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  • JohnS,

    Thanks for the advice. I found a faulty resistor (of all things?!)I and am proceeding.

    Is it possible to use a ceramic or crystal resonator to produce a certain frequency (like 1M&z) to run a FET driver? If so, that might simplify my particular objective once I experiment with it to know just what I need to acheive to produce the desired outcome.

    Almost there,

    Bob

    Comment


    • JohnS,

      I now have a saw tooth pulse coming out of sect. C, but only 1-2mV at pins 3 & 6. Sect. D gives a flat dash, no up and down at all. Also, neither pot changes anything. I will post pics of scope shot on Photobucket at:

      Pictures by bobfrench - Photobucket

      Thanks for all your help,

      Bob

      Comment


      • Hi Bob,
        sorry for your problems. What you measure is no sawtooth but definitely capacitive crosstalk from your signal section D.
        You should have the very same signal (real sawtooth = long ascending and instant descending) at transistor collector, U1A pin2 and U1B pin 7.

        The saw tooth shall end at the very level of U1A pin 3.

        Are you shure your op amp works with 5V supply?

        Please verify this and post pics from scope but make shure that we know the time set and the amplitude set.
        • Pic from all pins showing any movement
        • DC voltage from all pins not moving.


        We will get your baby running!
        JohnS
        Experts spend hours a day in order to question their doing while others stopped thinking feeling they were professionals.

        Comment


        • Help with components

          @JohnStone or anyone who knows!

          I'm just putting together the parts order for John's PWM, 2 items I would like help with please.

          Can you recommend a PNP transistor make/number for the current source part of the circuit. Sorry this may seem basic.

          I have some Toshiba K3176 MOFETS, 30amp 200v, will these switch ok for 12volts or should I buy another type of FET? I will be using the 555 ctt to drive the FET.

          Thanks in advance

          Regards

          John

          Comment


          • JohnS,

            Good to hear from you! I will try to work on this soon. I built another circuit that I am adding the NE555 driver and FET on to and I need to try it out today or tomorrow.

            What are you refering to by "op amp", the 393?

            BTW, if a circuit shows a 555 with pins 6 and 2 connected and a wire coming off the middle of them, does it matter if I run a wire from 2 to 6 then out, or does the last wire need to be between and equal-distant from pins 2 and 6? In the past, I have run a wire diagonally across the bottom to connect 2 ands 6, or 4 and 8.

            Thanks, friend. Hope all is well with you. Have a good Thanksgiving (or maybe that doesn't apply),

            Bob

            Comment


            • Originally posted by john_g View Post
              ...Can you recommend a PNP transistor make/number for the current source part of the circuit. Sorry this may seem basic.

              I have some Toshiba K3176 MOFETS, 30amp 200v, will these switch ok for 12volts or should I buy another type of FET? I will be using the 555 ctt to drive the FET.
              ...
              PNP i.e. 2N2907 / BC327, BC328 but any small signal transistor as pnp will do.

              your K3176 is fine. Not very fast but moderate. It is switched on above 5 or 6 Volt so if the 555 has 12V supply you will drive it fast enough.
              200V is a concern. You easily will get a coil to 200V if you stop current suddenly. So the 12V is not important but the inductivity and the max current will produce overvoltage if stopped.
              Imagine a flywheel. Not the accellerating force is important but the weight (= inducitvity)and the speed (max currrent) if you stop it suddenly.
              Use a neon parallel to D and S as protection. So start with short pulses up to the point where neon lights up then take a second one in series and prcoceede again.

              Nevertheless be prepared to replace them because of damage if you pulse seriously.
              Last edited by JohnStone; 11-21-2012, 08:46 PM.
              Experts spend hours a day in order to question their doing while others stopped thinking feeling they were professionals.

              Comment


              • Originally posted by bobfrench@fastmail.fm View Post
                ...What are you refering to by "op amp", the 393?
                BTW, if a circuit shows a 555 with pins 6 and 2 connected and a wire coming off the middle of them, does it matter if I run a wire from 2 to 6 then out, or does the last wire need to be between and equal-distant from pins 2 and 6? In the past, I have run a wire diagonally across the bottom to connect 2 ands 6, or 4 and 8.
                Thanks, friend. Hope all is well with you. Have a good Thanksgiving (or maybe that doesn't apply)...
                • Oh sorry I should have said compartor U1a / U1B
                • It is OK to make them as short as possible as you do it at bottom. If the wire needs to go further it does not matter where it starts exactly. This applies for small amperage only.
                  If one of the pins is an 555 output (i.e. 3) then the wire leading to the next component (i.e. a FET) shall start at the very output pin 3 and if necessary - another wire shall lead from pin 3 to another pin of the 555.
                  Same if you add a capcitor between 1/8 at 555 (power pins). NEVER connect the cap to pin 4 directly being connected to 8.
                  Please use an electrolitic 1µF or 10µF in parallel to 100nF (= 0.1µF) ceramic cap at power pins. they comprise a local store up to the time when the PSU ships some extra electrons from its own stock.The electrolitic cap is slow but has lots of electrons stored in teh cash and the 0.1µF is fast and can supply instantly some few electrons up to the time the electrolitic gets some electrons retrieved out of its stock. So both are a strong team.
                • Thanks for mentioning Thanksgiving. In Europe this is no major event but a smaller one being mentioned in church only - nevertheless important to give thanks to the creator and he shall bless all motivated FE tinkerers.
                Last edited by JohnStone; 11-21-2012, 08:52 PM.
                Experts spend hours a day in order to question their doing while others stopped thinking feeling they were professionals.

