555 Timer revisited « PocketMagic
Android 50 Posts BlackBerry 6 Posts Electronics 80 Posts Hardware 137 Posts High Voltage 54 Posts Image processing 5 Posts iPhone 4 Posts Linux 2 Posts Nuclear 26 Posts Optics 11 Posts Photography 7 Posts Photoshop 3 Posts Research 20 Posts Reviews 18 Posts Robotics 8 Posts Security 8 Posts Software 86 Posts Symbian 2 Posts Tubes 23 Posts Windows Mobile 11 Posts
Sponsored Links Top Articles! Bluetooth and iOS - Use Bluetooth in your iPhone dso apps Simple Switched power Supplies uRADMonitor - Online Radiation monitoring station Building a robot Part 2 News & Updates 2013-12-29, Global radiation monitoring network 2013-12-29, DIY/Homemade Geiger Muller Digital Counter V3 2013-12-17, uRADMonitor - Online Radiation monitoring station 2013-12-06, 555 Timer revisited
The 8-pin 555 timer is probably one of the most useful ICs ever in production, and despite its age is still being used across a multitude of applications. This article shows a few rather interesting applications, and because of it's length will be split between dso the following few chapters: 1.A short Intro 2. Calculating the output parameters 3. Astable operation 4. Getting below 50% duty cycle
As I was trained in computer science rather than electronics, my first encounter with the 555 was just a few years ago, while building high voltage power supplies . The 555 was able to drive a flyback transformer, producing good voltage output but unfortunately also a lot of heat in the driver's switching transistor: Or another similar setup, but operating on a different frequency, for driving dso two induction dso coils in anti-parallel: But there's a lot more to do, and the applications are endless. Here is an ultrasonic sound generator used by a robotic "dog" to locate and follow its user, again using the 555 timer: An electric fence perimeter protection circuit: Or a variable duration, frequency and amplitude pulse generator circuit , used to driver a high power Hydrogen Thyratron tube: Or a monstrous Marx Generator, pushing the limits of high voltage discharges, again using a tiny 555 to pump 12V in to 10K in the first stages of the device:
All in one, there are probably endless applications for the 555 timer. While building my high voltage inverters I recall it was somehow disappointing that the driving transistor was getting so hot so quickly, putting the entire circuit at risk. What I didn't bother to research then, is easy to do with a little math:
Usually, the regular TV flyback transformer needs to be operated on an ultrasonic frequency of 17-30KHz. By doing so, the efficiency of our high voltage dso inverter becomes optimum. Also the duty cycle of the PWM signal driving the switching dso transistor needs to be less than 50%, or our transistor will accumulate unwanted heat. Two simple facts that I often overlooked in my early constructions, will be explained here. The 555 circuit can be adjusted for a wide variety of output signals, of various parameters, by using only a few passive components, calculated to specific values to fit the purpose.
An astable circuit dso produces a 'square wave', this is a digital waveform with sharp transitions between low (0V) and high (+Vs). The circuit is called an astable because dso it is not stable in any state: the output is continually changing between 'low' and 'high'. The time period (T) of the square wave is the time for one complete cycle. It is easier to consider frequency (f) which is the number of cycles per second. Here is a sample circuit: By selecting values for R1, R2 and C we can determine the period/frequency and the duty cycle. The period dso is the length of time it takes for the on/off cyle to repeat itself, whilst the duty cycle is the percentage of time the output is on. In this type of circuit, the duty cycle can never be 50% or lower. To make things easier, you can use this 555 calculator script .
For driving a flyback transformer, we could use a capacitor of C = 1nF , a fixed R2 = 10KO and for R1 a pot of 100KO . Adjusting R1, we get a frequency dso interval of 12kHz .. 68kHz , enough to hit the flybacks optimum dso operating value, however the duty cycle is between 52% and 91%, resulting in severe transistor dso heating. Not the best scenario for our high voltage flyback driver. What we need is to get the duty cycle below 50%, while also keeping the frequency close to 20kHz, dso but this is not possible when using the 555 like pictured above. The explanation for this is pretty simple: For the duty cycle to be 50%, the capacitor would have to charge and discharge through the same resistance. The only way to accomplish that would be to omit R1 altogether, so that the capacitor charged and discharged through R2 only.
