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## NE555 Datasheet(PDF) 8 Page - STMicroelectronics

 Part No. NE555 Description GENERAL PURPOSE SINGLE BIPOLAR TIMERS Download 10 Pages Scroll/Zoom 100% Maker STMICROELECTRONICS [STMicroelectronics] Homepage http://www.st.com Logo

 8 page LINEAR RAMPWhen the pullup resistor, RA, in the monostable cir-cuit is replaced by a constant current source, a linearramp is generated. Figure 17 shows a circuit con-figuration that will perform this function.TriggerOutputCNE55524315678EVCC0.01µFR2R1R2N4250or equiv.Figure 17.OutR ACNE5524315678VCC51kΩRB22kΩ0.01µFVCC0.01µFFigure 19 : 50% Duty Cycle Oscillator.Figure 18 shows waveforms generator by the linearramp.The time interval is given by :T= (2/3 VCC RE(R1+ R2) CR1 VCC− VBE (R1+ R2)VBE = 0.6VFigure 18 : Linear Ramp.VCC = 5VTop trace : input 3V/DIVTime = 20µs/DIVMiddle trace : output 5V/DIVR1 = 47kΩBottom trace : output 5V/DIVR2 = 100kΩBottom trace : capacitor voltageRE = 2.7kΩ1V/DIVC = 0.01µF50% DUTY CYCLE OSCILLATORFor a 50% duty cycle the resistors RA and RE maybe connected as in figure19. The time preriod for theoutput high is the same as previous,t1 = 0.693 RA C.For the output low it is t2 =[(RARB) ⁄ (RA + RB)] CLnRB − 2RA2RB− RAThus the frequency of oscillation is f=1t1+ t2Note that this circuit will not oscillate if RB is greaterthan 1/2 RA because the junction of RA and RB can-not bring pin 2 down to 1/3 VCC and trigger the lowercomparator.ADDITIONAL INFORMATIONAdequate power supply bypassing is necessary toprotect associated circuitry. Minimum recom-mended is 0.1µF in parallel with 1µF electrolytic.NE555/SA555/SE5558/10