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8

FAN8303 and NCP718 Auxiliary Power Supplies

The FAN8303 is a non−isolated buck that is used as

converter from 15 Vdc to 5 Vdc output. The maximum

power demand is 2.9 W. Figure 6 depicts the schematic of

the 5 Vdc auxiliary power supply. Similarly to the

NCP1063, the design and sizing of the passive components

has been inspired by the applications notes in [4]. The

desired output voltage value can be set by tuning the values

of the voltage divider (R5 and R6) connected to the FB pin.

Additionally, the value of C17 on the COMP pin is tuned

empirically to reflect the desired voltage at the converter

output. The controller operates at fixed 370 kHz with an

efficiency up to 90%. This allows a design with only 22

mH

magnetizing inductance (see L3) and two 22

mF capacitors

(see C13 and C14). Finally, Figure 6 depicts the NCP718

LDO, which is responsible for the 3.3 Vdc rail generation.

Figure 6. Schematic of Auxiliary 5 Vdc and 3.3 Vdc Power Supply

Inverter Stage: Compact Intelligent Power Module

(IPM) Technology

This subsection shows how the necessary circuitry for

operation, measurement and protection is setup around the

NFAM5065L4B IPM. In addition, it illustrates the necessary

circuitry to provide and capture the signals around the

module (i.e. the output signals: T_MODULE, IPM_FAULT;

and the input signals: ITRIP, IPM_DIS, and gate driver

signals INH_U, INH_V, INH_W, INL_U, INL_V, INL_W).

Finally, it illustrates the provision of the voltage rails for the

IPM (15 Vdc rail reference), as well as the measurement of

the DC−Link and inverter−phase voltages. Activation of

IPM stage (connection to 15 Vdc power supply) is via J1

(soldered pads). Figure 7 shows the J1 pads at the bottom

side of the board; mind that pads should be soldered together

to enable the 15 Vdc to the IPM. Following, Figure 8 shows

the schematic of the inverter stage and the necessary

circuitry around it. Finally, Figure 8 depicts the DC−Link

voltage (voltage divider containing R46, R52, R53 and R55)

and the inverter output phase−voltage measurement

circuitry (voltage divider for phase−U containing R31, R34,

R40 and R42; voltage divider for phase−V containing R32,

R35, R41 and R43; and voltage divider for phase−W

containing R29, R33, R39 and R44). The inverter output

voltage phases can be used by the software for zero crossing

detection or other control purposes. The signals from the

10 m

W shunt resistors are going to current measurement and

over−current protection circuits. Details regarding the ADC

resolution of the above sensed electrical quantities can be

found in Table 1. Next paragraphs are dedicated to the

elaboration of the above mentioned circuitries.

Figure 7. J1 Pads at the Bottom of the Board (the Pads should be Soldered to Enable the 15 Vdc in the IPM)