Hello,
this is not for a course or anything, i am trying to learn about amplifiers and have hit a wall with this. i am using this:
http://www.learnabout-electronics.org/Amplifiers/amplifiers20.php
a site that shows you how to design a common emitter amplifier. i want an amplifier with a gain of 20, however this will come later. for now, i want to get this straight and understand it. i have followed along and got this circuit which i built on multisim.
it said to use 1uf-10uf for C1 and C2, so i chose 1uf. then it said to choose a value of C3 that would have a low reactance compared to Re.
so i thought that 1 ohm would be low compared to 1k ohm. so i used the formula for capacitive reactance and got 7957 uf at 20Hz.
the output is really distorted as well.
i chose these values
vcc = 9 v
quiescent current = 1mA
load resistor = half vcc divided by 1mA = 4500 ohms, real value 4700 ohms
value of Re= 12% of vcc = 1.08 volts, this divided by 1mA to get 1080 but i chose 1kohm because it gave more accurate voltages when measured compared to calculated results
base current = 6.6uA this from Q current over 150 which is the current gain of 2n3904 at 1mA
base boltage = 1.78volts
r1 and r2 bias current = base current * 10, 6.6 * 10 = 66 uA
r1 value= vcc - vb / 66uA, 9 - 1.78 / 66uA = 109394 ohms i chose 110k ohms
r2 value vb / 66uA , 1.78 / 66uA = 26970 ohms i chose 27k ohms
any help would be great
thanks
simon
this is not for a course or anything, i am trying to learn about amplifiers and have hit a wall with this. i am using this:
http://www.learnabout-electronics.org/Amplifiers/amplifiers20.php
a site that shows you how to design a common emitter amplifier. i want an amplifier with a gain of 20, however this will come later. for now, i want to get this straight and understand it. i have followed along and got this circuit which i built on multisim.
it said to use 1uf-10uf for C1 and C2, so i chose 1uf. then it said to choose a value of C3 that would have a low reactance compared to Re.
so i thought that 1 ohm would be low compared to 1k ohm. so i used the formula for capacitive reactance and got 7957 uf at 20Hz.
the output is really distorted as well.
i chose these values
vcc = 9 v
quiescent current = 1mA
load resistor = half vcc divided by 1mA = 4500 ohms, real value 4700 ohms
value of Re= 12% of vcc = 1.08 volts, this divided by 1mA to get 1080 but i chose 1kohm because it gave more accurate voltages when measured compared to calculated results
base current = 6.6uA this from Q current over 150 which is the current gain of 2n3904 at 1mA
base boltage = 1.78volts
r1 and r2 bias current = base current * 10, 6.6 * 10 = 66 uA
r1 value= vcc - vb / 66uA, 9 - 1.78 / 66uA = 109394 ohms i chose 110k ohms
r2 value vb / 66uA , 1.78 / 66uA = 26970 ohms i chose 27k ohms
any help would be great
thanks
simon