ON Semiconductor MC34261 MC33261 Power Factor Controllers The MC34261/MC33261 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, a one quadrant multiplier for near unity power factor, zero current detector to ensure critical conduction operation, high gain error amplifier, 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 input undervoltage lockout with hysteresis, cycle-by-cycle current limiting, and a latch for single pulse metering. These devices are available in dual-in-line and surface mount plastic packages. * Internal Startup Timer * One Quadrant Multiplier * Zero Current Detector * Trimmed 2% Internal Bandgap Reference * Totem Pole Output * Undervoltage Lockout with Hysteresis * Low Startup and Operating Current * Pinout Equivalent to the SG3561 * Functional Equivalent to the TDA4817 POWER FACTOR CONTROLLERS SEMICONDUCTOR TECHNICAL DATA P SUFFIX PLASTIC PACKAGE CASE 626 8 1 8 1 Simplified Block Diagram PIN CONNECTIONS Zero Current Detector 5 2.5V Reference Undervoltage Lockout 8 7 Multiplier, Latch, PWM, Timer, & Logic 4 Zero Current Detect Input VCC Voltage Feedback Input Compensation Multiplier Input Current Sense Input Multiplier Gnd 6 Semiconductor Components Industries, LLC, 2001 March, 2001 - Rev. 2 Compensation 8 VCC 2 7 Drive Output 6 Gnd 5 Zero Current Detect Input 3 4 Drive Output ORDERING INFORMATION Current Sense Input Device MC34261P Multiplier Input 3 1 (Top View) MC34261D Error Amp D SUFFIX PLASTIC PACKAGE CASE 751 (SO-8) MC33261D Vref Voltage Feedback 1 Input MC33261P Operating Temperature Range TA = 0 to +70C TA = -40 to +85C Package SO-8 Plastic DIP SO-8 Plastic DIP 2 1 Publication Order Number: MC34261/D MC34261 MC33261 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 mA 50 -10 Power Dissipation and Thermal Characteristics P Suffix, Plastic Package Case 626 Maximum Power Dissipation @ TA = 70C Thermal Resistance, Junction-to-Air D Suffix, Plastic Package Case 626 Maximum Power Dissipation @ TA = 70C Thermal Resistance, Junction-to-Air PD RJA 800 100 mW C/W PD RJA 450 178 mW C/W Operating Junction Temperature TJ +150 C Operating Ambient Temperature (Note 3) MC34261 MC33261 TA Storage Temperature Tstg C 0 to +70 -40 to +85 C -55 to +150 ELECTRICAL CHARACTERISTICS (VCC = 12 V, for typical values TA = 25C, for min/max values TA is the operating ambient temperature range that applies [Note 3], unless otherwise noted.) Characteristic Symbol Min Typ Max Unit 2.465 2.44 2.5 2.535 2.54 - 1.0 10 mV A ERROR AMPLIFIER VFB Voltage Feedback Input Threshold TA = 25C TA = Tlow to Thigh (VCC = 12 V to 28 V) Line Regulation (VCC = 12 V to 28 V, TA = 25C) Regline Input Bias Current (VFB = 0 V) V IIB - -0.3 -1.0 Open Loop Voltage Gain AVOL 65 85 - dB Gain Bandwidth Product (TA = 25C) GBW 0.7 1.0 - MHz Output Source Current (VO = 4.0 V, VFB = 2.3 V) ISource 0.25 0.5 0.75 mA VOH VOL 5.0 - 5.7 2.1 - 2.44 Dynamic Input Voltage Range Multiplier Input (Pin 3) Compensation (Pin 2) VPin 3 VPin 2 0 to 2.5 VFB to (VFB + 1.0) 0 to 3.5 VFB to (VFB + 1.5) - - Input Bias Current (VFB = 0 V) IIB - -0.3 -1.0 A Multiplier Gain (VPin 3 = 0.5 V, VPin 2 = VFB + 1.0 V) (Note 2) K 0.4 0.62 0.8 1/V Input Threshold Voltage (Vin Increasing) Vth 1.3 1.6 1.8 V Hysteresis (Vin