1
April 1998
ML4812
*
Power Factor Controller
GENERAL DESCRIPTION
The ML4812 is designed to optimally facilitate a peak
current control boost type power factor correction system.
Special care has been taken in the design of the ML4812
to increase system noise immunity. The circuit includes a
precision reference, gain modulator, error amplifier, over-
voltage protection, ramp compensation, as well as a high
current output. In addition, start-up is simplified by an
under-voltage lockout circuit with 6V hysteresis.
In a typical application, the ML4812 functions as a
current mode regulator. The current which is necessary to
terminate the cycle is a product of the sinusoidal line
voltage times the output of the error amplifier which is
regulating the output DC voltage. Ramp compensation is
programmable with an external resistor, to provide stable
operation when the duty cycle exceeds 50%.
BLOCK DIAGRAM
(Pin Configuration Shown is for DIP Version)
FEATURES
s
Precision buffered 5V reference (0.5%)
s
Current-input gain modulator reduces external
components and improves noise immunity
s
Programmable ramp compensation circuit
s
1A peak current totem-pole output drive
s
Overvoltage comparator helps prevent output
voltage "runaway"
s
Wide common mode range in current sense
comparators for better noise immunity
s
Large oscillator amplitude for better noise immunity
5V
OVP
ISENSE
GM OUT
EA OUT
ISINE
RAMP COMP
CT
RT
ERROR
AMP
IEA
OSC
1k
UNDER
VOLTAGE
LOCKOUT
SHDN
OUT
PWR GND
VREF
VCC
GND
CLOCK
VCC
EA
32V
5
1
2
10
12
11
14
13
15
9
3
4
6
7
16
8
+
5V
+
5V
+
5V
S
R
Q
Q
GAIN MODULATOR
* Some Packages Are End Of Life
ML4812
2
PIN CONFIGURATION
PIN
NAME
FUNCTION
1
I
SENSE
Input from the current sense
transformer to the non-inverting input
of the PWM comparator.
2
GM OUT
Output of gain modulator.
A resistor to ground on this pin
converts the current to a voltage.
This pin is clamped to 5V and tied
to the inverting input of the PWM
comparator.
3
EA OUT
Output of error amplifier.
4
EA
Inverting input to error amplifier.
5
OVP
Input to over voltage comparator.
6
I
SINE
Current gain modulator input.
7
RAMP
COMP
Buffered output from the oscillator
ramp (C
T
). A resistor to ground sets the
current which is internally subtracted
from the product of I
SINE
and I
EA
in
the gain modulator.
PIN
NAME
FUNCTION
8
R
T
Oscillator timing resistor pin. A 5V
source sets a current in the external
resistor which is mirrored to charge
C
T
.
9
CLOCK
Digital clock output.
10
SHDN
A TTL compatible low level on this
pin turns off the output.
11
PWR GND Return for the high current totem pole
output.
12
OUT
High current totem pole output.
13
V
CC
Positive Supply for the IC.
14
V
REF
Buffered output for the 5V voltage
reference.
15
GND
Analog signal ground.
16
C
T
Timing capacitor for the oscillator.
PIN DESCRIPTION
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
ISENSE
GM OUT
EA OUT
EA
OVP
ISINE
RAMP COMP
RT
CT
GND
VREF
VCC
OUT
PWR GND
SHDN
CLOCK
TOP VIEW
ML4812
16-Pin PDIP (P16)
TOP VIEW
ML4812
20-Pin PLCC (Q20)
EA OUT
EA
NC
OVP
ISINE
VREF
VCC
NC
OUT
PWR GND
GM OUT
I SENSE
NC
C
T
GND
RAMP COMP
R
T
NC
CLOCK
SHDN
4
5
6
7
8
18
17
16
15
14
3
2
1 20 19
9 10 11 12 13
ML4812
3
ABSOLUTE MAXIMUM RATINGS
Absolute maximum ratings are those values beyond
which the device could be permanently damaged.
Absolute maximum ratings are stress ratings only and
functional device operation is not implied.
Supply Current (I
CC
) ............................................... 30mA
Output Current Source or Sink (OUT) DC ................ 1.0A
Output Energy (capacitive load per cycle) .................. 5J
Gain Modulator I
SINE
Input (I
SINE
) ......................... 1.2mA
Error Amp Sink Current (EA OUT) .......................... 10mA
Oscillator Charge Current ........................................ 2mA
Analog Inputs (I
SENSE
, EA, OVP) .............. 0.3V to 5.5V
Junction Temperature ............................................. 150C
Storage Temperature Range ..................... 65C to 150C
Lead Temperature (soldering 10 sec.) ..................... 260C
Thermal Resistance (
JA
)
20-Pin PLCC .................................................... 60C/W
16-Pin PDIP ..................................................... 65C/W
OPERATING CONDITIONS
Temperature Range
ML4812CX ............................................... 0C to 70C
ML4812IX ............................................. 40C to 85C
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, V
CC
= 15V , R
T
= 14k
, C
T
= 1000pF, T
A
= Operating Temperature Range (Notes 1, 2).
