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Re: Ignition circuit issue.

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On 28/03/2017 10:25 AM, Jim Thompson wrote:
> 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 >:-}

Nah! Used a boost converter chip when I should have used a PIC. A 28 pin 
PIC32MX seems a bit over the top for this, but what the hell? It's not 
even more expensive.

>
> <http://www.analog-innovations.com/SED/CD-Ignition-Basic.pdf>
>
> <http://www.analog-innovations.com/SED/CDI_Inductor.jpg>  ...Jim
> Thompson
>

Don't quite see how that works - does it rely on the reverse breakdown
of D3?

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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