I did this oo..even used the spice file you provided with the My_3904 but yet can't seeLook at this image.
View attachment 194144
Also did thevenin like you did but notice Vth = 0.694 but the VB1 is greater than this.. it's 754mvIf you want to find the DC operating point.
We start by assuming β = ∞ and apply a Thevenin theorem to RP and RB.
Vth = 5V*1kΩ/(6.2kΩ + 1kΩ) = 0.694V and Rth = RP||RB = 0.861kΩ
And the situation will look like this:
View attachment 194161
Therefore from KVL we can write:
Vcc - Ic1*Rc - Vbe2 - Ix*RF - Vbe1- Ic1*RE = 0 (1)
Vcc - Ic1*Rc - Vbe2 - Ix*(RF + Rth) - Vth = 0 (2)
And we can solve this for Ic1 and Ix
\[ I_C = \frac{R_F (V_{TH} - V_{BE}) + R_{TH}*(V_{CC} - 2 V_{BE})}{R_C R_{TH} + R_E (R_F + R_{TH})} \approx 187\mu A \]
And if we know Ic1 we can find all other voltages and current in the circuit.
Ie2 ≈ ((Vcc - Ic1*Rc - Vbe) - Vee)/(Re1 + Re2) ≈ (0.286V - ( -5V))/4.9kΩ ≈ 1mA
Also, this circuit is very Vbe sensitive, changing the Vbe to 0.7V changes the current very much Ic1 ≈ 135μA and Ie2 ≈ 1.3mA.
Therefore exact calculations are redundant due to the fact that we do not know the exact value of a Vbe and Vbe mismatch, and the same we can say about beta value.
Thought the voltage will be less than Vth but see my mistake nowSo what? Vth is not the voltage at the T1 base.
Thanks so much for helping with insight but solution is 6/10 but thanks. Ib = 0...If you want to find the DC operating point.
We start by assuming β = ∞ and apply a Thevenin theorem to RP and RB.
Vth = 5V*1kΩ/(6.2kΩ + 1kΩ) = 0.694V and Rth = RP||RB = 0.861kΩ
And the situation will look like this:
View attachment 194161
Therefore from KVL we can write:
Vcc - Ic1*Rc - Vbe2 - Ix*RF - Vbe1- Ic1*RE = 0 (1)
Vcc - Ic1*Rc - Vbe2 - Ix*(RF + Rth) - Vth = 0 (2)
And we can solve this for Ic1 and Ix
\[ I_C = \frac{R_F (V_{TH} - V_{BE}) + R_{TH}*(V_{CC} - 2 V_{BE})}{R_C R_{TH} + R_E (R_F + R_{TH})} \approx 187\mu A \]
And if we know Ic1 we can find all other voltages and current in the circuit.
Ie2 ≈ ((Vcc - Ic1*Rc - Vbe) - Vee)/(Re1 + Re2) ≈ (0.286V - ( -5V))/4.9kΩ ≈ 1mA
Also, this circuit is very Vbe sensitive, changing the Vbe to 0.7V changes the current very much Ic1 ≈ 135μA and Ie2 ≈ 1.3mA.
Therefore exact calculations are redundant due to the fact that we do not know the exact value of a Vbe and Vbe mismatch, and the same we can say about beta value.
by Gary Elinoff
by Luke James
by Luke James