Decreasing) VH 40 110 200 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 Output Voltage Swing High State (ISource = 0.2 mA, VFB = 2.3 V) Low State (ISink = 0.4 mA, VFB = 2.7 V) V MULTIPLIER V ZERO CURRENT DETECTOR V NOTES: 1. Maximum package power dissipation limits must be observed. Pin 4 Threshold Voltage 2. K = VPin 3(VPin 2 - VFB) 3. Tlow = -40C for MC34261 3. Tlow = -40C for MC33261 Thigh = +70C for MC34261 Thigh = +85C for MC33261 http://onsemi.com 2 MC34261 MC33261 ELECTRICAL CHARACTERISTICS (VCC = 12 V, for typical values TA = 25C, for min/max values TA is the operating ambient temperature range that applies [Note 3], unless otherwise noted.) Characteristic Symbol Min Typ Max Unit Input Bias Current (VPin 4 = 0 V) IIB - -0.5 -2.0 A Input Offset Voltage (VPin 2 = 1.1 V, VPin 3 = 0 V) VIO - 3.5 15 mV tPHL (in/out) - 200 400 ns VOL - 1.8 9.8 7.8 0.3 2.4 10.3 8.3 0.8 3.3 - 8.8 14 16 18 CURRENT SENSE COMPARATOR 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) V Output Voltage Rise Time (CL = 1.0 nF) tr - 50 120 ns Output Voltage Fall Time (CL = 1.0 nF) tf - 50 120 ns VOH(UVLO) - 0.2 0.8 V tDLY 150 400 - s Vth 9.2 10.0 10.8 V VShutdown 7.0 8.0 9.0 V VH 1.75 2.0 2.5 V - - - 0.3 7.1 9.0 0.5 12 20 30 36 - Output Voltage with UVLO Activated (VCC = 7.0 V, ISink = 1.0 mA) 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 VZ mA V NOTES: 1. Maximum package power dissipation limits must be observed. Pin 4 Threshold Voltage 2. K = VPin 3(VPin 2 - VFB) V CS , CURRENT SENSE THRESHOLD VOLTAGE (V) Figure 1. Current Sense Input Threshold versus Multiplier Input 3.0 2.5 2.0 1.5 1.0 0.5 0 -0.5 -0.5 See Figure 2 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 V CS , CURRENT SENSE THRESHOLD VOLTAGE (V) Thigh = +70C for MC34261 Thigh = +85C for MC33261 3. Tlow = -40C for MC34261 3. Tlow = -40C for MC33261 Figure 2. Current Sense Input Threshold versus Multiplier Input 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0 -0.02 -0.12 VM, MULTIPLIER INPUT VOLTAGE (V) -0.08 -0.04 0 0.04 VM, MULTIPLIER INPUT VOLTAGE (V) http://onsemi.com 3 0.08 0.12 +4.0 Figure 4. Error Amp Open Loop Gain and Phase versus Frequency 100 VCC = 12 V Pins 1 to 2 0 -4.0 -8.0 -12 -16 -55 -25 0 25 50 75 100 125 80 Gain 60 Phase 20 120 150 0 -20 10 100 1.0 k 10 k 100 k 180 10 M 1.0 M f, FREQUENCY (Hz) Figure 6. Error Amp Large Signal Transient Response VCC = 12 V AV = -1.0 TA = 25C VCC = 12 V AV = -1.0 TA = 25C 200 mV/DIV 3.0 V 20 mV/DIV 2.5 V 2.5 V 2.0 V 2.45 V 1.0 s/DIV 0.5 s/DIV Figure 7. Error Amp Output Saturation versus Sink Current Figure 8. Restart Time Delay versus Temperature 5.0 525 VCC = 12 V VFB = 2.7 V TA = 25C 4.0 t DLY , RESTART TIME DELAY ( s) Vsat , OUTPUT SATURATION VOLTAGE (V) 60 90 Figure 5. Error Amp Small Signal Transient Response 3.0 2.0 1.0 0 30 40 TA, AMBIENT TEMPERATURE (C) 2.55 V 0 VCC = 12 V VO = 3.0 V to 3.5 V RL = 100 k TA = 25C , EXCESS PHASE ( C) Figure 3. Voltage Feedback Input Threshold Change versus Temperature A VOL, OPEN LOOP VOLTAGE GAIN (dB) VFB , VOLTAGE FEEDBACK THRESHOLD CHANGE (mV) MC34261 MC33261 0 0.5 1.0 1.5 ISink, OUTPUT SINK CURRENT (mA) 475 425 375 325 275 -55 2.0 http://onsemi.com 4 VCC = 12 V -25 0 25 50 75 TA, AMBIENT TEMPERATURE (C) 100 125 