IRMDSS1 Datasheet IRMDSS1 | P7-P9

k is given approximately by the following relationship:

k VBUS1 = (

VBUS1) - 0.1 VLLmax

= 0.75 VBUS1 - 0.1 VLLmax

Note that the value of k can be adjusted, if needed, by changing the value of

R79.

(b) If the bus voltage dips below k VBUS1 during the line outage,

then when the input voltage returns, the dc bus voltage is

ramped back by SCR phase control.

4(g) Temporary loss of one input phase.

If one input phase is lost during 3-phase operation, for more

than 1 to 1 1/2 cycles, the SCR firing pulses are removed,

deactivating the rectifier. When the missing phase returns, the bus

voltage ramps back to the set value.

Without this one-phase shut-down function, the following

operating problems could occur:

(a) If one input phase is lost while the bus voltage is being

regulated to less than the maximum value, the rectifier output

voltage can transiently jump to the maximum value when the

missing phase returns.

This is undesirable, unless there is sufficient inductance

in the ac input lines, or in the dc smoothing inductor, (if used),

to limit the resulting current.

(b) Transient loss of one phase during the early part of initial

ramp-up can cause a jump of bus voltage to the maximum

value, if the missing phase returns while ramp-up is still in

progress.

For these reasons, the IR 1110 Reference Design is factory-set

with the one-phase shut-down function enabled.

4(h) Disabling one-phase shut-down at maximum bus voltage, if the

voltage regulation function is not used.

If the bus voltage regulation function is not used, it may be

desired to disable the one phase shut-down function in normal

IRMDSS1

operation, allowing the rectifier to operate as a one phase bridge

when one phase is missing.

Note that these remarks apply to loss of one phase when the IR1110 is set

for normal 3-phase operation. If the IR1110 is set for dedicated 1-phase operation

(See Table 1), the 1-phase shut down function is inactive.

The following modifications disable the one-phase shut-down

function at full bus voltage - but keep this function enabled when

the output voltage is below a set value during ramp-up.

(1) Cut traces and add link as illustrated in Fig 7.

(2) Remove R92, R7.

(3) Add D14, R6, R95, R96, D15, Q5, Q6. Connect 0.1µF across base

and emitter of Q7. Add diode (MA 116CT) across the open

R85 pads, with cathode towards pin 41 of the IR 1110.

(4) Change R101 to 220k, R100 to 0 Ohm link.

(5) Change R53 to 470k, 5%, 1/16W. Change C19 to 0.1µF, 6.3V,

10%. Remove R58, insert R57 (0 Ohm, link).

4(i) DC bus short-circuit.

When operating from a 3-phase supply, the IR 1110 Reference

Design automatically limits the fault current when the dc bus is

short-circuited.

If a bus short-circuit exists when the line voltage is switched

on, the SCR firing angle will not advance to more than about 35

electrical degrees ahead of the line voltage crossover.

If a bus short-circuit occurs during operation, the SCR firing

angle is phased back in less than half a cycle, to within about 35

electrical degrees of the line voltage crossover.

Short circuit current is thus limited to a much lower level than

would be obtained with an uncontrolled rectifier bridge.

Note that this function is active when the IR 1110 Reference

Design is set up for 3-phase operation, but not for dedicated 1-phase

operation.

4(j) Omission of on-board SCR Snubbers/use of external-power supply.

The on-board SCR snubbers may not be required for dv/dt

protection, if external ac line filters are fitted.

If the on-board snubbers are omitted, it will be necessary to

provide external isolated +-15V (20mA) power to the PCB. The

required power supply connections to the PCB are shown in Fig 8.

IRMDSS1

Remove the following snubber and associated components:

C13, C14, R43, R44, D1, D2, R45, D3, C15, C16, R46, R47, D5, D6,

R48, D7, C17, C18, R49, R50, D9, D10, D11.

On-board dropping resistors and zener diodes create the

required internal +5V and -5V power for the IR 1110, from the

applied +-15V input. The rise time of the +-15V voltages during

power-up should not be less than 1 millisecond.

The primary source for the power supply must be derived

from the ac input voltage of the rectifier bridge. It cannot be taken

from the main dc bus voltage, because this voltage does not exist

until after the IR 1110 has been energized. During power-up, the

input to the power supply must be switched on synchronously with

the rectifier input voltage.

4(k) External shut-down.

External shut-down of the rectifier bridge is implemented by applying a

15mA input to opto-coupler U7, at JP5/3 (+) and JP5/4.

5 . Fault feedback signals.

Isolated fault feedback signals are delivered at the outputs of opto-

couplers U6 and U4, as shown in Fig 9(a) for the IR 1110 Reference Design,

as factory-set. U6 delivers a multiplexed 3-phase loss/1-phase loss signal;

U4 delivers a low line-voltage signal.

An integral part of the circuit modification described in Section 4(h),

is that opto coupler U6 delivers a 3-phase loss fault signal only, without

the multiplexed 1-phase loss signal. The one-phase loss signal is now

multiplexed with the low line signal. The fault signals for this mode are

illustrated in Fig 9(b).

6 . Use of the PCB with an external SCR half-controlled bridge.

For test purposes, the IR 1110 Reference Design PCB by itself can be

used with an external SCR half-controlled bridge. This is done by

detaching the PCB from the IRKH Addapak modules, and making wired

connections between the PCB and the external SCR bridge.

Fig 10 shows a connection diagram. Note that the wires from JP2, U,

V, W, and the wire from JP3/1, should be run as a twisted bundle. The

gate and auxiliary cathode leads for each SCR should be run as twisted

pairs. Also note that zero ohm links must be connected across the open

pads R13, R17, R21 that connect to the auxiliary cathode slots on the PCB.

IRMDSS1

7 . Inductance.

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P23

IRMDSS1

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KIT DESIGN IC REF SOFT START

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