Help with regulator circuit

[desoky675]

I have this circuit that needs 5v - 270mA to work, its a micro-controller circuit .
I found this regulator circuit http://www.satcure-focus.com/tutor/page5.htm and did all the calculations and found that I need 150R resistor and bc337 and zener diode 5.6v , so the problem is that whenever I connect the circuit , transistor gets too hot that I fear that the current is too much for it to withstand . What could I do?

 

[Resqueline]

I'd not use a zener-circuit to supply a uC. Why not a 7805 or some other regulator? But not minding that; what kind of supply voltage are you running it off?
At 270mA the BC337 can only handle about 2.3V before getting too hot, so a supply of 7.2V is the max it can take.

 

[(*steve*)]

What's the input voltage?

Does it get hot without the load?

 

[desoky675]

For: Resqueline

The supply voltage is about 10V , so is there is any transistor number that can withstand that voltage.

For: (*steve*)

It doesn't get hot before I connect the load.


Thank you for your answers , and forgive me cause I'm beginner

 

[(*steve*)]

OK, that means the transistor is carrying a current of 270mA and has 5V across it.

This means it is being asked to dissipate 1.35W (0.270 x 5)

The datasheet for the BC337 tells you that the maximum voltage across it (Vceo) id 45V and the maximum current (Ic) is 800mA, so you may think you're OK...

HOWEVER, the maximum power (Pd) without a heatsink (look for Ta) is 625mW, under half of what you are asking of it. It is possible to calculate the temperature of the device from other figures in the datasheet, but *VERY HOT* is probably an underestimate. The device will emit smoke if left like this for very long (and I am talking under a minute probably)

With a heatsink, the transistor can be asked to dissipate 1.5W, but it would have to be a very large heatsink, and it's simply not a viable proposition. (The reason is that this package is not designed for high power use and the heat cannot excape quickly enough (see Rθjc -- 83.3 degC/W)

You need to redo the calculations with a transistor capable of dissipating higher power. I'd be looking perhaps at a TIP31B perhaps. On this you would still be advised to have a small heatsink, but you could probably get away without it as long as the device was in relatively free air,

An even better solution would be a three terminal 5V regulator as this is designed for this purpose. These have some degree of protection so that they will shut down if they are grossly overloaded (although you can still damage them).