Hello, I am new to the site and to transistors. So I have read about the transistors few articles already and watched few tutorials(about the formulas of determining Ibmax and showing some example circuits)and decided that I have some small knowledge to build a simple circuit. I use 6v lead acid battery, transistor 2n3904, two resistors(300 Ohms, one for base of the transistor and one for the led that I try to lit), LDR at max resistance 50kOhms and one led with Imax=25mA. I have chosen resistor with resistance 300 Ohms for the base, because I calcula ted that with 6 volts I will have current at the base around 20mA and this will be enough to saturate the transistor making it possible for current to flow from the collector to the emitter.
I have looked at the datasheet of the transistor too, in order to check for Icmax, which is 200mA. I have calculated Ibmax at beta 20 and got 10 mAmps and at 6 volts I get that I need 600 ohms resistor.
So thought using something like 300 Ohms(the closest to 600 I had) will be okay, also I have 2 kOhms but I am afraid that this might let too less current in the base
The problem though is that the led is not being lit/glowing.
Am I wrong in the calculations ?
Datasheet that I have used: http://html.alldatasheet.com/html-pdf/11470/ONSEMI/2N3904/365/2/2N3904.html
Can you please tell me if I have made some of the readings wrongly(Vbe = 0.65V, Icmax= 200mA, hfe= 20, should I always take the lowest value of the hfe to determine resistor on the base) ?
The circuit that I have realized already in physical model on breadboard:
P.S. I have tried the same with 2 kOhms resistor(just from desperation, thinking that I give too much current with 300 ohms and this might fry the transistor) The result is the same(the led or the load in the case is not being lit)
Also if you know good books about transistors, their working and formulas explained simply, I am open for suggestions(the articles are not enough in-debt).
I have looked at the datasheet of the transistor too, in order to check for Icmax, which is 200mA. I have calculated Ibmax at beta 20 and got 10 mAmps and at 6 volts I get that I need 600 ohms resistor.
So thought using something like 300 Ohms(the closest to 600 I had) will be okay, also I have 2 kOhms but I am afraid that this might let too less current in the base
The problem though is that the led is not being lit/glowing.
Am I wrong in the calculations ?
Datasheet that I have used: http://html.alldatasheet.com/html-pdf/11470/ONSEMI/2N3904/365/2/2N3904.html
Can you please tell me if I have made some of the readings wrongly(Vbe = 0.65V, Icmax= 200mA, hfe= 20, should I always take the lowest value of the hfe to determine resistor on the base) ?
The circuit that I have realized already in physical model on breadboard:
P.S. I have tried the same with 2 kOhms resistor(just from desperation, thinking that I give too much current with 300 ohms and this might fry the transistor) The result is the same(the led or the load in the case is not being lit)
Also if you know good books about transistors, their working and formulas explained simply, I am open for suggestions(the articles are not enough in-debt).