VIPER37HE STMicroelectronics, VIPER37HE Datasheet - Page 20

• Manufacturer Part Number: VIPER37HE
• Description: AC/DC Switching Converters ViperPlus Fixed Freq 800V 30mQ 265 Vac
• Manufacturer: STMicroelectronics
• Type: Off Line Switcherr

Specifications of VIPER37HE

• Product Category: AC/DC Switching Converters
• Rohs: yes
• Input / Supply Voltage (max): 23.5 V
• Input / Supply Voltage (min): 8.5 V
• Switching Frequency: 115 kHz
• Supply Current: 3.5 mA
• Operating Temperature Range: - 40 C to + 150 C
• Mounting Style: Through Hole
• Package / Case: SDIP-10
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 25 C
• Number Of Outputs: 1
• Output Power: 25 W

Operation description
8.3
20/35
Power-up and soft-start
If the input voltage rises up to the device start threshold V
begins to grow due to the I
startup circuit. If the V
MOSFET starts switching and the HV current generator is turned off (see
The IC is powered by the energy stored in the capacitor on the V
supply circuit (typically an auxiliary winding of the transformer and a steering diode)
develops a voltage high enough to sustain the operation.
The C
needed voltage value higher than the V
could terminate the switching operation before the controller receives any energy from the
auxiliary winding.
The following formula can be used for the V
Equation 1
The t
estimated by the applicator according to the output stage configurations (transformer, output
capacitances, etc.).
During the converter startup time, the drain current limitation is progressively increased to
the maximum value. In this way the stress on the secondary diode is considerably reduced.
It also helps to prevent transformer saturation. The soft-start time lasts 8.5 ms and the
feature is implemented for every attempt of the startup converter or after a fault.
SSaux
VDD
capacitor must be sized correctly in order to avoid fast discharge and keep the
is the time needed for the steady-state of the auxiliary voltage. This time is
DD
voltage reaches the V
DDch
Doc ID 022218 Rev 1
current (see
C
VDD
DDoff
=
----------------------------------------
V
I
DDch
DD
DDon
Table 7
threshold. In fact, a too low capacitance value
capacitor calculation:
DDon
×
–
t
V
SSaux
) coming from the internal high voltage
DDoff
threshold (see
DRAIN_START
DD
Table 7
pin, C
, the V
Figure 25
VDD
), the Power
DD
, until the self-
voltage
VIPER37
).