Panasonic AN8032 Active filter control ic Datasheet

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
Similar pages