transistor problems?

Question

i have a print wich needs modernising, how does smd ans transistors work and how do i confine transistors in a smaal space without going to hot, aka cooling

Answer 1

SMD transistors work the same as transistors with wire-leads (through-hole parts). If there isn't a direct replacement part number for the transistors in your circuit (i.e 2N2222A through-hole; MBT2222A smd part), then there will probably be some other SMD part number that fits the specifications of the transistors in your circuit.

As for heat, you will need to do a thermal study of the heat dissipation of each transistor in the existing circuit. Multiply the worst-case steady state collector current in each transistor by the highest voltage across the collector-to-emitter.

If that power (V * I) is less than the maximum power rating of the transistor use it in the next calculation (below). If that power is close to, or above the max. power rating of the transistor, then you will have to do more extensive analysis of the exact power dissipated in the transistor (beyond the scope of this Y!A question).

Next, find the thermal resistance from junction-to-ambient and calculate the junction temperature.

Now, when you substitute your SMD transistor, recalculate the junction temperature with the new values for thermal resistance (junction-to-ambient). If your SMD junction temperature is less than the max., then you can substitute the SMD part without worrying about extra cooling. If it gets too hot, then you might have to re-design that part of the circuit.

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Answer 2

It's hard to understand what you really want (spell check and grammar check are your friends). SMD is just an acronym for a surface mount device. You need more than a simple Yahoo answer to explain how a transistor works. Try www.howstuffworks.com or dig through a google search or go take some classes.

As far as heating and cooling... As long as this is not a power circuit, you shouldn't have to worry too much about them getting hot. (If it is a power circuit and you don't understand this stuff, please take a class first - it can be dangerous). You can always find parts with heatsinks built in and attach them to larger ground planes or add fans if heat is a problem.

Answer 3

the only available subject i'm able to think of of is the enter impedance of photoisolator circuit is a powerful bit decrease than the enter impedance of the transistor circuit. which capability the photoisolator will draw extra modern-day from the microcontroller than the transistor circuit. as long as your micro-controller output can manage approximately 5ma you will no longer have a topic. 5ma isn't plenty modern-day. I additionally might evaluate putting a modern-day proscribing resistor between the coil and the capability grant. do you be conscious of the way plenty modern-day is needed interior the coil to swap on the relay?

Answer 4

transistors get hot because of the power they drop.
if you get better transistors they drop less power, use mosfets.
now for surface mount, the circuit board can become the heatsink. make big pads near the transistor to dissipate the heat. read the specs.