RS2051N データシートの表示（PDF） - Orister Corporation

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RS2051N

Novel Low Cost Green-Mode PWM Controller with Soft Start & Latch Mode

Orister Corporation 

Page No. : 6/13

Internal Synchronized Slop 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.

VSLOP

= 0.33× DUTY

DUTYMAX

= 0.4389 × DUTY

Slop Compensation

Current Sensing & Dynamic peak limiting

The current flowing by the power MOSFET comes into being a voltage VSENSE 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

the transformer. The transformer energy is

E

=

1

2

×

L×

I MAX

2.

So

adjusting

the

RSENSE

can

set

the

maximal

output

power

of

the power supple. The current flowing by the power MOSFET has an extra value ( ΔI

= VIN

LP

× TD ) due to the system delay

time that is from detecting the current through the Sense pin to power MOSFET off in the RS2051 (Among these, VIN is the

primary winding voltage of the transformer and LP is the primary wind inductance). VIN 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.

IPEAK MAX

=

0.65V

RSENSE

(VIN

= 264V )

IPEAK MAX

=

0.85V

RSENSE

(VIN

= 85V )

Soft Start

The RS2051 features an internal soft start during the initial power on. As soon as VDD reaches ON, the voltage on the internal

fixed capacitor is gradually increased from zero up to the maximum internal clamping level. The time of the soft start is fixed

about 1.2mS for the constant charge current and the fixed capacitor.

Frequency Jitter

The frequency jittering is introduced in the RS2051. As following figure, the internal oscillation frequency is modulated by itself.

A whole surge cycle includes 8 pulses and the jittering ranges from -4% to +4%. Thus, the function could minimize the

electromagnetic interferer from the power supply module.

DS-RS2051-02 September, 2007

Frequency Jitter

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