LM3101M datasheet(16/20 Pages) NSC

16 / 20 page

Typical Applications (Continued)

The maximum average current through the secondary and

the diode when the switch is off is the maximum load cur-

rent divided by the inverse of the duty cycle

ISEC(OFF) e ILOAD (1–D(MAX)) e 10A072

1390A

15A

The maximum average secondary current for the entire peri-

od is the maximum load current (10A)

The maximum reverse-bias voltage on the output rectifier is

VRV e VIN(MAX) (NS NP) a VO a VF e

(185V) (185) a 57V e 2747V

30V

A suitable diode for this circuit is the SR1606 which has a

reverse voltage rating of 60V and an average current rating

of 16A

Telecom Converter

The schematic of a flyback regulator used in Telecom appli-

cations is shown in

Figure 11 The circuit has many of the

component values that are in the offline converter Notable

exceptions are the power transformer in which the turns

ratio and primary inductance has changed (due to the

change in the input voltage range) and the Power MOS-

FET which has a lower on-resistance and a lower break-

down voltage rating

The most significant difference in the circuit design is the

change in the mode of operationfrom voltage mode to

current mode For current mode operation the LM3101

Mode Control pin (MC – pin 2) is connected to ground by a

6kX resistor and the Control Mode pin (CMI – pin 6) is

connected to the current sense transformer through a half-

wave rectifier circuit and a low-pass filter The filter is need-

ed to remove the leading edge spike on the current wave-

form caused by the rectifier recovery and interwinding ca-

pacitance of the power transformer

Smaller component differences include reducing the current

sensing resistor in the primary side ground path (to allow for

the larger primary current) and removing a primary side

snubber circuit (due to smaller peak voltages at the drain)

Also the output rectifier and Power MOSFET snubbers are

modified

TLH11436 – 17

FIGURE 11 Telecom Current Mode Flyback Regulator

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