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PDF MT7933 Data sheet ( Hoja de datos )
| Número de pieza | MT7933 | |
| Descripción | AC-DC LED Driver | |
| Fabricantes | Maxic Technology | |
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Maximizing IC Performance
MT7933
Single Stage, High PFC, AC-DC LED Driver
DESCRIPTION
MT7933 is a single-stage，primary side control
AC-DC LED driver with active power factor
correction. MT7933 integrates on-chip PFC
circuit operates in critical conduction mode (CRM)
to achieve high power factor and reduce the
power MOSFET switching loss. With MAXIC
Proprietary control technique, precision LED
current is achieved without secondary side
sense and feedback circuit including
opto-coupler.
MT7933 provides various protections, such as
over current protection (OCP), over voltage
protection (OVP), short circuit protection (SCP)
and over temperature protection (OTP), etc, to
improve system reliability.
Typical Application Circuit
FEATURES
Single-stage Active PFC for high power
factor and low THD
Primary side control eliminates opto-coupler
High precision LED current (+/-3%)
Critical Conduction Mode operation
Up to 20W driving capability.
Cycle-by-cycle current limiting
Under-voltage lockout (UVLO) protection
VDD and output over voltage protection
Adjustable constant current and output
power setting
Power on soft-start
Compact SOT23-6 package
APPLICATIONS
AC/DC LED driver applications
Signal and decorative LED lighting
E14/E27/PAR30/PAR38/GU10 LED lamp
T8/T10 LED String
MT7933 Rev. 1.10
www.maxictech.com
Copyright © 2012 Maxic Technology Corporation
Page 1
1 page  
MT7933
Maximizing IC Performance
Single Stage, High PFC, AC-DC LED Driver
by sensing DSEN’s waveform, which is sampled
from Auxiliary windings by the resistor-divider. As
DSEN’s waveform goes below 0V at OFF time,
which indicates the drain of power MOSFET
damps to its valley or nearby, MT7933 turns on
the power MOSFET. Besides, minimum OFF
time control provide noise immunity.
Furthermore, MT7933 features over-voltage
protection (OVP), short-circuit protection (SCP),
and over-current protection (OCP) functions.
Those protections are triggered by sensing the
auxiliary winding waveform information, as the
auxiliary winding voltage is proportional to the
output voltage (secondary winding voltage)
during the OFF time period. The auxiliary
winding voltage is sampled by DSEN pin, one
LEB (Leading Edge Blanking) time right after
DRV signal is turned off.
Auxiliary sensing function is shown in Fig.3.
the PWM switching signal, and VDD voltage
gradually drops to UVLO threshold, and the
system will be re-started. The threshold voltage
of over-voltage protection VOUT_OV, can be easily
defined as (refer to the application circuit in page
1):
VOUT_OV
3.2 (1
R3)
R4
Ns
Na
VD3
Where Ns is the secondary winding, Na is
auxiliary winding, VD3 is the forward bias of the
secondary side rectifier diode.
(2) If VDD pin’s voltage exceeds 24V three times,
MT7933 turns off the PWM switching signal, and
VDD gradually drops to UVLO threshold, and
then the system will be re-started. It is highly
recommended to set up the VDD voltage
between 12V and 22V by designed a proper Na
to Ns ratio of the transformer.
DRV
DSEN
Sampling Point
LEB=2uS
(typ)
Fig.3 Auxiliary Signal Sensing
Over-voltage Protection
MT7933 is implemented with two over-voltage
protection schemes: (1) If DSEN pin’s voltage is
detected above 3.2V for three times, (refer to
Auxiliary Sensing section), MT7933 turns off
Short-circuit Protection
The short-circuit protection is triggered if the
DSEN pin voltage is detected below 400mV at
OFF period for a continuous time of 5 to 10ms.
The gate drive switching will be turned off, and a
restart process will be kicked off when the VDD
voltage drops below the UVLO threshold.
This re-start process will repeat if the short-circuit
condition continues to exist.
Over-current Protection
MT7933 immediately turns off the power
MOSFET once the voltage at CS pin exceeds
1.8V. This cycle by cycle current limitation
scheme prevents the relevant components, such
as power MOSFET, transformer, etc. from
damage.
MT7933 Rev. 1.10
www.maxictech.com
Copyright © 2012 Maxic Technology Corporation
Page 5
5 Page | ||
| Páginas | Total 7 Páginas | |
| PDF Descargar | [ Datasheet MT7933.PDF ] | |
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