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UC3842 Datasheet(PDF) 6 Page - NXP Semiconductors

Part No. UC3842
Description  Current-mode PWM controller
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Maker  PHILIPS [NXP Semiconductors]
Homepage  http://www.nxp.com
Logo PHILIPS - NXP Semiconductors

UC3842 Datasheet(HTML) 6 Page - NXP Semiconductors

  UC3842 Datasheet HTML 1Page - NXP Semiconductors UC3842 Datasheet HTML 2Page - NXP Semiconductors UC3842 Datasheet HTML 3Page - NXP Semiconductors UC3842 Datasheet HTML 4Page - NXP Semiconductors UC3842 Datasheet HTML 5Page - NXP Semiconductors UC3842 Datasheet HTML 6Page - NXP Semiconductors UC3842 Datasheet HTML 7Page - NXP Semiconductors UC3842 Datasheet HTML 8Page - NXP Semiconductors  
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Philips Semiconductors Linear Products
Product specification
UC3842
Current-mode PWM controller
August 31, 1994
1105
OPEN-LOOP LABORATORY TEST FIXTURE
NOTE:
High peak currents associated with capacitive loads necessitate careful grounding techniques. Timing and bypass capacitors should be connected 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.
4.7k
ERROR AMP
ADJUST
4.7k
2N2222
100k
5k
ADJUST
COMP
1
2
3
4
8
7
6
5
OUTPUT
GND
1k
1W
OUTPUT
GND
VREF
VCC
RT
UC3842
VFB
ISENSE
RT/CT
VREF
VCC
0.1
µF
ISENSE
CT
A
0.1
µF
SHUTDOWN TECHNIQUES
NOTE:
Shutdown of the UC3842 can be accomplished by two methods; either raise Pin 3 above 1V or pull Pin 1 below a voltage two diode drops above ground. Either method causes 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 Pins 1 and/or 3 is removed. In the examples shown, an externally-latched shutdown may be accomplished by adding an SCR which will be reset by cycling
VCC below the lower UVLO threshold (10V). At this point all internal bias is removed, allowing the SCR to reset.
1
COMP
SHUTDOWN
TO CURRENT
SHUTDOWN
SENSE RESISTOR
4.7k
4.7k
8
3
500
ISENSE


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