Datasheet

V
PWR
V
IN
V
CC
8V - 15V (from
aux winding)
C1
LM5026
9V
0.1
0.1 PF
50
LM5026
V
IN
V
PWR
LM5026
www.ti.com SNVS363D –AUGUST 2005–REVISED APRIL 2013
Applications Information
LINE INPUT (VIN)
The LM5026 contains an internal high voltage start-up regulator that allows the input pin (VIN) to be connected
directly to a nominal 48V line voltage. The voltage applied to the VIN pin can vary in the range of 13 to 100V with
transient capability to 105V. When power is applied and the UVLO pin potential is greater than 0.4V, the VCC
regulator is enabled and sources current into an external capacitor connected to the VCC pin. When the voltage
on the VCC pin reaches the regulation point of 7.7V, the internal voltage reference (REF) is enabled. The
reference regulation set point is 5V. The controller outputs are enabled when the UVLO pin potential is greater
than 1.25V. In typical applications, an auxiliary transformer winding is connected through a diode to the VCC pin.
This winding must raise the VCC voltage above 8V to shut off the internal start-up regulator. It is recommended a
filtering circuit shown in Figure 27 be used to suppress transients, which may occur at the input supply, in
particular when VIN is operated close to the maximum operating rating.
Figure 27. Input Transient Protection
FOR APPLICATION > 100V
For applications where the system input voltage exceed 100V or IC power dissipation is a concern, the LM5026
can be powered from an external start-up regulator as shown in Figure 28. In this configuration, the VIN and the
VCC pins should be connected together, which allows the LM5026 to be operated below 13V. The voltage at the
VCC pin must be greater than 8V yet not exceed 15V. An auxiliary winding can be used to reduce the dissipation
in the external regulator once the power converter is active.
Figure 28. Start-Up Regulator for V
PWR
>100V
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