LinkSwitch-4
into Sleep mode, reducing its current consumption to IVCC(SLEEP). The
control circuitry will re-initialize if the input voltage is restored and
Functional Description
Power-Up/Power-Down Sequences
VVCC reaches VVCC(RUN)
.
Refer to Figure 10 and Figure 7. When mains input voltage (VIN) is
applied, current flows through the start-up resistors (RHT) and BJT.
Some of this current flows into the LinkSwitch-4 internal circuits,
ꢀꢀꢁꢁꢂRꢃꢄꢅ
which are in Sleep mode; the remainder charges capacitor CVCC
.
As soon as the VOLTAGE SUPPLY pin voltage rises to VVCC(RUN), the
LinkSwitch-4 changes to Initialise mode. Current consumption
increases to IVCC(RUN) while internal circuits are enabled. The emitter
switch is held at low impedance to ground (GND) and a short drive
pulse is output on the BASE DRIVE pin, during which time the voltage
at feedback is held at GND potential by current sourced from the
FEEDBACK pin. This enables the LinkSwitch-4 control circuit to
compare the rectified mains input voltage with thresholds for allowing
or preventing the next stage of power-up. If the input voltage is too
low (IFB <IFBHT(START)), the LinkSwitch-4 will not issue further drive
pulses, the VCC voltage will discharge to VVCC(SLEEP), and the power-up
sequence will repeat. If the mains input voltage is high enough (IFB >
IFBHT(START)), the LinkSwitch-4 will enter Run mode and drive pulses will
be output on the BASE DRIVE pin. To achieve smooth power-up
(monotonic rise in VOUT), CVCC must be large enough to power the
control circuitry during Initialize mode and the first few cycles of Run
mode, until sufficient power is provided by the transformer voltage
supply winding.
ꢀꢀꢁꢁ
ꢀꢀꢁꢁꢂꢆꢇꢈꢈꢉꢅ
ꢊꢋꢋ
ꢆꢌeeꢍ
ꢎꢏꢐꢑꢐꢒꢌꢐꢓe
Rꢔꢏ
ꢆꢌeeꢍ ꢊꢋꢋ
ꢉꢎꢕꢖꢗ5ꢖꢕ010815
Figure 7. VCC Waveforms.
If the input voltage falls below VMAINS(LO) (see Input Undervoltage
Protection), VVCC will fall below VVCC(SLEEP) and the LinkSwitch-4 will go
Mode
Description
From initial application of input power or from Run mode, if VVCC falls below VVCC(SLEEP), the LinkSwitch-4 goes to Sleep mode.
Non-essential circuits are turned off. Base and Emitter drives are turned off so BASE DRIVE and EMITTER DRIVE pins
become high impedance, allowing the bootstrap resistor (RHT) and BJT to start the circuit. Sleep mode is exited when VVCC
rises to VVCC(RUN) and the control circuitry goes to Initialize mode.
Sleep
Internal circuits are enabled and the LinkSwitch-4 issues one switching cycle to sample the input voltage via the FEEDBACK
pin. If VIN (hence VHT) is high enough, the LinkSwitch-4 changes to Run mode. If VIN is not high enough, no further base drive
Initialize
pulses are issued and the LinkSwitch-4 returns to Sleep mode when VVCC falls below VVCC(SLEEP)
.
Power conversion: The control circuitry is powered from the VCC rail and the internal VDD is regulated. If VVCC falls below
VVCC(SLEEP), the IC ceases power conversion and goes to Sleep mode.
Run
Table 2.
Summary of LinkSwitch-4 Operating Modes.
4
Rev. F 05/18
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