ice2qr4765z Infineon Technologies Corporation, ice2qr4765z Datasheet - Page 8

• Manufacturer Part Number: ice2qr4765z
• Description: Off-line Smps Quasi-resonant Pwm Controller With Integrated 650v Coolmos And Startup Cell In Dip- 7
• Manufacturer: Infineon Technologies Corporation

according to the feedback voltage, V
information about the output power. Indeed, in a typical peak
current mode control, a high output power results in a high
feedback voltage, and a low output power leads to a low
regulation voltage. Hence, according to V
up/down counter is changed to vary the power MOSFET off-
time according to the output power. In the following, the
variation of the up/down counter value according to the
feedback voltage is explained.
The feedback voltage V
threshold voltages V
period of 48ms. The up/down counter counts then upward,
keep unchanged or count downward, as shown in Table 1.
Table 1
In the ICE2QR4765Z, the number of zero crossing is limited
to 7. Therefore, the counter varies between 1 and 7, and any
attempt beyond this range is ignored. When V
V
allow the system to react rapidly to a sudden load increase.
The up/down counter value is also reset to 1 at the start-up
time, to ensure an efficient maximum load start up.
shows some examples on how up/down counter is changed
according to the feedback voltage over time.
The use of two different thresholds V
upward or downward is to prevent frequency jittering when
the feedback voltage is close to the threshold point.
However, for a stable operation, these two thresholds must
not be affected by the foldback current limitation (see
Section 3.4.1), which limits the V
prevent such situation, the threshold voltages, V
Version 2.0
always lower than V
always lower than V
FBR1
v
Always lower than V
Once higher than V
Once higher than V
Once higher than V
FB
voltage, the up/down counter is reset to 1, in order to
Operation of the up/down counter
FBZL
FBZL
FBZH
FBZH
FBR1
FBR1
FBZL
FB
, V
, but
, but
is internally compared with three
FBZH
and V
up/down counter
action
Count upwards till 7
Stop counting, no
value changing
Count downwards
till 1
Set up/down counter
to 1
FBZL
CS
FB
voltage. Hence, to
FBR1
and V
FB
, which contains
, the value in the
, at each clock
FBZH
FB
Figure 5
FBZL
to count
exceeds
and
8
V
levels.
Figure 5
3.3.1.2
In the system, the voltage from the auxiliary winding is
applied to the zero-crossing pin through a RC network,
which provides a time delay to the voltage from the auxiliary
winding. Internally, this pin is connected to a clamping
network, a zero-crossing detector, an output overvoltage
detector and a ringing suppression time controller.
During on-state of the power switch a negative voltage
applies to the ZC pin. Through the internal clamping
network, the voltage at the pin is clamped to certain level.
The ZC counter has a minimum value of 0 and maximum
value of 7. After the internal MOSFET is turned off, every
time when the falling voltage ramp of on ZC pin crosses the
100mV threshold, a zero crossing is detected and ZC counter
will increase by 1. It is reset every time after the DRIVER
output is changed to high.
The voltage v
detection. Once the voltage at this pin is higher than the
threshold V
is latched off after a fixed blanking time.
To achieve the switch-on at voltage valley, the voltage from
the auxiliary winding is fed to a time delay network (the RC
network consists of D
application circuit) before it is applied to the zero-crossing
detector through the ZC pin. The needed time delay to the
main oscillation signal Dt should be approximately one
fourth of the oscillation period (by transformer primary
inductance and drain-source capacitance) minus the
propagation delay from the detected zero-crossing to the
switch-on of the main switch t
t
FBZH
Up/down
counter
=
Case 1
Case 2
Case 3
, are changed internally depending on the line voltage
clock
T
------------ t
V
V
V
FBR1
FBZH
osc
V
FBZL
4
FB
ZCOVP
Up/down counter operation
–
Zero crossing (ZC counter)
4
2
7
ZC
delay
during off-time of the main switch, the IC
is also used for the output overvoltage
5
3
7
zc
6
4
7
, R
zc1
6
4
7
, R
Functional Description
delay
zc2
6
4
7
T=48ms
and C
, theoretically:
6
4
7
CoolSET
ICE2QR4765Z
5
3
6
zc
as shown in typical
4
2
5
May 25, 2011
3
1
4
1
1
1
1
®
- Q1
t
t
[2]