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Voltage Regulators
AN8031
Active filter control IC
s Overview
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 AN8031 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.
6.0±0.3 2.4±0.25 3.3±0.25
Unit: mm
8
0.5±0.1
7
23.3±0.3
6 5 4
1.5±0.25 1.5±0.25 1.4±0.3
3.0±0.3
2 1
0.3 +0.1 0.05
s Features
· 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. · 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.
s Applications
· Lighting equipment and switching power supply equipment
s Block Diagram
Under voltage Over voltage clamper clamper One shot 2.5 V VREF U.V.L.O. comp. 10 V/8 V 9 Timer
Drive
1 6
SVCC VB
PVCC VOUT
8
Current comp. 3
OVP comp. 2.6 V 2 Error amp. Multiplier 2.5 V 2.5 V 5 CS EI
MPI
7
GND
EO
4
30°
3
2.54
9
1
AN8031
s Pin Descriptions
Pin No. 1 2 3 4 5 6 7 8 9 Symbol SVCC CS MPI EO EI VB GND VOUT PVCC Description Control system supply-voltage pin Comparator input pin Multiplier input pin Error amplifier output pin / multiplier input pin
Voltage Regulators
Error amplifier inverting input pin / overvoltage protection input pin Transformer-reset detection pin Grounding pin Output pin Power system supply-voltage pin
s Absolute Maximum Ratings
Parameter Supply voltage CS allowable application voltage MPI allowable application voltage EI allowable application voltage Output allowable current Peak output current VB allowable flow-in current VB allowable flow-out current Power dissipation Operating ambient temperature Storage temperature
* *
Symbol VCC VCS VMPI VEI IO IOP IBI IBO PD Topr Tstg
Rating 35 - 0.5 to +7 - 0.5 to +7 - 0.5 to +7 ±150 ±1 +5 -5 874 -30 to +85 -55 to +150
Unit V V V V mA A mA mA mW °C °C
Note) *: Expect for the operating ambient temperature and storage temperature, all ratings are for Ta = 25°C.
s Recommended Operating Range
Parameter Supply voltage Symbol VCC Range 0 to 34 Unit V
s Electrical Characteristics at Ta = 25°C
Parameter Error detection feedback threshold voltage 1 Error detection low-level output voltage Error detection high-level output voltage Error detection input bias current Error detection output supply current 2 Symbol VEITH1 VEOL VEOH IEI IEO IEO = 0 mA, VEI = 5 V IEI = 0 mA, VEI = 0 V VEI = 0 V VEI = 0 V, VEO = 1 V Conditions Min 2.35 5.0 0.25 Typ 2.50 1.0 5.7 - 0.3 0.50 Max 2.65 1.6 -1.0 0.75 Unit V V V µA mA
Voltage Regulators
s Electrical Characteristics (continued) at Ta = 25°C
Parameter Symbol VEO = 5 V VEO = 5 V VMPI = 0 V Conditions Min 4.0 4.8 1.0 1.2 50 IB = 5 mA IB = -5 mA VCS = 0 V 7.0 - 0.3 2.45 70 IOUT = 100 mA IOUT = -100 mA 9.2 9.2 7.0 dVCC = VCCST - VCCSP VCC = 7 V VCC = 12 V 1.75 40 Typ 4.5 5.4 1.2 -1.5 1.5 100 7.5 - 0.2 3.5 - 0.5 2.60 100 0.9 10.2 0.8 10.0 8.0 2.00 80 6.0
AN8031
Max 1.4 -3.0 1.8 200 8.0 0 15 -2.0 2.75 130 1.5 1.5 10.8 9.0 2.50 120 10.0
Unit V V 1/V µA V mV V V mV µA V mV V V V V V V µA mA
Multiplier input D-range (upper limit) VMPIH Multiplier output D-range (upper limit) VMPOH Multiplier gain Multiplier input bias current Coil detection input threshold voltage Coil detection hysteresis width Coil detection high-level clamp voltage Coil detection low-level clamp voltage GMP IMPI VBTH dVB VBH VBL
Current detection input offset voltage VCSOFF Current detection input bias current Overvoltage detection input threshold voltage VOVP - VEITH1 Low-level output voltage High-level output voltage Standby output voltage U.V.L.O. start voltage U.V.L.O. stop voltage U.V.L.O. start - stop voltage difference Standby current Operation current without load · Design reference data ICS VOVP VOUTL VOUTH
VOUTSTB IOUT = 10 mA VCCST VCCSP dVCC ICCSTB ICC
Note) The characteristics listed below are reference values based on the IC design and are not guaranteed.
