Diode transistor logic problem

[GolamMostafa]

@OP

Let us analysis the circuit of Fig-1 of Post#17 to see that the output V₀ assumes LL-state when both inputs are at LH-state (3.3V) and the V_cc is connected to 3.3V.

1. Both inputs are at LH-states (3.3V).

2. Calculate base current I_B2 for transistor T2.
I_B2 = I_D - I_Rb

Calculate I_D:
I_D = current passing through diodes D1 and D2 = current passing through R =I_R

(DA, DB are revere biased; current passing through these diodes are negligible.)
I_D = (Vcc - Vp)/R [Vcc = Vp + I_D*R]
==> I_D = (3.3 - (V_D1 + V_D2 + V_B2))/2k = 0.525 mA

(I_D and I_B2 are sufficiently large to cause voltage drops across D1, D2, abd BE2 junction to approximately 0.75V.)

Calculate I_Rb
V_B2 = I_Rb*R_b + (-V_BB)
==> I_Rb = (V_B2 - (-V_BB))/R_b = (0.75 + 2)/20k =0.14 mA

I_B2 = I_D - I_Rb = 0.525 mA - 0.14 mA = 0.385 mA.

Considering h_FE = DC gain of T2 (consider C828 transistor) is about 130, the I_B2 (0.385 mA) current is sufficent to saturate transistor T2. Thus the output voltage (V₀) is ~= 0.2V which corresponds to LL-state. ( V_Rc = voltage drop across Rc resistor is: 0.385 mA * 130 * 2k ~= 100 V ----> 3.1V.)

[surepic]

Sorry for the delay.

After simulating different dtl,ttl to fit to the logic I ended up with simple circuit.

+5v->switch(nc)->load->collector
+3.3v->base of bjt

resistor values are approximate didnt do math yet..... at least its working in simulators (multisim and proteus). Here the simulation Couldnt upload it here cos of size limitation.

[TomGeorge]

Hi,
Sorry the YouTube video didn't explain anything.

Have you, in real life built a circuit to see if it will work?

Can you post a truth table, showing ALL your inputs and outputs and how you want them to work?

Is this your simple circuit?

The inputs marked 0 , are they the 3,3V inputs?

Tom..... :o :o :o

[surepic]

No truth table yet. Will do on weekend. In simulator they are 5v but in real circuit they will be 3.3v

In real circuit resistors in rc chain in 555s have different values.

Inputs are marked 0 as they have logical state of 0 at that moment switching them to on will provide 3.3v to transistor base. In the video i tried to show that.