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PDF TDA8385 Data sheet ( Hoja de datos )
| Número de pieza | TDA8385 | |
| Descripción | Control circuit for a Self-Oscillating Power Supply SOPS | |
| Fabricantes | NXP Semiconductors | |
| Logotipo |  |
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Philips Semiconductors
Control circuit for a Self-Oscillating
Power Supply (SOPS)
Preliminary specification
TDA8385
FEATURES
• Bandgap reference generator
• Slow-start circuitry
• Low-loss peak current sensing
• Over-voltage protection
• Hysteresis controlled stand-by
function
• Error amplifier with gain setting
• Programmable transfer character
generator
• Protection against open- and
short-circuited feedback loop
• Over-load current fold back
characteristic
• LED driver
• Demagnetization protection
• Programmable determination of
switch-on moment of switching
transistor for low-switching losses
• Feed-forward input
• Regulation-indicator output
• Programmable minimum on-time of
switching transistor
• Accurate peak-current setting.
GENERAL DESCRIPTION
The TDA8385 is intended to be used
in combination with the opto-coupler
(CNR50) as a control unit for a
self-oscillating power supply.
ORDERING INFORMATION
EXTENDED TYPE
NUMBER
TDA8385
PINS
16
PIN POSITION
DIL
PACKAGE
MATERIAL
plastic
CODE
SOT38WBE
March 1994
2
1 page  
Philips Semiconductors
Control circuit for a Self-Oscillating
Power Supply (SOPS)
Preliminary specification
TDA8385
Sawtooth generator (Block II)
CURRENT SIMULATION
(SEE FIGS 5 AND 16)
The current of the power supply
switching transistor is detected on the
secondary side by an indirect method
of current sensing.
Information of the collector current (Ic)
is obtained by integrating the voltage
of an auxiliary winding of the
transformer during transistor on-time
(Ton). An external capacitor C on pin 5
is charged during Ton by the current
source Isim. The current Isim is the
reflection of the current which flows
into pin 12. This current is obtained by
connecting an external resistor R12 to
the auxiliary transformer winding.
During transistor on-time this current
is related to the input voltage VI.
During transistor off time (Toff) the
capacitor C is discharged by switch
sw1. This switch is achtainvdeboodku, fruillnpgagethwiedth
total Toff time. In this way a sawtooth
voltage Vc is formed across C. This
sawtooth is a measure for the
collector current of the switching
transistor T1.
For the voltage Vc yields:
Vc = -I-s---i-m-----C-×----T----o---n-
(1)
Isim = p × n-n---hp- × R---V--1---I-2-
(2)
Where: p = reflection factor;
p = -I-Is--1-i-2m-- = 0.2
(2) → (1) gives:
Vc = C-p-- × nn----hp- × R---V--1---I-2- × Ton
(3)
latch
initialization
5.2 7.5
operation
VP (V)
20
MCD403
Fig.4 Latch initialization as a function of supply voltage VP.
L
np nh
VI Ic
T1 Vc
R12
12
I 12
5
C
I sim
sw1
Vc
Ton Toff
t
MCD404
Fig.5 Determination of the peak current Ic.
March 1994
6
5 Page 
Philips Semiconductors
Control circuit for a Self-Oscillating
Power Supply (SOPS)
Preliminary specification
TDA8385
Regulation indicator output (Block X)
Pin 1 can be used to reset the logic circuit in the TV receiver at power on and off. Sub-section 29 has an open-collector
output. The output of this block is LOW during the regulation mode (Vdiff < Vts; see Fig.12).
handbook, full pagewidth
V
2.5
Vfb
Vts
0
Vdiff
t
VP
0
V
RIO
t
VRIO : open-collector output
0
t MCD411
A desired delay at power-on reset can be made externally.
Fig.12 Regulation indicator output; pin 1.
March 1994
12
11 Page | ||
| Páginas | Total 21 Páginas | |
| PDF Descargar | [ Datasheet TDA8385.PDF ] | |
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