TOP201YN Datasheet, PDF (6/16 Pages) Power Integrations, Inc. – Three-terminal Off-line PWM Switch

TOP200-4/14
General Circuit Operation
Primary Feedback Regulation
The circuit shown in Figure 7 is a simple
5 V, 5 W bias supply using the TOP200.
This universal input flyback power
supply employs primary-side regulation
from a transformer bias winding. This
approach is best for low-cost applications
requiring isolation and operation within
a narrow range of load variation. Line
and load regulation of ±5% or better can
be achieved from 10% to 100% of rated
load.
Voltage feedback is obtained from the
transformer (T1) bias winding, which
eliminates the need for optocoupler and
secondary-referenced error amplifier.
High-voltage DC is applied to the
primary winding of T1. The other side
of the transformer primary is driven by
the integrated high-voltage MOSFET
transistor within the TOP200 (U1). The
circuit operates at a switching frequency
of 100 kHz, set by the internal oscillator
of the TOP200. The clamp circuit
implemented by VR1 and D1 limits the
leading-edge voltage spike caused by
transformer leakage inductance to a safe
value. The 5 V power secondary winding
is rectified and filtered by D2, C2, C3,
and L1 to create the 5 V output voltage.
The output of the T1 bias winding is
rectified and filtered by D3, R1, and C5.
The voltage across C5 is regulated by
U1, and is determined by the 5.7 V
internal shunt regulator at the
CONTROL pin of U1. When the
rectified bias voltage on C5 begins to
exceed the shunt regulator voltage,
current will flow into the control pin.
Increasing control pin current decreases
the duty cycle until a stable operating
point is reached. The output voltage is
proportional to the bias voltage by the
turns ratio of the output to bias windings.
C5 is used to bypass the CONTROL pin.
C5 also provides loop compensation for
the power supply by shunting AC
currents around the CONTROL pin
dynamic impedance, and also determines
the auto-restart frequency during start-
up and auto-restart conditions. See DN-
8 for more information regarding the use
of the TOP200 in bias supplies.
DC
INPUT
DRAIN
SOURCE
CONTROL
U1
TOP200YAI
VR1
1N4764
D1
UF4005
C5
47 µF
D2
1N5822
C2
330 µF
25 V
D3
1N4148
T1
R1
22 Ω
L1
(Bead)
C3
150 µF
25 V
5V
RTN
CIRCUIT PERFORMANCE:
Load Regulation - ±4%
(10% to 100%)
Line Regulation - ±1.5%
95 to 370 V DC
Ripple Voltage ±25 mV
Figure 7. Schematic Diagram of a Minimum Parts Count 5 V, 5 W Bias Supply Utilizing the TOP200.
PI-1749-012296
6D
7/96