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
OSCILLATOR
Initial Accuracy
T
J
= 25C
91
98
105
kHz
Voltage Stability
12V < V
CC
< 18V
0.3
%
Temperature Stability
2
%
Total Variation
Line, temperature
90
108
kHz
Ramp Valley to Peak
3.3
V
R
T
Voltage
4.8
5.0
5.2
V
Discharge Current (R
T
open)
T
J
= 25C, V
CT
= 2V
7.8
8.4
9.0
mA
V
CT
= 2V
7.3
8.4
9.3
mA
Clock Out Voltage Low
R
L
= 16k
0.2
0.5
V
Clock Out Voltage High
R
L
= 16k
3.0
3.5
V
REFERENCE
Output Voltage
T
J
= 25C, I
O
= 1mA
4.95
5.00
5.05
V
Line Regulation
12V < V
CC
< 25V
2
20
mV
Load Regulation
1mA < I
O
< 20mA
2
20
mV
Temperature Stability
0.4
%
Total Variation
Line, load, temp.
4.9
5.1
V
Output Noise Voltage
10Hz to 10kHz
50
V
Long Term Stability
T
J
= 125C, 1000 hours
5
25
mV
Short Circuit Current
V
REF
= 0V
30
85
180
mA
ERROR AMPLIFIER
Input Offset Voltage
15
mV
Input Bias Current
0.1
1.0
A
Open Loop Gain
1 < V
EA OUT
< 5V
60
75
dB
PSRR
12V < V
CC
< 25V
60
75
dB
Output Sink Current
V
EA OUT
= 1.1V, V
EA
= 6.2V
2
12
mA
Output Source Current
V
EA OUT
= 5.0V, V
EA
= 4.8V
0.5
1.0
mA
Output High Voltage
I
EA OUT
= 0.5mA, V
EA
= 4.8V
5.3
5.5
V
Output Low Voltage
I
EA OUT
= 1mA, V
EA
= 6.2V
0.5
1.0
V
Unity Gain Bandwidth
1.0
MHz
ML4812
4
ELECTRICAL CHARACTERISTICS
(Continued)
PARAMETER CONDITIONS MIN TYP MAX UNITS
GAIN MODULATOR
I
SINE
Input Voltage I
SINE
= 500A 0.4 0.7 0.9 V
Output Current (GM OUT) I
SINE
= 500A, EA = V
REF
20mV 430 470 510 A
I
SINE
= 500A, EA = V
REF
+ 20mV 3 10 A
I
SINE
= 1mA, EA = V
REF
20mV 860 940 1020 A
I
SINE
= 500A, EA = V
REF
20mV, 455 A
I
RAMP COMP
= 50A
Bandwidth 200 kHz
PSRR 12V < V
CC
< 25V 70 dB
OVP COMPARATOR
Input Offset Voltage Output Off 25 +5 mV
Hysteresis Output On 95 105 115 mV
Input Bias Current 0.3 3 A
Propagation Delay 150 ns
PWM COMPARATOR: I
SENSE
Input Offset Voltage 15 mV
Input Offset Current 1 A
Input Common Mode Range 0.2 5.5 V
Input Bias Current 2 10 A
Propagation Delay 150 ns
I
LIMIT
Trip Point V
GM OUT
= 5.5V 4.8 5 5.2 V
OUTPUT
Output Voltage Low I
OUT
= 20mA 0.1 0.4 V
I
OUT
= 200mA 1.6 2.2 V
Output Voltage High I
OUT
= 20mA 13 13.5 V
I
OUT
= 200mA 12 13.4 V
Output Voltage Low in UVLO I
OUT
= 5mA, V
CC
= 8V 0.1 0.8 V
Output Rise/Fall Time C
L
= 1000pF 50 ns
Shutdown V
IH
2.0 V
V
IL
0.8 V
I
IL
, V
SHDN
= 0V 1.5 mA
I
IH
, V
SHDN
= 5V 10 A
UNDER-VOLTAGE LOCKOUT
Startup Threshold 15 16 17 V
Shutdown Threshold 9 10 11 V
V
REF
Good Threshold 4.4 V
SUPPLY
Supply Current Start-Up, V
CC
= 14V, T
J
= 25C 0.8 1.2 mA
Operating, T
J
= 25C 20 25 mA
Internal Shunt Zener Voltage I
CC
= 30mA 25 30 34 V
Note 1: Limits are guaranteed by 100% testing, sampling, or correlation with worst-case test conditions.
Note 2: V
CC
is raised above the Startup Threshold first to activate the IC, then returned to 15V.
ML4812
5
FUNCTIONAL DESCRIPTION
OSCILLATOR
The ML4812 oscillator charges the external capacitor (C
T
)
with a current (I
SET
) equal to 5/R
SET
. When the capacitor
voltage reaches the upper threshold, the comparator
changes state and the capacitor discharges to the lower
threshold through Q1. While the capacitor is discharging,
Q2 provides a high pulse.
