Datasheet

Gate
Drive
tprop
LL
Low Line
High Line
LLI'
HLI'
Ipk/Rsense
tprop
HL
Vin
Lp
LM5023
www.ti.com SNVS961D –APRIL 2013–REVISED JANUARY 2014
Figure 13. Line Current Feed Forward
To improve the overpower limit accuracy over the full Universal Input Line; the LM5023 integrates Line Current
Limit Feed Forward. Line Current Limit Feed Forward improve the overpower limit by summing a current
proportional to the input rectified line into the current sense resistor R
SENSE
), refer to Figure 14. The current
proportional to the input line biases up the current sense pin, this turns off the Flyback MOSFET earlier at high
input line. This feature compensates for the propagation delays creating a overpower protection that is nearly
constant over the Universal Input Line.
To implement Line Current Limit Feed Forward, the first step is to calculate the QR switching frequency at low
line and then at high line when the power supply is operating in current limit.
For our example:
• Lp = 400 µH
• R
SENSE
= 0.15 Ω
• Vdc
min
= 127 V
• Vdc
max
= 325 V
• Tprop = 160 ns
• V
CS
= 0.5 V
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