UCS17005S

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

6 of 10

www.unisonic.com.tw

QW-R103-142.B

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FUNCTIONAL DESCRIPTION (Cont.)

(3) Internal Synchronized Slope Compensation

Built-in slope compensation circuit adds voltage ramp onto the current sense input voltage for PWM

generation, this greatly improves the close loop stability at CCM and prevents the sub-harmonic oscillation and thus

reduces the output ripple voltage.

(4) Frequency Hopping For EMI Improvement

The Frequency Hopping is implemented in the IC; there are two oscillators built-in the IC. The first oscillator

is to set the normal switching frequency; the switching frequency is modulated with a period signal generated by the

2nd oscillator. The relation between the first oscillator and the 2nd oscillator as followed Fig.5. So the tone energy is

evenly spread out, the spread spectrum minimizes the conduction band EMI and therefore eases the system design

in meeting stringent EMI requirement.

Fig.5 Frequency Hopping

(5) Constant Output Power Limit

When the primary current, across the primary wind of transformer, reaches the limit current, the output GATE

Higher input line voltage will result in a larger additional current and hence the output power limit is also higher than

that under low input line voltage. To compensate for this output power limit variation across a wide AC input range,

reduces the total PWM turn-on time and makes the output power equal to that of low line input. This proprietary

internal compensation ensures a constant output power limit for a wide AC input voltage range (90VAC to 264VAC).

(6) Protection section

The IC takes on more protection functions such as OLP, OVP and OTP etc. In case of those failure modes for

OLP

OVP