Virus Posted May 23, 2006 Author Report Share Posted May 23, 2006 audioguruI have built the unit (Reply #19 on: May 12, 2006, 05:44:34 PM ) on a breadboard, 1 ste time not lucky. The mosfet gets steaming hot instantly, if I clip + 12v to the circuit, with no out put to the led that I connected. I can hear the 555 oscillating. How can I test the opamp to see of it is working.I have checked and again checked and again checked and …. the wiring can’t find the fault. Should I rip it all up and redo it? Build it to a PCB ?Attached photos.Please help.Thanks Virus Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 24, 2006 Report Share Posted May 24, 2006 I can't remember how much current your fan draws, but it is a lot more than what the lousy contacts on your breadboard can handle.What resistor value did you use for the 2N3906 current source?Is the 555 oscillating?Does your power supply voltage drop too low when it is loaded, therefore the Mosfet doesn't have enough voltage on its gate to turn on properly? Quote Link to comment Share on other sites More sharing options...
allvol Posted May 24, 2006 Report Share Posted May 24, 2006 Hi Virus,If it is any consolation to you, I could not get the circuit to work, either. Quote Link to comment Share on other sites More sharing options...
Virus Posted May 24, 2006 Author Report Share Posted May 24, 2006 I can't remember how much current your fan draws, but it is a lot more than what the lousy contacts on your breadboard can handle.I only had the led connected, no fans at all, wanted to see if the circuit at least is working.What resistor value did you use for the 2N3906 current source?.Resistor RF = 90KohmIs the 555 oscillating?Yes, for the 555, I can hear it load enough.Does your power supply voltage drop too low when it is loaded, therefore the Mosfet doesn't have enough voltage on its gate to turn on properly?I use the 0 - 30 VDC power supply from this forum, it does not even blink.audioguru, is the theory of this circuit good ???, regarding the post of allvol Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 24, 2006 Report Share Posted May 24, 2006 It is a lousy circuit.The transistors T1 and T2 aren't needed.Pin 3 of the 555 can drive a resistor in series with the timing capacitor and the triangle wave on the capacitor can feed the input of the opamp. I would use a faster, newer opamp or a proper comparator instead of a slow opamp that causes the Mosfet to heat-up. Quote Link to comment Share on other sites More sharing options...
Virus Posted May 24, 2006 Author Report Share Posted May 24, 2006 audioguruThanks for the circuit update, will build it this weekend and give you feed back.What should the value of D1 be ? ???I will bug you a bit more later, I would like to get rid of the RDC 10K and rather use a solid resistor, with a 10 K thermistor, iaw, make it a circuit with a solid predetermined value for the temp sensor to react on.ThanksVirus :D Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 24, 2006 Report Share Posted May 24, 2006 What should the value of D1 be?D1 is not necessary since every Mosfet has a very powerful zener diode inside connected like D1.You would use an additional very fast diode if the PWM was at a very high frequency. Quote Link to comment Share on other sites More sharing options...
allvol Posted May 24, 2006 Report Share Posted May 24, 2006 Gosh! Quote Link to comment Share on other sites More sharing options...
Virus Posted May 25, 2006 Author Report Share Posted May 25, 2006 allvolI like say it, "If you are right you are right.", sorry for ignoring you. Quote Link to comment Share on other sites More sharing options...
allvol Posted May 25, 2006 Report Share Posted May 25, 2006 Hey Virus,Thanks.I could not get that circuit to work.... and probably never would. Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 25, 2006 Report Share Posted May 25, 2006 I could not get that circuit to work.... and probably never would.Which circuit? Did you try the circuit I fixed?I have a DC motor speed control circuit using PWM that works perfectly. I use a dual opamp as an integrator and schmitt trigger to make a triangle wave and use another opamp as a comparator of the triangle wave to the DC setting of a pot like in this circuit.The 555 circuit that I fixed should work perfectly the same. Quote Link to comment Share on other sites More sharing options...
allvol Posted May 25, 2006 Report Share Posted May 25, 2006 We're talking about the original circuit, the one you called lousy. Quote Link to comment Share on other sites More sharing options...
allvol Posted May 25, 2006 Report Share Posted May 25, 2006 Okay, Virus, maybe this will clear it all up.In my attachment below, audioguru's version of the 555 as a pulse width generator is compared with the textbook version, as offered by the 555 Timer Pro program from the Schematica web site. Quote Link to comment Share on other sites More sharing options...
