Voltage Regulators AN8032 Active filter control IC ■ Overview Unit: mm 2.4±0.25 6.0±0.3 3.3±0.25 2.54 9 8 0.5±0.1 7 23.3±0.3 6 1.5±0.25 5 1.5±0.25 3 2 1 30° 4 1.4±0.3 In supplying electric power from commercial power supply to various electrical equipment, there is a possibility that the harmonic distortion generated in the power line may give obstruction to the power facilities or other electrical equipment. The use of active filter is one of the methods to solve the harmonic distortion problems. The AN8032 is a monolithic IC which incorporates the control and protection functions into one package so that the active filter can be constructed easily. It is most suitable for the measures against the harmonic distortion problems such as lighting equipment. 0.3 +0.1 –0.05 ■ Features 3.0±0.3 • Self-excited peak current mode is adapted. SIP009-P-0000C • Built-in protection circuit for preventing the overvoltage generated under a small load • Easy constant setting with enlarged dynamic range of multiplier and error amplifier. • Overvoltage protection terminal separately set to pass the short test of the safety standards • Using totem pole output circuit which allows the power MOSFET to be directly driven. • Built-in low voltage protection circuit which ensures the on-resistance during the power MOSFET operation. • Timer circuit is built in for realizing automatic start. ■ Applications • Lighting equipment and switching power supply equipment ■ Block Diagram VBTH One shot Under voltage Over voltage clamper clamper 6 U.V.L.O. comp. 2.5 V VREF Drive 8 OVP comp. 2.6 V 5 Current comp. 1 Error amp. 2 VCC VB 10 V/8 V Timer Multiplier 4 VOUT OVP CS EI 2.5 V 3 EO 7 2.5 V GND MPI 9 1 AN8032 Voltage Regulators ■ Pin Descriptions Pin No. Symbol Description 1 CS Comparator input pin 2 MPI Multiplier input pin 3 EO Error amplifier output pin / multiplier input pin 4 EI Error amplifier inverted-input pin 5 OVP 6 VB 7 GND Grounding pin 8 VOUT Output pin 9 VCC Power supply-voltage pin Overvoltage detection pin Transformer-reset detection pin ■ Absolute Maximum Ratings Parameter Symbol Rating Unit Supply voltage VCC 35 V CS allowable application voltage VCS − 0.5 to +7 V MPI allowable application voltage VMPI − 0.5 to +7 V EI allowable application voltage VEI − 0.5 to +7 V Output allowable current IO ±150 mA Peak output current IOP ±1 A VB allowable flow-in current IBI +5 mA VB allowable flow-out current IBO −5 mA PD 874 mW Topr −30 to +85 °C Tstg −55 to +150 °C Power dissipation Operating ambient temperature Storage temperature * * Note) *: Expect for the operating ambient temperature and storage temperature, all ratings are for Ta = 25°C. ■ Recommended Operating Range Parameter Supply voltage Symbol Range Unit VCC 0 to 34 V ■ Electrical Characteristics at Ta = 25°C Parameter 2 Symbol Conditions Min Typ Max Unit 2.35 2.50 2.65 V Error detection feedback threshold voltage 1 VEITH1 Error detection low-level output voltage VEOL IEO = 0 mA, VEI = 5 V 1.0 1.6 V Error detection high-level output voltage VEOH IEI = 0 mA, VEI = 0 V 5.0 5.7 V Error detection input bias current IEI VEI = 0 V − 0.3 −1.0 µA Error detection output supply current IEO VEI = 0 V, VEO = 1 V 0.25 0.50 0.75 mA Voltage Regulators AN8032 ■ Electrical Characteristics (continued) at Ta = 25°C Parameter Symbol Conditions Min Typ Max Unit Multiplier input D-range (upper limit) VMPIH VEO = 5 V 4.0 4.5 V Multiplier output D-range (upper limit) VMPOH VEO = 5 V 4.8 5.4 V 1.0 1.2 1.4 1/V −1.5 −3.0 µA Multiplier gain GMP Multiplier input bias current IMPI Coil detection input threshold voltage VBTH 1.2 1.5 1.8 V Coil detection hysteresis width dVB 50 100 200 mV Coil detection high-level clamp voltage VBH IB = 5 mA 7.0 7.5 8.0 V Coil detection low-level clamp voltage VBL IB = −5 mA − 0.3 − 0.2 0 V 3.5 15 mV − 0.5 −2.0 µA VOVP 2.45 2.60 2.75 V 70 100 130 mV VMPI = 0 V Current detection input offset voltage VCSOFF Current detection input bias current Overvoltage detection input threshold voltage VOVP − VEITH1 ICS VCS = 0 V Low-level output voltage VOUTL IOUT = 100 mA 0.9 1.5 V High-level output voltage VOUTH IOUT = −100 mA 9.2 10.2 V 0.8 1.5 V Standby output voltage VOUTSTB IOUT = 10 mA U.V.L.O. start voltage VCCST 9.2 10.0 10.8 V U.V.L.O. stop voltage VCCSP 7.0 8.0 9.0 V U.V.L.O. start - stop voltage difference dVCC dVCC = VCCST − VCCSP 1.75 2.00 2.50 V Standby current ICCSTB VCC = 7 V 40 80 120 µA ICC VCC = 12 V 6.0 10.0 mA Max Unit 2.7 V Operation current without load • Design