AN2388 datasheet(25/54 Pages) STMICROELECTRONICS

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AN2388

Hardware design

25/54

Figure 21.

Components placement

3.3.2

Auxiliary supply

This Buck converter uses a VIPer12A providing start-up capability, integrated PWM

controller as well as thermal and over-current protection. This PWM controller is very simple

and does not require any external feedback compensation networking. The regulation circuit

is decoupled from the supply circuit, using a separate diode D2 and capacitor C2 to supply

the zener diode D3 on the FB pin. The diode D2 is a low voltage diode (1N4148) and allows

the voltage on Vdd to reach the start-up value. D2 and C2 together form a peak detector for

the output voltage.

To prevent disturbance resulting in possible output over-voltage or incorrect start-up, a zener

D6 is connected across the output. For further details please refer to the application notes

AN1317 and AN1357

An axial insulated inductor can be used. An inductor of this type meets low cost

considerations but features a high series resistance that affects the efficiency of the

converter. The current capability of this kind of inductor is determined, for a given package,

by its series resistance. For example, a 1.5mH inductor has a current capability of about

100mA since its series resistance is about 30R. The 5V is supplied from the 15V using a

L78L05 three-terminal positive regulator. It provides internal current limiting and thermal

shutdown. The 5V Zener diode D5 decreases the voltage regulator temperature in lifetime

sensitive applications.

Note:

When the line voltage is lower than 44V, an external 15V auxiliary supply is mandatory. It

must be plugged to CON2 while removing J14 & J8

AC inputs

VDC

15V supply

BEMF & Hall sensor

Tacho inputs

Motor output

AN2388 Datasheet(PDF) 25 Page - STMicroelectronics