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NE555 Datasheet(PDF) 8 Page - STMicroelectronics |
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NE555 Datasheet(HTML) 8 Page - STMicroelectronics |
8 / 10 page ![]() LINEAR RAMP When the pullup resistor, RA, in the monostable cir- cuit is replaced by a constant current source, a linear ramp is generated. Figure 17 shows a circuit con- figuration that will perform this function. Trigger Output C NE555 2 4 3 1 5 6 7 8 E VCC 0.01 µF R2 R1 R 2N4250 or equiv. Figure 17. Out R A C NE55 2 4 3 1 5 6 7 8 VCC 51k Ω RB 22k Ω 0.01 µF VCC 0.01 µF Figure 19 : 50% Duty Cycle Oscillator. Figure 18 shows waveforms generator by the linear ramp. The time interval is given by : T = ( 2/3 VCC RE (R1+ R2) C R1 VCC ± VBE (R1+ R2) VBE = 0.6V Figure 18 : Linear Ramp. VCC = 5V Top trace : input 3V/DIV Time = 20 µs/DIV Middle trace : output 5V/DIV R1 = 47k Ω Bottom trace : output 5V/DIV R2 = 100k Ω Bottom trace : capacitor voltage RE = 2.7k Ω 1V/DIV C = 0.01 µF 50% DUTY CYCLE OSCILLATOR For a 50% duty cycle the resistors RA and RE may be connected as in figure19. The time preriod for the output high is the same as previous, t1 = 0.693 RA C. For the output low it is t2 = [ (RARB) ⁄ (RA + RB)] CLn RB ± 2RA 2RB ± RA Thus the frequency of oscillation is f = 1 t1 + t2 Note that this circuit will not oscillate if RB is greater than 1/2 RA because the junction of RA and RB can- not bring pin 2 down to 1/3 VCC and trigger the lower comparator. ADDITIONAL INFORMATION Adequate power supply bypassing is necessary to protect associated circuitry. Minimum recom- mended is 0.1 µF in parallel with 1µF electrolytic. NE555/SA555/SE555 8/10 |
Similar Part No. - NE555_95 |
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Similar Description - NE555_95 |
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