reference data Note) The characteristics listed below are reference values based on the IC design and are not guaranteed. Parameter Error detection feedback threshold voltage 2 Symbol VEITH2 Conditions Ta = −25°C to +85°C Min Typ 2.3 Error detection open-loop gain GAV 85 dB Error detection gain band width fBW 1.0 MHz Multiplier input D-range (lower limit) VMPIL VEO = 5 V 0 V Multiplier output D-range (lower limit) VMPOL VEO = 5 V 0 V Current detection − output delay tdCS 200 ns Overvoltage detection − output delay tdOVP 500 ns Output rise time tr VCC = 12 V, VOUT = 10% → 90% 50 ns Output fall time tf VCC = 12 V, VOUT = 90% → 10% 50 ns Timer delay time tdTIM 400 µs 3 AN8032 Voltage Regulators ■ Terminal Equivalent Circuits Pin No. Equivalent circuit 1 Description Approx. 7.1 V To high-speed converter 1 2 Approx. 7.1 V I/O CS: The input terminal of comparator which detects the current value flowing in power MOSFET. The output level of multiplier and the current value of power MOSFET input from the CS terminal are compared. If the later becomes larger than the former, the VOUT is set to low level and the power MOSFET ouput is cut. I MPI: The input terminal of multiplier The voltage after a full-wave rectified AC input voltage are monitored. I EO: The output terminal of error amplifier / the input terminal of multiplier. The error amplifier monitors the output voltage of active filter and amplifies its error portion and outputs to the multiplier. Therefore, this terminal serves as another input terminal of the multiplier. O EI: The inverted input terminal of error amplifier the overvoltage protection input terminal. To the noninverted input terminal, the internal reference voltage of IC (2.5 V typ.) is input. I OVP: Overvoltage detection pin It is an input terminal with over-voltage detection function which can detect the overvoltage of the output voltage to shut off the power MOSFET. I 2 3 Approx. 7.1 V Approx. 7.1 V Error amplifier output Multiplier input 3 4 Approx. 7.1 V Approx. 7.1 V 4 Error amplifier input 5 Approx. 7.1 V Approx. 7.1 V Overvoltage protection input 4 5 Voltage Regulators AN8032 ■ Terminal Equivalent Circuits (continued) Pin No. Equivalent circuit 6 PVCC Approx. 7.1 V Approx. 7.1 V Upper limit voltage clamp 6 Lower limit voltage clamp VB Comparator input 7 Power system ground 7 Signal system ground 8 9 Description I/O VB: The terminal is connected via the transformer's sub-coil and resistor. The reset of transformer is detected and the trigger signal to turn on the power MOSFET is sent. Since the coil signal of transformer is input as current, the IC incorporates the circuit which clamps the upper/lower limit voltage to prevent malfunction. I GND: Grounding terminal This terminal is used in common for grounding the control system and the power system. VOUT: The output terminal. It is capable of driving the gate of power MOSFET directly. O VCC: The supply voltage terminal. The supply voltage terminal for the power system and that for the signal system are put together as one terminal with internal connection in order to greatly decrease the common impedance. This double-functioning terminal monitors the supply voltage, and has start/stop operation threshold. 8 9 9 U.V.L.O. VB Upper limit voltage clamp Inside bias (Appox. 7.1 V) Power MOSFET drive block 5 AN8032 Voltage Regulators ■ Application Notes [1] PD Ta curve of SIP009-P-0000C PD T a 1 000 900 874 Power dissipation PD (mW) 800 Independent IC without a heat sink Rth( j−a) = 143°C/W PD = 874 mW (25°C) 700 600 500 400 300 200 100 0 0 25 50 75 85 100 125 150 Ambient temperature Ta (°C) [2] Operation descriptions 1. Normal control 1) Application outline As shown in figure 1, the standard application of the AN8032 is a booster chopper circuit, which inputs the voltage rectified from the commercial supply of 100 V/200 V (A in figure 1) and outputs the DC voltage of 400 V (B in figure 1). It controls so that the input current proportional to the input voltage (C, D in figure 1) could be flown. The reason for selecting the output voltage of 400 V is that the withstanding voltage of components and the operation limitation of booster chopper (input voltage < output voltage) under the worldwide input voltage are taken into consideration. Booster circuit so that set at: EIN(max) < EOUT A. Voltage after rectification (EIN) E D. Input current (IIN) B. Output voltage (EOUT) IN(max) 0A 400 VDC 0V 0V Active filter IIN Input current proportional to input voltage