The Oscillator period can be described by the following
relationship:
Figure 2. Oscillator Timing Resistance vs. Frequency
Figure 1. Oscillator Block Diagram
Figure 3. Output Saturation Voltage vs. Output Current
10
SYNC
Q
2
Q
1
9
RT
16
CT
EXTERNAL
CLOCK
+
-
5.6V
ISET
8.4mA
CT
RT
ISET
CSYNC
RSYNC
CLOCK
tD
RAMP VALLEY
RAMP PEAK
V(CT)
10
R
T
(k
)
OSCILLATOR FREQUENCY (kHz)
10
100
1000
8
5
3
2
1
MAXIMUM DUTY CYCLE (%)
10nF
20nF
5nF
2nF
1nF
85%
80%
70%
90%
15
14
13
3
2
1
0
OUTPUT SA
TURA
TION
V
O
L
T
A
GE (V)
OUTPUT CURRENT (mA)
0
200
400
800
600
VCC
VCC = 15V
80s PULSED LOAD
120Hz RATE
GND
SOURCE SATURATION
LOAD TO GROUND
SINK SATURATION
LOAD TO VCC
T
T
T
OSC
RAMP
DEADTIME
=
+
where:
V
V
D
OUT
IN
ON
=
-
1
and:
T
C
V
mA I
DEADTIME
T
RAMP VALLEY TO PEAK
SET
=
-
8 4
.
ML4812
6
OUTPUT DRIVER STAGE
The ML4812 output driver is a 1A peak output high speed
totem pole circuit designed to quickly drive capacitive
loads, such as power MOSFET gates. (Figure 3)
ERROR AMPLIFIER
The ML4812 error amplifier is a high open loop gain,
wide bandwidth, amplifier.(Figures 4-5)
GAIN MODULATOR
The ML4812 gain modulator is of the current-input type
to provide high immunity to the disturbances caused by
high power switching. The rectified line input sine wave is
converted to a current via a dropping resistor. In this way,
small amounts of ground noise produce an insignificant
effect on the reference to the PWM comparator. The
output of the gain modulator is a current of the form: I
OUT
is proportional to I
SINE
I
EA,
where I
SINE
is the current in
the dropping resistor, and I
EA
is a current proportional to
FUNCTIONAL DESCRIPTION
(Continued)
Figure 5. Error Amplifier Open-Loop Gain and
Phase vs Frequency
Figure 7. Gain Modulator Linearity
5V
EA
4
3
+
8V
0.5mA
EA OUT
Figure 4. Error Amplifier Configuration
the output of the error amplifier. When the error amplifier
is saturated high, the output of the gain modulator is
approximately equal to the I
SINE
input current. The gain
modulator output current is converted into the reference
voltage for the PWM comparator through a resistor to
ground on the gain modulator output. The gain modulator
output is clamped to 5V to provide current limiting.
Ramp compensation is accomplished by subtracting 1/2
of the current flowing out of RAMP COMP through a
buffer transistor driven by C
T
which is set by an external
resistor.
UNDER VOLTAGE LOCKOUT
On power-up the ML4812 remains in the UVLO
condition; output low and quiescent current low. The IC
becomes operational when V
CC
reaches 16V. When V
CC
drops below 10V, the UVLO condition is imposed.
During the UVLO condition, the 5V V
REF
pin is "off",
making it usable as a "flag" for starting up a downstream
PWM converter.
6
2
7
16
CT
RAMP COMP
GM OUT
ISINE
ERROR CURRENT
9V
5V
IRAMP COMP
ISINE
ERROR CURRENT
IRAMP COMP/2
Figure 6. Gain Modulator Block Diagram
500
400
300
200
100
0
MUL
TIPLE OUTPUT CURRENT (A)
ERROR
AMP OUTPUT
V
O
L
T
A
G
E (V)
SINE INPUT CURRENT (A)
0
200
300
500
400
100
4.5
4.0
3.5
3.0
2.5
2.0
1.5
A
VO
L, OPEN LOOP GAIN (dB)
FREQUENCY (Hz)
10
1k
1M
100
10k
10M
100k
100
80
60
40
20
0
-20
EXCESS PHASE (degr
ees)
0
-30
-60
-90
-120
-150
-180
GAIN
PHASE
ML4812
7
ENABLE
VREF
VREF
GEN.
9V
INTERNAL
BIAS
5V VREF
VCC
+
I CC
(mA)
VCC (V)
0
30
20
40
10
25
20
15
10
5
0
25
20
15
10
5
0
SUPPL
Y CURRENT (mA)
TEMPERATURE (degrees)
60
20
60
140
100
20
40
40
80
120
0
OPERATING CURRENT
STARTUP
V
REF
(mV)
IREF (mA)
0
40
100
20
60
120
80
0
-4
-8
-12
-16
-20
-24
Figure 10. Reference Load Regulation
Figure 8. Under-Voltage Lockout Block Diagram
Figure 9a. Total Supply Current vs. Supply Voltage
Figure 9b. Supply Current (I
CC
) vs. Temperature
TYPICAL APPLICATIONS
INPUT INDUCTOR (L1) SELECTION
The central component in the regulator is the input boost
inductor. The value of this inductor controls various
critical operational aspects of the regulator. If the value is
too low, the input current distortion will be high and will
result in low power factor and increased noise at the
input. This will require more input filtering. In addition,
when the value of the inductor is low the inductor dries
out (runs out of current) at low currents. Thus the power
factor will decrease at lower power levels and/or higher
line voltages. If the inductor value is too high, then for a
given operating current the required size of the inductor
core will be large and/or the required number of turns
will be high. So a balance must be reached between
distortion and core size.
