UC2838, UC2838A
UC3838, UC3838A
SLUS221A APRIL 2000 REVISED MAY 2001
MAGNETIC AMPLIFIER
CONTROLLER
UDG-97174
10
VCC
VREF
9
2.5 V
REFERENCE
INV. IN
8
E/A OUT
3
INV. IN
6
7
N.I. IN
2
1
N.I. IN
C/L OUT
C/L
E/A
3.5 V
15 DR 1
16 DR 2
RESET
14
VM
11
5
12
13
4
GND GND GND GND
+
+
20
1 k
5 k
1
www.ti.com
FEATURES
D
Independent 1% Reference
D
Two Uncommitted, Identical Operational
Amplifiers
D
100-mA Reset Current Source With 120-V
Capability
D
5-V to 40-V Analog Operation
D
5-W DIP Package
BLOCK DIAGRAM
DESCRIPTION
The UC3838 and the UC3838A family of magnetic
amplifier controllers contains the circuitry to
generate and amplify a low-level analog error
signal along with a high voltage-compliant current
source. This source provides the reset current
necessary to enable a magnetic amplifier to
regulate and control a power supply output in the
range of 2 A to 20 A.
The UC3838A originally was a parametric
improvement version of the UC3838 which since
has been used for both versions. There is no
difference between the UC3838A and UC3838
version.
By controlling the reset current to a magnetic
amplifier, this device defines the amount of
volt-seconds the magnetic amplifier blocks before
switching to the conducting state. Magnetic
amplifiers are ideal for post-regulators for
multiple-output power supplies where each output
can be independently controlled with efficiencies
up to 99%. With a square or pulse-width
modulated input voltage, a magnetic amplifier
blocks a portion of this input waveform, allowing
just enough to pass to provide a regulated output.
With the UC3838/A, only the magnetic amplifier
coil, three diodes, and an output L-C filter are
necessary to implement a complete closed-loop
regulator.
AVAILABLE OPTIONS
Packaged Devices
TA = TJ
SOIC Wide
(DW)
PDIP (N)
PLCC (Q)
20
C to 85
C
UC2838DW
UC2838N
UC2838Q
20
C to 85
C
UC2838ADW
UC2838AN
UC2838AQ
0
C to 70
C
UC3838DW
UC3838N
UC3838Q
0
C to 70
C
UC3838ADW
UC3838AN
UC3838AQ
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
UC2838, UC2838A
UC3838, UC3838A
SLUS221A APRIL 2000 REVISED MAY 2001
2
www.ti.com
description (continued)
The UC3838/A contains a precision 2.5-V reference, two uncommitted high-gain operational amplifier and a
high-gain PNP-equivalent current source which can deliver up to 100 mA of magnetic amplifier reset current
and with 120-V capability.
These devices are available in a plastic batwing DIP (N), wide body SOIC (DW), and PLCC (Q) package for
operation over a 20
C to 85
C temperature range.
19
20
1
3
2
17
18
16
15
14
13
12
11
9
10
5
4
6
7
8
RESET
N/C
N/C
GND
VM
C/L INV.IN
GND
N/C
N/C
E/A INV.IN
C/LN.I.IN
C/LOUT
N/C
DR2
DR1
E/A
OUT
N/C
VREF
VCC
E/A
N.I.IN
Q PACKAGE
(TOP VIEW)
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
C/L OUT
C/L N.I. IN
C/L INV. IN
GND
GND
E/A INV. IN
E/A N.I. IN
E/A OUT
DR2
DR1
RESET
GND
GND
VM
VCC
VREF
DW AND N PACKAGES
(TOP VIEW)
absolute maximum ratings over operating free-air temperature (unless otherwise noted)
Supply voltage, V
CC
40 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Magnetic amplifier source voltage, VM
40 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reset output voltage, VR
120 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Total current source voltage, VM VR
140 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Amplifier input range
0.3 V to VCC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reset input current, DR1 and DR2
10 mA
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power dissipation at T
A
= 25
C
Q, N, DW package
2 W
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power dissipation at T (leads/case) = 25
C
Q, N, DW package
5 W
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating temperature range, T
J
55
C to 125
C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Storage temperature range, T
stg
65
C to 150
C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lead temperature (soldering, 10 sec)
300
C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions beyond those indicated under "recommended operating conditions" is not
implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
All voltages are with respect to ground pins. All currents are positive into the specified terminal. Consult packaging section of data book for thermal
limitations and considerations of package.
