PROJECT to replace a vibrator in a ignition test instrument.

Thread Starter

debe

Joined Sep 21, 2010
1,390
Since im not competent in design, im seeking help. The first picture is the set up driving an ignition coil & the wave forms. But the problem i have is the coil needs to be connected betwean the Emitter & ground. The last picture is how i have tried to get it to work. Is there a way i can get it to work? The darlington transistor is an automotive ign coil drver type.A1.jpgA2.JPGA3.JPGA4.jpg
 

Thread Starter

debe

Joined Sep 21, 2010
1,390
Since im not competent in design, im seeking help. The first picture is the set up driving an ignition coil & the wave forms. But the problem i have is the coil needs to be connected betwean the Emitter & ground. The last picture is how i have tried to get it to work. Is there a way i can get it to work? The darlington transistor is an automotive ign coil drver type.View attachment 287717View attachment 287718View attachment 287719View attachment 287720
Mod:lightened your image.

A5.jpg
 
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ericgibbs

Joined Jan 29, 2010
19,003
hi deb,
Say 5V, you lose about 1.4V across the two Base/Emitter junctions of the Darlington, this means as the load is in the Emitter circuit the load has only 5V-1.4V = 3.6V initially across across it.

Is it possible to place the load in the Collector of the Darlington?

E
 

Alec_t

Joined Sep 17, 2013
14,379
My initial thought is that if the coil has to connect between the Darlington emitter and ground then this is similar to the situation of driving the high-side FET in an H-bridge circuit. So some sort of boot-strap circuit ought to work?

Edit:
Simulation shows that a boot-strap arrangement using an IR2104 driver for a high-side FET or NPN Darlington works ok if a supply >9V or so is available.
 
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LesJones

Joined Jan 8, 2017
4,211
With the coil in the collector circuit on an NPN transitor it allows the collector to go more positive than the base or emitter voltage. when the coil is in the emitter circuit the emitter can only go more negative than the base by about 1.2 volts for a darlington transitor. This means that you will not get a high voltage pulse across the primary of the coil. To do what you want you will need to use a high voltage PNP transistor to do the switching. (This will also reguire the driver circuit to be changed.

Les.
 

Thread Starter

debe

Joined Sep 21, 2010
1,390
The first circuit its in the Collector / positive rail, & works. But it realy needs to be in the Emitter to Ground circuit. So i need a PNP darlington transistor? The other problem is i cant find a PNP IGN drive transistor. What i was trying to achieve is replace Vibrator to solid state as used in a Merc o Tronic IGN tester. The vibrators are no longer avalable. This is the basic circuit of the coil test in the unit. MERCO 9800 . IGN COIL TEST.jpg
 

ericgibbs

Joined Jan 29, 2010
19,003
hi deb.
You can easily make your own PNP Darlington by using two PNP transistors.
E

@debe
Like this option, added 2nd image

If you are interested, let me know the Coil current etc and I will create a circuit.
EG57_ 618.png

EG57_ 619.png
 
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Thread Starter

debe

Joined Sep 21, 2010
1,390
Hi ericgibbs, the max current draw would be 4 Amps. Appreciate your input, as its midnight here so off to bed for me.
 
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Danko

Joined Nov 22, 2017
1,843
But it realy needs to be in the Emitter to Ground circuit. So i need a PNP darlington transistor?
Сircuit below is equivalent to circuit with vibrator and SCR,
because of same 300 V on ignition coil primary.
Unfortunately, PNP transistor with parameters like GA10JT12,
not exist in nature.
Therefore, I think, only way to solve your problem is replace vibrator,
transformer and bridge with DIY converter 7VDC/300VDC.
ADDED: GA10JT12 price US $3.50 @ https://www.scrtransistor.com/transistor?search=GA10JT12-247
1676682095045.png
 

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Thread Starter

debe

Joined Sep 21, 2010
1,390
This is pictures of a beat up Merc o Tronic ignition tester i found in a scrap yard. It does work but the vibrator is in poor condition, hence the need to build something to replace it. Thats why there is some specific conditions in how its done. The circuits i have drawn are only specific to how the vibrator is wired for coil & CDI testing.M.3.JPGM4.JPGM5.JPG
 

Thread Starter

debe

Joined Sep 21, 2010
1,390
That article on all aboutcircuits input was from me. That lot of pictures of the vibrator were mine & its not in good condition. On Smoke stack forum theres others looking for a suitable solidstate alternative. Thats why i have posted here for ideas.
 

MrSalts

Joined Apr 2, 2020
2,767
That article on all aboutcircuits input was from me. That lot of pictures of the vibrator were mine & its not in good condition. On Smoke stack forum theres others looking for a suitable solidstate alternative. Thats why i have posted here for ideas.
There seems to be plenty of those old-school vibrators in ebay but $40 to $100+ - ouch.
 

crutschow

Joined Mar 14, 2008
34,690
You best bet is probably to rewire the device so the coil is not grounded but is in the transistor collector to V+ as shown in your first diagram.
The coil won't work if it's connected in the emitter circuit.
 
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