MC34261 MC33261 Figure 10. Output Saturation Voltage versus Load Current 40 0 Vsat , OUTPUT SATURATION VOLTAGE (V) VCC -2.0 VCC = 12 V Upper Threshold (Vin Increasing) 0 -6.0 -20 Lower Threshold (Vin Decreasing) -40 -55 -25 Source Saturation (Load to Ground) -4.0 0 25 50 75 TA, AMBIENT TEMPERATURE (C) 100 Gnd 0 VO , OUTPUT VOLTAGE VCC = 12 V CL = 1.0 nF TA = 25C 10 % 100 ns/DIV 16 Figure 12. Drive Output Cross Conduction VCC = 12 V CL = 15 pF TA = 25C 100 ns/DIV 12 8.0 VFB = 0 V Current Sense = 0 V Multiplier = 0 V CL = 1.0 nF f = 50 kHz TA = 25C 4.0 0 10 20 30 VCC , SUPPLY VOLTAGE (V) 11 12 0 320 Figure 14. Undervoltage Lockout Thresholds versus Temperature Figure 13. Supply Current versus Supply Voltage I CC , SUPPLY CURRENT (mA) 80 160 240 IO, OUTPUT LOAD CURRENT (mA) I CC , SUPPLY CURRENT 90 % Sink Saturation (Load to VCC) 2.0 0 125 Figure 11. Drive Output Waveform 4.0 5.0 V/DIV 20 VCC = 12 V 80 s Pulsed Load 120 Hz Rate 100 mA/DIV V th , THRESHOLD VOLTAGE CHANGE (mV) Figure 9. Zero Current Detector Input Threshold Voltage Change versus Temperature 40 10 9.0 8.0 Minimum Operating Threshold (VCC Decreasing) 7.0 6.0 -55 VCC, SUPPLY VOLTAGE (V) http://onsemi.com 5 Startup Threshold (VCC Increasing) -25 0 25 50 75 TA, AMBIENT TEMPERATURE (C) 100 125 MC34261 MC33261 FUNCTIONAL DESCRIPTION Multiplier Introduction Most electronic ballasts and switching power supplies use a bridge rectifier and a filter capacitor to derive raw dc voltage from the utility ac line. This simple rectifying circuit draws power from the line when the instantaneous ac voltage exceeds the capacitor's voltage. This occurs near the line voltage peak and results in a high charge current spike. 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. The MC34261, MC33261 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. 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. A single quadrant, two input multiplier is the critical element that enables this device to control power factor. The ac 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. A graph of the Multiplier transfer curve is shown in Figure 1. Note that both inputs are extremely linear over a wide dynamic range, 0 V to 3.2 V for the Multiplier input (Pin 3), and 2.5 V to 4.0 V for the Error Amp output (Pin 2). The Multiplier output controls the Current Sense Comparator threshold (Pin 4) as the ac voltage traverses sinusoidally from zero to peak line. This has the effect of forcing the MOSFET peak current to track the input line voltage, thus making the preconverter load appear to be resistive. Pin 4 Threshold 0.62(VPin 2 - VFB)VPin 3 Zero Current Detector The MC34261 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's 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 1.6 V. To prevent false tripping, 110 mV of hysteresis is provided. 