arc lighter circuit working

Thread Starter

Dabu WhiteHacker

Joined Sep 5, 2017
68
Hi, few days ago I got a broken arc lighter used to ignite gas stove. I thought of taking it a apart and look inside the circuit but as per to my knowledge it is confusing me a lot, I hope you guys will be able to remove my confusion so here is the detail.
Data
It uses 1.5V AA cell to work.
This the schematic that I was able to draw from the circuit.
Schematic_arc lighter_2020-07-23_10-35-54.png
Now there are two coils in it. One is small and the other is big. Here is a visual pic of it.
Note that I have removed small coil in this pic.
WhatsApp Image 2020-07-23 at 10.34.20 AM (1).jpeg
Here is what bottom of the circuit looks like
WhatsApp Image 2020-07-23 at 10.34.20 AM.jpeg
I know all components but only expect the small coil which has four pins. I tested all its pins but I was not able to understand it inner construction.
Here is the details of small coil.
Untitled.png
Pin 1-2 has 7.1 ohms, Pin 2-3 has 8.5 ohms, Pin 3-4 has 81.3 ohms, 1-3 has 1.8 ohms, Pin 2-4 has 72.8 ohms, Pin 3-4 81.3 ohms.
WhatsApp Image 2020-07-23 at 10.34.19 AM.jpeg

My understanding
  1. Positive is connected to pin 1 of small coil and also pin 3is connected to ground using PNP transistor so these two pins would probably contain the primary coil.
  2. Pin 2 of small coil would me another small auxiliary winding with other terminal as pin 3 so this pin drives the transistor.
  3. Pin 4 is the high voltage pin as it separated from other pins and also goes to the input of second coil.
  4. Big coil creates a large voltage probably in thousand by using the input voltage of around 50+ and has a capacitor at its output to create a resonance circuit with it.
  5. Zener diode is probably used to limit the input voltage of big coil to below 75V
  6. I know the working of Thyristor.
My confusions
  1. How is the small coil internally wired as the measurements i took does not satisfy what I think it is.
  2. Why gate of Thyristor is connected to its Anode using a zener diode.
  3. How is the driver circuit of PNP transistor is working.
  4. How is the driver circuit for Thyristor is working
  5. What is the purpose of D3 and D4 diodes.

It is requested to kindly give me guideline of how this works and it would be very great If you list the steps of its working and also answer my confusion.
If you need any further data, just ask me.
WhatsApp Image 2020-07-23 at 10.34.20 AM (1).jpeg
 
The circuit is a 1.5V DC-DC converter using the little coil (transformer) to generate high voltage DC.
This charges the 0.47uF capacitor through the large HV transformer until there is about 70VDC at which point the 1N4148 avalanches (like a zener) conducts and triggers the SCR. When the SCR turns on, it forms a path to allow the (70VDC charged) 0.47uF cap to discharge into the coil and generate a spark. {I didn't see the thread moved yet}
stove ignitor sch.jpg
 

Thread Starter

Dabu WhiteHacker

Joined Sep 5, 2017
68
The circuit is a 1.5V DC-DC converter using the little coil (transformer) to generate high voltage DC.
This charges the 0.47uF capacitor through the large HV transformer until there is about 70VDC at which point the 1N4148 avalanches (like a zener) conducts and triggers the SCR. When the SCR turns on, it forms a path to allow the (70VDC charged) 0.47uF cap to discharge into the coil and generate a spark. {I didn't see the thread moved yet}
View attachment 212982
I know how the basic principle of its working
but that was not my question
these are my question

My confusions
  1. How is the small coil internally wired as the measurements i took does not satisfy what I think it is.
  2. Why gate of Thyristor is connected to its Anode using a zener diode.
  3. How is the driver circuit of PNP transistor is working.
  4. How is the driver circuit for Thyristor is working
  5. What is the purpose of D3 and D4 diodes.
 

DickCappels

Joined Aug 21, 2008
6,535
My confusions
  1. How is the small coil internally wired as the measurements i took does not satisfy what I think it is.
  2. Why gate of Thyristor is connected to its Anode using a zener diode.
  3. How is the driver circuit of PNP transistor is working.
  4. How is the driver circuit for Thyristor is working
  5. What is the purpose of D3 and D4 diodes.
• I've seen transformers that look like that to trigger xenon flash lamps. They are usually wired as an autotransformer.
• When the voltage gets high enough for the diode to break down it supplies current to the gate to turn on the thyristor.
• The PNP is connected with the transformer to make a blocking oscillator.
• They thyristor latches on when the voltage is enough to break down the 1N4148.
• I don't know. What comes out of pin 5 of the large coil?
 

jeffl_2

Joined Sep 17, 2013
26
Here's the problem I have, in no way is a 1N4148 "intentionally designed as" a zener diode, it's a general purpose computer diode. If someone were counting on that device to "break down" at some repeatable voltage in order to make the circuit work, then how well it could be manufactured would depend on the particular characteristics of the diode as manufactured by the original vendor, and a commercial substitution might not work at all. These types of circuits frequently originally used diac devices to trigger the gate of an SCR, which are a bit hard to locate nowadays (perhaps the reason for the substitution) but you might want to look into a device like the NTE6412. You didn't specify whether this was the specific issue you were looking into but to my way of thinking it's the most "inscrutable" part of the schematic as drawn.
 
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