Electronics/zener diode shunt regulator
QUESTION: Hi, I'm struggling to answer a question and just wondered if you could please provide me with any help. The question is regarding a zener diode shunt regulator circuit, where Rs is connected in series with the diode and then RL is in parallel with the diode. I need to calculate the value of RS that will allow the regulator to function as designed. I'm given that the circuit requires 15V, it will draw 15mA under normal conditions and the zener diode requires 3.73mA. I know that the supply current (IS) = IL + IZ, therefore 15mA - 3.75mA = 11.27mA (IL). Also that RS can be calculated by RS= (Vin-Vout)/IR and because the load is in parallel with the diode the voltage across the load(VL) and diode(Vz) should be the same. However I 'm not sure how to calculate the VL or VZ, any help would be greatly appreciated. Kind Regards, Max
ANSWER: You did not send the schematic diagram so it leaves me guessing a little on your naming of voltages and currents.
However, it is a simple solution using ohms law for current and voltages. The voltage drop across Rs is easily calculated since you know the current to be 15ma. The current then is divided between the zener and the load resistance. You know the voltage at the zener/load junction now so the current passing through the zener and load resistor are known as well. The load resistor is calculated using ohms law since you know the current and the voltage.
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QUESTION: I apologise I don't think I worded the question correctly and I've included a picture of the question and circuit diagram. Please tell me if I'm being wrong but I'm not able to calculate the voltage drop across Rs straightaway because I don't have the resistance to use voltage drop = vin* (rs/Rtotal). So I don't know if I'm making it more difficult than it is but from what you have said I still don't think I can answer it at the moment. Is there anymore help or advise you could provide? Kind Regards Max
Yes, it is a simple circuit. You must know the zener voltage or V0 in order determine the circuit parameters. It is driving a reverb circuit so you should consider that as part of the solution. It looks like it needs a 15v supply but not all of the discussion was included in your photo.
So, you must know more than what is given in the problem. It would be good to know what the supply voltage is for the regulator circuit or if you can arbitrarily select it.