DM330023-2 datasheet(38/64 Pages) MICROCHIP

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dsPICDEM™ MCHV Development System User’s Guide

DS70605A-page 32

 2009 Microchip Technology Inc.

The 3.3 volts rail is created using a step-down regulator which is attached to the 15

volts regulator. The maximum output current is 0.650 A, thus the resultant maximum

power is 2.145 W.

The 3.3 volts rail required for the analog circuits such as the current feedback and the

Analog-to-digital converter is generated by a decoupling circuitry attached to the 3.3

volts regulator.

4.1.5

Fault Circuitry

Given the development nature of the system, robust independent FAULT protection is

provided on the PFC Stage Board. Two different fault categories are used to indicate a

FAULT to the dsPIC® DSC.

DC Bus Overcurrent, this fault signal is generated when the maximum current limit of

15A is reached. The comparison of the threshold value and the actual current is done

by comparator U8. The threshold limit is set by R56 and R57. R69 is a shunt jumper

resistor that can disconnect the overcurrent fault to the dsPIC DSC.

DC Bus Overvoltage, this fault signal is generated when the maximum voltage limit on

the DC bus rails is reached. The threshold value is set to 432 V. The comparison of the

threshold value and the actual DC bus voltage is done by comparator U7. The thresh-

old limit is set by R60, R61 and R62. R66 is a shun jumper resistor that can disconnect

the overvoltage fault to the dsPIC DSC.

4.1.6

Board Connectors

The PFC stage board has four tab fast-on connectors, one AC inlet and one 14-pin

keyed connector for attaching a flat cable.

For the AC mains supply input, standard double-insulated, 3-core flex cable should be

used with a minimum current rating of 10A (1 mm2 18 AWG). A computer power cable

can be used. The recommended cable size is 1.0 to 1.5 mm2 (18-16 AWG) and it

should have a 600V rating. This cable should also be double insulated or have a

protective ground screen.

The tab fast-on connectors AC_N and AC_L provides the connections to the bridge

rectifier BR1. The recommended cable size is 16-18 AWG or 1.0 to 1.5mm2. It is also

recommended that cables used for the power connections should be terminated with

blue or red crimp terminals. If crimp terminals are not used, care should be taken to

ensure that stray strands of wire do not short to adjacent terminals or the enclosure. If

possible, all wires should be stripped and tinned with solder before connecting to the

dsPICDEM MCHV development board terminals.

Note: Both comparators are open-drained and need an external pull-up resistor.

Both circuits share this pull-up resistor creating an OR condition at the

output.

Note 1: The system is designed for installation category II. Therefore, the

incoming mains cable should be wired into a standard non-locking 2-pin

in addition with an earth ground type plug.

2: The unit is designed to be connected to the AC mains supply via a

standard non-locking plug. As the unit has no mains switch, this plug

constitutes the means of disconnection from the supply. Therefore, the

user must have unobstructed access to this plug during operation.

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