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Internal Synchronized Slope Compensation
Although there are more advantages of the current mode control than conventional voltage mode control, there are still several
drawbacks of peak-sensing current-mode converter, especially the open loop instability when it operates in higher than 50% of
the duty-cycle. To solve this problem, the RS2051 is introduced an internal slope compensation adding voltage ramp to the
current sense input voltage for PWM generation. It improves the close loop stability greatly at CCM, prevents the sub-harmonic
oscillation and thus reduces the output ripple voltage.
DUTY
V
SLOP
=
0.33
×
=
0.4389
×
DUTY
DUTY
MAX
Slope Compensation
Current Sensing & Dynamic peak limiting
the transformer. The transformer energy is
E
=
The current flowing by the power MOSFET comes into being a voltage V
SENSE
on the Sense pin cycle-by-cycle, which compares
to the internal reference voltage, and controls the reverse of the internal register, limits the peak current IMAX of the primary of
1
×
L
×
I
MAX 2
. So adjusting the R
SENSE
can set the maximal output power of
2
V
the power supple. The current flowing by the power MOSFET has an extra value (
Δ
I
=
IN
×
T
D
) due to the system delay time
L
P
that is from detecting the current through the Sense pin to power MOSFET off in the RS2051 (Among these, V
IN
is the primary
winding voltage of the transformer and L
P
is the primary wind inductance). V
IN
ranges from 85VAC to 264VAC. To guarantee the
output power is a constant for universal input AC voltage, there is a dynamic peak limit circuit to compensate the system delay T
that the system delay brings on.
Vsense
1.10
1.05
1.00
0.95
0.90
0.85
0.80
0.75
0.70
Duty Cycle
0.65
0% 10%20%30%40%50%60%70%80%90%
Frequency Jiggling for EMI improvement
The Frequency Jiggling Technique is introduced in the RS2051. As following figure, the internal oscillation frequency is
modulated by itself. A whole surge cycle includes 128 pulses and the Jiggling ranges from -4% to +4%. Thus, the function could
minimize the electromagnetic interferer from the power supply module.
Frequency(HZ)
70K
65K
60K
Frequency Jiggling for EMI
Time
DS-RS2051-09 No v, 2010
www.Orister.com
ORISTER [ ORISTER CORPORATION ]
