STMicroelectronics LED815 Evaluation Boards EVALHVLED815W15 EVALHVLED815W15 Fiche De Données
Codes de produits
EVALHVLED815W15
Device description
HVLED815PF
26/36
Doc ID 023409 Rev 4
Figure 20.
Load-dependent operating modes: timing diagrams
4.9
Soft-start and starter block
The soft start feature is automatically implemented by the constant current block, as the
primary peak current will be limited from the voltage on the C
primary peak current will be limited from the voltage on the C
LED
capacitor.
During start-up, as the output voltage is zero, the IC will start in constant current (CC) mode
with no high peak current operations. In this way the voltage on the output capacitor will
increase slowly and the soft-start feature will be ensured.
with no high peak current operations. In this way the voltage on the output capacitor will
increase slowly and the soft-start feature will be ensured.
Actually the C
LED
value is not important to define the soft-start time, as its duration depends
on others circuit parameters, like transformer ratio, sense resistor, output capacitors and
load. The user will define the best appropriate value by experiments.
load. The user will define the best appropriate value by experiments.
4.10 Hiccup
mode
OCP
The device is also protected against short-circuit of the secondary rectifier, short-circuit on
the secondary winding or a hard-saturated flyback transformer. An internal comparator
monitors continuously the voltage on CS pin and activates a protection circuitry if this
voltage exceeds an internally fixed threshold VCSdis (1 V typ. - see
the secondary winding or a hard-saturated flyback transformer. An internal comparator
monitors continuously the voltage on CS pin and activates a protection circuitry if this
voltage exceeds an internally fixed threshold VCSdis (1 V typ. - see
To distinguish an actual malfunction from a disturbance (e.g. induced during ESD tests), the
first time the comparator is tripped the protection circuit enters a "warning state". If in the
subsequent switching cycle the comparator is not tripped, a temporary disturbance is
assumed and the protection logic will be reset in its idle state; if the comparator will be
tripped again a real malfunction is assumed and the device will be stopped.
first time the comparator is tripped the protection circuit enters a "warning state". If in the
subsequent switching cycle the comparator is not tripped, a temporary disturbance is
assumed and the protection logic will be reset in its idle state; if the comparator will be
tripped again a real malfunction is assumed and the device will be stopped.
This condition is latched as long as the device is supplied. While it is disabled, however, no
energy is coming from the self-supply circuit; hence the voltage on the V
energy is coming from the self-supply circuit; hence the voltage on the V
CC
capacitor will
decay and cross the UVLO threshold after some time, which clears the latch. The internal
start-up generator is still off, then the VCC voltage still needs to go below its restart voltage
before the VCC capacitor is charged again and the device restarted.
start-up generator is still off, then the VCC voltage still needs to go below its restart voltage
before the VCC capacitor is charged again and the device restarted.
AM13570v1
I
DS
V
COMPL
COMP
t
t
50 mV hysteresis (Hys)
Burst-mode
Normal-mode
Normal-mode