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PDF UC2844 Data sheet ( Hoja de datos )
| Número de pieza | UC2844 | |
| Descripción | Current Mode PWM Controller | |
| Fabricantes | Unitrode | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de UC2844 (archivo pdf) en la parte inferior de esta página. Total 8 Páginas | ||
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Current Mode PWM Controller
UC1842/3/4/5
UC2842/3/4/5
UC3842/3/4/5
FEATURES
• Optimized For Off-line And DC
To DC Converters
• Low Start Up Current (<1mA)
• Automatic Feed Forward
Compensation
• Pulse-by-pulse Current Limiting
• Enhanced Load Response
Characteristics
• Under-voltage Lockout With
Hysteresis
• Double Pulse Suppression
• High Current Totem Pole
Output
• Internally Trimmed Bandgap
Reference
• 500khz Operation
• Low RO Error Amp
DESCRIPTION
The UC1842/3/4/5 family of control ICs provides the necessary features to im-
plement off-line or DC to DC fixed frequency current mode control schemes
with a minimal external parts count. Internally implemented circuits include un-
der-voltage lockout featuring start up current less than 1mA, a precision refer-
ence trimmed for accuracy at the error amp input, logic to insure latched
operation, a PWM comparator which also provides current limit control, and a
totem pole output stage designed to source or sink high peak current. The out-
put stage, suitable for driving N Channel MOSFETs, is low in the off state.
Differences between members of this family are the under-voltage lockout
thresholds and maximum duty cycle ranges. The UC1842 and UC1844 have
UVLO thresholds of 16V (on) and 10V (off), ideally suited to off-line applica-
tions. The corresponding thresholds for the UC1843 and UC1845 are 8.4V
and 7.6V. The UC1842 and UC1843 can operate to duty cycles approaching
100%. A range of zero to 50% is obtained by the UC1844 and UC1845 by the
addition of an internal toggle flip flop which blanks the output off every other
clock cycle.
BLOCK DIAGRAM
Note 1: A/B A = DIL-8 Pin Number. B = SO-14 Pin Number.
Note 2: Toggle flip flop used only in 1844 and 1845.
4/97
1 page  
UNDER-VOLTAGE LOCKOUT
UC1842/3/4/5
UC2842/3/4/5
UC3842/3/4/5
During under-voltage lock-out, the output driver is biased to ground with a bleeder resistor to prevent activating the power
sink minor amounts of current. Pin 6 should be shunted to switch with extraneous leakage currents.
CURRENT SENSE CIRCUIT
Peak Current (IS) is Determined By The Formula
ISMAX
≈
1.0V
RS
A small RC filter may be required to suppress switch transients.
OSCILLATOR SECTION
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet UC2844.PDF ] | |
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