IR1110 International Rectifier Corp., IR1110 Datasheet - Page 17

• Manufacturer Part Number: IR1110
• Description: Soft Start Controller Ic In A 64-lead Mqfp Package
• Manufacturer: International Rectifier Corp.

of the load connected to the DC bus. The rate of increase of applied |V
necessary, to limit the bus capacitor charging current.
Adjustment of DC loop gain
loads which have unusually high ripple voltage. Such ripple instability, if it occurs, can be corrected by
reducing the DC loop gain. Figure 6 shows how this is done with a voltage divider, R1 and R2, in the
voltage regulation loop.
SCR Timing Comparators
neously greater than the Timing Wave Reference. The leading edge is the demanded initiation point
for the SCR firing pulse.
needed to fire the SCR, because the Timing Wave remains higher than the Timing Wave Reference
for a significant portion, if not all, of the total cycle time. See Figure 5.
SCR Voltage Comparators
SCR with a fixed reference, SCR
sent an actual anode-cathode voltage of about 15V, before attenuation through the input divider
resistors.
Voltage comparator is high. The outputs of the SCR Voltage and Timing Comparators are ANDed to
obtain the output SCR timing pulses, SCRU, SCRV, SCRW.
as the SCR turns on
generated.
about 13usec at reduced output voltage.
SCR Gate Drivers
SCRW timing pulses. C1 and R2 stretch the duration of the output pulse to 60-80usec. This is
generally necessary to ensure reliable SCR turn-on.
within 5usec. The maximum average current consumed by the three SCR driver circuits is about
10mA.
decreased to say 33
current will now increase to about 20mA.
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a) they do not occur when the Timing Wave is less than the Timing Wave Reference
b) they do not occur unless the instantaneous SCR voltage is at least 15V positive
c) they are terminated when the instantaneous anode-cathode voltage falls below 15V; -i.e. as soon
The voltage regulation loop may exhibit uneven firing angle from one SCR to the next, with
Each SCR Timing Comparator delivers a high output whenever the Timing Wave is instanta-
The duration of the output pulse of the SCR timing comparator is generally much longer than
Each SCR Voltage Comparator compares the instantaneous anode-cathode voltage of the
When the instantaneous SCR anode voltage is greater than 15V, the output of the SCR
The SCRU, SCRV, SCRW output pulses are thus controlled so that;
With discontinuous output current, more than one firing pulse per cycle for each SCR may be
The pulse width of SCRU, SCRV, SCRW is about 6usec at maximum output voltage, and
The SCR gate driver circuit, shown in Figure 7, amplifies and stretches the SCRU, SCRV,
C2 and R4 provide an initial peak turn-on firing current of about .45A, decaying to about .2A
If C2 and R4 are omitted, the peak firing current will be reduced to about .2A. R3 can be
W
, to restore the peak firing current to .45A; the maximum average supply
REF
, which is set by R
ADVANCE INFORMATION
SG1
and R
SG2
. This reference is set to repre-
BUSREF
| should be limited if
IR1110
17