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Re: Ignition circuit issue.

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On 28/03/2017 10:31 AM, Lasse Langwadt Christensen wrote:
> Den tirsdag den 28. marts 2017 kl. 01.25.23 UTC+2 skrev Jim
> Thompson:
>> On Sun, 26 Mar 2017 15:36:06 +1100, Sylvia Else
>> <sylvia@not.at.this.address> wrote:
>>
>>> I'm using this circuit to provide 250V pulses to an ignition
>>> coil.
>>>
>>> https://www.dropbox.com/s/1w33uss3eedem05/ignition2.pdf?dl=0
>>>
>>> The IC is a Linear Technology LT1243.
>>>
>>> 12V is provided on G$1 to the left. G$2 accepts a trigger pulse,
>>> and G$3 is ground.
>>>
>>> LTSpice says that this works, and indeed the real implementation
>>> does. Mostly.
>>>
>>> The difference is that after the circuit has been triggered once,
>>> it won't charge the capacitor again (above about 25 volts) for a
>>> varying period that can be up to half a minute. It's as if the
>>> wrong level is being used internally to compare with the feedback
>>> pin. In that regard, I'll mention that Q3 is used to pull FB up
>>> so that the circuit stops driving the FET, since otherwise the
>>> SCR never turns off. I've checked, and the problem is not that Q3
>>> remains on, nor is it that the SCR fails to turn off. In any
>>> case, the 1.5uF capacitor C1 does get charged somewhat, as I
>>> mentioned above.
>>>
>>> When the issue resolves, it does so rapidly, within a fraction of
>>> a second.
>>>
>>> Connecting an oscilloscope probe to the RT/CT pin of the IC
>>> restores function, but only if the scope is set to DC coupling -
>>> not AC coupling - and functioning continues only as long as the
>>> probe remains connected - until the aforesaid varying period has
>>> elapsed. Touching the pin with a finger has a similar effect.
>>>
>>> That is, connect probe; works. Disconnect; stops working.
>>> Reconnect; works, etc. until eventually it starts working
>>> continuously.
>>>
>>> This cannot be capacitive loading - there's already a
>>> significant capacitance between RT/CT and ground.
>>>
>>> The fact that the coupling has to be DC made me think that some
>>> small current was flowing to ground through the scope, so I
>>> bridged C4 with a 100K resistor. It didn't make any difference.
>>>
>>> I tried changing the IC (a pain, given that it's surface
>>> mounted), but again it made no difference.
>>>
>>> Any other ideas about what might be happening here.
>>>
>>> Sylvia.
>>
>> Using a PIC when you should have gone analog >:-}
>>
>> <http://www.analog-innovations.com/SED/CD-Ignition-Basic.pdf>
>>
>> <http://www.analog-innovations.com/SED/CDI_Inductor.jpg>
>
> why even bother with CDI? most car do fine with regular coils, many
> coils even have the driver igbt buildin all you need is a 5V driver
> for a few ms of dwell time
>

My application is a backup "portable" generator. One useful feature of 
CDI in this application is that it doesn't require a large input 
current, meaning that I can start the generator using cheap dry cells, 
and then let it power itself. No need for limited life failure prone 
rechargeable batteries that need to be kept topped up lest they die.

Sylvia.

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Thread

Ignition circuit issue. Sylvia Else <sylvia@not.at.this.address> - 2017-03-26 15:36 +1100
  Re: Ignition circuit issue. John Larkin <jjlarkin@highlandtechnology.com> - 2017-03-25 22:33 -0700
    Re: Ignition circuit issue. Sylvia Else <sylvia@not.at.this.address> - 2017-03-26 17:33 +1100
      Re: Ignition circuit issue. Larry Sheldon <lfsheldon@gmail.com> - 2017-03-27 00:54 -0500
        Re: Ignition circuit issue. Sylvia Else <sylvia@not.at.this.address> - 2017-03-27 19:34 +1100
      Re: Ignition circuit issue. dagmargoodboat@yahoo.com - 2017-03-27 07:16 -0700
        Re: Ignition circuit issue. makolber@yahoo.com - 2017-03-27 09:18 -0700
        Re: Ignition circuit issue. Sylvia Else <sylvia@not.at.this.address> - 2017-03-28 11:13 +1100
  Re: Ignition circuit issue. Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-03-27 16:25 -0700
    Re: Ignition circuit issue. Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-03-27 16:31 -0700
      Re: Ignition circuit issue. Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-03-27 16:36 -0700
      Re: Ignition circuit issue. Sylvia Else <sylvia@not.at.this.address> - 2017-03-28 15:19 +1100
        Re: Ignition circuit issue. Neon John <no@never.com> - 2017-03-31 14:41 -0400
          Re: Ignition circuit issue. Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-03-31 11:55 -0700
    Re: Ignition circuit issue. Sylvia Else <sylvia@not.at.this.address> - 2017-03-28 12:03 +1100
      Re: Ignition circuit issue. piglet <erichpwagner@hotmail.com> - 2017-03-28 08:39 +0100
        Re: Ignition circuit issue. Sylvia Else <sylvia@not.at.this.address> - 2017-03-28 20:54 +1100

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