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CONTROL CIRCUIT FOR SWITCH MODE POWER SUPPLIES USING MOS TRANSISTORS
TDA4605
CONTROL CIRCUIT FOR SWITCH MODE POWER SUPPLIES
USING MOS TRANSISTORS
.
FOLD-BACK CHARACTERISTIC PROVIDES
OVERLOAD PROTECTION FOR EXTERNAL
DIODES
.
BURST OPERATION UNDER SHORT-CIR-
CUIT AND NO LOAD CONDITIONS
.
LOOP ERROR PROTECTION
.
SWITCH-OFF IN CASE OF TOO LOW LINE
VOLTAGE (under voltage switch-off)
.
LINE VOLTAGE COMPENSATION OF OVER-
LOAD POINT
.
SOFT-START FOR SMOOTH START-UP
.
CHIP OVER-TEMPERATURE PROTECTION
(thermal shutdown)
DIP8
(Plastic Package)
.
ON-CHIP PARASITIC TRANSFORMER OS-
CILLATION SUPPRESSION CIRCUITRY
ORDER CODE :
TDA4605
.
DECREASE OF REGULATED VOLTAGE FOR
LOW POWER CONSUMPTION
DESCRIPTION
The IC TDA4605 controls the MOS Power Transis-
tor and performs all necessary regulation and
monitoring functions in free running flyback con-
verters. Since good load regulation over a wide
load range is attained, this IC is particularly suitable
for Consumer as well as Industrial Power Supplies.
SO8
(Plastic Micropackage)
ORDER CODE :
TDA4605D
Alternative source of the TDA4605 is also avail-
able from SIEMENS Semiconductors Consumer
Electronics A.G.
PIN CONNECTIONS
REGULATION INPUT
1
8
ZERO CROSSING DETECTOR INPUT
PRIMARY CURRENT SIMULATION
2
7
SOFT-START
PRIMARY VOLTAGE MONITORING
3
6
SUPPLY VOLTAGE
GROUND
4
5
OUTPUT
April 1996
1/6
TDA4605
PIN CONFIGURATION
Pin
Number
Description
1
Regulating voltage : information input concerning secondary voltage.
By comparing the regulating voltage obtained from the regulating winding of the transformer with the
internal reference voltage, the output pulse width on Pin 5 is adapted to the load of the secondary side
(normal, overload, short circuit, no load)
2
Primary current simulation : information input regarding the primary current. The primary current rise in the
primary winding is simulated at Pin 2 as a voltage rise by means of external RC element. When a value is
reached that is derived from the regulating voltage at Pin 1, the output pulse at Pin 5 is terminated. The
RC element serves to set the maximum power at the overload point.
3
Primary voltage detector : input for primary voltage monitoring. When the line voltage is too low the IC is
switched-off by comparing V
3
with an internal reference. Voltage at Pin 3 is used for overload point
compensation.
4
Ground
5
Output : push-pull output for charge and discharge of the gate capacitance of the power MOS transistor.
6
Supply voltage : Supply voltage input. From it are derived a stable internal reference voltage (V
REF
) and
the switching threshold V
6A
,V
6E
,V
6 max
and V
6 min
for the supply voltage detector.
if V
6
>V
6E
the V
REF
is switched on and switched off when V
6
<V
6A
. In addition the logic is only enable for
V
6 min
<V
6
<V
6 max
.
7
Soft-start : input for soft-start and integration network. Start-up will begin with short pulses by connecting a
capacitor between Pin 7 to ground. This capacitor together with a resistor connected between Pin 7 and
error amplifier output also as acts an integrator network for regulation.
8
Zero detector : Input for the oscillator feedback. After starting oscillator, every zero transit of the feedback
voltage (falling edge) triggers an output pulse at Pin 5. The trigger threshold is at typically - 50mV
BLOCK DIAGRAM
6
2
5
TDA4605
Re fere nce
Volta ge
(typ. 3V)
S upply
Voltage
Monitor
V
2B
Primary
Current
Recopy
Output S ta ge
and
Current Limit
V
REF
S ta rting
Impulse
G e ne ra tor
4
V
6min
V
6A
V
6E
V
6ma x
V
st
Logic
Current
S ource
V
R
Re gula ting
& Ove rloa d
Amplifier
Stop
Comp.
