MT7953 Datasheet PDF - Maxic Technology
| Part Number | MT7953 | |
| Description | Primary-side AC-DC LED Driver | |
| Manufacturers | Maxic Technology | |
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MT7953
High Accuracy, Primary-side AC-DC LED Driver
DESCRIPTION
MT7953 is a primary-side controller for AC-DC
LED lighting. It operates in constant current
control mode and works in discontinuous
conduction mode, suitable for flyback converter
under universal input, the output power of the
system should less than 5W.
MT7953 adopts primary side sensing and
regulation technology, no secondary side
feedback circuit is needed. Further, the loop
compensation components are also eliminated
while maintaining system stability. With building
in 600V power MOSFET, low component counts
and low BOM cost are achieved.
By using Maxic proprietary current regulation
method, the MT7953 achieves ±3% accuracy
of LED current along with excellent line
regulation and load regulation.
MT7953 provides plenty of protections, such as
LED short circuit protection, LED open circuit
protection, over-temperature protection, VDD
over voltage protection, VDD under voltage
lock-out, etc.
Typical Application Circuit
FEATURES
Build in 600V power MOSFET
110V to 220V AC line voltage range
Primary side sensing and regulation, no
need of secondary side feedback
High precision constant LED current (+/-3%)
Cycle-by-cycle peak current control
LED short-circuit/open circuit protection
VDD under voltage lock-out protection
VDD over voltage protection
Over temperature protection
Suitable for less than 5W applications
Built-in leading edge blanking (LEB)
Extremely minimum external components
Available in SOP8 package
APPLICATION
GU10/E27 LED bulb, spot light
1-5W LED lighting application
MT7953 Rev. 1.25
www.maxictech.com
Copyright © 2011 Maxic Technology Corporation
Page 1
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MT7953
High Accuracy, Primary-side AC-DC LED Driver
compared with the internal 500mV reference
voltage, the MOSFET is turned off when the
voltage on the CS reaches the threshold. The
comparator also includes a 500nS leading edge
blanking time to block the transient noise as the
power switch just turned on.
The primary side peak current is given by:
I P _ PK
500
(mA)
RCS
where RCS is the peak current sensing resistor,
i.e. the resistor R1 in the application circuit in
page 1.
The current in LED can be calculated by the
following equation:
I LED
I P _ PK
4
NP
NS
500
4 RCS
NP
NS
(mA)
where NP is the turns of the primary winding, NS
is the turns of the secondary winding, IP_PK is the
primary side peak current. Shown in the above
equation, the output current is determined by the
turns ratio of the transformer and the current
sense resistor value, insensitive to the
inductance of the transformer.
between 40KHz to 80KHz through properly
design transformer parameters.
Auxiliary Winding Feedback and Sensing
MT7953 detects the secondary side output
current through the feedback of the auxiliary
winding. The auxiliary winding directly ties to the
AUX pin, then divided by the internal resistor
string. The upper resistor is 90Kohm (RUP in the
block diagram in page 4), the bottom resistor is
15Kohm (RDN in the block diagram in page 4),
results in a 6:1 ratio. To block the switching noise,
a 2uS leading edge blanking time is embedded
inside the chip. Refer to Fig.2.
MT7953 features over-voltage protection (OVP),
LED open circuit protection, turn-off time control
functions. Those functions are triggered by
sensing the auxiliary winding waveform
information through AUX pin.
DRV
LEB time
Switching Frequency
MT7953 is designed to operating in
discontinuous conduction mode and no external
loop compensation is needed to maintain system
stability. The maximum duty cycle is limited to
42%. It’s highly recommended to limit the
maximum switching frequency less than 100KHz
and the minimum switching frequency more than
20KHz.
The switching frequency can be set by formula:
fSW
8
N
2
P
VLED
N
2
S
Lp
I
LED
where, NP is the turns of the primary winding, NS
is the turns of the secondary winding, Lp is the
transformer primary winding inductance.
Customer should set the switching frequency
Aux
Fig.2 Auxiliary Signal Sensing
Over-voltage (LED open circuit)
Protection
MT7953 is implemented with two over-voltage
protection schemes: (1) If AUX pin’s voltage is
detected above pre-determined threshold for four
times, MT7953 turns off 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 and
block diagram in page 4):
MT7953 Rev. 1.25
www.maxictech.com
Copyright © 2011 Maxic Technology Corporation
Page 5
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Part DetailsOn this page, you can learn information such as the schematic, equivalent, pinout, replacement, circuit, and manual for MT7953 electronic component. |
| Information | Total 8 Pages | |
| Link URL | [ Copy URL to Clipboard ] | |
| Download | [ MT7953.PDF Datasheet ] | |
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