Virus Posted May 27, 2006 Author Report Share Posted May 27, 2006 GuysI HAVE FOUND THE PROBLEM, I had the Mosfets supply and drian short-circuited on the breadboard as soon as the circuit switches on. DEAD SHORT INSTANT HEAT.With that sorted out I have successfully built the circuit in post number 19 (with the MC34071 opamp) and the one in number 34 audioguru’s circuit.I choose for now to go with the audioguru’s circuit, with less components, and is still on the board. As I got the same results from both circuits.I have replaced the 4.7k resistor with a 1k resistor, the fans where making a very lousy high pitch sound, then measured with my MM, I get 21kHz, on pin 6 of the 555.First I replaced R5 with a 10K resistor (because the thermistors value is changing and need a fix value to work from), and adjusted RDC to give an output of 4.5 volts, with the fans just start turning. Then I replaced R5 with the 10 k thermistor, the output voltage varies with MC34071-D.pdf Quote Link to comment Share on other sites More sharing options...
allvol Posted May 27, 2006 Report Share Posted May 27, 2006 Hello, VirusAs long as you are still breadboarding, you could go ahead with the original 555 circuit to see what happens.But before you do, make the changes to Audioguru's latest circuit, to conform to the textbook version. Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 27, 2006 Report Share Posted May 27, 2006 Pin 6 of the 555 is a triangle wave that feeds an input of the comparator. It is a sensitive spot and its frequency is affected a little by the resistance and capacitance of the frequency counter in the DMM. Quote Link to comment Share on other sites More sharing options...
allvol Posted May 28, 2006 Report Share Posted May 28, 2006 Hello, AudioguruMan, I respect your longevity on this forum and your experience, but I must disagree with you on your circuit for this project, in that it does not follow proper operation procedure for the 555 timer. Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 28, 2006 Report Share Posted May 28, 2006 Hi Allvol,"My" 555 circuit is the classic "triangle wave into a comparator with the other comparator's input connected to a variable DC voltage" PWM circuit that usually uses a opamp integrator and a Schmitt trigger oscillator to make the triangle wave.The 555's timing capacitor is charged and discharged symmetrically by a resistor from the 555's output pin 3. The capacitor is also connected to pins 2 and 6 for its threshold voltages and has a curved triangle wave across it."Your" 555 circuit with its steering diodes also works well for PWM. Quote Link to comment Share on other sites More sharing options...
Virus Posted May 28, 2006 Author Report Share Posted May 28, 2006 HiP1 is the 555 circuit of audioguru and measured on my MM. (Was running the fans etc.)P2 is the “textbook version” of allvoll and as measured after replacing the 47uF cap with a .47uF cap. My MM does not read if it is to slow. Yes, I did get the LED to flash, with the 47 uF cap.As mentioned before both circuits are working. The original 555 with the opamp and the 2 transistor, and the audioguru version are working. The fans are running OK.Now lets get the range with the thermistor in place, where to from here?ThanxVirus Quote Link to comment Share on other sites More sharing options...
allvol Posted May 29, 2006 Report Share Posted May 29, 2006 rr fb VirusGlad to hear your fans are working at last. Quote Link to comment Share on other sites More sharing options...
Virus Posted May 31, 2006 Author Report Share Posted May 31, 2006 AllvolI had a ball playing with the fan’s. Did the 10k trim pot as per your diagram fan1.gif, works excellent, can get the fans down to just- just- just- turning (long pulses). I also left the other trim pot in place, between the 2 pot’s and changing the cap C2 with different values, what a range?, with some setting nice (annoying) music on the fans !I have a question though, how much of what, here, will do the trick?This project started out with resistors and a dip switch, because of the circuit in Quote Link to comment Share on other sites More sharing options...
allvol Posted May 31, 2006 Report Share Posted May 31, 2006 Hi Virus,I'm due at the golf course shortly, so don't have but a minute.Glad it's working! Quote Link to comment Share on other sites More sharing options...
Virus Posted May 31, 2006 Author Report Share Posted May 31, 2006 AllvolEnjoy tee, remember still need a answer on this side. Luckily, accumulatively, on this forum there is a couple of years worth of experience. Awaiting your solutions and advices.Virus Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 31, 2006 Report Share Posted May 31, 2006 Changing the DC voltage of pin 5 on a 555 changes both the frequency and the duty-cycle of the pulses. Using the steering diodes circuit or the triangle-wave circuit changes the duty-cycle of the pulses without changing the frequency much. Then the frequency can be high enough that it isn't audible. Quote Link to comment Share on other sites More sharing options...
Virus Posted May 31, 2006 Author Report Share Posted May 31, 2006 audioguruI was wondering why it is recommended to use Quote Link to comment Share on other sites More sharing options...
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