Advanced Power

Electronics Corp.

APE1912

FUNCTION DESCRIPTION

PWM Control

Setting the Output Voltage

Table 1 Resistor select for output voltage setting

Input Capacitor Selection

FUNCTION DESCRIPTION

Output Capacitor Selection

4

The APE1912 consists of DC/DC converters that employ a pulse-width modulation

(PWM) system. In converters of the APE1912, 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 APE1912 adjustable

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

equation:

R3

R4

5V

3K

12K

12V

1K

11K

15V1.3K18K

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.

The output capacitor is required to keep the output voltage ripple small and to

ensure regulation loop stability. The output capacitor must have low impedance at the

switching frequency. A low ESR capacitor sized for maximum RMS current must be

used. The low ESR requirements needed for low output ripple voltage.

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.