dc to ac converter using 555 timer - Page 1
Forum section: electronics / beginners

author: Adhith
author_rank: Frequent Contributor
timestamp: January 22, 2016, 08:14:45 am
content: hello everyone...i have made a dc to ac converter using 555 timer ic for my stun gun project . for 9v input i got 6.2 v output when DMM set in dc mode but 0 volt when set in ac mode. is it because,since output is a pulsating dc so it works only on dc mode of DMM??. i have also connected a new bug zapper transformer to increase the voltage but no output. can anyone help ?? i have attached the circuit diagram .

author: deshmukhmalhar
author_rank: Contributor
timestamp: January 22, 2016, 04:24:49 pm
content: Hi! first of all, fix he image attached. it is broken. you cannot boost/buck DC voltage with bare transformer. Please give more detail about the project you want to do.Regards,-Malhar.

author: Adhith
author_rank: Frequent Contributor
timestamp: January 22, 2016, 04:50:58 pm
content: sir.. i have attached the full circuit diagram. till now i have only built the left handside of the circuit.

author: tooki
author_rank: Super Contributor
timestamp: January 22, 2016, 05:47:55 pm
content: Is it possible that circuit just can't work? How does it begin to oscillate, since there's nothing going into the Trigger pin except the output itself? (This circuit doesn't seem to be any of the three typical 555 configurations.)Where in the circuit are you measuring the 6.2VDC?

author: Zero999
author_rank: Super Contributor
timestamp: January 22, 2016, 08:45:03 pm
content: It should oscillate.The 555 is configured as a Schmitt trigger and is inverting so it works like a 74HC14 oscillator.As to why it's not generating a high voltage. It could be because the transformer is not being driven at the correct frequency or the turns ratio is incorrect: are you sure you've got the correct winding connected to the transistor?

author: Adhith
author_rank: Frequent Contributor
timestamp: January 23, 2016, 03:29:38 am
content: Quote from: tooki on January 22, 2016, 05:47:55 pmthe voltage was measured between the collector & the 4,8 shorted line(where one terminal of supply was given).

author: Adhith
author_rank: Frequent Contributor
timestamp: January 23, 2016, 03:37:30 am
content: Quote from: Hero999 on January 22, 2016, 08:45:03 pmiam not using the transformer specified in the circuit diagram(ie 1k:8R) instead am using a transformer of bug zapper. but when i measured the output in ac mode of DMM either it shows a wrong value or zero volts.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 23, 2016, 05:22:26 am
content: OK... so you have not yet built the voltage multiplier part of the circuit, right? And you are using a different transformer. OK.When you are measuring your output, are you looking across the transformer secondary?Please check the DC resistances of the primary and secondary of the transformer you are using, with the transformer disconnected from the rest of the circuit.Please check to make sure you have the Darlington transistor BD679 connected properly. The pinout from the ST data sheet is indicated on my edit of your diagram below.

author: deshmukhmalhar
author_rank: Contributor
timestamp: January 23, 2016, 05:55:00 am
content: What is the AC voltage across secondary of the transformer measured after connecting the 555 IC and its peripheral part correctly?

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 23, 2016, 06:55:31 am
content: Well, I can at least confirm that the circuit does oscillate, at about 2kHz with the components and supply voltage as shown. When connected to a random stepup transformer from my junkbox it generates enough voltage to light up a NE-2 neon on the secondary. So once the C-W voltage multiplier is added it should work as designed.

author: station240
author_rank: Unknown
timestamp: January 23, 2016, 08:07:53 am
content: I'd wrap a few of turns of insulated wire around the outside of the transformer, and measure the voltage on this third winding. That way you can measure if it's operating without blowing your multimeter up.

author: Zero999
author_rank: Super Contributor
timestamp: January 23, 2016, 08:43:47 am
content: Quote from: alsetalokin4017 on January 23, 2016, 06:55:31 amPehaps it didn't work with the bug zapper transformer because it's designed to work at a much higher frequency than 2kHz.An ordinary mains transformer should work. I've managed to create a few kV using a mains transformer in a flyback circuit with no voltage multiplier, so be careful you don't destroy the diodes, capacitors or even the insulation on the transformer.

author: Adhith
author_rank: Frequent Contributor
timestamp: January 23, 2016, 09:50:43 am
content: Quote from: alsetalokin4017 on January 23, 2016, 05:22:26 amno iam measuring the output without connecting the transformer and it reads arround 6v(DMM in dc mode). transformer secondary shows 0v when connected. The resistance is 2ohm primary & 220 ohm secondary. the transformer looks like centre tapped but no resistance for the other terminals. i have connected the transistor correctly . Now i have made the voltage multiplier & when i connected it to the 555 circuit no voltage output. since the voltage multiplier needs ac or pulsating dc to work..i think the 555 is not doing its oscillation. what should i do??