flows. EIN EOUT Output C. Input voltage (VIN) Commercial power supply (AC) VIN Diode bridge AN8032 SBD Input 0V Booster chopper circuit Figure 1. Application outline description 6 Load Voltage Regulators AN8032 ■ Application Notes (continued) [2] Operation descriptions (continued) 1. Normal control (continued) 2) Control outline description (Refer to figure 2 and figure 3.) (1) Input voltage (EIN) detection The voltage which is divided from the input voltage of chopper circuit (EIN) by using the external resistor is input to the multiplier input terminal of the AN8032 (MPI terminal). (2) Output voltage (EOUT) detection The voltage which is divided from the output voltage of chopper circuit (EOUT) by using the external resistor is amplified by the error amplifier of the AN8032 (Input to noninverting input terminal (EI terminal)) and input to another multiplier input (EO terminal, which also functions as output for error amplifier). (3) Multiplication of input voltage and output voltage The signals input to the multiplier are multiplied and outputted from the multiplier. This output is a signal which monitors both the input voltage and output voltage of the chopper circuit. MPI input voltage 0V Time Approx. 2.5 V typ. EI input voltage 0V Time Multiplier output (MPO) voltage 0V Enlarged Time Power MOS turned off Multiplier output (MPO) voltage Power MOSFET current detection (CS) voltage 0V Power MOS turned off Time VB lower limit voltage (regulated inside IC) Transformer reset voltage detection (VB) Power MOS turned on = bias coil voltage generated Reset operation of transformer = bias coil voltage inversion VB lower limit voltage (regulated inside IC) 0V Time Figure 2. Explanation of normal control operation 7 AN8032 Voltage Regulators ■ Application Notes (continued) [2] Operation descriptions (continued) 1. Normal control (continued) 2) Control outline description (Refer to figure 2 and figure 3.) (continued) EIN (4) Switching device current The voltage generated in the current detection resistor which is connected to the switching device (power MOSFET) is detected at the CS terminal. (for the above resistor, low resistance value is selected, considering the power dissipation). (5) Switching device turn-off The CS terminal voltage and the multiplier output voltage are compared by the current detection comparator. When the former value becomes larger than the latter one, the current detection comparator sends the reset signal to the RS latch circuit to turn off the switching device. (6) Output current supply When the switching device is turned off, the current flowing in the transformer is cut off. The diode is turned-on with inertia current of inductor, and supplies a current to the output of chopper circuit (EOUT). Power MOS → On Lower limit voltage clamp VBTH Upper limit voltage clamp Power MOS → Off 9 VCC 6 VB One shot Turn-on signal VREF 2.5 V 10 V/8 V Low voltage protection EOUT Timer Latch circuit Drive SBD 8 VOUT Power MOSFET 2.6 V 5 OVP Overvoltage detection 1 CS Input voltage monitor Turn-off signal Current detection comparator 4 EI Error amp. MPI 2 Multiplier EO 3 GND 7 2.5 V 2.5 V Current detection resistor Figure 3. Explanation of block diagram and normal operation (7) Transformer reset signal (VB) detection When the excitation energy has been discharged and the inertia current of the inductor has been lost, the transformer starts resonance with the frequency which depends on parasitic capacitance of the board or parts and inductance of the inductor. This operation is detected at the VB terminal through sub-coil of the transformer. 8 Voltage Regulators AN8032 ■ Application Notes (continued) [2] Operation descriptions (continued) 1. Normal control (continued) 2) Control outline description (Refer to figure 2 and figure 3.) (continued) (8) Switching device turn-on By resonance, the turn-on signal is sent to the switching device, timed with the sub-coil voltage when it swings from high to low. (9) Continuation of operation When the switching device is turned on, current flows in the inductor so that the above operation is repeated. <Summary> • When the excitation energy of inductor is lost and the free resonance is started, the switching device turns on. • The switching device will turn off when the following two elements cross each other: The product of the input voltage (EIN) and output one (EOUT) of the chopper circuit, and the switching device current. • The fluctuation of input voltage and load current