UC3848G-D08-T UTC [Unisonic Technologies], UC3848G-D08-T Datasheet - Page 6

• Manufacturer Part Number: UC3848G-D08-T
• Description: HIGH PERFORMANCE CURRENT MODE CONTROLLERS
• Manufacturer: UTC [Unisonic Technologies]

UC3848
LINEAR INTEGRATED CIRCUIT
FUNCTIONAL DESCRIPTION(Cont.)
(2) Switch Frequency Set
The maximum switch frequency is set to 68kHz. Switch frequency is modulated by output power P
during IC
OUT
operating. At no load or light load condition, most of the power dissipation in a switching mode power supply is from
switching loss on the MOSFET transistor, the core loss of the transformer and the loss on the subber circuit. The
magnitude of power loss is in proportion to the number of switching events within a fixed period of time. So lower
switch frequency at lower load, which more and more improve IC’s efficiency at light load. At from no load to light
load condition, The IC will operate at from Burst mode to Reducing Frequency Mode. The relation curve between f
SW
and P
/P
as followed FIG.4.
OUT
OUT (MAX)
FIG.4 The relation curve between f
and relative output power P
/ P
SW
OUT
OUT (MAX)
(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.
UNISONIC TECHNOLOGIES CO., LTD
6 of 11
www.unisonic.com.tw
QW-R103-033.F