TDA4605.PDF

(643 KB) Pobierz
Control IC for Switched-Mode Power Supplies
using MOS-Transistors
TDA 4605
Bipolar IC
Features
q
Fold-back characteristic provides overload protection for
q
q
q
q
q
q
q
external components
Burst operation under short-circuit conditions
Loop error protection
Switch-off if line voltage is too low (undervoltage switch-off)
Line voltage compensation of overload point
Soft-start for quiet start-up
Chip-over temperature protection (thermal shutdown)
On-chip parasitic transformer oscillation suppression
circuitry
P-DIP-8-1
Type
TDA 4605
Ordering Code
Q67000-A8078
Package
P-DIP-8-1
The IC TDA 4605-1 controls the MOS-power transistor and performs all necessary regulation and
monitoring functions in free running flyback converters. Since good load regulation over a wide load
range is attained, this IC is applicable tor consumer and industrial power supplies.
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 the load via the secondary winding. By varying 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 independent ot 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.
Semiconductor Group
33
06.94
TDA 4605
In the different load ranges the switched-mode power supply (SMPS) behaves as follow:
No load operation:
The power supply unit oscillates at its resonant frequency typ. 100 kHz to 200 kHz. Depending upon
the transformator windings the output voltage can be slightly above nominal value.
Nominal operation:
The switching frequency declines with increasing load and decreasing AC-voltage. The duty factor
primarly depends on the AC-voltage. The output voltage is load-dependent only.
Overload point:
Maximal output power is available at this point ot the output characteristic.
Overload:
The energy transferred per operation cycle is limited at the top. Therefore the output voltage
declines by secondary overloading.
Semiconductor Group
34
TDA 4605
Pin Definitions and Functions
Pin No.
1
Function
Regulating Voltage:
Information input concerning secondary voltage.
By comparing the regulating voltage - obtained from the regulating winding ot the
transformer - with the internal reference voltage, the output impulse width on pin 5
is adapted to the load ot the secondary side (normal, overload, short-circuit, no
load).
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 ot external RC-element. When a value is reached that is derived
from the regulating voltage at pin 1, the output impulse at pin 5 is terminated. The
RC-element serves to set the maximum power at the overload point set.
Input for Primary Voltage Monitoring:
In the normal operation
V
3
is moving
between the thresholds
V
3H
and
V
3L
(V
3H
>
V
3
>
V
3L
).
V
3
<
V
3L
: SMPS is switched OFF (line voltage too low).
V
3
>
V
3H
: Compensation of the overload point regulation (controlled by pin 2)
starts at
V
3H
:
V
3L
= 1.7.
Ground
Output:
Push-pull-output provides
±
1 A for rapid charge and discharge of the
gate capacitance ot the power MOS-transistor.
Supply Voltage Input:
A stable internal reference voltage
V
REF
is derived from
the supply voltage also the switching thresholds
V
6A
,
V
6E
,
V
6 max
and
V
6 min
for
the supply voltage detector. If
V
6
>
V
6E
then
V
REF
is switched on and swiched off
when
V
6
<
V
6A
. In addition the logic is only enable for
V
6 min
<
V
6
<
V
6 max
.
Soft-Start:
Input for soft-start. Start-up will begin with short pulses by connecting
a capacitor from pin 7 to ground.
Zero Detector:
Input tor the oscillation feedback. After starting oscillation, every
zero transit of the feedback voltage (falling edge) triggers an output impulse at
pin 5. The trigger threshold is at + 50 mV typical.
2
3
4
5
6
7
8
Semiconductor Group
35
TDA 4605
Block Diagram
Semiconductor Group
36
TDA 4605
Circuit Description
Application Circuit
Application circuit shows a flyback converter for video recorders with a power rating of 50 W. The
circuit is designed as a wide-range power supply tor AC-line voltages ot 90 to 270 V. The AC-input
voltage is rectified by bridge rectifier GR1 and smoothed by
C
1
. The NTC limits the rush in current.
In the period before the switch-on threshold is reached the IC is supplied via resistor
R
1
; during the
start-up phase it uses the energy stored in
C
2
, under steady-state conditions the IC receives its
supply voltage from transformer winding
n
1
via diode D1. The switching transistor T1 is a BUZ 90.
The parallel-connected capacitor
C
3
and the inductance ot primary winding 112 determine the
system resonance frequency. The
R
2
-
C
4
- D2 circuitry limits overshoot peaks, and
R
3
protects the
gate of T1 against static charges.
While T1 conducts, the current rise in the primary winding depends on the winding’s inductance
and the
V
C1
voltage. A voltage reproduction ot the current rise is tabbed using the
R
4
-
C
5
network
and forwarded into pin 2 ot the IC. The RC-time constant ot
R
4
,
R
5
must be dimensioned correctly
in order to prevent driving the transformer core into saturation.
The
R
10
/
R
11
divider ratio provides the line voltage threshold controlling the undervoltage control
circuit in the IC. The voltage present at pin 3 also determines the overload. Detection of overload
together with the current characteristic at pin 2 controls the on period ot T1. This keeps the cut-off
point stable even with higher AC-line voltages.
Regulation of the switched-mode power supply is via pin 1. The control voltage of winding
n
1
during
the off-period of T1 is rectified by D3, smoothed by
C
6
and stepped down at an adjustable ratio by
R
5
,
R
6
and
R
7
. The
R
6
-
C
7
network suppresses parasitic overshoots (transformer oscillation).
The peak voltage at pin 2, and thus the primary peak current, is adjusted by the IC so that the
voltage applied across the control winding, and hence the output voltages, are at the desired level.
When the transformer has supplied its energy to the load, the control voltage passes through zero.
The IC detects the zero crossing via series resistors
R
9
connected to pin 8. But zero crossings are
also produced by transformer oscillation after T1 has turned off if output is short-circuited. Therefore
the IC ignores zero crossings occurring within a specitied period of time after T1 turn-off.
The capacitor
C
8
connected to pin 7 causes the power supply to be started with shorter pulses to
keep the operating ftrequency outside the audible range during start-up.
On the secondary side, tive output voltages are produced across winding
n
3
to
n
7
rectified by D4 to
D8 and smoothed by
C
9
to
C
13
. Resistors
R
12
,
R
14
and
R
19
to
R
21
are used as bleeder resistors.
Fusable resistors
R
15
to
R
18
protect the rectifiers against short circuits in the output circuits, which
are designed to supply only small loads.
Semiconductor Group
37

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika:

Zgłoś jeśli naruszono regulamin