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Pulse width modulation using 555 - del00011

IC1 astable gives a fixed square wave at pin 3, C1 and R1 derive uS trigger pulses from IC1 and this will trigger IC2 monostable or single shot, the voltage at pin 5 of IC2 will change the pulse width output of IC2, to get it working all the three RC combinations have to be figured out.

555 multivibrator like power oscillator

You can even build a small SMPS with this or even control the temperature of your soldering iron using the SSR solid state relay circuits in power section, then you need to think and design the cycle time of a soldering iron heat control system, it  will be in seconds but then above circuit is running at audio frequencies, then you have to work that out yourself..

Pulse width
            modulation using 555

The 555 was the first SmartChip of the early days, in those days we had Opamp and Logic Chips, this was a Mixed
Signal Design chip that was Field Programmable, with presets of course. Innovation Par-Excellence.

LM311 Square Triangle Oscillator for PWM

This circuit can control the pulse width or on-duration by a control voltage. This makes it useful for close loop control systems in energy or heating control.

Edit the circuit Eagle file,

Control Voltage

Pin 5, used for filtering in noisy environs. By imposing a voltage at 5, it is possible to vary the timing independent of RC. The CV can be from 45% to 90% of Vcc in Monostable mode. Control Voltage1.7V to Vcc in astable mode.

This control gives immense possibilities for making Musical Instruments and Sound Effects. It has been popular way in which Bells, Metronomes and Electronic Organs have been made by Hobby DIY Enthusiasts.

555 Control Voltage

Linear PWM or Pulse width Modulator on 555

The PWM uses the Control Voltage Pin 5 like the above circuit. A matched pair of PNP transistors are used to create a Constant Current Source. This way this circuit below is more Linear that the circuit above, this is a PNP Current Mirror. The waveform you will see across the Capacitor is a Nice Linear Ramp.

Linear PWM 555

Images above are from the Original Signetics 555 Datasheet

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delabs Technologies

20th Apr 2020


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