Parameter Error detection feedback threshold voltage 2 Error detection open-loop gain Error detection gain band width
Symbol VEITH2 GAV fBW VEO = 5 V VEO = 5 V
Conditions Ta = -25°C to +85°C
Min 2.3
Typ
Max 2.7
Unit V dB MHz V V ns ns ns ns µs
85 1.0 0 0 200 500 VCC = 12 V, VOUT = 10% 90% VCC = 12 V, VOUT = 90% 10% 50 50 400
Multiplier input D-range (lower limit) VMPIL Multiplier output D-range (lower limit) VMPOL Current detection - output delay Overvoltage detection - output delay Output rise time Output fall time Timer delay time tdCS tdOVP tr tf tdTIM
3
AN8031
s Terminal Equivalent Circuits
Pin No. 1
1
Voltage Regulators
Equivalent circuit
Description SVCC: The supply voltage terminal for control system. It monitors the supply voltage and has operating threshold value for start/stop.
I/O I
U.V.L.O.
Internal bias (Approx. 7.1 V)
2
Approx. 7.1 V To high-speed converter 2
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 output is cut.
I
3
Approx. 7.1 V
MPI: The input terminal of multiplier The voltage after a full-wave rectified AC input voltage are monitored.
I
3
4
Approx. 7.1 V Approx. 7.1 V
EO: The output terminal of error amplifier / the input terminal of multiplier. The error amplifier monitors the output voltage
O
Error amplifier output
Multiplier input 4
of active filter and amplifies its error portion and outputs to the multiplier. Therefore, this terminal serves as another input terminal of the multiplier.
5
Approx. Approx. 7.1 V 7.1 V
Approx. Approx. 7.1 V 7.1 V
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. Since this terminal monitors the output voltage of
I
Overvoltage protection input
5
Error amplifier output
the active filter, it also functions as the input terminal for the overvoltage protector which detects the overvoltage of output voltage and cuts off the power MOSFET.
4
Voltage Regulators
s Terminal Equivalent Circuits (continued)
Pin No. 6 PVCC Equivalent circuit Approx. 7.1 V Approx. 7.1 V
Upper limit voltage clamp
AN8031
Description 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. GND: Grounding terminal This terminal is used in common for grounding the control system and the power system.
I/O I
6
Lower limit voltage clamp
VB
Comparator input
7
7
8
9
VOUT: The output terminal. It is capable of driving the gate of power MOSFET directly.
O
8
9
9 VB
upper limit voltage clamp Power MOSFET drive block
PVCC: The supply voltage terminal for power. It determines the upper limit of output drive voltage. Normally, it is used at the same potential of SVCC .
5
AN8031
s Application Notes
[1] PD Ta curve of SIP009-P-0000C
1 000 900 874 800 Independent IC without a heat sink Rth( j-a) = 143°C/W PD = 874 mW (25°C)
Voltage Regulators
PD Ta
Power dissipation PD (mW)
700 600 500 400 300 200 100 0 0 25 50
75 85
100
125
150
[2] Operation descriptions 1. Normal control
Ambient temperature Ta (°C)
1) Application outline As shown in figure 1, the standard application of the AN8031 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 D. Input current (IIN) 0A A. Voltage after rectification (EIN) E
IN(max)
B. Output voltage (EOUT) 400 VDC 0V Active filter
0V
Input current proportional to input voltage flows. Input
IIN
EIN SBD
AN8031
EOUT Output
C. Input voltage (VIN) Commercial power supply (AC) 0V
Load
VIN
Diode bridge
Booster chopper circuit Figure 1. Application outline description
6
Voltage Regulators
s Application Notes (continued)
[2] Operation descriptions (continued) 1. Normal control (continued) 2) Control outline description (Refer to figure 2 and figure 3.)
AN8031
(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 AN8031 (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 AN8031 (Input to inverted 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 EI input voltage 0V Time Approx. 2.5 V typ.
