Microchip Technology dsPICDEM MCHV-3, Руководство пользователя, Страница: 34 / 68

dsPICDEM™ MCHV-3 Development Board User’s Guide
DS50002505A-page 34
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2016 Microchip Technology Inc.
3.1.4 Power Supplies
The PFC Stage Board provides the 15V power supply required to fire the power module
IGBTs. The 15V power supply is built using a low-power offline SMPS primary switcher.
The switching frequency is fixed to 60 kHz; the feedback signal to the power supply is
provided by the optocoupler. The output voltage is regulated at 15V with a maximum
output current of 0.750A, with the resultant maximum power at 11.25W. The input
voltage range for this power supply is from 90 VAC to 265 VAC.
The PFC stage board also provides the 3.3V to powering up the Microchip PIC
MCU/dsPIC
DSC devices, the isolation circuitry, the communication ports, the Starter Kit
programmer, etc. It also generates the 3.3V for powering the analog circuits and the
analog reference for the Analog-to-Digital Converter (ADC) module.
The 3.3V rail is created using a step-down regulator, which is attached to the
15V regulator. The maximum output current is 0.650A, thus the resultant maximum
power is 2.145W.
The 3.3V 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
3.3V regulator.
3.1.5 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 Microchip PIC MCU/dsPIC DSC devices.
DC Bus Overcurrent:
This Fault signal is generated when the maximum current limit
of 13A 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 Microchip PIC MCU/dsPIC
DSC devices.
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 412V. The comparison of
the threshold value and the actual DC bus voltage is done by comparator, U7. The
threshold limit is set by R96, R60, R61 and R62. R66 is a shunt jumper resistor that can
disconnect the overvoltage Fault to the Microchip PIC MCU/dsPIC DSC devices.
Note:
Both comparators are of an open-drain type and need an external pull-up
resistor. Both circuits share this pull-up resistor, creating an OR condition
at the output.