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PDF UC1854B Data sheet ( Hoja de datos )
| Número de pieza | UC1854B | |
| Descripción | Enhanced High Power Factor Preregulator | |
| Fabricantes | UNITRODE | |
| Logotipo |  |
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Enhanced High Power Factor Preregulator
UC1854A/B
UC2854A/B
UC3854A/B
FEATURES
• Controls Boost PWM to Near Unity
Power Factor
• Limits Line Current Distortion To <3%
• World-Wide Operation Without Switches
• Accurate Power Limiting
• Fixed Frequency Average Current Mode
Control
• High Bandwidth (5MHz), Low Offset
Current Amplifier
• Integrated Current and Voltage Amp
Output Clamps
• Multiplier Improvements: Linearity,
500mV VAC Offset (eliminates external
resistor), 0-5V Multout Common Mode
Range
• VREF "GOOD" Comparator
• Faster and Improved Accuracy ENABLE
Comparator
• UVLO Threshold Options
(16/10V / 10.5/10V)
• 300µA Startup Supply Current
UVLO Turn on UVLO Turn off
UC1854A
16V
10V
UC1854B
10.5V
10V
DESCRIPTION
The UC1854A/B products are pin compatible enhanced versions of the
UC1854. Like the UC1854, these products provide all of the functions
necessary for active power factor corrected preregulators. The
controller achieves near unity power factor by shaping the AC input line
current waveform to correspond to the AC input line voltage. To do this
the UC1854A/B uses average current mode control. Average current
mode control maintains stable, low distortion sinusoidal line current
without the need for slope compensation, unlike peak current mode
control.
The UC1854A/B products improve upon the UC1854 by offering a wide
bandwidth, low offset Current Amplifier, a faster responding and
improved accuracy enable comparator, a VREF "good" comparator,
UVLO threshold options (16/10V for offline, 10.5/10V for startup from
an auxiliary 12V regulator), lower startup supply current, and an
enhanced multiply/divide circuit. New features like the amplifier output
clamps, improved amplifier current sinking capability, and low offset
VAC pin reduce the external component count while improving
performance. Improved common mode input range of the Multiplier
output/Current Amp input allow the designer greater flexibility in
choosing a method for current sensing. Unlike its predecessor, RSET
controls only oscillator charging current and has no effect on clamping
the maximum multiplier output current. This current is now clamped to
a maximum of 2 * IAC at all times which simplifies the design process
and provides foldback power limiting during brownout and extreme low
line conditions.
A 1% 7.5V reference, fixed frequency oscillator, PWM, Voltage
Amplifier with softstart, line voltage feedforward (VRMS squarer), input
supply voltage clamp, and over current comparator round out the list of
features.
BLOCK DIAGRAM
6/98
UDG-93001-1
1 page  
UC1854A/B
UC2854A/B
UC3854A/B
FUNCTIONAL DESCRIPTION (cont.)
offset of the UC1854A/B guarantees that the PWM circuit
will not drive the MOSFET if the current command is zero
(both Current amplifier inputs zero.).Previous designs
required an external offset cancellation network to
implement this key feature. The bandwidth of the Current
Amplifier has been improved as well to 5mHz typical.
While this is not generally an issue at 50 or 60Hz inputs, it
is essential for 400Hz input avionics applications.
MISCELLANEOUS
Several other important enhancements have been
implemented in the UC1854A/B. A VCC supply voltage
clamp at 20V allows the controller to be current fed if
desired. The lower startup supply current (250µA typical),
substantially reduces the power requirements of an offline
startup resistor. The 10.5/10V UVLO option (UC1854B)
enables the controller to be powered off of an auxiliary
12V supply.
The VREF "GOOD" comparator guarantees that the
MOSFET driver output remains low if the supply or the
7.5V reference are not yet up. This improvement
eliminates the need for external Schottky diodes on the
PKL and CA+ pins that some UC1854 designs require.
The propagation delay of the disable feature has been
improved to 300ns typical. This delay was proportional to
TYPICAL CHARACTERISTICS at TA = TJ = 25°C
Gate Drive Rise and Fall Time
700
600
500
400
ns
300
200
100
0
0
Rise Time
Fall Time
0.01 0.02 0.03 0.04
Load Capacitance, µF
0.05
Gate Drive Maximum Duty Cycle
100%
95%
90%
Duty
Cycle
85%
80%
75%
70%
1
10
RSET, k Ω
100
UC1854A/B Multiplier Linearity
VAOUT = 3.5V
1.2
1.16
1.12
1.08
1.04
K1
0.96
VRMS=
1.5V
VRMS=
3.0V
VRMS=
5.0V
0.92
0.88
0.84
0.8
0
50 100 150
IAC Current (µA)
200
250
UC1854A/B Multiplier Linearity
VAOUT = 5V
1.2
1.16
1.12
1.08
1.04
K1
0.96
VRMS=
1.5V
VRMS=
3.0V
VRMS=
5.0V
0.92
0.88
0.84
0.8
0
50 100 150
IAC Current (µA)
200
250
5
5 Page | ||
| Páginas | Total 7 Páginas | |
| PDF Descargar | [ Datasheet UC1854B.PDF ] | |
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