NE5562 Просмотр технического описания (PDF) - Philips Electronics
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NE5562 Datasheet PDF : 29 Pages
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Philips Semiconductors
Switched-mode power supply control circuit
Product specification
NE/SE5562
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.
SW
DO
–
VIN
δ
L
CO
RL
* VIN
VOUT + 1 * d
COM
+
SL00396
Figure 9. Negative Output Flyback Converter
L
DO
+
+
VIN
SW
δ
VIN
CO
RL VOUT + 1 * d
COM
–
SL00397
Figure 10. Positive Output Flyback Converter
SW
+
tSWON
WHERE d + TPERIOD
L
+
VIN
δ
DB
CO
RL VOUT + dVIN
COM
–
SL00398
Figure 11. Forward Converter (Single Inductor) Step Down
ISW
L
+
VIN
UNREGULATED
DC
PWM
–
REGULATED
OUTPUT
+
IL
C
RL
–
+
VREF
A
R2
–
RF
R1
SL00399
Figure 12. The Forward (Buck) Converter (VOUT = VIN(δ))
Di
E
Dt + L
SWITCH
CURRENT
MAGNETIZATION
CURRENT
LOAD CURRENT
DIODE
CURRENT
TOTAL
INDUCTOR
CURRENT
AVERAGE
INDUCTOR
CURRENT
SL00400
Figure 13. PWM Switching Waveforms
1994 Aug 31
9
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