uc3842a-s08-t Unisonic Technologies, uc3842a-s08-t Datasheet - Page 6

• Manufacturer Part Number: uc3842a-s08-t
• Description: Pwm Controllers With Low Start-up Current
• Manufacturer: Unisonic Technologies

UC3842A/3843A
compensation for converts requiring duty cycles over 50%.Note that capacitor C, forms a filter with R2 to suppress
the leading edge switch spikes.
A fraction of the oscillator ramp can be resistively summed with the current sense signal to provide slope
CURRENT SENSE CIRCUIT
SLOPE COMPENSATION
OSCILLATOR SECTION
UNISONIC TECHNOLOGIES CO., LTD
100
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0.1
10
1
1
Rs
Dead time vs. C
R
Is
Peak current (Is) determined by the formula: Ismax=10V/Rs.
A small RC filter be required to suppress switch transients.
CT (nF)
8
4
5
C
10
1
3
5
8
4
3
RT
CT
T
(R
T
Large RT
Large CT
Small CT
Small RT
>5kΩ)
Error Amplifier
CT
100
RT
R1
2R
R
C
R2
100
10
1
1V
Timing Resistance vs. Frequency
10 2
INTERNAL CLOCK
INTERNAL CLOCK
Rsense
Isense
LINEAR INTEGRATED CIRCUIT
Current Sense Comparator
V4
V4
10
3
Frequency (Hz)
CT=100nF
CT=47nF
CT=22nF
10
CT=10nF
CT=4.7nF
4
CT=2.2nF
10
5
10
6
QW-R103-002,D
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