is controlled by changing the peak value height of switching device current. • The purposes of mixing two signals by using the multiplier are: to stabilize the control system to reduce the number of components required 3) Description of each function (1) VB • Function It detects the discharge of the excitation energy of the inductor (reset operation) and turns on the power MOSFET at the next cycle. • Method When the inductor is reset, the sub-coil provided on the inductor (bias winding) starts free resonance. It is difficult from the view point of withstanding voltage to input this voltage directly to the IC. For this reason, it is input to the VB terminal through resistor. • Function of upper limit voltage clamper It prevents the damage when the VB terminal voltage exceeds the withstanding voltage. Function of lower limit voltage clamper It prevents the malfunction when the VB terminal voltage swings to negative voltage: generally, in the case of monolithic IC, malfunction (such as latch-up) occurs when the terminal voltage decreases to a value below -VBE and the parasitic device is activated. • IC inside The VB terminal voltage is input to the comparator with hysteresis inside the IC. For this reason, if the VB terminal voltage is under the threshold value, the power MOSFET is turned on. However, if the off signal has been given to the power MOSFET by the overvoltage protection function, this function precedes the former. Power MOSFET OFF ON OFF VB terminal input voltage VBTH (1.5 V typ.) 0V Figure 4. VB terminal description 9 AN8032 Voltage Regulators ■ Application Notes (continued) [2] Operation descriptions (continued) 1. Normal control (continued) 3) Description of each function (continued) (1) VB (continued) ID SDB VB lower limit voltage clamp current IDS ID VB upper limit voltage clamp current VCC Time VB Clamp upper limit voltage VB AN8032 Lower limit voltage clamp IDS Upper limit voltage clamp VB threshold value VB Time Clamp upper limit voltage GND Reset operation of inductor Figure 5. Explanation of VB operation <Setting the VB terminal constant> • Regulation by clamper in/out-current value The allowable output current of the upper limit voltage clamper is −5 mA and the allowable input current of the lower limit voltage clamper is +5 mA. Either one of these allowable values is exceeded, the voltage clamp operation of the VB terminal is not guaranteed. Therefore, RB should be set so that these values are not exceeded. • Consumption current and delay When the RB value is too large, the VB threshold could be exceeded. When the RB value is too small, the consumption current becomes too large. In order to determine the RB value properly, the input voltage range and the dispersion of components should be taken into consideration and it should be confirmed that a stable operation can be ensured under start/overload conditions or under a small load condition. 10 ±5 mA or less AN8032 VB RB RB too large: Consumption current becomes small, however, TOFF is extended by the delay amount because of low speed. RB too small: Speed is high, however, consumption current is small and undershoot tends to be generated easily. Voltage Regulators AN8032 ■ Application Notes (continued) [2] Operation descriptions (continued) Delay capacitor 1. Normal control (continued) 3) Description of each function (continued) AN8032 (1) VB (continued) <Setting the VB terminal constant> (continued) • Zero-cross switching Zero-cross switching can be realized by using the local resonance when turning on the power MOSFET in order to suppress the loss. By connecting the resonance capacitor CP between the drain and source of the power MOSFET, and using the inductance of the transformer's primary side LP, the resonance is produced after discharging the accumulated energy of the transformer. The capacitor for delay should be connected to the VB terminal so that the next turn-on could occur at the time when the resonance occurred and the drain voltage of the power MOSFET has reached around 0 V. However, it is necessary to take care that the zero-cross conditions could deviate since the delay amount varies depending on the conditions such as the input voltage. LP A B VB RB CB VOUT CP Resonance capacitor Resonance by LP − CP A-point voltage Zero-cross switching 0V B-point voltage VBTH 0V Delay Power MOSFET On (2) CS Power MOSFET Off The terminal for detecting the current when the power MOSFET is turned on. The current flow when the power MOSFET is