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. Device destruction can result if this input is shorted to ground. An external resistor must be used in series with the auxiliary winding to limit the current through the clamps. Operating Description The MC34261, MC33261 contains 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 UC3842 series. Referring to the block diagram in Figure 15, note that a multiplier has been added to the current sense loop and that this device does not contain an oscillator. A description of each of the functional blocks is given below. Error Amplifier A fully compensated Error Amplifier with access to the inverting input and output is provided. It features a typical dc voltage gain of 85 dB, and a unity gain bandwidth of 1.0 MHz with 58 of phase margin (Figure 4). 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 -1.0 A 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 Error Amp output voltage is relatively constant over a given ac line cycle. The output stage consists of a 500 A current source pull-up with a Darlington transistor pull-down. It is capable of swinging from 2.1 V to 5.7 V, assuring that the Multiplier can be driven over its entire dynamic range. Current Sense Comparator and RS Latch The Current Sense Comparator RS Latch configuration 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 R9 in series with the source of output switch Q1. This voltage is monitored by the Current Sense Input and compared to the Multiplier output voltage. The peak inductor current is controlled by the threshold voltage of Pin 4 where: Ipk = http://onsemi.com 6 Pin 4 Threshold R9 MC34261 MC33261 With the component values shown in Figure 16, 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 propagation delay is typically 200 ns. 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 C5 from an overvoltage condition. This feature is desirable if external circuitry is used to delay the startup of the preconverter. Timer Output 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 400 s after the inductor current reaches zero. The MC34261/MC33261 contain a single totem pole output stage specifically designed for direct drive of power 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 pull-down resistor. The totem pole output has been optimized to minimize cross conduction current during high speed operation. The addition of two 10 resistors, one in series with the source output transistor and one in series with the sink output transistor, reduces the cross conduction current, as shown in Figure 12. 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. Undervoltage Lockout An Undervoltage Lockout comparator guarantees 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 10 V and the lower threshold at 8.0 V (Figure 14). In the standby mode, with VCC at 7.0 V, the required supply current is less than 0.5 mA (Figure 13). This hysteresis and low startup current allow the implementation of efficient bootstrap startup techniques, making these devices ideally suited for Table 1. Design Equations Calculation Notes Calculate the maximum required output power. Required Converter Output Power Calculated at the minimum required ac line for regulation. Let the efficiency n = 0.95. Peak Inductor Current Formula PO = VO IO 2 IL(pk) = Let the switching cycle t = 20 s. 2t Inductance 2 PO Vac(LL) VO 2 L = - Vac Vac2 VO Vac(LL) IL(pk) 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 C6. 2 PO L ton = Switch On-Time Vac2 The off-time toff is greatest at peak ac line and approaches zero at the ac line zero crossings. Theta () represents the angle of the ac line voltage. Switch Off-Time The minimum switching frequency occurs at peak ac line and increases as toff decreases. 