GPS Power Supply construction tips

Quite a few people have asked me to indicate a typical way I have constructed the power supply, however, I have to admit that the one I have been using is an earlier prototype which did not have the trip pot fitted to adjust the overload point. Instead I used a combination of zener diodes to achieve the same result. I felt for ease of setting up, the circuit I have shown was a better idea. I have had to make a new power unit recently for a friend, so I have decided it's a good time to publish the construction here.

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First unit made in 1999
The first unit was fitted in the ash tray compartment of my Daewoo Leganza until I changed my car Dec 2001. I had a seperate data cable feed to my datalogger stuck to the side of the driver's footwell. My new car, a Citroën Picasso, does not lend itself to a separate power unit and data cable, so I made the mark2 unit by removing the stripboard and placed all the parts into a diecast box. The new unit has a 9w D connector fitted to feed my datalogger , and the whole unit fits inside the box at the bottom of the centre console, held in place with two Velcro strips. The power and data cable feed out behind the bin, and the bin can be fully closed when the power unit is working. (see below) In addition it has a 5v supply built in to feed an external GPS antenna (More of this later)


Mk2 unit made Dec 2001 (Not fully finished at time of picture)		Citroën Picasso centre console

So, now onto the latest unit, which fully conforms to the circuit shown here on the website.

First up some problems:

There appears to be a lot of confusion and problems caused by the thyristor type C106P. It appears that many people in other countries are having problems sourcing this, so the following types are all suitable, they only vary by the different case styles, but will all work perfectly here: C106D1, C106M1, C106M, or CP106D. In the first unit I used a C106M, in the latest a C106D1. I chose the "P" type because this was a small case style - but it appears to have backfired !!
Whilst on the subject of problems, only use the 317T (1.5A) regulator, not the small case version (TO92). This version is only rated at 100mA, with a short circuit limit of 200mA. As the fuse is 250mA, it will never blow, but the 317 gets mighty hot!!
Finally, the BZY88 5v6 zener diode. Again apologies for using a UK style part number, in fact any 5.6 volt zener diode rated at 400mW or larger will work here.

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Remember that the 317T metal heatsink is not isolated, so it must be insulated if you are mounting it to a metal box. These pictures show the hardware used and also the connections for the regulator. Although it is not essential that the box be connected to ground(0v) I consider this good practice which allows the box to act as a shielded enclosure

These pictures show the general component placing. I use stripboard for this, as the component density is light and you can suit the size within limits to fit the case you wish to use. Note the 470 ohm resistor feeding the power "on" LED indicator. This is not shown on my circuit but is mentioned in the text.

Here I have shown the underside of the stripboard, showing where the copper tracks need to be cut. Note - one cut has a link soldered across it - my mistake! The other view shows clearly the placement of all parts.

And finally the finished unit, fitted into the diecast box, with fuse and LED along with cables for the GPS and cigar lighter socket. In this instance, I tested and set up the voltage and trip setting before assembling into the box.