turned on is equivalent to the current flow in the inductor. Therefore, the necessary power value can be controlled by controlling the peak value of the above current. The input D-range of this terminal is from 0 V to 5 V. However, since dissipation becomes larger if the power MOSFET current detecting resistance is set at larger value. A value from 0.22 Ω to 0.47 Ω is the standard considering the relationship with the S/N. The charge and discharge current to and from the parasitic capacitance of the power MOSFET, transformer or printed circuit wiring flow in the power MOSFET detection resistor at turning-on and off. Since such current generates noise and causes malfunction, it is necessary to incorporate a filter to remove such irregular element. Parasitic capacitance Spike VB Filter ICS 0A Spike Figure 6. CS terminal explanation (3) MPI The MPI is the terminal for monitoring the AC input voltage. The voltage which is resistance-divided from the input voltage after full-wave rectification is input. The input D-range of the multiplier is from 0 V to 4.5 V typical and output D-range is from 0 V to 5.4 V typical. 11 AN8032 Voltage Regulators ■ Application Notes (continued) [2] Operation description (continued) 1. Normal control (continued) 3) Description of each function (continued) (4) EI/EO The resisitance-devided voltage of the active filter output is input to the EI. The EI is the error amplifier's inverted input, and the temperature-compensated reference voltage (2.5 V typical) is input as the noninverted input. The error amplifier amplifies the error amount between the output voltage, and the reference voltage and outputs to the multiplier. The resistor between the EI and EO is used for determining the gain of error amplifier. As for the resistance-dividing for decreasing the active filter's output voltage to the input D-range of EI, if an attempt is made to use a small-sized resistor for suppressing the dissipation, its resistance value becomes high because of the high output voltage. For this reason, note that if the capacitance inserted between the EI and EO for phase compensation is large, the delay element between it and the resistancedivider of high resistance becomes large, so that the characteristics at the time of sudden change of load (overshoot or undershoot) is degraded. Therefore, as the value for phase compensation capacitor, select the minimum value with which the oscillation can be prevented. Output Error amplifier 4 EI SBD To multiplier EO 3 Reference voltage (2.5 V typ.) Resistor determining the gain Phase compensation capacitor Figure 7. EI/EO terminal description (5) VOUT For the drive circuit, the AN8032 employs the totem pole type by which the power MOSFET can be directly driven. Since the peak output current is ±1 A, the TO-220 class power MOSFET can be driven. For the TOP-3 class, the buffer circuit should be added outside because its capability is not sufficient for that class. The power MOSFET momentarily swings to minus due to the parasitic capacitance between the drain and gates at the time of turn-off and this causes malfunction in some cases. Therefore, the Schottky barrier diode should be inserted between the VOUT and GND if necessary. Power MOSFET On VD PVCC Totem pole type output circuit Off Parasitic capacitance 0V VOUT Capacitive coupling VD VG VG GND 0V Swing to negative voltage Figure 8. VOUT terminal description 12 Voltage Regulators AN8032 ■ Application Notes (continued) [2] Operation descriptions (continued) 1. Normal control (continued) 3) Description of each function (continued) (6) VCC The supply voltage terminal other than the output. The U.V.L.O. depends on this VCC voltage. (The characteristics of U.V.L.O. are shown in the right figure.) ICC IC operation U.V.L.O. characteristics 0 8 10 VCC V (Stop voltage) (Start voltage) <Notes on the methods of providing VCC> • The method to give bias from sub-coil There is only 2 V typical difference between the start voltage 10 V typical and the stop voltage 8 V typical. Be careful that the value for C1 shown in the right figure must be set at a large value, otherwise, the IC does not easily start. • Giving bias from power supply In the case such as of fluorescent lamp inverter circuit, separate power supply is provided so as to give the bias from the separate power supply. Start resistance R1 VCC AN8032 VOUT GND VCC AN8032 GND <VCC interference> For the AN8032, the following method is used to suppress the interference between