One more condition where the inductor can dry out is
analyzed below where it is shown to be maximum duty
cycle dependent.
For the boost converter at steady state:
V
V
D
OUT
IN
ON
=
-
1
(1)
Where D
ON
is the duty cycle [T
ON
/(T
ON
+ T
OFF
)]. The
input boost inductor will dry out when the following
condition is satisfied:
V t V
D
IN
OUT
ON
( )
(
)
<
-
1
(2)
or
V
D
V
INDRY
ON
OUT
= -
[
(max)]
1
(3)
V
INDRY
: voltage where the inductor dries out.
V
OUT
: output DC voltage.
Effectively, the above relationship shows that the resetting
volt-seconds are more than setting volt-seconds. In energy
transfer terms this means that less energy is stored in the
inductor during the ON time than it is asked to deliver
during the OFF time. The net result is that the inductor
dries out.
ML4812
8
The recommended maximum duty cycle is 95% at
100KHz to allow time for the input inductor to dump its
energy to the output capacitors. For example, if: V
OUT
=
380V and D
ON
(max) = 0.95, then substituting in (3)
yields V
INDRY
= 20V. The effect of drying out is an
increase in distortion at low voltages.
For a given output power, the instantaneous value of the
input current is a function of the input sinusoidal voltage
waveform, i.e. as the input voltage sweeps from zero volts
to a maximum value equal to its peak so does the current.
The load of the power factor regulator is usually a
switching power supply which is essentially a constant
power load. As a result, an increase in the input voltage
will be offset by a decrease in the input current.
By combining the ideas set forth above, some ground
rules can be obtained for the selection and design of the
input inductor:
Step 1: Find minimum operating current.
I
P
V
IN
PEAK
IN
IN
(min)
.
(min)
(max)
=
1414
(4)
V
IN
(max) = 260V
P
IN
(min) = 50W
then:
I
IN
(min)
PEAK
= 0.272A
Step 2: Choose a minimum current at which point the
inductor current will be on the verge of drying
out. For this example 40% of the peak current
found in step 1 was chosen.
then:
I
LDRY
= 100mA
Step 3: The value of the inductance can now be found
using previously calculated data.
L
V
D
I
f
V
mA
KHz
mH
INDRY
ON
LDRY
OSC
1
20
0 95
100
100
2
=
=
=
(max)
.
(5)
The inductor can be allowed to decrease in value when
the current sweeps from minimum to maximum value.
This allows the use of smaller core sizes. The only
requirement is that the ramp compensation must be
adequate for the lower inductance value of the core so
that there is adequate compensation at high current.
Step 4: The presence of the ramp compensation will
change the dry out point, but the value found
above can be considered a good starting point.
Based on the amount of power factor correction
the above value of L1 can be optimized after a
few iterations.
Gapped Ferrites, Molypermalloy, and Powdered Iron
cores are typical choices for core material. The core
material selected should have a high saturation point and
acceptable losses at the operating frequency.
One ferrite core that is suitable at around 200W is the
#4119PL00-3C8 made by Philips Components
(Ferroxcube). This ungapped core will require a total gap
of 0.180" for this application.
OSCILLATOR COMPONENT SELECTION
The oscillator timing components can be calculated by
using the following expression:
f
R
C
OSC
T
T
=
136
.
(6)
For example:
Step 1: At 100kHz with 95% duty cycle T
OFF
= 500ns
calculate C
T
using the following formula:
C
T
I
V
pF
T
OFF
DIS
OSC
=
= 1000
(7)
Step 2: Calculate the required value of the timing
resistor.
R
f
C
KHz
pF
k choose R
k
T
OSC
T
T
=
=
=
W
=
W
136
136
100
1000
136
14
.
.
.
(8)
TYPICAL APPLICATIONS
(Continued)
ML4812
9
CURRENT SENSE AND SLOPE (RAMP) COMPENSATION
COMPONENT SELECTION
Slope compensation in the ML4812 is provided internally.
Rather than adding slope to the noninverting input of the
PWM comparator, it is actually subtracted from the
voltage present at the inverting input of the PWM
comparator. The amount of slope compensation should be
at least 50% of the downslope of the inductor current
during the off time, as reflected to the inverting input of
the PWM comparator. Note that slope compensation is
required only when the inductor current is continuous
and the duty cycle is more than 50%. The downslope of
the inductor current at the verge of discontinuity can be
found using the expression given below:
di
dt
V
V
L
V
V
mH
A
s
L
OUT
INDRY
=
-
=
-
=
m
380
20
2
0 18
.
/
(9)
The downslope as reflected to the input of the PWM
comparator is given by:
S
V
V
L
R
N
PWM
OUT
INDRY
S
C
=
-
(10)
S
V
mH
V
s
PWM
=
-
=
m
380
20
2
100
80
0 225
.