                Comment


                • Originally posted by JohnStone View Post
                  PNP i.e. 2N2907 / BC327, BC328 but any small signal transistor as pnp will do.

                  your K3176 is fine. Not very fast but moderate. It is switched on above 5 or 6 Volt so if the 555 has 12V supply you will drive it fast enough.
                  200V is a concern. You easily will get a coil to 200V if you stop current suddenly. So the 12V is not important but the inductivity and the max current will produce overvoltage if stopped.
                  Imagine a flywheel. Not the accellerating force is important but the weight (= inducitvity)and the speed (max currrent) if you stop it suddenly.
                  Use a neon parallel to D and S as protection. So start with short pulses up to the point where neon lights up then take a second one in series and prcoceede again.

                  Nevertheless be prepared to replace them because of damage if you pulse seriously.
                  John

                  Many thanks for the advice. Can you suggest a better FET to use rather than the ones I have, or should I be looking at 600V +?

                  Regards

                  John

                  Comment


                  • Originally posted by john_g View Post
                    .....Can you suggest a better FET to use rather than the ones I have, or should I be looking at 600V +?....
                    600V seems to be OK.

                    Any type I suggest could be not available in your area. You might want to scavenge some PC PSUs. There you find those guys up to 900V mounted ready on a heatsink along nice diodes. Along that you have a switch, fans and a nice casing...... Casing is important if you have higher voltages later on in order to give you and your loved a chance to survive

                    BTW: see Nice work but the drivers shall be as near to FETs as possible and conneced with THICK wires. At the pic mentioned above you see at right hand a copper bus bar protruding from the bottom of the PCB - that's GOOD!
                    JohnS
                    Last edited by JohnStone; 11-22-2012, 03:22 PM.
                    Experts spend hours a day in order to question their doing while others stopped thinking feeling they were professionals.

                    Comment


                    • Thanks John.

                      Originally posted by JohnStone View Post
                      600V seems to be OK.

                      Any type I suggest could be not available in your area. You might want to scavenge some PC PSUs. There you find those guys up to 900V mounted ready on a heatsink along nice diodes. Along that you have a switch, fans and a nice casing...... Casing is important if you have higher voltages later on in order to give you and your loved a chance to survive

                      BTW: see Nice work but the drivers shall be as near to FETs as possible and conneced with THICK wires. At the pic mentioned above you see at right hand a copper bus bar protruding from the bottom of the PCB - that's GOOD!
                      JohnS

                      Thanks John Stone, i'm pretty sure i will have to pick your brains in the future, if thats ok.
                      Warm Regards Cornboy.

                      Comment


                      • Welcome Cornboy in this thread as well
                        Please explain what those white components are on your setup - optos or drivers. You did it nice. Please make shure that the wire between FET driver and gate including GND are THICK wire - stranded if possible. Is there a pic from bottom side?
                        You need to understand that radio frequency and all its implication begin at 10...20 KHz. If we pulse with i.e. 10Hz only but narrow or / and steep pulses radio frequencies apply as well.
                        If you require pulse slopes of i.e. 0.5 µS you easily can operate those pulses up to 500KHz. So your design shall face 500KHz requirements - even if pulsed at 1 Hz only.
                        But don't worry - you will get help.
                        Imagine a gun. If you operate it once a day you can not expect the bullet to propagate within half a day in order to kill the deer. The deer might die but because of laughing to death.
                        JohnS
                        Experts spend hours a day in order to question their doing while others stopped thinking feeling they were professionals.

                        Comment


                        • Don't shoot!