the two power supply lines : The supply voltage supply line of the power system and that for the signal line are separately provided in the IC chip and they are put together when wired to the pin of the package. Thus the interference between 2 power supply lines is suppressed. The same method is also used for the GND line. However, the above method can not prevent all the malfunctions due to noise. Therefore, in regard to the current pass in which the drive current of the power MOSFET flows, the pattern wiring should be provided as short as possible, in the same way as conventional practice to suppress the invasion of noise of the drive system. C1 To fluorescent lamp inverter circuit block C1 Totem pole type output circuit PVCC R1 Drive current at turning on VOUT R2 Drive current at turning off GND 13 AN8032 Voltage Regulators ■ Application Notes (continued) [2] Operation descriptions (continued) 2. Protection circuit 1) Timer In control of this IC, the chopper circuit does not start unless the first on-signal is input to the switching device. The chopper circuit does not re-start, if the turn-on timing of switching device is missed due to some abnormality. For the above reasons, this IC is incorporating the timer circuit and generating the start pulse once in every approx. 400 µs (typical) when the chopper circuit stops, eliminating the need for an external part to cope with this problem. (Refer to figure 9.) However, in order to prevent the output rise of the chopper circuit, the timer circuit does not operate as long as the overvoltage protector is operating. When operation start Timer trigger signal (signal inside the IC) Input voltage applied operation start One-shot pulse 0A Time 400 µs typ. Input voltage Power MOSFET current 0V Time Start When abnormal stop Timer start Timer trigger signal (signal inside the IC) One-shot pulse 400 µs typ. 0A Time Input voltage Power MOSFET current 0V Time Abnormal stop Figure 9. Explanation of timer operation 14 Re-start Voltage Regulators AN8032 ■ Application Notes (continued) [2] Operation descriptions (continued) 2. Protection circuit (continued) 2) Overvoltage protection (1) Cause of overvoltage In the booster chopper circuit, control is carried out so that the input power becomes zero when the load current reaches zero. However, in the actual condition, the input power can not be decreased to zero. The output voltage is brought to out of control state, so that it rises. The cause of the out-of-control condition is that there is a delay time from the turn-on to the turn-off of the switching device, so that the control to stop the operation of switching device becomes impossible. (Refer to figure 10.) In order to prevent the occurrence of such problem, the AN8032 has the built-in overvoltage protection circuit, so that the number of component to be added to the external part is drastically reduced. Power MOS off-time current Power MOS on-time current Input voltage Under light load SBD AN8032 Output voltage Under no load condition, this voltage decreases to around 0 V. At this time, the frequency of power MOS current rises, however, there is circuit delay, so that the current does not reach 0 A. Multiplier output Power MOS on-time current Power MOS off-time current 0A Time 0A Time Under light load Multiplier output Power MOS on-time current Power MOS off-time current Figure 10. Explanation of operation 15 AN8032 Voltage Regulators ■ Application Notes (continued) [2] Operation descriptions (continued) 2. Protection circuit (continued) 2) Overvoltage protection (continued) (2) Description of overvoltage protector operation With respect to the AN8032 IC, the input of the error amplifier which detects the output voltage is provided separately from the input of the overvoltage protection comparator. This is the point which differs from the AN8031. Each setting is shown as follows: • Control reference voltage of the error amplifier: 2.50 V typical • Detection voltage of the overvoltage comparator: 2.63 V typical [Without hysteresis] (Voltage of 5% higher than the control reference voltage of the error amplifier) If the output voltage becomes more than 5% higher than the normal control voltage at the time of start up or abnormality occurrence, the overvoltage comparator operates to cut off the switching device. The timer circuit is cut off when overvoltage is detected. This prevents the output voltage to increase further. Otherwise, the timer circuit will re-start the power