author: Adhith
author_rank: Frequent Contributor
timestamp: January 23, 2016, 09:54:00 am
content: when i opened a bug zapper i havent seen any 555 timer. just transistor diodes & capacitors. so is there any simple alternate way for oscillation.??

author: Adhith
author_rank: Frequent Contributor
timestamp: January 23, 2016, 12:10:47 pm
content: is there any connection for pin no. 7 ?? i just leaved it as it is

author: Zero999
author_rank: Super Contributor
timestamp: January 23, 2016, 02:55:52 pm
content: Quote from: Adhith on January 23, 2016, 09:54:00 amYes. The simplest way to make an oscillator with a transformer is to use a blocking oscillator and is very common in bug zappers.

author: Adhith
author_rank: Frequent Contributor
timestamp: January 23, 2016, 04:13:53 pm
content: Quote from: Hero999 on January 23, 2016, 02:55:52 pmi do have bug zapper transformer with me. so can you give me a idea about the specifications about the resistor,transistor & capacitor??can i make it with the components in the stun gun circuit??

author: Zero999
author_rank: Super Contributor
timestamp: January 23, 2016, 06:47:01 pm
content: Plenty of examples of the blocking oscillator circuit can be found using a search engine.The transformer needs a tap in the primary or another winding for feedback. It may be difficult to identify which winding is for the feedback and which is the drive.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 23, 2016, 09:28:28 pm
content: Quote from: Adhith on January 23, 2016, 09:50:43 amI guess you do not have an oscilloscope. What kind of DMM are you using, does it have a "frequency" setting?Almost all DMMs will do a fair averaging when set to DC and measuring an oscillating DC pulse signal. This circuit produces such a signal, and when I measure the Pin 3 output with respect to Ground (Pin 1) I get "around" 6V (with 12 volt supply) using either a very cheap 4 dollar DMM or a Fluke 87-III. The Fluke reports a frequency just over 2 kHz, which agrees with the oscilloscope's measurement also. See the images below.(Your voltage measurements of the 555 side of the circuit should be made with respect to the Ground, Pin 1 negative power supply rail, unless you are measuring the output side of the transformer, in which case they should be across the transformer secondary itself.)No, the Pin 7 is not connected in this circuit.I think the fact that you are getting your "around" 6V probably means your circuit IS oscillating, and there is something else wrong on the output side. You certainly should be able to measure _something_ on the secondary of the transformer otherwise.What are you using for a power supply? This circuit will switch the output of the power supply directly into the transformer primary, and if your primary is 2 ohms DC resistance, at 12 volts that means I = V/R or 6 amps during the ON state of the pulse. (Neglecting the resistance of the transistor and inductive impedance of the primary). Some power supplies may see this as a direct short circuit and shut down or fold back.Just to check the 555/transistor part of the circuit, try connecting an LED + 1k resistor instead of the transformer primary.(Personally, I would use a mosfet instead of the Darlington transistor in this application.....)

author: Adhith
author_rank: Frequent Contributor
timestamp: January 24, 2016, 08:37:00 am
content: Quote from: alsetalokin4017 on January 23, 2016, 09:28:28 pmno my DMM dont have frequency settings. its just an ordinary DMM. when i used a 9v (ac to dc) adapter to power the supply i saw that the 555 is getting warmer, does it indicates anything??.Does suppling a higher voltage 12v make any difference for the oscillation??

author: MrSlack
author_rank: Frequent Contributor
timestamp: January 24, 2016, 03:24:34 pm
content: Your 555 isn't too hot yet. This one is (similar circuit, actually still operating):If it's hot it's probably oscillating. Can you measure any AC voltage at the transistor base with your meter? Also are you actually using a BD679?

