Re: Bipolar Power Supply

[Fred Townsend]

The 24 volt unit makes sense if placed before the inductor. Here is why. TVS react in nanoseconds. MOVs react in milliseconds. That's six orders of manatude difference. The choke will choke off anything faster than milliseconds.  So way put in a fast device if it costs more and doesn't give more protection and does not protect the inductor? When placed ahead the TVS will remove fast spikes, limit surges including lightning, and protect the inductor. Caution: TVSs (and many MOVs) fail shorted so always fuse. Fred Townsend Syd H. Levine wrote: From a review of the literature, it looks like the TVS should be a unidirectional 24 volt unit and should be placed after the choke.  Does that sound reasonable?  (They actually make a special TVS for this application, and it is a 24 volt unit for 12 volt vehicles.)   Thanks.   Syd ----- Original Message ----- From: Fred Townsend To: Multiple recipients of list CHIPDIR-L Sent: Monday, September 19, 2005 1:09 PM Subject: Re: Bipolar Power Supply Declan Moriarty wrote: Recently, Somebody Somewhere wrote these words This thing always sits in the truck logging cab compartment, so it is not exposed to anything too terribly awful. I have decided to definitely add a choke and capacitor to the front end. I am curious about your suggestion for transient protection. Are you thinking of one of the little transient suppression diodes? If so, what value would be appropriate? I think vehicle DC power is 13.8 volts nominal when the alternator is fired up. You need to be aware of a few phenomena 1. Spikes as mentioned in my previous post up to 1000V when the alternator brushes get an open spot between sections on the commutator. Tilt!  Alternators have slip rings, not commutators. Fred Townsend