I'm interested in creating a low voltage white noise generator by means of a zener diode, as detailed here: Zener & BJT Noise Generator. Specifically, I want to use the circuit here, in order to minimise PCB real estate and number of components: .
I'd like to replace some of the parts (D1 & Q1) chosen by the original author, as the article was written in 1990 and better/smaller parts are now commonly available. Hence I'd like to be able to analyse the circuit, rather than just take a guess at suitable values of components.
I'll use the following circuit for the discussion:
VSS = 3.3V and V_Zener = 2.0V. I want to know the power dissipation of the BJT in order to determine what is a suitable choice (I want to use a small SMT BJT, not a 2N2222). I've kept R1 & R2 to be the same value as the original circuit, simply for the sake of the analysis.
My understanding is that the zener is reverse biased and results in a reverse current flow (that is noisy) that is determined by the voltage to which it is reverse biased - is this correct? Do I therefore find the reverse current flow (into the base of the BJT) in Fig 4 of the Data sheet? If this is the case, then is the current flow through the collector then = IBE * gain of BJT?
Or does the analysis start by saying that the voltage at V_Zener with respect to ground is V_zener (2.0V) + VBE (0.6V) = approx 2.6V. Therefore steady state voltage(ignoring noise) at node 'Noise' is calculated by the divider R1/((R2 + R_zener) paralleled with R_Q1)? Not sure where I would go in the analysis after this?
It's been a very long time since I did this sort of stuff, so any tips would be really helpful.
Having worked out ICE, power dissipation in the BJT = V_collector * ICE?