UC3843D8 UNITRODE, UC3843D8 Datasheet - Page 7

• Manufacturer Part Number: UC3843D8
• Description: PWM CONTROLLER, SMD, 3843, SOIC8
• Manufacturer: UNITRODE

Specifications of UC3843D8

• Input Voltage: 15V
• Output Voltage: 5V
• Output Current: 200mA
• Frequency: 500kHz
• Power Dissipation Pd: 650mW
• Supply Voltage Range: 12V To 25V
• Digital Ic Case Style: SOIC
• No. Of Pins: 8
• Operating: RoHS Compliant

OPEN-LOOP LABORATORY FIXTURE
High peak currents associated with capacitive loads necessitate careful grounding techniques. Timing and bypas
capacitors should be conected close 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.
SHUTDOWN TECHNIQUES
Shutdown of the UC1842 can be accomplished by two methods; either raise pin 3 above 1 V or pull pin 1 below
a voltage two diode drops above ground. Either method causses the output of the PWM comparator to be high
(refer to block diagram). The PWM latch is reset dominant so that the output will remain low until the next clock
cycle after the shutdown condition at pin 1 and/or 3 is removed. In one example, an externally latched shutdown
may be accomplished by adding an SCR which will be reset by cycling V
this pint the reference turns off, allowing the SCR to reset.
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ERROR AMP
SHUTDOWN
ADJUST
4.7 kW
4.7 kW
1 kW
330 W
ADJUST
I
100 kW
SENSE
2N2222
5 kW
1 kW
500 W
To Current
SENSE RESISTOR
R1
1
2
3
4
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8
3
COMP
V
I
R
SENSE
FB
T
V
I
SENSE
/ C
REF
T
UC1842
GROUND
C
OUTPUT
T
V
REF
V
CC
SHUTDOWN
8
7
6
5
CC
0.1 mF
below the lower UVLO threshold. At
SLUS223C – APRIL 1997 – REVISED JUNE 2007
0.1 mF
A
1 kW 1 W
1
COMP
UC1842/3/4/5
UC2842/3/4/5
UC3842/3/4/5
V
V
OUTPUT
GROUND
REF
CC
7