NE5562D Philipss, NE5562D Datasheet - Page 9

• Manufacturer Part Number: NE5562D
• Description: Switched-mode power supply control circuit
• Manufacturer: Philipss

Philips Semiconductors
THE NE/SE5562 THEORY OF OPERATION
INTRODUCTION
Switched-mode power conversion relies on the principle of pulsed
energy storage in an inductive or capacitive element. Capacitive
switched converters are typically used with low power systems for
which only tens of milliamperes are required. Medium and high
power converters tend to use inductive storage elements as shown
in Figures 9-11 with which a single switch may be moved around to
create step-up (flyback) positive or negative polarity and step-down
(forward or buck) conversion from a fixed-voltage source. The
relationship between input and output voltage in each case is
controlled by the switching on-to-off ratios, which is termed duty
cycle. Duty cycle modulation is the common factor in this basic type
of power control mechanism. By adding a high-gain operational
amplifier, having one input tied to a stable DC reference voltage,
configured in a negative feedback loop to maintain a constant output
voltage as shown in Figure 12, the switched-mode controller
becomes a dynamic voltage regulator. It is this single-switch
topology that is most readily adapted to the NE/SE5562 SMPS
Control IC.
The ability to switch inductor currents at rates up to 600kHz with
state-of-the-art power FETs makes the design of small, efficient
switching power converters an attainable reality. Protective features
such as programmable slow-start and cycle-by-cycle current limiting
allow safe, maintenance-free power supplies to be mass-produced
at reduced cost to the manufacturer. Integrated technology makes
long-term reliability a predictably achievable goal.
1994 Aug 31
COM
Switched-mode power supply control circuit
COM
V
V
+
IN
IN
Figure 10. Positive Output Flyback Converter
Figure 9. Negative Output Flyback Converter
L
SW
SW
D
O
L
D
O
C
C
O
O
–
+
R
+
R
–
L
L
V
V
OUT
OUT
SL00397
SL00396
1
1
V IN
V IN
9
COM
Figure 11. Forward Converter (Single Inductor) Step Down
UNREGULATED
Figure 12. The Forward (Buck) Converter (V
INDUCTOR
V
CURRENT
CURRENT
CURRENT
+
IN
SWITCH
TOTAL
DIODE
V
DC
IN
+
–
SW
i
t
Figure 13. PWM Switching Waveforms
E
L
PWM
D
I
SW
B
R
A
L
F
+
–
C
WHERE
L
O
R
V
1
REF
NE/SE5562
C
+
–
R
R
Product specification
L
T
2
t
PERIOD
MAGNETIZATION
CURRENT
LOAD CURRENT
AVERAGE
INDUCTOR
CURRENT
SW
I
OUT
L
V
ON
OUT
REGULATED
OUTPUT
= V
+
–
R
IN
SL00398
SL00399
L
SL00400
( ))
V IN