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 to 276 Vac) operation. Peak Switch Current R9 = Set the multiplier input voltage VM to 3.0 V at high line. Empirically adjust VM for the lowest distortion over the ac line range while guaranteeing startup at minimum line. Multiplier Input Voltage The IIB R1 error term can be minimized with a divider current in excess of 100 A. Converter Output Voltage The bandwidth is typically set to 20 Hz for minimum output ripple over the ac line haversine. ton toff = VO 2 Vac Sin Error Amplifier Bandwidth The following converter characteristics must be chosen: VO - Desired output voltage Vac - AC RMS line voltage Vac(LL) - AC RMS low line voltage IO - Desired output current http://onsemi.com 7 VM = VO = Vref -1 1 ton + toff VCS IL(pk) Vac R7 R3 R2 R1 2 +1 +1 - IIB R2 1 BW = 2 R1 R2 R1 + R2 C1 MC34261 MC33261 Figure 15. 80 W Power Factor Controller C6 1 D2 92 to RFI 138 Vac Filter 100k R8 8 D4 D1 Zero Current Detector D3 1.2V + + 36V + + 16V Timer R Drive Output Delay RS Latch Current Sense Comparator 7.5k R3 100 C5 22k R5 T 10V 10 MUR130 D5 MTP 8N50E Q1 10 7 R6 10 + Error Amp Vref 0.1 R9 1.0nF C3 VO + 230V/ 100 0.35A C4 1.0M R2 330 R4 4 0.5mA 0.01 C2 + UVLO 2.5V Reference 2.2M R7 5 6.7V 1.6V 1N4934 D6 Multiplier 3 11k R1 1 2 6 0.68 C1 Power Factor Controller Test Data DC Output AC Line Input Current Harmonic Distortion (%) Vrms Pin PF THD 2 3 5 7 VO(pp) VO IO PO n(%) 90 85.6 -0.998 2.4 0.11 0.52 1.3 0.67 10.0 230 0.350 80.5 94.0 100 85.1 -0.997 5.0 0.13 1.7 2.4 1.4 10.1 230 0.350 80.5 94.6 110 84.8 -0.997 5.3 0.12 2.5 2.6 1.5 10.2 230 0.350 80.5 94.9 120 84.5 -0.997 5.8 0.12 3.2 2.7 1.4 10.2 230 0.350 80.5 95.3 130 84.2 -0.996 6.6 0.12 4.0 2.8 1.5 10.2 230 0.350 80.5 95.6 138 84.1 -0.995 7.2 0.13 4.5 3.0 1.6 10.2 230 0.350 80.5 95.7 This data was taken with the test set-up shown in Figure 17. T = Coilcraft N2881-A Primary: 62 turns of # 22 AWG Secondary: 5 turns of # 22 AWG Core: Coilcraft PT2510, EE 25 Gap: 0.072 total for a primary inductance of 320 H Heatsink = AAVID Engineering Inc. 5903B, or 5930B http://onsemi.com 8 MC34261 MC33261 Figure 16. 175 W Universal Input Power Factor Controller 1 D2 85 to 265 RFI Vac Filter C6 100k R8 8 D4 D1 Zero Current Detector D3 1.2V + + 36V + + 16V Timer R Drive Output Delay RS Latch 12k R3 22k R5 T 10V 10 MUR460 D5 MTW 14N50E Q1 10 7 R6 10 330 R4 4 Current Sense Comparator 0.5mA 0.01 C2 100 C5 UVLO 2.5V Reference 1.3M R7 + 5 6.7V 1.6V 1N4934 D6 + Error Amp Vref 0.1 R9 1.0nF C3 VO + 400V/ 180 0.44A C4 1.6M R2 Multiplier 3 10k R1 1 2 6 0.68 C1 Power Factor Controller Test Data DC Output AC Line Input Current Harmonic Distortion (%) Vrms Pin PF THD 2 3 5 7 VO(pp) VO IO PO n(%) 90 187.5 -0.998 2.0 0.10 0.98 0.90 0.78 8.0 400.7 0.436 174.7 93.2 120 184.6 -0.997 1.8 0.09 1.3 1.3 0.93 8.0 400.7 0.436 174.7 94.6 138 183.6 -0.997 2.3 0.05 1.6 1.5 1.0 8.0 400.7 0.436 174.7 95.2 180 181.0 -0.995 4.3 0.16 2.5 2.0 1.2 8.0 400.6 0.436 174.7 95.6 240 179.3 -0.993 6.0 0.08 3.7 2.7 1.4 8.0 400.6 0.436 174.7 97.4 268 178.6 -0.992 6.7 0.16 2.8 3.7 1.7 8.0 400.6 0.436 174.7 97.8 