/
Where R
S
is the current sense resistor and N
C
is the turns
ratio of the current transformer (T1) used. In general,
current transformers simplify the sensing of switch
currents (especially at high power levels where the use of
sense resistors is complicated by the amount of power
they have to dissipate). Normally the primary side of the
transformer consists of a single turn and the secondary
consists of several turns of either enameled magnet wire
or insulated wire. The diameter of the ferrite core used in
this example is 0.5" (SPANG/Magnetics F41206-TC). The
rectifying diode at the output of the current transformer
can be a 1N4148 for secondary currents up to 75mA
average.
Sense FETs or resistive sensing can also be used to sense
the switch current. The sensed signal has to be amplified
to the proper level before it is applied to the ML4812.
The value of the ramp compensation (SC
PWM
) as seen at
the inverting terminal of the PWM comparator is:
SC
R
R
C
R
PWM
M
T
T
SC
=
25
.
(11)
The required value for R
SC
can therefore be found by
equating: SC
PWM
= A
SC
S
PWM,
where A
SC
is the amount
of slope compensation and solving for R
SC
. The value of
GM OUT depends on the selection of RAMP COMP.
R
V
I
mA
k
P
IN
PEAK
SINE PEAK
=
=
=
(max)
.
.
(
)
260 1414
0 5
750
(12)
R
V
R
V
k
k
M
CLAMP
P
IN PEAK
=
=
=
(
)
.
.
.
49 750
90 1414
288
(13)
The peak of the inductor current can be found
approximately by:
I
P
V
A
LPEAK
OUT
IN RMS
=
=
=
1414
1414 200
90
314
.
.
.
(
)
(14)
Selection of N
C
which depends on the maximum switch
current, assume 4A for this example is 80 turns.
R
V
N
I
S
CLAMP
C
LPEAK
=
=
=
W
49 80
4
100
.
(15)
Where R
S
is the sense resistor, and V
CLAMP
is the current
clamp at the inverting input of the PWM comparator. This
clamp is internally set to 5V. In actual application it is a
good idea to assume a value less than 5V to avoid
unwanted current limiting action due to component
tolerances. In this application, V
CLAMP
was chosen as
4.9V.
Having calculated R
S,
the value S
PWM
and of R
SC
can
now be calculated:
R
R
A
S
R
C
R
k
K nF
k
SC
M
SC
PWM
T
T
SC
=
=
=
25
25 288
07 0 225 10
14
1
33
6
.
.
.
.
( .
)
(16)
The following values were used in the calculation:
R
M
= 28.8k
A
SC
= 0.7
R
T
= 14k
C
T
= 1nF
VOLTAGE REGULATION COMPONENTS
The values of the voltage regulation loop components are
calculated based on the operating output voltage. Note
that voltage safety regulations require the use of sense
resistors that have adequate voltage rating. As a rule of
thumb if 1/4W resistors are chosen, two of them should
be used in series. The input bias current of the error
amplifier is approximately 0.5A, therefore the current
available from the voltage sense resistors should be
significantly higher than this value. Since two 1/4W
resistors have to be used the total power rating is 1/2W.
The operating power is set to be 0.4W then with 380V
output voltage the value can be calculated as follows:
R
V
W
k
1
2
380
0 4
360
=
=
(
) / .
(17)
Choose two 178k
, 1% connected in series. Then R2 can
be calculated using the formula below:
R
V
R
V
V
V
k
V
V
k
REF
OUT
REF
2
1
5
356
380
5
4747
=
-
=
-
=
.
(18)
TYPICAL APPLICATIONS
(Continued)
ML4812
10
Choose 4.75k
, 1%. One more critical component in the
voltage regulation loop is the feedback capacitor for the
error amplifier. The voltage loop bandwidth should be set
such that it rejects the 120Hz ripple which is present at
the output. If this ripple is not adequately attenuated it
will cause distortion on the input current waveform.
Typical bandwidths range anywhere from a few Hertz to
15Hz. The main compromise is between transient
response and distortion. The feedback capacitor can be
calculated using the following formula:
C
R
BW
C
k
Hz
F
F
F
=
=
=
m
1
3142
1
3142 356
2
0 44
1
.
.
.
(19)
OVERVOLTAGE PROTECTION (OVP) COMPONENTS
The OVP loop should be set so that there is no interaction
with the voltage control loop. Typically it should be set to
a level where the power components are safe to operate.
Ten to fifteen volts above V
OUT
is generally a good
setpoint. This sets the maximum transient output voltage
to about 395V. By choosing the high voltage side resistor
of the OVP circuit the same way as above i.e. R
4
= 356K
then R
5
can be calculated as:
R
V
R
V
V
V
k
V
V
k
REF
OVP
REF
5
4
5
356
395
5
4564
=
-
=
-
=
.
(20)
Choose 4.53k
, 1%. Note that R
1
, R
2
, R
4
and R
5
should
be tight tolerance resistors such as 1% or better.
