Ignition questions & the Nat semi Injector driver

[John S Gwynne]

--------

   In message <199604140544.FAA25983 at freenet.msp.mn.us> , you write:
 
|     2nd, could I use this driver to control a ignition circuit?
| 
|     3. What is a good design for an electronic igniton system. Particularly h
| ow 
| do I stop the Back EMF from blowing everything apart after ignition? I though
|  
| about placing several (4) tip120 darlingtons to switch the current, and then 
| a 


Jim, this is the proto circuit I used to evaluate the LM1949 with a
Harris HGTP14N40F3VL (this part clamps the primary at 400V) for the
efi332 project. It duplicates the data I collected from a Buick 3.1L V6
w/ DIS.

lm1949
pin 1 : input
pin 2 : IGBT gate
pin 3 : 0.0022uF : 82k : IGBT gate
pin 4 : 68 / 1.2k voltage divider to 0.147 sense resistor
pin 5 : sense resistor ground
pin 6 : +5VDC return
pin 7 : +5VDC
pin 8 : 10k to pin +5VDC

comments:

- The 0.147 ohm sense resistor was only what I had on hand. It needs
to be more like 0.03 ohms to ensure Vgate is large enough.

- a small resistor should be added between pin 2 and the IGBT gate.

- The "trick" in using this (any) circuit is stabilizing the feed
back loop as on pin 3. (The feedback loop limits the maximum
current.) If you use a different transistor or significantly change 
the circuit, you will have alter the compensation for a stable well
behaved transfer function.

- 3mH at 10A is 150mJ. I seem to recall a stun gun is like 25mJ, and
50mJ through the heart can be fatal. (Is that correct???) Anyways,
becareful with the thing. :)


Buick system data:

coil: Buick 3.1L V6 w/ DIS

      primary:
        0.344 Ohms DC (room temp.; @250mA)
        3.00 mH open @ 1 kHz (wo/ compensation of DC resistance)
        0.235 mH short @ 1 kHz
      secondary:
        5.47 k Ohms DC
        28.0 H open @ 1 kHz
        4.5 H short @ 1 kHz

      forgot to measure the turns ratio..(from inductance measurement,
      it must be around 90-100).

      The primary current waveform was very well behaved.


            |
            |              -------|
            |             /       |
            |            /        |
            |          /          |
            |        /            |
            |      /              |
            |    /                |
            |  /                  |
            --------------------------
           
       build time 2.75mS
       hold time 0.70 mS
       peak current 8.9A (note: measured sense resistor (copper) at 70 
         deg. F.; made the test at about 30 deg. F. Should compensate for 
         temp. Actual value may be closer to 10A.)

       driver voltage:

            |
            |
            |             |-------
            |             |
            |             |
            |             |
            |             |
            |    ---------
            |----
            --------------------------
       rose to 2V during build time
       abruptly transitioned to 7.5V during the hold time.
       (other side of coil was about 14V w/ a voltage drop of 3V at the peak)


                                       John S Gwynne
                                          Gwynne.1 at osu.edu
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