VIPER25
Off-line high voltage converters
Features
■
■
■
■
■
■
■
■
800 V avalanche rugged power section
Quasi-resonant (QR) control for valley
switching operation
Standby power < 50 mW at 265 Vac
Limiting current with adjustable set point
Adjustable and accurate overvoltage
protection
On-board soft-start
Safe auto-restart after a fault condition
Hysteretic thermal shutdown
SO16 narrow
SO-16
DIP-7
Description
The device is an off-line converter with an 800 V
rugged power section, a PWM control, double
levels of overcurrent protection, overvoltage and
overload protections, hysteretic thermal
protection, soft-start and safe auto-restart after
any fault condition removal. Burst mode operation
and device very low consumption helps to meet
the standby energy saving regulations. The quasi-
resonant feature reduces EMI filter cost. Brown-
out and brown-in function protects the switch
mode power supply when the rectified input
voltage level is below the normal minimum level
specified for the system. The high voltage start-up
circuit is embedded in the device.
Figure 1.
Typical topology
Applications
■
■
Adapters for PDA, camcorders, shavers,
cellular phones, cordless phones, videogames
Auxiliary power supply for LCD/PDP TV,
monitors, audio systems, computer, industrial
systems, LED driver, No el-cap LED driver,
utility power meter
SMPS for set-top boxes, DVD players and
recorders, white goods
■
Table 1.
Device summary
Order codes
Package
DIP-7
SO16 narrow
Packaging
Tube
Tube
Tape and reel
Doc ID 15585 Rev 4
1/40
www.st.com
40
VIPER25LN / VIPER25HN
VIPER25HD / VIPER25LD
VIPER25HDTR / VIPER25LDTR
July 2010
Contents
VIPER25
Contents
1
2
3
4
Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Typical power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1
4.2
4.3
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5
6
7
Typical electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Typical circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Operation description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9
7.10
7.11
7.12
7.13
7.14
7.15
7.16
Power section and gate driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
High voltage startup generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Power-up description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Power-down description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Auto-restart description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Quasi-resonant operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Frequency foldback function and valley skipping mode . . . . . . . . . . . . . . 22
Double blanking time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Starter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Current limit set point and feed-forward option . . . . . . . . . . . . . . . . . . . . . 24
Overvoltage protection (OVP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Summary on ZCD pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Feedback and overload protection (OLP) . . . . . . . . . . . . . . . . . . . . . . . . . 28
Burst-mode operation at no load or very light load . . . . . . . . . . . . . . . . . . 32
Brown-out protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2nd level over current protection and hiccup mode . . . . . . . . . . . . . . . . . 34
2/40
Doc ID 15585 Rev 4
VIPER25
Contents
8
9
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Doc ID 15585 Rev 4
3/40
Block diagram
VIPER25
1
Block diagram
Figure 2.
Block diagram
2
Typical power
Table 2.
Typical power
230 V
AC
Part number
VIPER25
Adapter
(1)
18 W
Open frame
(2)
20 W
85-265 V
AC
Adapter
(1)
10 W
Open frame
(2)
12 W
1. Typical continuous power in non ventilated enclosed adapter measured at 50 °C ambient.
2. Maximum practical continuous power in an open frame design at 50 °C ambient, with adequate heat
sinking.
4/40
Doc ID 15585 Rev 4
VIPER25
Pin settings
3
Pin settings
Figure 3.
Connection diagram (top view)
Note:
The copper area for heat dissipation has to be designed under the DRAIN pins.
Table 3.
Pin n.
Name
DIP-7 SO16
1
-
2
1...2
4
5
GND
N.A.
VDD
This pin represents the device ground and the source of the power section.
Not available for user. It can be connected to GND (pins 1-2) or left not
connected.
Supply voltage of the control section. This pin also provides the charging
current of the external capacitor during power-up.
This is a multifunction pin.
1. Input for the zero current detection circuit for transformer demagnetization
sensing. (i.e. R
LIM
, R
FF
, R
OVP
and D
OVP
,
Figure 32)
2. User defined drain current limit set-point and voltage feed forward.The
resistor, R
LIM
, connected between ZCD pin and GND causes the current
I
ZCD
and then it limits the static maximum drain current.
3. The resistor R
FF
, between ZCD pin and the auxiliary winding, performs
the feed-forward operation and then the drain current limitation changes
according to the converter input voltage.
4. Output overvoltage protection. A voltage exceeding V
OVP
threshold,
(see
Table 8 on page 8),
shuts the IC down reducing the device
consumption. This function is strobed and digitally filtered for high noise
immunity.
Control input for duty cycle control. Internal current generator provides bias
current for loop regulation. A voltage below the threshold V
FBbm
activates
the burst-mode operation. A level close to the threshold V
FBlin
means that
we are approaching the cycle-by-cycle over-current set point.
Brownout protection input with hysteresis. A voltage below the threshold
V
BRth
shuts down (not latch) the device and lowers the power consumption.
Device operation restarts as the voltage exceeds the threshold V
BRth
+
V
BRhyst
. It can be connected to ground when not used.
Function
Pin description
3
6
ZCD
4
7
FB
5
8
BR
7,8
High voltage drain pin. The built-in high voltage switched start-up bias
13...16 DRAIN current is drawn from this pin too. Pins connected to the metal frame to
facilitate heat dissipation.
Doc ID 15585 Rev 4
5/40
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