2 Starter kit approach

PFC for ST7MC Starter Kit

6/20

Figure 3.

Modifications to be performed in the Starter Kit

To get the Bus voltage value a voltage divider with R16-R17 and R20 is used. To get 5 Volts as

a maximum voltage for the AD converter with the new Bus voltage max value, R20 must be

replaced with a 6.2K resistance.

To connect the Power Add On board with the starter kit, use two control cables, one to

communicate the PWM for the Add on coming from starter kit and one to get the zero crossing

from the Add on to the starter kit. The connection of the zero crossing cable is critical. The

shunt resistor has been connected near the pin of the starter kit to avoid a capacitive parasite

effect of the cable acting as a filter for the zero crossing signal and a capacitor of 12pF has

been added to filter the noise.

To generate the PWM for the PFC, the Timer B of the micro is used. The PWM signal of the

PFC Power Add On is connected to the OCMP1_B pin of the micro (J10 Pin 3) and the Zero

Crossing signal of the Add On reaches the ICAP1_B pin of the micro (J10 Pin 7).

The PE2 pin it is connected with ICAP1_B, because it is used to force the reset of PWM when

the ZCD signal is missed.

This could happen for example when the instantaneous input voltage is too low to energize the

inductor.

The Vout of the Add On is the Mains for the Starter Kit board so must be connected to the Pin 2

and Pin 3 of J3.

The ground signal is connected directly from the ground of the micro to the ground of the driver

in the Add On.

The connections are depicted in Figure 4.

C11

100nF

400V

Z4

BZW50-100

C13

1000uF

200V

R2

47K

1W

R16

470K

HV Bus

R17

470K

R20

12K

TP11

R1

47K

1W

C12

1000uF

200V

W2

12

TO SOLDER

Z2

BZW50-120

Z3

BZW50-120

Phase B

TP17

C20

33nF

400V

R21

0.047R

4W

TP14

7NB60HDFP

T5

B60HDFP

T4

FOR 110VAC

R20 6.2K

C20:33nF 600V

R1, R2: 68K - 1Watt

C13, C12:

470uF 450V

Z2, Z3: BZW50-

180 transil