IR1110 International Rectifier Corp., IR1110 Datasheet - Page 15

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

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V
normally connected to ground via Q1. The time constant of R
changes of amplitude of the timing waves that take place over a number of cycles, while maintain-
ing an essentially smooth waveform.
Ramp Circuit
whenever Q3 has been conducting, then switches OFF. The maximum value of VRAMP is
clamped at VPK.
parabolic form, which gives an approximately linear rise of DC bus voltage with a capacitive load.
some influence on the initial rate of change, but more influence later during the ramp-up period.
The minimum and maximum permissible values of C
ramp-up time can be increased above the values shown by increasing R
C
that worst case cumulative tolerances of the governing external components cause sufficient
phase-to-phase unbalance that firing on one phase only occurs during the early part of ramp-up.
the voltage regulation function is not used, and the circuit of Figure 13 is not used, the Figure
15(b) circuit can be used in place of the Figure 15(a) circuit for the same purpose. With either
circuit, both t
Ramp Clamp Circuit
Error Amplifier. This amplifier compares |V
output drives Q3 in a linear mode, diverting I
equal to V
PK
RAMP
Store
=3.3uF and R
C
The current source, IRAMP, creates an increasing voltage, VRAMP, across CRAMP,
VRAMP controls the ramp-up rate of the bus voltage. RRAMP shapes VRAMP to a
The rate of change of VRAMP at the start of the ramp is set by CRAMP. RRAMP also has
The greater the initial rate of rise of VRAMP, the greater the maximum first firing angle.
Typical relationships between C
The maximum first firing angle is specified at maximum AC input voltage, and assumes
The circuit in Figure 15(a) will reduce the maximum first firing angle to 17 , if desired. If
When Q4 is OFF, the ramp clamp is enabled, and Q3 is controlled by the output of the Ramp
PK
BUSO
stores a voltage, V
DPWR
x R
C
0.68
CLAMP2
and t
RAMP
3.3
2.2
uF
1
RAMP
RAMP
/R
open, ramp-up time increases to about 1.2 seconds.
CLAMP1
will increase to about 400msec.
PK
R
130
k
82
47
30
.
RAMP
, that is essentially equal to the peak of the timing waves. R
ADVANCE INFORMATION
RAMP
BUSO
RAMP
(typical)
,R
msec
|, via R
t
165
190
230
270
DPWR
RAMP
from C
,t
CLAMP1
RAMP
DPWR
RAMP
are 0.68uF and 3.3uF respectively. Total
, t
, with V
(typical)
and forcing V
RAMP1
msec
t
PKD
RAMP
100
150
220
330
with C
, and t
RAMP
, via R
PK
D1FIRE
RAMP
RAMP
degrees
allows V
t
(max)
D1FIRE
35
32
25
22
CLAMP2
. For example, with
are as follows:
to be essentially
PK
. The amplified
IR1110
to track
PKD
15
is