
2
IRMDSS1
1. Introduction
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 design-
in 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.
2. Input voltage and output current ratings.
The IR 1110 Reference design is fitted with IR’s 1600V rated IRKH
series Addapak SCR-diode modules. Components on the PCB are factory set
for an input operating voltage range of 320V to 550V rms, 3-phase, 47 to
63Hz. Operation at other input line voltages is possible by changing
component values on the PCB, as specified in Table 1.
The IR 1110 Reference Design can be set up for dedicated 1-phase
operation, as detailed in Table 1.