Major problem fixed!

Tom Cloud cloud at peaches.ph.utexas.edu
Mon Mar 24 18:13:54 GMT 1997


My first guess is that a slow, rectifier-type, diode was used.  But,
a zener is as slow, if not slower.  The diode allows the coil to go
to a high voltage in one direction and clamps it to about 1 volt
in the other.  The zener clamps it both directions -- go figure.

>I'm not sure, but even on the lm1951 1 amp driver, the uses something like
>an internal zener to clamp the voltage, opposed to one of the other parts
>lm1921 which uses just an internal diode. I take a stab at it, that the
>zener will let the coil move instead of giving it a dead short (back through
>the diode), then when the voltage reaches the zener voltage, just clamp it.
>This may allow the coil to move off the seat faster. Or this could all be
>BS. I'll look in some data books and see what they say. Pretty good question!
>
>Sandy
>
>At 09:16 AM 3/24/97 -0600, you wrote:
>>>I have not really looked at it, but I would not expect too much. The
>>>recommened approach is to use the zener instead of a regular diode. I can't
>>>remember when I stuck the scope on it and watched the input and outputs, but
>>>I don't remember seeing anything fishy.
>>>
>>>Sandy
>>>
>>>At 10:57 AM 3/24/97 +1200, you wrote:
>>>>I finally got my system running reasonably. Problem turned
>>>>out to be that, when using a LM1949 (or in my case a 
>>>>discrete copy), Using a diode to absorb the inductive kick
>>>>lengthens the pulse by about 2.5ms!. Not good when idle requires
>>
>>why would a zener work better ???  if the coil is clamped with
>>a diode, it could saturate and take a while to come back, but
>>the zener will clamp it too (after it is a diode also).  The
>>zener is slower than a switching diode (all diodes turn ON fast,
>>its t-rr that's slow).  The only advantage I can see from a zener
>>is that it limits the voltage in BOTH directions, but it's
>>t-rr is VERY slow ???
>>
>>Tom Cloud <cloud at peaches.ph.utexas.edu>
>>
>>
>
>
>

Tom Cloud <cloud at peaches.ph.utexas.edu>




More information about the Diy_efi mailing list