Which transistor is best suited for high temperature applications??? - aluminium heat sink
I use a BC548 Darlington configuration switch between applications (for activating a relay 6V 30 ohms). Relay between the emitter junction and Vcc = 9 V supply connected. The circuit works well, except that it starts to malfunction due to overheating of the transistor. the temperature of the transistor, when the increase of about 50 ° C, because the voltage drop on the relay is reduced to about 8V to V 4 to 5. Is there a solution for this? I have tried to use an aluminum heat sink, but it does not work. To a different model of a transistor that the company is able to propose their works at high temperatures.
Friday, January 22, 2010
Aluminium Heat Sink Which Transistor Is Best Suited For High Temperature Applications???
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2 comments:
The BC548 is rated at 100 mA max current collectors. 30 ohm relay coil will be used with 9 V rest, 300 mA, 3-times the maximum capacity of BC548. The BC548 is desperate for its implementation. When you enter the room, (5 Darlington NPN TIP122 a maximum collector current, A-220-case) should work well and cost about 45 cents. The application should not require heat sinks. There are hundreds of other transistors that work well.
Another model will not change, as the transistor.
Darlington connections for high temperatures, such as theft is increased from the base of the first transistor badly by the transistor HFE.
Some corrections. using a transistor with lower losses. Watch ICEO specification.
Add the strength of the base to the emitter of the first transistor bypass to some of the leak.
A heat sink should help.
What I recommend: Use a different circuit. There is no reason to use a 6-volt relay with a 9-volt source. The loss of the 3-volt causes the heat. When properly configured, the decrease of the transistor must be less than 0.3 volts.
to see http://ourworld.compuserve.com/homepages ...
Figure C shows an example. There are many others.
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