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 24, 2016, 07:32:39 pm
content: I don't think your 555 should be getting hot. Check your wiring and component values carefully.The _transistor_ should probably be getting hot if you are driving that 2 ohm transformer primary with it.What voltage (DC) do you see when you test the Pin 3 output wrt Pin 1 ground? Also what voltage (DC) do you see when you test the Collector of the transistor wrt the Emitter (also Pin 1 ground)?(Depending on the meter, DMMs may or may not give proper AC readings when testing a pulsing _DC_ signal. On the DC setting, though, they will usually give a correct _average_ voltage for such a signal.)At 9V supply voltage, my breadboard of your circuit oscillates at about 1.8 kHz, and at 12 volt supply it is almost exactly 2 kHz. My build produces a very short spike pre-pulse before the main pulse. This pre-pulse throws off the automatic frequency measurement of the scope but the cursors show that the main pulse is at about 2 kHz. See the scopeshot below, of the Pin 3 output wrt Pin 1 ground.Try putting in a 1 uF (one microFarad) capacitor instead of the 10 nF between Pin 2 and Pin 1. This will slow down the oscillation to something you can see with your eyes. Instead of the transformer primary, connect an LED + 1k resistor as load (Positive rail>1k resistor>LED anode>LED cathode>transistor collector). You should see it flashing. If you don't, there is something wrong with your circuit.

author: Adhith
author_rank: Frequent Contributor
timestamp: January 26, 2016, 12:24:58 pm
content: Quote from: MrSlack on January 24, 2016, 03:24:34 pmno ac voltage can be seen. yes am sure that it is BD679.

author: Adhith
author_rank: Frequent Contributor
timestamp: January 26, 2016, 12:40:34 pm
content: Quote from: alsetalokin4017 on January 24, 2016, 07:32:39 pmthe voltage across pin 1 & 3 of 555 ia arround 4.3v collector wrt emitter is 0.30v & collector wrt pin1 is also the same(0.30v). iwill change the capacitance and the post it. thanks..

author: Adhith
author_rank: Frequent Contributor
timestamp: January 26, 2016, 12:44:09 pm
content: SORRY to trouble you guys.. the problem was with the transformer that i connected . when i connected a new 230v/9v transformer in reverse i got an ac output of 180v(also i could hear a low humming noise too) . now i just need to have the required transformer which will give a higher voltage. can any one help me.. ?? also i would like to know why the previous transformer was not responding to the voltage.

author: Adhith
author_rank: Frequent Contributor
timestamp: January 26, 2016, 01:28:25 pm
content: Thank you very much my friends for your support ,especially those who made the circuit and given me the readings.your detailed answers was very helpfull...

author: ali6x944
author_rank: Frequent Contributor
timestamp: January 26, 2016, 07:20:08 pm
content: or u could try the 555 in push -pull configuration with a hand wind toroidal transformer

author: Adhith
author_rank: Frequent Contributor
timestamp: January 27, 2016, 05:31:58 am
content: i have identified the primary and secondary pins of the transformer. but when i connect any load or the voltage multiplier the transformer stops working , after reconnecting the battery & removing the load, the transformer works. it simply stops working when connected to any load. what may be the reason?? there are 3 legs in the transformer but no resistance can be found for the other pins using DMM. should i ground the the other legs or something to do with the other legs??

author: Adhith
author_rank: Frequent Contributor
timestamp: January 27, 2016, 05:36:27 am
content: Quote from: Hero999 on January 23, 2016, 06:47:01 pmdoes the problem with the transformer is related to feedback??

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 27, 2016, 07:33:39 am
content: As I mentioned earlier, this circuit switches the entire input power across the transformer primary when the transistor is in the ON state (555 pin 3 output High). The current is limited only by the internal resistances of the transformer primary and the Darlington transistor itself.If you are trying to power this circuit with a 9V battery, it is very likely that the voltage is sagging so much that it just won't work.Please place your voltmeter directly across the battery terminals, and then press the "on" button of your circuit. Do you see the voltage dropping?Also, without knowing the precise details of the transformer you are using, there isn't any way to answer your question. No, the problem is not related to the "feedback", this is not that kind of circuit. If you post a photo of your transformer, and show where you are measuring the resistances and where you get "no resistance can be found" it may make it possible for us to help.You may be interested in the attached scopeshots. This is the performance of my breadboarded version of your circuit. The Yellow trace is the secondary output of the transformer I am using, and the Blue trace is the Pin 3 output of the 555 timer. These traces are telling me that the oscillation frequency of the 555 is much too low for best performance from the transformer I'm using. However, even with only 9V input to the circuit, the transformer is still producing peaks of over 200 volts on the secondary output. But because the peaks are just a small part of each cycle and there is a lot of "dead time", there isn't really much power in the output.You might try raising the frequency of your oscillator by lowering the value of the 10 nF capacitor and/or the 33k resistor. For example if you change the 33k to 2.2k the oscillator's frequency will go up to around 27 kHz. With my transformer this works a lot better. See the third scopetrace below. This is with 9V input from a regulated power supply, and is lighting up a NE-2 neon from the secondary.

