HEAT SINK
SPECIFICATIONS
HEAT SINK SPECIFICATIONS
The choice of a particular type of heat sink depends largely to
the thermal budget allowed for the heat sink and external
conditions surrounding the heat sink.
It is to be emphasized that there can never be a single value of
thermal resistance assigned to a given heat sink, since the
thermal resistance varies with external cooling conditions.
When selecting a heat sink, it is necessary to classify the air flow as
natural, low flow mixed, or high flow forced convection.
Natural convection occurs when there is no externally induced flow and
heat transfer relies solely on the free buoyant flow of air surrounding the
heat sink.
Forced convection occurs when the flow of air is induced by mechanical
means, usually a fan or blower.
There is no clear distinction on the flow velocity that separates the mixed
and forced flow regimes.
The thyristor data sheet specifies the maximum allowable
junction temperature Tjmax and ϴjc.
premissible heatsink thermal resistance
Tj-TA= PAV(ϴjc+ ϴCS+ ϴSA.
The continous d.c current rating of the device can be
evalulated with the use of the on state voltage current chara.
Junction temperatures can be determined for given on state
current and ambient temperature.
TYPES
Stampings:
Copper or aluminum sheet metals are stamped into desired
shapes.
used in traditional air cooling of electronic components.
offer a low cost solution to low density thermal problems.
Extrusion:
These allow the formation of elaborate two-dimensional
shapes capable of dissipating large heat loads.
They may be cut, machined, and options added
Bonded/Fabricated Fins:
Most air cooled heat sinks are convection limited, and the
overall thermal performance of an air cooled heat sink can
often be improved significantly if more surface area can be
exposed to the air stream.
Castings:
Sand, lost core and die casting processes are available with
or without vacuum assistance, in aluminum or copper/bronze
Folded Fins:
• Corrugated sheet metal in either aluminum or copper
increases surface area and, hence, the volumetric
performance.
• The heat sink is then attached to either a base plate or
directly to the heating surface via epoxying or brazing.
THYRISTOR MOUNTING
LEAD MOUNTING
This method is used when load current is of small value.
The SCR does not require cooling device or heat sink in this
method because most of the heat is dissipated by radiation and
convection.
Bolt mounting
There is one hole is provided in the SCR.
The heat sink and SCR are joined by the bolt.
The mica or fibre insulation is kept in between the heat sink
and SCR
Stud Mounting
There are two molybdenum plates kept on both sides of SCR.
The anode is soldered with aluminium resulting one stud is
created.
The SCR is joined to heat sink by this stud.
PRESS FIT
The pacakage is designed primarily for forced insertion into
into a slightly undesirded hole in the exchanger.
Large rating thyristor.
cost very less.
Pressure mounting
This device clamped under a very large external force
Hocky puk SCRs
Very high current ratings.
THANK YOU
