UM0723 datasheet(17/48 Pages) STMICROELECTRONICS

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UM0723

Board description

Doc ID 15870 Rev 4

17/48

Figure 9.

Power supply block diagram

3.3.2

Inrush limitation

The input stage of the demonstration board is provided with the 10

Ω NTC resistor to

eliminate input inrush current peak during charging of the bulk capacitors. To achieve

a higher efficiency of the inverter, it is possible to bypass the NTC after the startup phase.

The NTC bypass signal is provided from the MCU board through the J5 connector. The

yellow D27 LED diode is turned off when the inrush NTC is bypassed.

The STEVAL-IHM023V2 demonstration board contains only a basic EMI filter based on X2

and Y2 capacitors. The main function of this demonstration board is as a universal testing

platform. For this reason, the EMI filter is not able to absorb EMI distortion coming from the

inverter for all ranges of the applications used and the design of the filter is up to the user.

The EMI filter must be designed according to the motor and final target applications used.

The heatsink itself is connected to the earth pin in the input J1 connector. If the

demonstration board is used only with DC voltage, it is recommended to connect the

heatsink to a negative voltage potential - common ground.

3.3.3

Brake function

The hardware brake feature has been implemented on the STEVAL-IHM023V2

demonstration board. This feature connects the external resistive load applied to the J6

connector to the bus to eliminate overvoltage generated when the motor acts as

a generator. Such a connected load must be able to dissipate all motor generated energy.

The brake feature functions automatically in the case of bus overvoltage. Voltage on the bus

is sensed through the voltage divider with resistors R23, R24, and R31 and compared to the

voltage reference built around the Zener diode D26. The brake dummy load is switched on

when voltage on the bus reaches 440 VDC and is switched off when the voltage falls below

420 VDC. This voltage level has been chosen to be fully compliant with the possible use of

front-end PFC stage. Another possibility, to activate the brake dummy load, is to use the

external signal coming through the J5 motor connector (PWM_Brake signal) from the

connected MCU board. This function is active with the jumper W5 in position “R_BRAKE”.

The brake threshold levels can be modified by calculating R23, R24, and R34 new values.

The D28 red LED diode indicates acting brake switch.

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