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PDF MT7838 Data sheet ( Hoja de datos )
| Número de pieza | MT7838 | |
| Descripción | BUCK LED Driver | |
| Fabricantes | Maxic Technology | |
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Maximizing IC Performance
MT7838
Non-Isolated, High PFC, BUCK LED Driver
DESCRIPTION
The MT7838 is a single-stage buck average
constant current controller. With MAXIC
proprietary control technique, the system with
MT7838 can achieve both high current accuracy
and power factor correction. MT7838 works in
critical conduction mode (CRM) to reduce
switching losses.
The MT7838 can be powered up directly by the
main-line voltage wit hout the need of start-up
resistors, achieving an ult ra fast start-up time of
less than 100ms.
The MT7838 provides various protections, such
as over current protection (OCP), over voltage
protection (OVP ), short circuit protection (S CP)
and over temperat ure protection (OTP ), etc, to
maintain system reliability.
FEATURES
Single-stage active power factor correction
(PFC > 0.90)
Ultra-fast start-up time (<100mS )
High accurate LE D current
Critical conduction mode (CRM) operation
Up to 60 watt driving capability.
Various protection schemes.
Adjustable constant current and output
power setting
Power-on soft-start
Compact package: SOP8
APPLICATIONS
E14/E27/PAR30/PAR38/GU10 LED lamp
T8/T10 LE D tube
Other LE D lighting applications
Typical Application Circuit
L
XP1
N
F1
D2
BR
R3
C1
D1
L1
+
R4 LED
C4
-
4 VDD
HV 8
R1
7 NC
DRV 2
MT7838
5 DSEN
CS 3
6 COMP
GND 1
R2 C3 C2
M1
RS
MT7838 Rev. 1.10
www.maxictech.com
Copyright © 2013 Maxic Technology Corporation
Page 1
1 page  
Maximizing IC Performance
MT7838
Non-Isolated, High PFC, BUCK LED Driver
considered to be UVLO, the PWM signal of DRV
goes low ， and the voltage of COMP is
discharged to 0V. The detailed start-up sequence
is shown in Fig. 1.
Auxiliary Sensing
The voltage waveform of the auxiliary winding is
sensed during PWM OFF period for switching
logic control and over-voltage (OVP ),
short-circuit protection (S CP).
The DSEN senses the auxiliary winding voltage
through a resistor divider. The sampling strobe
window is 2us LEB (Leading Edge Blanking) time
right after the DRV signal is low for better noise
immunity as shown in Fig. 2.
The stand-by mode keeps the system at low
power dissipation state during fault conditions,
enhancing system reliability.
.Over-voltage Protection
The MT7838 is implemented with two
over-voltage protection schemes: (1) If DSEN
voltage is det ected above 3.2V for three times in
a row (refer to Auxiliary Sensing section), the
LED driver gets in stand-by mode. The thres hold
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
R1)
R2
Np
Na
DRV
DSEN
Sampling Point
Where Np is the primary winding, Na is auxiliary
winding; (2) If V DD exceeds 24V three times in a
row, the LED driver gets in stand-by mode. It is
highly recommended to set up the V DD voltage
between 12V and 22V through choosing a proper
Na/Np ratio of the transformer.
LEB=2uS
(typ)
Fig.2 Auxiliary Signal Sensing
Stand-by Mode
Any detected fault conditions, such as,
over-voltage (OV), short-circuit (SC) conditions,
will force MT7838 into stand-by mode, and PWM
signal goes low. VDD is therefore set to 9V for a
fixed time of 800ms, typically. Then V DD
continues to drop below UVLO threshold. A
start-up sequence is initiated. If the fault
conditions are removed, the LE D driver goes
back to normal.
Short-circuit Protection
The short-circuit protection is triggered if the
DSEN voltage is detected below 400mV during
OFF period for a continuous time of 2.5 to 5ms.
The MT7838 gets in stand-by mode.
Over-current Protection
The MT7838 immediately turns off the power
MOSFET once the voltage at CS pin exceeds
1.2V. This cycle by cycle current limitation
scheme prevents the relevant components, such
as power MOSFE T, transformer, etc. from
damage.
MT7838 Rev. 1.10
www.maxictech.com
Copyright © 2013 Maxic Technology Corporation
Page 5
5 Page | ||
| Páginas | Total 7 Páginas | |
| PDF Descargar | [ Datasheet MT7838.PDF ] | |
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