1
Ove rloa d
Point
Corre ction
V
u
Low Volta ge
P rote ction
Monitoring
Ze ro
Crossing
De te ctor
3
7
8
2/6
TDA4605
ABSOLUTE MAXIMUM RATINGS
Symbol
Parameter
Pin
Value
Unit
V
1
1
-0.3, +3
V
V
2
2
-0.3
V
V
3
Supply Voltage
3
-0.3
V
V
4
4
-0.3
V
V
6
6
-0.3, +20
V
V
7
7
-0.3
V
I
1
1
3
mA
I
2
2
3
mA
I
3
3
3
mA
I
4
Supply Current
t
p
3
50
m
s, V
3
0.1
4
- 1.5
A
I
5
t
p
3
50
m
s, V
3
0.1
5
-0.5, +1.5
A
I
6
t
p
3
50
m
s, V
3
0.1
6
0.5
A
I
7
7
3
mA
I
8
8
-3, +3
mA
T
j
Junction Temperature (autom. thermal disjunction)
+125
o
C
T
stg
Storage Temperature
-40, +125
o
C
THERMAL DATA
Symbol
Parameter
Value
Unit
R
th(j-a)
Junction-ambient Thermal Resistance
80
o
C/W
R
th(j-c)
Junction-case Thermal Resistance
45
o
C/W
o
T
amb
Ambient Temperature
-20, +85
C
ELECTRICAL CHARACTERISTICS
(V
CC
= 10V, T
amb
=25
o
C, unless otherwise specified)
Symbol
Parameter
Test Conditions
Min. Typ. Max. Unit
START-UP HYSTERESIS
I
6E0
Start-up Current Drain
V
6
=V
6E
0.6
0.8
mA
V
6E
Switch-on Voltage
11
12
13
V
V
6A
Switch-off Voltage
4.5
5
5.5
V
I
6E1
Switch-on Current
V
6
=V
6E
11
mA
I
6A1
Switch-off Current
V
6
=V
6A
10
mA
VOLTAGE CLAMP (V
6
= 10V, IC Switched off)
V
2(Max.)
At Pin 2 (V
6
<V
6E
)
I
2
= 1mA
5.6
6.6
9
V
V
3(Max.)
At Pin 3 (V
6
<V
6E
)
I
3
= 1mA
5.6
6.6
9
V
CONTROL RANGE
V
1R
Control Input Voltage
400
410
420
mV
-V
R
Voltage Gain of the Control Circuit in the Control
Range
V
R
= d(V
2S
-V
2B
)/dV
1
f = 1kHz
43
dB
PRIMARY CURRENT SIMULATION VOLTAGE
V
2B
Basic Value
0.955 1.00
1.03
V
OVERLOAD RANGE AND SHORT CIRCUIT OPERATION
V
2O
Peak Value in the Range of Secondary Overload V
1
=V
1R
- 10mV
2.8
2.95
3.1
V
DV
2
Maximum Ramp Amplitude
V
2O
-V
2B
1.82
1.95
2.08
V
V
2S
Peak Value in the Range of Secondary Short
Circuit Operation
V
1
= 0
2.3
2.5
2.7
V
FOLDBACK POINT CORRECTION
-I
2
Foldback Point Correction Current
V
3
= 3.7V
300
500
650
m
A
3/6
TDA4605
ELECTRICAL CHARACTERISTICS
(V
CC
= 10V, T
amb
=25
o
C, unless otherwise specified) (continued)
Symbol
Parameter
Test Conditions Min. Typ. Max. Unit
GENERALLY VALID DATA (V
6
= 10V)
VOLTAGE OF THE ZERO Transition DETECTOR
V
8P
Positive Clamping Voltage
I
8
= 1mA
0.75
V
V
8N
Negative Clamping Voltage
I
8
= -1mA
-0.2
V
V
8S
Threshold Value
40
50
mV
TUL
Suppression of Transformer Ringing
3
3.8
4.5
m
s
-I
8
Input Current
V
8
=0
0
4
m
V
PUSH-PULL OUTPUT STAGE
SATURATION VOLTAGES
V
SatU
Pin 5 Sourcing
I
5
= -0.1A
1.5
2.0
V
V
SatU
Pin 5 Sinking
I
5
= +0.1A
1.0
1.2
V
V
SatU
Pin 5 Sinking
I
5
= +0.5A
1.4
1.8
V
OUTPUT SLOW RATE
+dV
5
/dt Rising Edge
70
V/
m
s
-dV
5
/dt Falling Edge
100
V/
m
s
REDUCTION OF CONTROL VOLTAGE
-I
1
Current to reduce the Control Voltage
V
7
=1V
50
m
A
PROTECTION CIRCUIT
V
6(Min.)
