IRMDSS1

The IR 1110 Soft Start Control IC for a 3-phase half-controlled SCR bridge offers a superior means of precharging the dc bus capacitor, in systems such as variable frequency motor drives. It eliminates the commonly used capacitor precharge resistor, and offers other major system operating advantages, as highlighted below.

The purpose of the IR 1110 Reference Design is to provide the potential user of the IR 1110 ASIC with a fully functional front-end converter, that can be quickly and easily connected into an overall system, for the purpose of demonstrating the operation, evaluating system performance, and reducing designin time.

The IR 1110 Reference Design, shown in Fig. 1, is a self-contained input converter assembly, that accepts three phase or one phase ac line power and delivers controlled dc output to an external bus capacitor and load. A basic schematic is shown in Fig 2.

The Reference Design consists of a PCB, containing IR 1110 Soft Start Controller IC and peripheral components, and three attached IRKH SCR/Diode Add-a-pak modules. The IR 1110 and peripheral circuits float at the potential of the positive terminal of the rectifier, and drive the SCR gates directly without isolation. Opto-couplers mounted on the PCB deliver isolated line fault feedback signals.

Snubbers mounted on the PCB provide dv/dt protection for the SCRs. DC supply voltage for the IR 1110 is derived from the snubber current, and no additional external power supply is required when operating from 3-phase input. When operating continuously from one phase input, an external power supply may be required. (see Section 4 (j) )

It is necessary only to mount the SCR modules to a heatsink, connect ac power to the input terminals, and dc bus capacitor and load to the output terminals. The IR 1110 Reference Design is then ready for operation. This Manual provides information necessary to operate the IR 1110 Reference Design as a functional unit. It is recommended that the user also review the data sheet for the IR 1110 ASIC.