CONTROLLER SHUTDOWN
The ML4812 provides a shutdown pin which could be
used to shutdown the IC. Care should be taken when this
pin is used because power supply sequencing problems
could arise if another regulator with its own bootstrapping
follows the ML4812. In such a case a special circuit
should be used to allow for orderly start up. One way to
accomplish this is by using the reference voltage of the
ML4812 to inhibit the other controller IC or to shut down
its bias supply current.
OFF-LINE START-UP AND BIAS SUPPLY GENERATION
The ML4812 can be started using a "bleed resistor" from
the high voltage bus. After the voltage on V
CC
exceeds
16V, the IC starts up. The energy stored on the 330F,
C15, capacitor supplies the IC with running power until
the supplemental winding on L1 can provide the power to
sustain operation.
The values of the start-up resistor R10 and capacitor C15
may need to be optimized depending on the application.
The charging waveform for the secondary winding of L1 is
an inverted chopped sinusoid which reaches its peak
when the line voltage is at its minimum. In this example,
C9 = 0.1F, C15 = 330F, D8 = 1N4148, R10 = 39k
,
2W.
ENHANCEMENT CIRCUIT
The power factor enhancement circuit shown in Figure 12
is described in detail in Application Note 11. It improves
the power factor and lowers the input current harmonics.
Note that the circuit meets IEC 1000-3-2 specifications
(with the enhancement) on the harmonics by a large
margin while correcting the input power factor to better
than 0.99 under most steady state operating conditions.
CONSTRUCTION AND LAYOUT TIPS
High frequency power circuits require special care during
breadboard construction and layout. Double sided printed
circuit boards with ground plane on one side are highly
recommended. All critical switching leads (power FET,
output diode, IC output and ground leads, bypass
capacitors) should be kept as small as possible. This is to
minimize both the transmission and pick-up of switching
noise.
There are two kinds of noise coupling; inductive and
capacitive. As the name implies inductive coupling is due
to fast changing (high di/dt) circulating switching currents.
The main source is the loop formed by Q1, D5, and
C3C4. Therefore this loop should be as small as possible,
and the above capacitors should be good high frequency
types.
The second form of noise coupling is due to fast changing
voltages (high dv/dt). The main source in this case is the
drain of the power FET. The radiated noise in this case can
be minimized by insulating the drain of the FET from the
heatsink and then tying the heatsink to the source of the
FET with a high frequency capacitor (C
H
in Figure 12).
The IC has two ground pins named PWR GND and Signal
GND. These two pins should be connected together with
a very short lead at the printed circuit board exit point. In
general grounding is very important and ground loops
should be avoided. Star grounding or ground plane
techniques are preferred.
TYPICAL APPLICATIONS
(Continued)
ML4812
11
TYPICAL APPLICATIONS
(Continued)
MAGNETICS TIPS
L1 -- Main Inductor
As shown in Table 1, one of several toroidal cores can be
used for L1. The T184-40 core above is the most
economical, but has lower inductance at high current.
This would yield higher ripple current and require more
line EMI filtering. The value for R
SC
(slope compensation
resistor on RAMP COMP) was calculated for the T225-8/
90 and should be recalculated for other inductor
characteristics. The various core manufacturers have a
range of applications literature available. A gapped ferrite
core can also be used in place of the powdered iron core.
One such core is a Philips Components (Ferroxcube) core
#4229PL00-3C8. This is an ungapped core. Using 145
turns of #24 AWG wire, a total air gap of 0.180" is
required to give a total inductance of about 2mH. Since
1/2 of the gap will be on the outside of the core and 1/2
the gap on the inside, putting a 0.09" spacer in the center
will yield a 0.180" total gap. To prevent leakage fields
from generating RFI, a shorted turn of copper tape should
be wrapped around the gap as shown in Figure 11. For
production, a gapped center leg can be ordered from most
core vendors, eliminating the need for the external
shorted copper turn when using a potentiometer core.
COPPER FOIL
SHORTED TURN
0.09" GAP
Figure 11. Copper Foil Shorted Turn
MATERIAL
MANUFACTURER
PART #
TURNS (#24AWG)
Powdered Iron
Micrometals
T225-8/90
200
Powdered Iron
Micrometals
T184-40
120
Molypermalloy
SPANG (Mag. Inc.)
58076-A2 (high flux)
180
Table 1. Toroidal Cores (L1)
T1 -- Sense Transformer
In addition to the core type mentioned in the parts list, the
following Siemens cores should be suitable for
substitution and may be more readily available in Europe.
MATERIAL
SIZE CODE
PART #
N27
R16/6.3
B64290-K45-X27
N30
R16/6.3
B64290-K45-X830
The N27 material is for high frequency and will work
better above 100KHz but both are adequate. In addition,
Philips Components (Ferroxcube) core 768T188-3C8 can
be used. Please also refer to the list of core vendors below
SPANG/Magnetics Inc.
1 (800) 245-3984, or
(412) 282-8282
Micrometals
1 (800) 356-5977
Philips Components
(914) 247-2064
ML4812
12
Figure 12. Typical Application, 200W Power Factor Correction Circuit
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
90 TO
260 VAC
AC IN
P
1
FUSE F1
5A 250V
L
N
C
1
1
F
630V
D
1
1N5406
D
2
1N5406
D
3
1N5406
R
GMOUT
27k
D
10
1N5406
OPTIONAL
ENHANCEMENT
CKT.