                          Originally posted by JohnStone View Post
                          Welcome Cornboy in this thread as well
                          Please explain what those white components are on your setup - optos or drivers. You did it nice. Please make shure that the wire between FET driver and gate including GND are THICK wire - stranded if possible. Is there a pic from bottom side?
                          You need to understand that radio frequency and all its implication begin at 10...20 KHz. If we pulse with i.e. 10Hz only but narrow or / and steep pulses radio frequencies apply as well.
                          If you require pulse slopes of i.e. 0.5 µS you easily can operate those pulses up to 500KHz. So your design shall face 500KHz requirements - even if pulsed at 1 Hz only.
                          But don't worry - you will get help.
                          Imagine a gun. If you operate it once a day you can not expect the bullet to propagate within half a day in order to kill the deer. The deer might die but because of laughing to death.
                          JohnS


                          spoken with great humour john, you're a funny man.
                          think i get what your'e saying, Thanks Friend.
                          Last edited by Cornboy 555; 01-18-2013, 06:37 AM.

                          Comment


                          • Originally posted by JohnStone View Post
                            Welcome Cornboy in this thread as well
                            Please explain what those white components are on your setup - optos or drivers. You did it nice. Please make shure that the wire between FET driver and gate including GND are THICK wire - stranded if possible. Is there a pic from bottom side?
                            You need to understand that radio frequency and all its implication begin at 10...20 KHz. If we pulse with i.e. 10Hz only but narrow or / and steep pulses radio frequencies apply as well.
                            If you require pulse slopes of i.e. 0.5 µS you easily can operate those pulses up to 500KHz. So your design shall face 500KHz requirements - even if pulsed at 1 Hz only.
                            But don't worry - you will get help.
                            Imagine a gun. If you operate it once a day you can not expect the bullet to propagate within half a day in order to kill the deer. The deer might die but because of laughing to death.
                            JohnS


                            Sorry John They are FOD 3180 opto,s.

                            Comment


                            • Hi Cornboy,
                              You did a good job. I assume the red/black wires are the power for the optos secondary side. I can't see any electrolitic cap there. In the data sheet they have 22µF and 100nF attatched to the IC directly.
                              Imagine:
                              The inherent cap in the FET being a jug with 1.5 nF. You intend to fill the jug up to the hight of 12V.
                              At the opto you have a jug of 100nF / 12V but you can utilize only the upper volume of this jug in order to fill the first one. It will supply current (water) instantly down to that hight and then refuse to supply more.
                              Nearby you have big vat of 100µF and you can refill your 100nF jug through a hose being not of big diameter. The supply wil be delayed. The refill action shall start immediatly in order to give the 100nF jug support when required.
                              I hope this imagination can help you to understand the highly dynamic actions in this apparently simple setup. In fact there are some additional implications involved.

                              BTW: My humour is for education sake and fun as well. I beg you never will forget the nature of short pulses
                              rgds JohnS
                              Last edited by JohnStone; 11-23-2012, 10:13 PM.
                              Experts spend hours a day in order to question their doing while others stopped thinking feeling they were professionals.

                              Comment


                              • Pwm

                                Originally posted by JohnStone View Post
                                Hi Cornboy,
                                You did a good job. I assume the red/black wires are the power for the optos secondary side. I can't see any electrolitic cap there. In the data sheet they have 22µF and 100nF attatched to the IC directly.
                                Imagine:
                                The inherent cap in the FET being a jug with 1.5 nF. You intend to fill the jug up to the hight of 12V.
                                At the opto you have a jug of 100nF / 12V but you can utilize only the upper volume of this jug in order to fill the first one. It will supply current (water) instantly down to that hight and then refuse to supply more.
                                Nearby you have big vat of 100µF and you can refill your 100nF jug through a hose being not of big diameter. The supply wil be delayed. The refill action shall start immediatly in order to give the 100nF jug support when required.
                                I hope this imagination can help you to understand the highly dynamic actions in this apparently simple setup. In fact there are some additional implications involved.

                                BTW: My humour is for education sake and fun as well. I beg you never will forget the nature of short pulses
                                rgds JohnS

                                Hello John, yes you assumed correctly, no electrolitic, yes guilty.Will fix if i rebuild this unit based on your much valued suggestions.

                                If you are not already familiar with RM Cybernetics PWM's, could you do me a favour and check out their web site for me and let me know if these units can be used to drive high power fet bank gates directly from battery with resistor? Like Darlington pair maybe?

                                The pics are one i have that has still survived spikes from directly pulsing coils.AS they are adjustable for pulse width and duty cycle it may be a simple solution for me. Everything you need is in the user manual online.

                                Yeh i know it's cheating, and that i need to know exactly how things work, but i have a 7 days a week job and dislike spending valuable r&d time on tiny stuff that drives me bonkers.Rather build a nice big high torque, iron based, motor UFO style.

                                Many thanks Friend, i understand why UFO calls you Sir.
                                Thanks in advance.
                                Last edited by Cornboy 555; 01-18-2013, 06:37 AM.

                                Comment

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