In a recent thread of mine (i dont know how to link that) i asked some questions about transistors, learned a great deal about that but one transistors is broken (don't know if that was already the case or it just died). but i dont have them of that type anymore, BC547A, i only have the BC547B/C. they are kinda the same but there are some differences in DC-current gain and breakdown voltages. but i don't know enough to determite if i can just replace it with the same base resistor 270ohm for the A version.
here is a part of the datasheet that has the info of the different info:
Digital/switching circuits are not as critical as analog circuits.
Higher Hfe (current gain) doesn't hurt in switching circuits. If the Hfe is too low, the transistor may not turn fully-on, which in addition to making your circuit not function properly, can cause the transistor to overheat (depending on the current).
If you are near the current limits, of course you shouldn't use a transistor with lower current rating. (Same for power rating, although in switching applications the current limit is usually what matters.)
Usually the most important spec is the maximum current rating.
There are two common ways of burning-out a transistor.
Too much power. If the transistor is too hot to touch, it's probably too hot and you may need a heatsink. If you can hold your finger on it, it's probably OK.
Voltage "kickback" from a coil (usually a motor or solenoid). That's prevented with a "flyback diode" wired in reverse to "short-out" the reverse kick-back voltage. (With LEDs, that's not a problem.)
good looking out! that was an old calculation i suppose. R2 is 82ohm rn and that works fine. because i have 2 transistors each 4 leds in parallel with their own resistors.
You haven't provided a schematic that truly describes your circuit. You wasted my time commenting on a circuit that isn't actually being used. Thanks for that.
because there is, i was just saying that i have 2 equal circuits consisting of the same components. so that is why i know it is not my wiring but my transistor, the led are functional.
here a quick sketch of the circuit that it is all about:
and then i have this circuit 2x 1 for left side and 1 for right side. and the right side works.
that was what i was trying to tell but my mind thinks you already know what i am talking about but that is ofcourse not true!
You shouldn't use a BC54x for that circuit. Current through the transistor depends on Vf of the LEDs, but could be 200mA with IR LEDs. The BC547 will only stand a chance with white or blue LEDs. A BC337 or 2N2222 could be a better choice.
Leo..
Also with two of these circuits you are stretching the limits of what a USB connector can supply. And also what the pins of an Arduino can cope with. Consider these two extracts from the data sheet.
The BC547 will only stand a chance with white or blue LEDs.
good thing i am using white leds. so that is fine. but i will keep it in mind for later in life.
Also with two of these circuits you are stretching the limits of what a USB connector can supply.
i understand what you mean, but looking at the circuit i provided it doesn't show me connecting it to any USB or arduino. it is just +5V. it is originally connected to a V.reg coming from a 3cell Li-ion pack. but that info was not necessary in the circuit (in my opinion) +5V was enough.
so my question is answered. it is safe to just replace the BC547A with the BC547C without changing anything else within the circuit.