Multiplier output (MPO) voltage 0V
Enlarged
Time
Power MOS turned off Multiplier output (MPO) voltage Power MOSFET current detection (CS) voltage Power MOS turned off Time
0V
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) Time Figure 2. Explanation of normal control operation
0V
7
AN8031
s Application Notes (continued)
[2] Operation descriptions (continued) 1. Normal control (continued) 2) Control outline description (Refer to figure 2 and figure 3.) (continued)
Voltage Regulators
(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). EIN
Power MOS On Power MOS Off Lower limit voltage clamp Upper limit voltage clamp
VBTH
One shot
1 SVCC 6 VB
Turn-on signal
2.5 V
VREF
10 V/8 V
Low voltage protection 9 PVCC
EOUT SBD
Timer Latch circuit Drive
8 VOUT
Power MOSFET
2.6 V
Overvoltage detection Input voltage monitor Current detection comparator
2 CS
Turn-off signal
MPI 3
Error amp. Multiplier
5 EI 2.5 V
GND 7
EO 4
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
s Application Notes (continued)
[2] Operation descriptions (continued) 1. Normal control (continued) 2) Control outline description (Refer to figure 2 and figure 3.) (continued)
AN8031
(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. · 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 VB terminal input voltage VBTH (1.5 V typ.) 0V OFF ON OFF
Figure 4. VB terminal description
9
AN8031
s Application Notes (continued)
[2] Operation descriptions (continued) 1. Normal control (continued) 3) Description of each function (continued) (1) VB (continued)
Voltage Regulators
ID SDB
VB lower limit voltage clamp current VB upper limit voltage clamp current
IDS
ID
Time
VCC AN8031
Lower limit voltage clamp
VB VB
Clamp upper limit voltage
IDS
VB
VB threshold value
Upper limit voltage clamp
Time Clamp upper limit voltage Reset operation of inductor
GND
Figure 5. Explanation of VB operation
· 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.
±5 mA or less
AN8031 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.
10
Voltage Regulators
s Application Notes (continued)
[2] Operation descriptions (continued) 1. Normal control (continued) 3) Description of each function (continued) (1) VB (continued) (continued) · Zero-cross switching Zero-cross switching can be realized by using the local resonance when turning off 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. (2) CS
AN8031 VB VOUT B CB
Delay capacitor
AN8031
LP RB
A
CP
Resonance capacitor Resonance by LP - CP A-point voltage Zero-cross switching
0V
B-point voltage
VBTH
0V
Delay Power MOSFET Power MOSFET
On
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 to 0.47 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 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
AN8031
s Application Notes (continued)
[2] Operation descriptions (continued) 1. Normal control (continued) 3) Description of each function (continued)
Voltage Regulators
(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 5 EI SBD To multiplier
Reference voltage (2.5 V typ.)
Resistor determining the gain
EO 4
Phase compensation capacitor
Figure 7. EI/EO terminal description (5) VOUT For the drive circuit, the AN8031 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 PVCC Totem pole type output circuit Parasitic capacitance VOUT VG GND 0V 0V VD VG VD
Off
On
Capacitive coupling
Swing to negative voltage Figure 8. VOUT terminal description
12
Voltage Regulators
s 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
U.V.L.O. characteristics IC operation
AN8031
0
8
10
(Stop voltage) (Start voltage)
VCC
V
· 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.
Start resistance R1 VCC AN8031 VOUT GND
C1
· 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.
VCC AN8031 GND C1
To fluorescent lamp inverter circuit block
(7) PVCC Drive current supply terminal of output block The high voltage of the power MOSFET gate drive pulse is determined by this terminal voltage. In the case of limiting the power MOSFET drive current, if the R1 is connected to the PVCC terminal and the R2 is connected to the VOUT terminal as shown in the right figure, the R1 + R2 limits the drive current when the power MOSFET is turned on and the R2 limits the drive current when it is turned off. In that way, the speed of turnon and turn-off can be changed.
Totem pole type output circuit PVCC R1
Drive current at turning on
VOUT
R2
Drive current at turning off
GND
13
AN8031
s Application Notes (continued)
[2] Operation descriptions (continued)
Voltage Regulators
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
Input voltage applied operation start
One-shot pulse
0A
400 µs typ.