author: Zero999
author_rank: Super Contributor
timestamp: January 27, 2016, 09:53:10 am
content: Quote from: alsetalokin4017 on January 27, 2016, 07:33:39 amThat's if transformer is driven into core saturation.If the transistor is turned off before the core saturates, then it will be much more efficient. This is probably why it works much better at a higher frequency.

author: Connoiseur
author_rank: Regular Contributor
timestamp: January 27, 2016, 01:30:54 pm
content: Well it's a long story if you are new to electronics (and/or electrical) I would suggest you visit NPTEL website and look for electrical course materials, they are awesome(and absolutely free), you won't regret the time you spend.Just as Hero999 pointed out it appears from your description is that your bug zapper transformer was rated for higher frequency than what the 555 oscillator was doing. The core was getting saturated (ferrite saturates at about 0.2T whereas CRGO steel may go upto 1.5T)There's an equation which relates the flux density, frequency and volts/turn you can supply to a transformer.E=4.44*(flux density in tesla)*(area of core in sq metres)*(frequency in hertz)Where, E is rms voltage per turn of conductor.You can use it to wind your own transformer or modify an existing one.(However the above equation is accurate only for sinusoidal voltage waveforms, once it's shape changes a lot of other factors come into play, which are beyond the scope of this discussion)

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 27, 2016, 03:21:38 pm
content: I think this entire discussion is beyond the scope of this discussion.(which is why I focussed only on practical matters rather than theory....)

author: Adhith
author_rank: Frequent Contributor
timestamp: January 28, 2016, 05:58:18 am
content: Quote from: alsetalokin4017 on January 27, 2016, 07:33:39 amthank you for your support alsetalokin4017. this is the transformer that iam using. the winding resistance is also mentioned. does it gives you any idea??

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 28, 2016, 06:19:36 am
content: OK, I've numbered the pins on the transformer for our discussion.Note the thick wire attached to Pin 1. Is there also this same thickness wire attached to Pin 6? And if there is, do you get a "0 ohm" reading between Pins 1 and 6?Also, what pins have you connected to your circuit? Can you post the schematic again, including the transformer, and the pin numbers I've used here, please?

author: Adhith
author_rank: Frequent Contributor
timestamp: January 28, 2016, 08:49:23 am
content: Quote from: alsetalokin4017 on January 28, 2016, 06:19:36 amyes a same thickness wire is there for pin 6 too. no, i got 1 ohm resistance between pin 1 & pin 6. i have connected the output from 555 to the pins having 2 ohm and leaved the pins having 220 ohm as transformer output. but as soon as my voltmeter touches the pins the transformer stops working and no voltage can be detected. when i used a different transformer( ie 230v/9v) in reverse i can measure arround 180v & accidently i got shock from it too & its working. but this transformer(ie 230v/9v) also stops working when loaded. you said about posting a schematic again. what schematic do you want, can you make it little more clear please..

author: Zero999
author_rank: Super Contributor
timestamp: January 28, 2016, 10:40:25 am
content: Quote from: ali6x944 on January 26, 2016, 07:20:08 pmThe trouble with that configuration is the driving transistors have a huge voltage drop. They're arranged as emitter followers which drop over 0.8V under load, plus the voltage drop of the transistors in the 555 timer output stage.Quote from: Adhith on January 27, 2016, 05:36:27 amDid you try looking for blocking oscillator using your favourite search engine?

author: Adhith
author_rank: Frequent Contributor
timestamp: January 28, 2016, 11:13:24 am
content: Quote from: Hero999 on January 28, 2016, 10:40:25 amyes i did. actually i bought all the components for it . since my 555 circuit is working, i havnt done it. does blocking oscillator circuit will make any difference when compared to my 555 circuit??

author: Adhith
author_rank: Frequent Contributor
timestamp: January 28, 2016, 04:54:42 pm
content: Quote from: Connoiseur on January 27, 2016, 01:30:54 pmthank you for the information about NPTEL . looking forward to join a course. actually am studing mechanical engineering but intrested in electronics too. so i can make use of this website for sure.the main supply frequency in India is about 50 hertz and the 230v/9v transformer that i used must work properly right...? or is there more factors to be considered..?