This data was taken with the test set-up shown in Figure 17. T = Coilcraft N2880-A Primary: 78 turns of # 16 AWG Secondary: 6 turns of # 18 AWG Core: Coilcraft PT4215, EE 42-15 Gap: 0.104 total for a primary inductance of 870 H Heatsink = AAVID Engineering Inc. 5903B http://onsemi.com 9 MC34261 MC33261 Figure 17. Power Factor Test Set-Up Line 115 Vac Input 2X Step-Up Isolation Transformer RFI Filter HI AC POWER ANALYZER PM 1000 W Autoformer 0 I Neutral Vcf O 7 VA 1 PF Vrms Arms 2 3 11 A T 0.005 1.0 0.1 V 5 0 to 270 Vac Output Power Factor Controller Circuit 0.005 Acf Ainst FREQ HARM 9 HI 13 LO LO Voltech Earth An RFI filter is required for best performance when connecting the preconverter directly to the AC line. Commercially available two stage filters such as the Delta Electronics 03DPCG5 work excellent. The simple single stage test filter shown above can easily be constructed with a common mode transformer. Transformer (T) is a Coilcraft CMT3-28-2 with 28 mH minimum inductance and a 2.0 A maximum current rating. Figure 18. Soft-Start Circuit + Figure 19. Error Amp Compensation To VO 0.5 mA 10A 1 1 2 C + R2 Error Amp + R1 1.0M 2 6 To VCC C1 tSoft-Start 9000C in F Startup overshoot can be eliminated with the addition of a Soft-Start circuit. http://onsemi.com 10 MC34261 MC33261 Figure 20. Printed Circuit Board and Component Layout (Circuits of Figures 15 and 16) http://onsemi.com 11 MC34261 MC33261 OUTLINE DIMENSIONS P SUFFIX PLASTIC PACKAGE CASE 626-05 ISSUE L 8 NOTES: 1. DIMENSION L TO CENTER OF LEAD WHEN FORMED PARALLEL. 2. PACKAGE CONTOUR OPTIONAL (ROUND OR SQUARE CORNERS). 3. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982. 5 -B- 1 4 F -A- NOTE 2 L C J -T- N SEATING PLANE D H M K G 0.13 (0.005) M T A M B M http://onsemi.com 12 DIM A B C D F G H J K L M N MILLIMETERS MIN MAX 9.40 10.16 6.10 6.60 3.94 4.45 0.38 0.51 1.02 1.78 2.54 BSC 0.76 1.27 0.20 0.30 2.92 3.43 7.62 BSC --10 0.76 1.01 INCHES MIN MAX 0.370 0.400 0.240 0.260 0.155 0.175 0.015 0.020 0.040 0.070 0.100 BSC 0.030 0.050 0.008 0.012 0.115 0.135 0.300 BSC --10 0.030 0.040 MC34261 MC33261 OUTLINE DIMENSIONS D SUFFIX PLASTIC PACKAGE CASE 751-07 (SO-8) ISSUE W -X- NOTES: 1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982. 2. CONTROLLING DIMENSION: MILLIMETER. 3. DIMENSION A AND B DO NOT INCLUDE MOLD PROTRUSION. 4. MAXIMUM MOLD PROTRUSION 0.15 (0.006) PER SIDE. 5. DIMENSION D DOES NOT INCLUDE DAMBAR PROTRUSION. ALLOWABLE DAMBAR PROTRUSION SHALL BE 0.127 (0.005) TOTAL IN EXCESS OF THE D DIMENSION AT MAXIMUM MATERIAL CONDITION. A 8 5 0.25 (0.010) S B 1 M Y M 4 K -Y- G C N X 45 SEATING PLANE -Z- 0.10 (0.004) H M D 0.25 (0.010) M Z Y S X S http://onsemi.com 13 J DIM A B C D G H J K M N S MILLIMETERS MIN MAX 4.80 5.00 3.80 4.00 1.35 1.75 0.33 0.51 1.27 BSC 0.10 0.25 0.19 0.25 0.40 1.27 0 8 0.25 0.50 5.80 6.20 INCHES MIN MAX 0.189 0.197 0.150 0.157 0.053 0.069 0.013 0.020 0.050 BSC 0.004 0.010 0.007 0.010 0.016 0.050 0 8 0.010 0.020 0.228 0.244 MC34261 MC33261 Notes http://onsemi.com 14 MC34261 MC33261 Notes http://onsemi.com 15 MC34261 MC33261 ON Semiconductor and are trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice to any products herein. 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