Time
Power MOSFET current
0V
Start
Time
When abnormal stop Timer start Timer trigger signal (signal inside the IC) 0A Time Input voltage 400 µs typ. One-shot pulse
Power MOSFET current 0V Time Abnormal stop Re-start
Figure 9. Explanation of timer operation
14
Voltage Regulators
s Application Notes (continued)
[2] Operation descriptions (continued) 2. Protection circuit (continued) 2) Overvoltage protection
AN8031
(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 AN8031 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 SBD
Power MOS on-time current
Input voltage
AN8031
Output voltage
Under light load Multiplier output Power MOS on-time current Power MOS off-time current 0A
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.
Time
Under light load Multiplier output Power MOS on-time current Power MOS off-time current 0A Figure 10. Explanation of operation Time
15
AN8031
s Application Notes (continued)
[2] Operation descriptions (continued) 2. Protection circuit (continued) 2) Overvoltage protection (continued)
Voltage Regulators
(2) Description of overvoltage protector operation With respect to the AN3081 IC, the input of the error amplifier which detects the output voltage is also commonly used as the input of the overvoltage protection comparator. This is the point which differs from the AN8032. 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 420 V 400 V
Created by offset amount of overvoltage comparator
Output voltage of active filter
Power MOSFET current 0A Time
Operation condition of active filter
Operating
Stop
Operating
Stop
Figure 11. Protection of overvoltage protection operation
16
Voltage Regulators
s Application Notes (continued)
[2] Operation descriptions (continued) 2. Protection circuit (continued) 2) Overvoltage protection (continued)
AN8031
(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 even when the proper output voltage is obtained, causing the overshoot of output voltage. The AN8031 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
AN8031
s Application Notes (continued)
[3] Difference between the AN8031 and the AN 8032
Voltage Regulators
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.
SBD EO(+)
PVCC
VCC
VOUT
EIN(+)
MPI
Output voltage monitor
VB
EI EO CS
Separately require 5 to 10 external components Excessively large overvoltage, generated when the short circuit testing, can not be suppressed.
EIN(-)
Overvoltage detection
AN8031
COM
EO(-)
2) Countermeasures The output voltage system and the overvoltage detection system are separated from each other.
SBD EO(+)
Increase of 2 more external components
VCC
VOUT EI EO OVP CS
EIN(+)
MPI
Output voltage monitor
VB
EIN(-)
AN8032
Overvoltage detection
COM
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
· Application circuit
L1 R1 1 M SBD C3 47 µF
Load
+ L2 R8 1.5 M
Voltage Regulators
EI EO(DC 400 V)
A
G
B C2 1 µF R2 13 k SBD C R4 12 D R6 0.33 1W R3 10 k R7 330
s Application Circuit Example
C1
R9 10 k COM
-
COM
VCC 12 V E 2 CS F
VOUT 8
SVCC 1
PVCC 9
VB 6
MPI 3 5 EI C4 10 µF C5 0.01 µF
4 EO 7 GND
C7 0.1 µF C6 0.001 µF
R10 10 M
AN8031
19
AN8031
s Application Circuit Example (continued)
· Normal operation waveforms
Horizontal axis
Voltage Regulators
1 ms/div
Measuring point
10 ms/div
140 V
140 V
20 V/div
A (EIN)
0V
20 V/div
0V 2V 0V 7V 7V 0V
B (MPI)
1 V/div
0.4 V/div
C (VB)
1 V/div
0V 12 V 0V
12 V
2 V/div
D (VOUT)
2 V/div
0V 0.8 V 0V
0.2 V/div
0.2 V/div 0.5 V/div
E (CS)
0.8 V
0V
2.5 V
2.5 V
F (EI)
0.5 V/div
0V
0V
500 V
G (EO)
20
50 V/div
100 V
Voltage Regulators
s Application Circuit Example (continued)
· Waveforms at start
Horizontal axis
AN8031
20 ms/div
Measuring point
1.2 V
E (CS)
0.2 V/div
0V 400 V
G (EOI)
· Waveforms at stop
Horizontal axis
50 V/div
100 V
20 ms/div
Measuring point
0.2 V/div 50 V/div
E (CS)
0.8 V
0V
400 V
G (EOI)
100 V
(Conditions) · Input voltage : 100 V (AC) · Output voltage : 400 V (DC) · Output current : 200 mA (resistive load 2 k)
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