The IsoBlock Defender Overvoltage Protector (OVP)

23 May 2024

For some history, it was late 1993 when I designed this. All of it is my work; the concept, the electronics design, the circuit board, and the physical design, I am to blame. I had this wild idea that I might be able to peddle a few of these as a sort of novelty product. The design is actually pretty solid and very functional. For the afficionado, the circuit has two sections; one for 5 volts and the other for 12 volts. Each section has a zener based transient absorber, and a crowbar circuit. The crowbar has an IC comparator which drives a transistor that finally drives the gate of a 25Amp crowbar SCR. The two sections can be linked so that a trip from either one triggers both crowbars. Nothing complex like rocket appliances, just a simple yet quite functional expedient.

So I actually did sell a small number of these devices. At the end of 1995, the last day of 1995, I went to work for the Veterans Health Administration as a computer specialist.

An “internal surge suppressor” being an example of some 1995 Vintage Technology

This actually had a small measure of exposure by being an item in Byte magazine’s What’s New Hardware page for the June 1995 issue as shown here below. The cover photo above is a print that was mailed out. The phone number and address in the Byte page is not in use by IsoBlock.

These next two images are a top and bottom view of the device. At this time sadly enough I no longer have the image files for the aluminum block or the circuit board artwork or the schematic and parts list else I’d display them as well. And the phone number and address in the bottom view is not in use by IsoBlock. The plastic cover has been peeled back and the bracket is not attached. But this is the actual “as shipped” item. ☺

One concept was to use a standard size foldup shipping box to hold the OVP and a manual and quick install guide. a bracket to use in a card slot to mount the OVP, and a tie wrap as an alternative. The top of the box had this design idea. The shipped boxes had no cool design aesthetic.

The bottom of the box had a synopsis of the device specifications.

But what is of more import is the printed matter inside the box. One item was a Quick Install Guide backed with a copy of the warranty, shown here next.

The second item of print material was a User’s Manual which is presented here below.

The back cover is next below.

It was interesting to see the postmarks on the inquiries received as a result of the Byte magazine mention. Anyway I hope you found this entertaining and or informative. ☺ as always, comments, criticisms, and suggestions are welcome. God bless all.