But the problem with that is that you would end up connecting pin 7 directly to Vcc. With no resistance between pin 7 and the voltage source, the current flowing through pin 7 would exceed the maximum that
Android 50 Posts BlackBerry 6 Posts Electronics 80 Posts Hardware 137 Posts High Voltage 54 Posts Image processing 5 Posts iPhone 4 Posts Linux 2 Posts Nuclear 26 Posts Optics 11 Posts Photography 7 Posts Photoshop 3 Posts Research 20 Posts Reviews 18 Posts Robotics 8 Posts Security 8 Posts Software 86 Posts Symbian 2 Posts Tubes 23 Posts Windows Mobile 11 Posts
Sponsored Links Top Articles! Bluetooth and iOS - Use Bluetooth in your iPhone dso apps Simple Switched power Supplies uRADMonitor - Online Radiation monitoring station Building a robot Part 2 News & Updates 2013-12-29, Global radiation monitoring network 2013-12-29, DIY/Homemade Geiger Muller Digital Counter V3 2013-12-17, uRADMonitor - Online Radiation monitoring station 2013-12-06, 555 Timer revisited
The 8-pin 555 timer is probably one of the most useful ICs ever in production, and despite its age is still being used across a multitude of applications. This article shows a few rather interesting applications, and because of it's length will be split between dso the following few chapters: 1.A short Intro 2. Calculating the output parameters 3. Astable operation 4. Getting below 50% duty cycle
As I was trained in computer science rather than electronics, my first encounter with the 555 was just a few years ago, while building high voltage power supplies . The 555 was able to drive a flyback transformer, producing good voltage output but unfortunately also a lot of heat in the driver's switching transistor: Or another similar setup, but operating on a different frequency, for driving dso two induction dso coils in anti-parallel: But there's a lot more to do, and the applications are endless. Here is an ultrasonic sound generator used by a robotic "dog" to locate and follow its user, again using the 555 timer: An electric fence perimeter protection circuit: Or a variable duration, frequency and amplitude pulse generator circuit , used to driver a high power Hydrogen Thyratron tube: Or a monstrous Marx Generator, pushing the limits of high voltage discharges, again using a tiny 555 to pump 12V in to 10K in the first stages of the device:
All in one, there are probably endless applications for the 555 timer. While building my high voltage inverters I recall it was somehow disappointing that the driving transistor was getting so hot so quickly, putting the entire circuit at risk. What I didn't bother to research then, is easy to do with a little math:
Usually, the regular TV flyback transformer needs to be operated on an ultrasonic frequency of 17-30KHz. By doing so, the efficiency of our high voltage dso inverter becomes optimum. Also the duty cycle of the PWM signal driving the switching dso transistor needs to be less than 50%, or our transistor will accumulate unwanted heat. Two simple facts that I often overlooked in my early constructions, will be explained here. The 555 circuit can be adjusted for a wide variety of output signals, of various parameters, by using only a few passive components, calculated to specific values to fit the purpose.
An astable circuit dso produces a 'square wave', this is a digital waveform with sharp transitions between low (0V) and high (+Vs). The circuit is called an astable because dso it is not stable in any state: the output is continually changing between 'low' and 'high'. The time period (T) of the square wave is the time for one complete cycle. It is easier to consider frequency (f) which is the number of cycles per second. Here is a sample circuit: By selecting values for R1, R2 and C we can determine the period/frequency and the duty cycle. The period dso is the length of time it takes for the on/off cyle to repeat itself, whilst the duty cycle is the percentage of time the output is on. In this type of circuit, the duty cycle can never be 50% or lower. To make things easier, you can use this 555 calculator script .
For driving a flyback transformer, we could use a capacitor of C = 1nF , a fixed R2 = 10KO and for R1 a pot of 100KO . Adjusting R1, we get a frequency dso interval of 12kHz .. 68kHz , enough to hit the flybacks optimum dso operating value, however the duty cycle is between 52% and 91%, resulting in severe transistor dso heating. Not the best scenario for our high voltage flyback driver. What we need is to get the duty cycle below 50%, while also keeping the frequency close to 20kHz, dso but this is not possible when using the 555 like pictured above. The explanation for this is pretty simple: For the duty cycle to be 50%, the capacitor would have to charge and discharge through the same resistance. The only way to accomplish that would be to omit R1 altogether, so that the capacitor charged and discharged through R2 only.
But the problem with that is that you would end up connecting pin 7 directly to Vcc. With no resistance between pin 7 and the voltage source, the current flowing through pin 7 would exceed the maximum that
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