Advanced Power

Electronics Corp.

APE1911

FUNCTION DESCRIPTION

PWM Control

Setting the Output Voltage

Table 1 Resistor select for output voltage setting

Inductor Selection

Input Capacitor Selection

4

The APE1911 consists of DC/DC converters that employ a pulse-width

modulation (PWM) system. In converters of the APE1911, the pulse width varies in a

range from 0 to 85%, according to the load current. The ripple voltage produced by the

switching can easily be removed through a filter because the switching frequency

remains constant. Therefore, these converters provide a low-ripple power over broad

ranges of input voltage and load current.

Application circuit item shows the basic application circuit with APE1911 adjustable

output version. The external resistor sets the output voltage according to the following

equation:

For most designs, Low inductance values are physically smaller but require faster

switching, which results in some efficiency loss. The inductor value can be derived from

the following equation:

Where is inductor Ripple Current. Large value inductors lower ripple current and small

value inductors result in high ripple currents. Choose inductor ripple current approximately

The DC current rating of the inductor should be at least equal to the maximum load

current plus half the ripple current to prevent core saturation (2.4A+0.18A).

The input capacitor reduces the surge current drawn from the input and switching

noise from the device. The input capacitor impedance at the switching frequency shall be

less than input source impedance to prevent high frequency switching current passing to

the input. A low ESR input capacitor sized for maximum RMS current must be used.

The capacitor voltage rating should be at least 1.5 times greater than the input

voltage, and often much higher voltage ratings are needed to satisfy.

9V

12V

15V

18V

L1 Value

18uH

22uH

25uH

33uH

R3

R4

12V

1K

11K

15V1.3K18K

18V1.3K22K

24V1.3K30K

32V2.2K68K