MOSFET, and actuate it to increase the output voltage further at the time of the overvoltage detection. Therefore, under no load condition, the output voltage of the chopper circuit is stabilized at the value which is 5% higher than the normal control voltage and does not exceed that value. (Refer to figure 11.) The increase/decrease of the output voltage is created by the offset amount of the overvoltage comparator. Stabilized at 5% higher voltage Output voltage of active filter Created by offset amount of overvoltage comparator 420 V 400 V Power MOSFET current 0A Operation condition of active filter Time Operating Stop Operating Stop Figure 11. Protection of overvoltage protection operation 16 Voltage Regulators AN8032 ■ Application Notes (continued) [2] Operation descriptions (continued) 2. Protection circuit (continued) 2) Overvoltage protection (continued) (3) Output voltage overshoot at start At operation start, the output overload condition is created because the smoothing capacitor which is connected to the output is charged. Under this condition the chopper circuit operates with full power. However, it does not immediately come out of the full-power-operation (due to control delay of the entire feedback system) even when the proper output voltage is obtained, causing the overshoot of output voltage. The AN8032 overvoltage protector operates even at operation starts and prevents the worst cases such as damage of used parts. (Refer to figure 12.) Overvoltage protector operation Operation start Overvoltage condition Set output voltage Output voltage of active filter 0A Time Start under output short-circuit condition → Current peak value is high Power MOSFET current 0A Time Operation condition of active filter Operating Stop Operating Figure 12. Output voltage overshoot when operation starts 17 AN8032 Voltage Regulators ■ Application Notes (continued) [3] Difference between the AN8031 and the AN 8032 AN8031 → EI terminal is used in common for both the output voltage monitor function and the overvoltage detection function. AN8032 → Exclusive-use terminal for each function (VCC terminal is used in common for both PVCC and VCC). EI terminal : Exclusively used for the output voltage monitor function. OVP terminal : Exclusively used for the overvoltage detection function. 1) Reasons for change The excessively large overvoltage, generated when the short-circuit test between the pins of the active filter output voltage monitoring resistor, can not be suppressed. EIN(+) VOUT MPI Output voltage monitor EIN(−) EO(+) VCC PVCC VB SBD Separately require 5 to 10 external components EI Overvoltage detection EO CS COM AN8031 Excessively large overvoltage, generated when the short circuit testing, can not be suppressed. EO(−) 2) Countermeasures The output voltage system and the overvoltage detection system are separated from each other. SBD EO(+) EIN(+) VCC VB Increase of 2 more external components VOUT MPI Output voltage monitor EIN(−) AN8032 COM Overvoltage detection EI EO OVP CS The control operation is stopped by the separately provided circuit for overvoltage system even if excessively large overvoltage is generated. EO(−) Note) The OVP terminal is arranged beside the EI terminal after taking the board pattern design into consideration. 18 C1 L1 − + R2 13 kΩ C4 10 µF B C R3 10 kΩ L2 R4 12 Ω D R6 0.33 Ω 1W VOUT 8 VCC 9 4 EI 5 OVP 1 CS SBD E R9 10 kΩ R8 1.5 MΩ C7 0.1 µF C3 47 µF C6 0.001 µF R7 330 Ω SBD G R12 10 MΩ F R11 10 kΩ VCC 12 V COM R10 1.5 MΩ EO(DC 400 V) • Application circuit C5 0.01 µF MPI 2 R1 1 MΩ A Load COM C2 1 µF EI Voltage Regulators AN8032 ■ Application Circuit Example 3 EO 7 GND VB 6 19 AN8032 Voltage Regulators ■ Application Circuit Example (continued) • Normal operation waveforms Horizontal axis 1 ms/div 10 ms/div Measuring point 140 V 20 V/div 20 V/div 140 V A (EIN) B (MPI) 0.4 V/div 0V 0V 2V 0V 1 V/div 12 V 2 V/div 12 V 0V 0V 0.8 V 0.8 V 0V 0V 50 V/div 500 V G (EO) 100 V 20 0V 2.5 V 0.5 V/div 0.5 V/div 2.5 V F (EI) 0.2 V/div E (CS) 0V 2 V/div D (VOUT) 7V 0V 0.2 V/div C (VB) 1 V/div 7V 0V Voltage Regulators AN8032 ■ Application Circuit Example (continued) • Waveforms at start Horizontal axis 20 ms/div Measuring point E (CS) 0.2 V/div 1.2 V 0V G (EO) 50 V/div 400 V 100 V • Waveforms at stop Horizontal axis 20 ms/div Measuring point 0.8 V 0.2 V/div E (CS) 0V G (EO) 50 V/div 400 V 100 V (Conditions) • Input voltage : 100 V (AC) • Output voltage : 400 V (DC) • Output current : 200 mA (resistive load 2 kΩ) 21