LS7339(2001) Ver la hoja de datos (PDF) - LSI Corporation

Número de pieza

componentes Descripción

Fabricante

LS7339
(Rev.:2001)

AUTO SHUT-OFF AC POWER SWITCH WITH PROGRAMMABLE TIMER

LSI Corporation  

FIGURE 6. PRODUCING VERY LONG TIME-OUTS BY PULSE MODULATING THE OSCILLATOR

R2

D1

R1

Waveform A

Oscillator

Components

-V

4

3

2

1

TRIG V DD OFF ON

+V

LS7339

D2

R3

C2

-+

V SS OSC CAP SYNC

5

6

7

8

CD4093

C1 = 0.1µF

-V

T1

Waveform A

T2

Waveform B

Waveform B (Pulse Modulator)

T1

T1 ≈ R1 C1

T2 ≈ (R1 + R2)C1

Period = T1 + T2

Pulse Duty Cycle = T1/Period

Inverse of Pulse Duty Cycle = Period/T1 = 1 +T2/T1 = 2 + R2/R1

DESCRIPTION:

The Oscillator resistor is normally returned to the negative terminal of the DC Supply. If this resistor is returned to

a negative-going pulse instead, the Oscillator R-C becomes effectively multiplied by the inverse of the Pulse Duty

Cycle, because the Oscillator R-C can charge only while the pulse is present. (Pulse Modulation)

In Figure 6, the Oscillator R is R3, the Oscillator C is C2 and the Pulse Modulator is Waveform B through

isolation diode D2. The Multiplier, M = 2 + R2/R1 (the inverse of the Pulse Duty Cycle).

EXAMPLE: R3 = 5.1MΩ , C2 = 1.0µF, Pulse Modulator = Waveform B and desired TD1 = 8 hours = 28,800 sec.

Since TD1 = 255 x M x R3 x C2, M calculates to be 22 for the selected Oscillator Components.

With M = 22, R2/R1 = 20. If R2 = 3MΩ , R1 = 150kΩ .

7339-060201-5

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