Undervoltage Protection for V
6
:
Voltage at Pin 5 = V
5(Min.)
if V
6
<V
6(Min.)
7.0
7.25
7.5
V
V
6(Max.)
Overvoltage Protection for V
6
:
Voltage at Pin 5 = V
5(Min.)
if V
6
>V
6(Max.)
15
16
16.5
V
V
3A
Undervoltage Protection for V
AC
:
Voltage at Pin 5 = V
5(Min.)
if V
3
<V
3A
V
2
= 0V
970
1005 1040 mV
Oj
Over Temperature : at the given chip temperature the
IC will switch V
5
to V
5(Min.)
150
o
C
V
3Sat
Voltage at Pin 3 if one of the protection functions was
triggered ; (V
3
will be clamped until V
6
<V
6A
)
I
3
= 750
m
A
0.4
0.8
V
I
6
Current Drain during Burst Operation
V
3
=V
2
=0V
8
mA
FUNCTIONAL DESCRIPTION
In free running fly-back converters, the TDA4605
assumes control of a MOS power transistor and all
necessary regulation and monitoring functions.
The serial circuit of power transistor and primary
winding of the flyback transformer is connected to
the input voltage. During the switch-on period of the
transistor, energy is stored in the transformer and
during the switch-off period it is fed to te load via
the secondary winding. By varing the switch-on
time of the power transistor, the IC controls each
portion of energy transferred to the secondary side
such that the output voltage remains nearly inde-
pendent of load variations.
The required control information is taken from the
input voltage during the switch-on period and from
a regulation winding during the switch-off period. A
new cycle begins as soon as the energy stored in
the transformer has been totally delivered to the
secondary side.
In different load ranges, the SMPS will behave as
follows :
-
No-Load Operation :
The power supply unit
oscillates in non continuous mode at a typical
frequency of 20 to 40kHz. Depending upon the
transformer winding and the regulated voltage
divider, the output voltage can be slightly above
the nominal value.
-
Normal Operation :
Starting from typ. 200kHz,
the switching frequency falls with increasing load
and decreasing AC voltage. The duty cycle de-
pends primarily on the AC voltage. The output
voltage is only slightly load-dependen t.
-
OverloadPoint :
Maximum output power is avail-
able at this point of the output characteristics
-
Overload :
The energy transferred per operation
cycle is limited at the top. Therefore, the output
voltage will fall with secondary oveloading.
4/6
TDA4605
PACKAGE MECHANICAL DATA
8 PINS - PLASTIC DIP
Dimensions
Millimeters
Inches
Min.
Typ.
Max.
Min.
Typ.
Max.
A
3.32
0.131
a1
0.51
0.020
B
1.15
1.65
0.045
0.065
b
0.356
0.55
0.014
0.022
b1
0.204
0.304
0.008
0.012
D
10.92
0.430
E
7.95
9.75
0.313
0.384
e
2.54
0.100
e3
7.62
0.300
e4
7.62
0.300
F
6.6
0260
I
5.08
0.200
L
3.18
3.81
0.125
0.150
Z
1.52
0.060
5/6
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