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I know that u can use 2 resistors as potential dividers, but can anyone enlighten me on why a zener diode-resistor arrangement is a better solution, since I was told that commercially, a zener-diode potential divider is more popular. Any help on this?
Hi, so am i right to say that with a zener diode, not only will there be less power dissipation, but also that the output will be more stable and constant? What about the choice of diodes? I read somewhere that the load resistance cannot be too big, but how do u find the impedance of a diode?
A simple resistor divider is ok for dropping voltage to a circuit that draws a constant current and does not require a precise voltage level.
A resistor-zener diode circuit will supply a circuit with a fairly constant current and voltage. You must know how much current and voltage your circuit requires before selecting the resistor and zener combination.
Whether a zener/resistor combination is "better" than a two resistor divider depends on what you're trying to use it for. Are you using the output as a voltage reference, or as a power supply regulator?
Output from a resistive divider is only as accurate as the supply or reference it's driven from (plus the tolerance of the resistors).
The zener diode/resistor will have a much lower output impedance than a resistive divider, on the order of a few ohms. A zener is a shunt regulator, and dissipates some power regardless of whether a load is connected. The 3-terminal regulator mentioned above is a series-type regulator, and also consumes some quiescent (standby) current. The low-dropout types can be very power efficient when the input voltage is close to the output voltage. For large differences between input and output voltages a switching regulator will provide the best conversion efficiencies.
So the important question is, what are you planning to use the circuit for?
Is it a reference or a power supply regulator. Does the output voltage need to be absolute or proportional to the input supply?
Sorry, I wasn't clear. I meant that the heat losses due to the regulator chip is usually much higher correct? I made the statement based on the diagram in the link refered to above as I have used a regulator chip fed with a 9V directly to convert to 5V and it became hot fairly quickly.
Actually, when we use a zener diode, we can get a more accurate output voltage, so the regulator is just to ensure a constant output with minimal quirks correct? Am I right to say that I am actually stepping down an external input voltage twice, once from the divider and once from the regulator, which usually requires 2V difference between the input and output? If I were to do this, can I say that the output is close to an ideal constant DC Voltage?
As for the zener diode, my aim is actually to use it as a reference voltage, so I gather that a resistive divider is actually more suitable as I don't need such an accurate value. Am I rght to say that for either arrangements, power will be dissipated, but if my chouce of resistor is reasonable, it will incur less losses than a zener diode arrangement? Let me read up on switching regulators for a better idea on how it works. Any reccomended readings?
Actually, I am trying to charge a battery using some form of AC, so after rectifying the AC to a DC, I need to put in the DC-DC converter to ensure a constant voltage and current. Since the power generated from my AC is fairly low, I am trying to minimise power losses as much as I can for efficient conversion.
I'm sorry, you meant the heat losses due to the regulator are much higher than what?
9V to 5V with a linear regulator isn't a very efficient setup, but it's often ok for low current uses. At 1 Amp, a regulator would have to dissipate (9 - 5)V x 1A = 4 Watts, you didn't mention what the current draw of your circuit was. A two stage approach using linear or shunt regulators doesn't improve efficiencies, but spreads out the power dissipation. A better approach for dealing with large input/output differences is to use a switching regulator. A quick web search will provide you with plenty of reading material.
I was thinking that there might be more efficient ways, since like I mentioned, the regulator got heated up fairly quickly, an indication that much power is lost as heat. I saw a simple circuit using a switching regulator, and since it is connected with an inductor-resistor, it should be more power efficient, so I think this is more efficient than a linear regulator, even if the current drawn is 1A. So if I were to use a switching regulator, I gather that a zener diode arrangement is not necessary to connect AC-DC conversion part to DC-DC conversion part, esp since this diode actually dissipates power. something not very efficient?