UC3842 Просмотр технического описания (PDF) - Fairchild Semiconductor

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производитель

UC3842

SMPS Controller

Fairchild Semiconductor 

UC3842/UC3843/UC3844/UC3845

Electrical Characteristics (Continued)

(VCC=15V, RT=10kΩ, CT=3.3nF, TA= 0°C to +70°C, unless otherwise specified)

Parameter

PWM SECTION

Max. Duty Cycle

Min. Duty Cycle

TOTAL STANDBY CURRENT

Start-Up Current

Operating Supply Current

Zener Voltage

Symbol

Conditions

D(Max)

D(Max)

D(MIN)

UC3842/UC3843

UC3844/UC3845

-

IST

ICC(OPR)

VZ

-

Vpin3=Vpin2=ON

ICC = 25mA

Min. Typ. Max. Unit

95

97 100 %

47

48

50

%

-

-

0

%

- 0.45 1 mA

-

14 17 mA

30

38

-

V

Adjust VCC above the start threshould before setting at 15V

Note:

1. Parameter measured at trip point of latch

2. Gain defined as:

A = ∆-----V----p---i-n---1-

∆Vpin3

,0 ≤ Vpin3 ≤ 0.8V

3. These parameters, although guaranteed, are not 100 tested in production.

UC3842

Figure 1. Open Loop Test Circuit

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 5kΩ potentiometer are used to sample the

oscillator waveform and apply an adjustable ramp to pin 3.

4

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