Help redesigning simple ignition coil driver cct to use NPN transistor instead of PNP

[Err404]

Here's the circuit:

http://www.cs.berkeley.edu/~wkahan/TransIgn.pdf

It's simply designed to ensure that on an old engine with the spark controlled by points the points will not have to carry the current for the coil.

I have access to some BUV46 NPNs
http://www.datasheetcatalog.org/datasheet/SGSThomsonMicroelectronics/mXyzqqvu.pdf

Vce = 400V, Ic = 5A

So I think I can use two in parallel to allow the Vce = 320V, Ic = 10A needed for the original design.
I'm confused as to how to drive the NPN bases in this alternative circuit.

Any help much appreciated!

 

[hanif]

Hi,

below is the link for a ignition coil driver ckt using 2n3055 NPN transistor. You can get the idea from here then you can convert yours., i hope it will help you


RMCybernetics - DIY Homemade Ignition Coil Driver

 

[Err404]

Thanks for the link - I think I follow the example cct okay.

I am just wondering about the original cct's design - I notice that it has a 2.5mH choke shunting the coil.
Can anyone explain what purpose this has in the original circuit.
It seems to me that there is no equivalent inductor in the suggested RMCYbernetics cct.
I have already purchased the Chokes for making a batch of these circuits so I would like to use the principles of the original design if at all possible - But clearly I want to use a Si NPN where a Ge PNP was required & I realise this may change things far too much, so if you can help me then I will be majorily impressed - as I can see it's a big ask!

 

[FvM]

I don't want to put too much into this antique circuit, but I assume that the inductor's purpose is to achieve maximum fast transistor turn-off. I think, that it's basically a clever, low-part count solution under the given prerequisites. But there are of course alternative ways to achieve the same with a NPN or NMOS switch.