R
12
1K
C
17
Q
3
C
19
+
D
13
D
12
D
11
R
3
22k
C
F
D
4
1N5406
R
2A
10k
R
2B
3.9k
R
5B
3.9k
R
5A
10k
R
1B
180k
R
4B
180k
R
PB
150k
R
PA
360k
R
4A
180k
1
2
N
P
N
S
R
10
39k
2W
R
SC
33k
R
T
7.5k
ML4812
IC
1
C
16
100F
25V
+
D
9
D
8
Q
2
7812
C
T
2nF
C15
P3*
C10
1F
330F
25V
V
CC
D
5
MUR850
OFF-LINE START-UP
AND BIAS SUPPLY
C
18
R
11
33k
C
11
1nF
D
6
T
1
A
B
R
S
100
C
9
0.1
F
C
8
0.1
F
R
G
10
+
Q
1
IRF840
HEATSINK
C
H
6.8nF
R
7
150k
1W
R
6
150k
1W
C
3
6.8nF
1kV
C
4
1
F
630V
C
5
680F
200V
C
6
680F
200V
P
2
V
OUT
380 VDC
** SEE NOTES BELOW
NOTES:
1. ALL UNSPECIFIED DIODES ARE 1N4148.
2. ALL UNSPECIFIED RESISTORS ARE 1/4 WATT.
3. ALL UNSPECIFIED CAPACITOR VOLTAGE RATINGS ARE 50V.
4. ADJUST R
2A
AND R
5A
WITH CAUTION TO AVOID OVER VOLTAGE CONDITIONS.
Q
3
= 2N2222 OR EQUIVALENT.
P3 IS USED AT INITAL TURN-ON TO
CHECK THE IC FOR PROPER OPERATION.
APPLY
16VDC.
FIXED RESISTORS CAN BE USED FOR THE SENSING
COMPONENTS. BELOW ARE 1% STANDARD
RESISTORS THAT WILL FORCE THE CORRECT
OUTPUT VOLTAGES R1A, R1B, R4A, R4B = 178k
1%,
R2B = 4.75 1%, R5B = 4.53k
1%.
USE JUMPERS INSTEAD OF R2A AND R5A (POTS).
FOR HIGHER POWER USE MORE V
CC
DECOUPLING.
2
F OR MORE BE REQUIRED AT 1KW LEVELS.
*
**
***
R
13
22k
R
1A
180k
L
1
***
+
+
ML4812
13
REFERENCE
DESCRIPTION
C1, C4
1F, 630V Film (250VAC)
C3, C
H
6.8nF, 1KV Ceramic disk
C5, C6
680F, 200V Electrolytic
C8, C9
0.1F, 50V Ceramic
C10, C19
1F, 50V Ceramic
C11
0.001F, 50V Ceramic
C15
330F, 25V Electrolytic
C16
100F, 25V Electrolytic
C17
10F, 25V Electrolytic
C
F
0.47F, 50V Ceramic
C
T
0.002F, 50V Ceramic
D1, D2, D3, D4, D10
1N5406 (Motorola)
D5
MUR850 (Motorola)
D6, D8, D9
1N4148
D11, D12, D13
F1
5A, 250V 3AG with clips
IC1
ML4812CP (Micro Linear)
L1
2mH, 4A I
PEAK
(see note)
Q1
IRF840 or MTPN8N50
Q2
LM7815CT
Q3
2N2222 or equivalent
Notes:
All resistors 1/4W unless otherwise specified. Some reference designators
are skipped (e.g. C2, C12, etc.) and do not appear on the schematic.
These designators were used in previous revisions of the board and are
not used on this revision. Additional information on key components is
included in the attached appendix.
Table 2. Component Values/Bill of Materials for Figure 12
REFERENCE
DESCRIPTION
R1A, R1B, R4A, R4B
180k
R2A, R5A
10k
TRIMPOT BOURNS
3299 or equivalent
R2B, R5B
3.9k
R3, R13
22k
R6, R7, RPB
150k
R10
39k
, 2W
R11
33k
R12
1k
RG
10
RM
27k
RPA, R15
360k
RS
100k
RSC
33k
RT
7.5k
T1
SPANG F41206-TC
N
S
= 80, N
P
= 1 (see note)
ML4812
14
Figure 13. 1kW Input Power, Power Factor Correction Circuit
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
+
C12
1
F
630V
C10
680
F
250V
C11
680
F
250V
GND
V
OUT
C9
15
F
630V
C8
15
F
630V
D5 MUR3050
R4
150K
1W
R5
150K
1W
APT5025
GND
1T
Q2
APT5025
Q1
T1
D4
80T
C14
1
F
***
RG1
3
RG2
3
C7
0.1
F
C4
0.1
F
RS
22
C5
1nF
V
CC
CT 2.2nF
R3
33K
R7
22K
IC1
ML4812
RT
6.2K
RSC
51K
L1
566
H
RPA
360K
RPB
150K
R4A
360K
R4B
180K
R1B
180K
R1A
180K
CF
R5A
5K
R5B
3K
R2B
3K
R2A
5K
RM
27K
D1
1N5406
BRIDGE
RECTIFIER
C3
1
F
500V
C2
1
F
500V
C1
1
F
500V
FUSE F1
15A 250V
L
AC
IN
N
R1
R2
330K
22K
R6
C13
10
F
GND
V
CC
Q3
D2
V
Z
3.5V
+
ENHANCEMENT CIRCUIT SEE TEXT
2N2222
**
C6
1
F
NOTES:
