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UC3843AD

P1-P3P4-P6P7-P8
C URRENT MODE PWM CONTROLLER
UC184xA/284xA/384xA
PRODUCT DATABOOK 1996/1997
7
Copyright © 1995
Rev. 1.2a 10/25
P RODUCTION DATA SHEET
TYPICAL APPLICATION CIRCUITS (continued)
FIGURE 6. — SLOPE COMPENSATION
FIGURE 7. — OPEN LOOP LABORATORY FIXTURE
2
3
4
8
7
6
5
COMP
V
FB
I
SENSE
R
T
C
T
V
REF
V
CC
OUTPUT
GROUND
0.1µF 0.1µF
A
UCx84xA
R
T
2N2222
100K
4.7K
1K
4.7K
5K
I
SENSE
ADJUST
ERROR AMP
ADJUST
C
T
1K
GROUND
OUTPUT
V
CC
V
REF
1
OSCILLATOR
V
REF
GOOD LOGIC
S
R
5V
REF
INTERNAL
BIAS
8(14)
4(7)
2(3)
1(1)
R
F
C
F
R
d
R
i
From V
O
R
SLOPE
2N222A
R
T
5V
UVLO
2.5V
ERROR
AMP
C
T
1V
2R
R
C.S.
COMP
PWM
LATCH
5(9)
3(5)
5(8)
CR
S
R
6(10)
7(11)
7(12)
V
CC
DC BUS
V
O
Q1
UCx84xA
Due to inherent instability of current mode converters running above 50% duty cycle, slope compensation should be added to either
the current sense pin or the error amplifier. Figure 6 shows a typical slope compensation technique.
High peak currents associated with capacitive loads necessitate careful grounding techniques. Timing and bypass capacitors should be
connected to pin 5 in a single point ground. The transistor and 5k potentiometer are used to sample the oscillator waveform and apply an
adjustable ramp to pin 3.
C URRENT MODE PWM CONTROLLER
UC184xA/284xA/384xA
PRODUCT DATABOOK 1996/1997
Copyright © 1995
Rev. 1.2a 10/25
8
P
RODUCTION DATA SHEET
TYPICAL APPLICATION CIRCUITS (continued)
FIGURE 8. — OFF-LINE FLYBACK REGULATOR
SPECIFICATIONS
Input line voltage: 90VAC to 130VAC
Input frequency: 50 or 60Hz
Switching frequency: 40KHz ±10%
Output power: 25W maximum
Output voltage: 5V +5%
Output current: 2 to 5A
Line regulation: 0.01%/V
Load regulation: 8%/A*
Efficiency @ 25 Watts,
V
IN
= 90VAC: 70%
V
IN
= 130VAC: 65%
Output short-circuit current: 2.5Amp average
* This circuit uses a low-cost feedback scheme in which the DC
voltage developed from the primary-side control winding is
sensed by the UC3844A error amplifier. Load regulation is
therefore dependent on the coupling between secondary and
control windings, and on transformer leakage inductance.
7
150kW
100pF
V
FB
COMP
V
REF
R
T
/C
T
4700µF
10V
5V
2-5A
ISOLATION
BOUNDARY
3600pF
400V
1N4935
820pF
2.5k
W
1N4935
IRF830
27k
W
0.01µF
10µF
20V
1N4935
1k
W
470pF
0.85k
W
MBR735TI
4.7k
W
2W
140kW
1/2W
220µF
250V
4.7k
W
1W
1N4004
1N40041N4004
1N4004
AC
INPUT
V
CC
OUT
CUR
SEN
GND
UC3844A
20kW
3.6k
W
10kW
.0022µF0.01µF
16V
3
6
2
1
8
4
5
P1-P3P4-P6P7-P8

UC3843AD

Mfr. #:
Buy UC3843AD
Manufacturer:
Texas Instruments
Description:
Switching Controllers Current Mode
Lifecycle:
New from this manufacturer.
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