Electronic component search and free download site.
Transistors,MosFET ,Diode,Integrated circuits
Part Name  

LD7550 View Datasheet(PDF) - Unspecified

Part NameLD7550 ETC
Unspecified 
DescriptionGreen-Mode PWM Controller
LD7550 Datasheet PDF : 10 Pages
1 2 3 4 5 6 7 8 9 10
LD7550
reduce the switching cycles under light-load or no-load
condition either by skip some switching pulses or reduce the
switching frequency.
What LD7550 used to implement the power-saving
operation is Leadtrend Technology’s own IP2. In such
approach, as shown in the block diagram, 2 oscillators are
implemented in LD7550. The first oscillator is to take care
the normal switching frequency, which can be set by the RT
pin through an external resistor. Under this operation mode,
as shown in Fig. 10, the 2nd oscillation (green-mode
oscillator) is not activated. Therefore, the rising-time and the
falling-time of the internal ramp will be constant to achieve
good stability over all temperature range. Under the
normal operation, this oscillator is dominated the switching
frequency.
COMP
CS
OSC
EN=1
Green-Mode Osc is not activated
under normal operation.
EN
Green-Mode
Osc
2R
R
LEB
Set
S
V+
Reset
V-
RQ
PWM
Comparator
++
Ramp from
Oscillator
OUT
Fig. 10
(voltage controlled oscillator), is a variable frequency
oscillator. The rising time of the VCO is proportional to
(VGREEN-V+), thus the lower voltage on V+ will generate
longer rising time on VCO as well as lower frequency on
VCO.
By using this dual-oscillator control, the green-mode
frequency can be well controlled and further to avoid the
generation of audible noise.
from OSC
"Set" Signal
(to OSC & Nor gate)
Green-Mode
Oscillator
V+
V-
VCO
Level-detector
& Counter
Vgreen
(V+ -Vgreen) >=0, VCO disabled
(V+ -Vgreen) <0, VCO activated
V+
Normal Mode
Green Mode
Vgreen
Ramp of
OSC
Green-Mode
Oscillator activated
Ramp of
VCO
Fig. 11
2 Note: Patent pending
As shown in Fig. 11, the green-mode oscillator detects the
Comp pin signal to determine if it is within the green-mode
operation. When the detected signal V+ is lower than the
green-mode threshold VGREEN, the green-mode oscillator is
on. The green-mode oscillator, implemented by a VCO
8
Leadtrend Technology Corporation
LD7550-DS-00 August 2004
Direct download click here

 

Share Link : 
All Rights Reserved© datasheetq.com 2015 - 2019  ] [ Privacy Policy ] [ Request Datasheet  ] [ Contact Us ]