1. ALL UNSPECIFIED DIODES ARE 1N4148.
2. ALL UNSPECIFIED RESISTORS ARE 1/4 WATT.
3. ALL UNSPECIFIED CAPACITOR VOLTAGE RATINGS ARE 50V.
4. ADJUST R
2A
AND R
5A
WITH CAUTION TO AVOID OVER VOLTAGE CONDITIONS.
Q
3
= 2N2222 OR EQUIVALENT.
AT INITIAL TURN-ON TO CHECK
THE IC FOR PROPER OPERATION,
APPLY
16VDC.
FIXED RESISTORS CAN BE USED FOR THE SENSING
COMPONENTS. BELOW ARE 1% STANDARD
RESISTORS THAT WILL FORCE THE CORRECT
OUTPUT VOLTAGES R1A, R1B, R4A, R4B = 178k
1%,
R2B = 4.75
1%, R5B = 4.53k
1%.
USE JUMPERS INSTEAD OF R2A AND R5A (POTS).
FOR HIGHER POWER USE MORE V
CC
DECOUPLING.
*
**
***
ML4812
15
PHYSICAL DIMENSIONS
inches (millimeters)
SEATING PLANE
0.240 - 0.260
(6.09 - 6.61)
PIN 1 ID
0.295 - 0.325
(7.49 - 8.26)
0.740 - 0.760
(18.79 - 19.31)
0.016 - 0.022
(0.40 - 0.56)
0.100 BSC
(2.54 BSC)
0.008 - 0.012
(0.20 - 0.31)
0.015 MIN
(0.38 MIN)
16
0 - 15
1
0.055 - 0.065
(1.40 - 1.65)
0.170 MAX
(4.32 MAX)
0.125 MIN
(3.18 MIN)
0.02 MIN
(0.50 MIN)
(4 PLACES)
Package: P16
16-Pin PDIP
0.100 - 0.110
(2.54 - 2.79)
PIN 1 ID
SEATING PLANE
0.385 - 0.395
(8.89 - 10.03)
0.350 - 0.356
(8.89 - 9.04)
0.013 - 0.021
(0.33 - 0.53)
0.165 - 0.180
(4.19 - 4.57)
1
0.350 - 0.356
(8.89 - 9.04)
0.385 - 0.395
(8.89 - 10.03)
6
11
16
0.290 - 0.330
(7.36 - 8.38)
0.025 - 0.045
(0.63 - 1.14)
(RADIUS)
0.009 - 0.011
(0.23 - 0.28)
0.026 - 0.032
(0.66 - 0.81)
0.042 - 0.048
(1.07 - 1.22)
0.042 - 0.056
(1.07 - 1.42)
0.200 BSC
(5.08 BSC)
Package: Q20
20-Pin PLCC
0.146 - 0.156
(3.71 - 3.96)
0.050 BSC
(1.27 BSC)
ML4812
1
DS4812-01
Micro Linear 1998.
is a registered trademark of Micro Linear Corporation. All other trademarks are the property of their respective owners.
Products described herein may be covered by one or more of the following U.S. patents: 4,897,611; 4,964,026; 5,027,116; 5,281,862; 5,283,483;
5,418,502; 5,508,570; 5,510,727; 5,523,940; 5,546,017; 5,559,470; 5,565,761; 5,592,128; 5,594,376; 5,652,479; 5,661,427; 5,663,874; 5,672,959;
5,689,167; 5,714,897; 5,717,798. Japan: 2,598,946; 2,619,299; 2,704,176. Other patents are pending.
Micro Linear reserves the right to make changes to any product herein to improve reliability, function or design. Micro Linear does not assume any
liability arising out of the application or use of any product described herein, neither does it convey any license under its patent right nor the rights of
others. The circuits contained in this data sheet are offered as possible applications only. Micro Linear makes no warranties or representations as to
whether the illustrated circuits infringe any intellectual property rights of others, and will accept no responsibility or liability for use of any application
herein. The customer is urged to consult with appropriate legal counsel before deciding on a particular application.
ORDERING INFORMATION
PART NUMBER
TEMPERATURE RANGE
PACKAGE
ML4812CP
0C to 70C
Molded PDIP (P16)
ML4812CQ
0C to 70C
Molded PLCC (Q20)
(End Of Life)
ML4812IP
40C to 85C
Molded PDIP (P16)
(End Of Life)
ML4812IQ
40C to 85C
Molded PLCC (Q20)
(End Of Life)
2092 Concourse Drive
San Jose, CA 95131
Tel: (408) 433-5200
Fax: (408) 432-0295
www.microlinear.com
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