UC2838, UC2838A
UC3838, UC3838A
SLUS221A APRIL 2000 REVISED MAY 2001
3
www.ti.com
electrical characteristics, T
A
= 20
C to 85
C for the UC2838/A, and T
A
= 0
C to 70
C for the
UC3838/A, V
CC
= 20 V, VM = 5 V, T
A
= T
J
, (unless otherwise stated)
reference
PARAMETER
TEST CONDITIONS
UC2838/UC2838A
UC3838/UC3838A
UNITS
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
Supply current
VCC = VM = 40 V
4
8
4
8
mA
Reference output
TA = 25
C
2.47
2.50
2.53
2.45
2.50
2.55
V
Line regulation
VCC = 5 V to 30 V
1
5
1
10
mV
Load regulation
IO = 0 mA to 2 mA
5
20
5
20
mV
Short-circuit current
VREF = 0 V
30
60
30
60
mA
Temperature stability
See Note 1
15
25
10
25
mV
NOTE: 1.These parameters are ensured by design but not 100% tested in production.
amplifier (each amplifier)
PARAMETER
TEST CONDITIONS
UC2838/UC2838A
UC3838/UC3838A
UNITS
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
Offset voltage
VCM = 2.5 V
5
10
mV
Input bias current
VIN = 0 V
1
1
A
Input offset voltage
100
100
nA
Minimum output swing
0.4
18
0.4
18
V
Output sink current
VO = 5 V
1
10
30
1
10
30
mA
Output source current
VO = 0 V
1
10
20
1
10
20
mA
AVOL (open loop gain)
VO = 1 V to 11 V
100
120
100
120
dB
CMRR (common mode rejection ra-
tio)
VIN = 1 V to 11 V
70
80
70
80
dB
PSRR (power supply rejection ratio)
VCC = 10 V to 20 V
70
100
70
100
dB
Gain bandwidth
See Note 1
0.6
0.8
0.6
0.8
MHz
NOTE: 1.These parameters are ensured by design but not 100% tested in production.
reset drive
PARAMETER
TEST CONDITIONS
UC2838/UC2838A
UC3838/UC3838A
UNITS
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
Input leakage
VDR = 40 V
10
10
A
Output leakage
VR = 120 V
100
100
A
Input current
IR = 50 mA
1
2
1
2
mA
Maximum reset current
IDR = 3 mA
100
120
200
100
120
200
mA
Transconductance
IR = 10 mA to 50 mA
0.03
0.042
0.055
0.03
0.042
0.055
A/V
UC2838, UC2838A
UC3838, UC3838A
SLUS221A APRIL 2000 REVISED MAY 2001
4
www.ti.com
typical application
NOTE: 12 V, 4 A output with switching frequency = 50 kHz.
+
+
3
2
6
7
4.7 k
0.47
8
16
15 k
0.1
1
15
20
14
11
10
REF
9
4, 5, 12, 13
2.5 V
300
1 W
UES1003
UES2403
UES2403
100
0.02
100
9.1 k
1000
3.6 k
12 k
2 k
2.4 k
+
GND
+V O
100
H
UC3838/A
15 V
AUXILLIARY
SUPPLY
12 V
SECONDARY
WINDING
MAGNETIC
AMPLIFIER
45 TURNS
50B101D CORE
APPLICATION INFORMATION
Figure 1.
0.1
10
1 k
10 k
1 M
0
20
40
60
80
100
120
Signal Frequency Hz
360
315
270
225
180
1.0
100
0.1 M
Phase
Gain
VO
VIN
+
VIN
2.5 V
VO
Gain = 20 Log
140
Gain Magnitude
dB
GAIN MAGNITUDE/PHASE
vs
SIGNAL FREQUENCY
Phase
C
Figure 2.
0.2
0.4
0.8
1.0
1.2
20
40
60
Input Current mA
80
100
0
0.6
1.4
0
120
T J= 25 C
T J= 55 C
T J= 125 C
GAIN MAGNITUDE
vs
SIGNAL FREQUENCY
Reset
Current
mA
UC2838, UC2838A
UC3838, UC3838A
SLUS221A APRIL 2000 REVISED MAY 2001
5
www.ti.com
APPLICATION INFORMATION
Figure 3.
0
20
60
80
100
20
40
60
Reset Voltage V
80
100
0
T
J
= 25 C
IB = 0.4 mA
IB = 0.6 mA
IB = 0.8 mA
IB = 1.0 mA
IB = 1.2 mA
40
Reset
Current
mA
RESET CURRENT
vs
RESET VOLTAGE
120
Figure 4.
Gain Magnitude
dB
GAIN MAGNITUDE/PHASE
vs
SIGNAL FREQUENCY
Phase
C
1 k
10 k
100 k
1 M
10 M
30
25
20
15
10
5
0
5
Signal Frequency Hz
360
315
270
225
180
GAIN
PHASE
5 V
VO
VIN
GAIN = 20 LOG
IO (dc) = 50 mA
RI = 10
IO (ac) = 10 mA
VO
VIN
Figure 5.
1
3
4
5
20
40
60
Input Voltage V
80
100
0
2
0
6
120
T J = 25 C
T J = 125 C
VM = 5 V
VIN
IR
Reset
Current
mA
RESET CURRENT
vs
INPUT CURRENT
T J = 55 C
Figure 6.
50
0
50
100
150
2.45
2.46
2.47
2.48
2.49
2.50
2.51
Junction Temperature
2.52
2.53
2.54
2.55
Reference
V
oltage Output
V
REFERENCE VOLTAGE OUTPUT
vs
JUNCTION TEMPERATURE
C
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2001, Texas Instruments Incorporated
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