for each of the regulators. Clear off any swarf and, twisting with your hand only, use an 8mm
drill bit to lightly deburr the edges of the holes. There should be no bumps around the holes.
The regulators are both TO-220 devices. They both need to be fitted to the panel mechanically
and thermally but not electrically. That is the metal tab on each device that will be mounted to
the panel should not make electrical contact with the metal panel. To achieve both thermal
transfer and electrical insulation we use an insulator. These can be made of a 'soft' flexible
material in the form of an insulating pad or a rigid thin glass like plate made from mica. If
using the mica you will also need to use heat transfer paste. Since the paste is somewhat messy
I recommend you use the insulating pads. Both types are normally available in 'mounting kits'.
Also in the kit is a mounting bush. This top hat shaped piece of stiff plastic prevents the
mounting screw from touching the regulator's metal tab.
Now place the mounting bush into the hole of the power device, with the flange of the bush
lying on the top side of the device. Take one of the insulating pads and place it against the rear
of the regulator. Match up the hole in the pad with the bush that is sticking out from the
underside of the tab. You may find the mounting bush does not stick out from the underside of
the regulator. This is fine – you will just need to be a little more careful that the pad doesn't
slip when you fasten the device to the panel. However, you may find that any plastic that does
stick out is too big to fit into the hole in the insulating pad. I find that carefully removing the
excess plastic rim from the bush, with a very sharp knife, is the best way to solve this problem.
If you do have part of the bush sticking out you may also want to check at this point that the
bush will fit into your panel hole. If not, you can either make the hole bigger, or trim the
excess plastic of the bush.
Now place the power device, bush and pad flat against the rear of the panel so that the bush
fits into the panel. Make sure the pad does not slip out of place when you do this. Insert a
10mm countersunk M3 screw into the hole from the reverse side of the panel, and fit a spring
washer and nut onto the screw but do not tighten fully. Do the same for the other regulator
making sure, of course, that each one is in the correct hole.
Now if you have done all this correctly, you should find that the when the power supply PCB
is fitted back onto the four screws, you can coax the power devices’ legs through the
respective solder pads on the board. With both the board and power devices secured to the
panel with their mounting hardware you can solder the regulators' leads from the top side of
the board.
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