author: Zero999
author_rank: Super Contributor
timestamp: January 28, 2016, 09:24:15 pm
content: Quote from: Adhith on January 28, 2016, 11:13:24 amA blocking oscillator relys on the properties of the transformer and automatically adjusts its frequency to suit. It's much simpler than a 555 timer circuit, more reliable and is most commonly used in simple boost converters such as a bug zapper.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 28, 2016, 10:47:45 pm
content: Quote from: Adhith on January 28, 2016, 08:49:23 amSo.... we have established that your basic 555 circuit _is_ oscillating, since you would not have gotten a little shock otherwise.I think that the actual Primary of your transformer is the winding with the thickest wire, pins 1 and 6 on my numbering scheme. The Secondary is the 220 ohm winding. The third winding is probably a trigger winding for a different type of circuit. So you could try using the 1-6 winding as the primary.I also think that the oscillation frequency of your 555 circuit is very much too slow. Change the 33K resistor to 2.2k or 2.7 k or 3.3 k or something in that range, to raise the frequency to the 15kHz-25kHz range.Also, you never reported what happens to the input voltage. Please connect your voltmeter across the battery or power supply terminals and report what happens to the voltage when you press the circuit's "on" button.I'm afraid that when you go to a blocking oscillator, we will be starting over from the beginning.... so I would really like to see you get this 555 circuit working to your satisfaction before you do that.

author: Adhith
author_rank: Frequent Contributor
timestamp: January 30, 2016, 02:49:45 pm
content: Quote from: Hero999 on January 28, 2016, 09:24:15 pmok.. thank you Hero999. since i do have the components let me make it & see what happens..

author: Adhith
author_rank: Frequent Contributor
timestamp: January 30, 2016, 04:25:24 pm
content: Quote from: alsetalokin4017 on January 28, 2016, 10:47:45 pmyes iam sure thats its working. when i used pin 1 & pin 6 as primary & 220 ohm winding as secondary it didnt seems working. but when i used a 230v/9v transformer to provide the input of the othe transformer(the yellow one) i could see only 4 v as output. i also tried reducing the resistance by placing a 100k resistor parallel to 33k which makes arround 25k effective resistance but is droped the voltage from 280v to 240v & it dont seems working either..yes, the voltage is severely droping. when i connected an individual switch for transformer i noted that the voltage is droping from 7.5v to 2.5v (approx). my 9v battery reads 8.5v when barely connected to DMM. when 555 circuit was alone operated(& transformer is switched off) the voltage droped to 7.5v, does it indicates any problem..??

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 31, 2016, 12:53:01 am
content: Yes, it seems that your "9V" battery is nearly dead if it measures only 8.5 V when it is not loaded and is dropping to 7.5 V for the 555 only and 2.5 V when transformer is connected. This might be your entire problem.As I said before, the circuit switches the entire available current from your power source into the transformer primary, with the current limited only by the transistor's on-state resistance and the resistance of the transformer primary, when the pulse is HI. And for the purists, yes, it is entirely likely that the core will saturate especially at the low frequency originally specified.This circuit needs a power supply that will be able to provide 2-4 amps of current at 9V without the voltage sagging, and it seems that your battery isn't capable of doing that.

author: Brumby
author_rank: Unknown
timestamp: January 31, 2016, 12:59:52 am
content: +1What sort of 9v battery are you using?

author: Adhith
author_rank: Frequent Contributor
timestamp: January 31, 2016, 04:02:46 pm
content: Quote from: alsetalokin4017 on January 31, 2016, 12:53:01 amok i understand. if i use two 9v battery in series will that make any difference..?? or any method to raise the current..??

author: Adhith
author_rank: Frequent Contributor
timestamp: January 31, 2016, 04:04:30 pm
content: Quote from: Brumby on January 31, 2016, 12:59:52 aman ordinary non rechargeable battery.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 01, 2016, 01:02:23 am
content: You need more current, not necessarily more voltage. 9V is sufficient if you can sustain the current required without drooping the voltage. You could try several 9v batteries in _parallel_.

author: Brumby
author_rank: Unknown
timestamp: February 01, 2016, 01:56:43 am
content: Quote from: Adhith on January 31, 2016, 04:04:30 pmDo you mean something like this?....

author: Adhith
author_rank: Frequent Contributor
timestamp: February 01, 2016, 05:34:37 am
content: Quote from: alsetalokin4017 on February 01, 2016, 01:02:23 amok. what will be the max current that can be drawn from a single 9v battery if iam using that type of battery that "brumpy" posted.

author: Adhith
author_rank: Frequent Contributor
timestamp: February 01, 2016, 05:37:08 am
content: Quote from: Brumby on February 01, 2016, 01:56:43 amyes

author: Brumby
author_rank: Unknown
timestamp: February 01, 2016, 06:59:35 am
content: Have a look at the discharge tests on this page:http://www.powerstream.com/9V-Alkaline-tests.htm