation and 20 ms for fixed input (92 to 138 Vac, or 184 to 276 Vac) operation. In theory the on−time ton is constant. In practice ton tends to increase at the ac line zero crossings due to the charge on capacitor C5. Let Vac = Vac(LL) for initial ton and toff calculations. Inductance 2 IL(pk) = t LP = ǒ VO − Vac(LL) 2 Ǔ h Vac(LL)2 2 VO PO Switch On−Time 2 PO LP ton = The off−time toff is greatest at the peak of the ac line voltage and approaches zero at the ac line zero crossings. Theta (q) represents the angle of the ac line voltage. Switch Off−Time The minimum switching frequency occurs at the peak of the ac line voltage. As the ac line voltage traverses from peak to zero, toff approaches zero producing an increase in switching frequency. Switching Frequency f= Set the current sense threshold VCS to 1.0 V for universal input (85 Vac to 265 Vac) operation and to 0.5 V for fixed input (92 Vac to 138 Vac, or 184 Vac to 276 Vac) operation. Note that VCS must be