For low voltage shunt regulation either use a series regulator LDO or a device such as the TL which has a band gap reference, and an opamp in a 3-poin package to create an almost perfect “Zener diode”. If you increase the resistor the voltage across the zener should go down. Actually, this does explain what I’m seeing and your result is pretty spot on with what I’m reading. Email Required, but never shown.
It’s incorrect to add a voltage at the test current because of the dynamic resistance. Even so I expect that the diode you have does match its data sheet.
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(PDF) 1N4729A Datasheet download
If you want decent accuracy throw the zeners away and use some low dropout 3. Actually, it was a candidate for a regulated supply fed by a CCS. Zeners are notoriously power inefficient even at no load. If you want to get 3.
WhatRoughBeast 49k 2 28 The dynamic resistance of the Zener may not be able to drop low enough, even with 70mA available to it, to make the proper resistor divider equivalent for the node to be equal to 3.
Working out the current limiting resistor we have: What’s odd is that the BZX55C is showing more-or-less the same behaviour although 1n4729x different resistors. Does this conflict with what Kvegaoro is saying?
Indeed it would seem to be a much easier solution to just get an adjustable LDO, if this thing is meant to be used as regulated supply voltage. That part of kveagaro’s answer is not correct. Home Questions Tags Users Unanswered. Kvegaoro 2, 11 The problem is how you are modeling your circuit, because the series resistance you are using is so close the zener resistance, it must included in the circuit model. It seems odd then that the datasheets would specify an Izt of 69mA if it didn’t show the zener in the best light.
The next problem is that at 70mA and 4 volts, the power is 0. Spehro Pefhany k 4 As I pointed out in my query, I used the test currents from the relevant datasheets as a guide.
Can you expand on the statement: Is that the dynamic resistance of the zener? The dynamic resistance describes the small-signal behavior near the test current.
1NA Datasheet pdf – V, 1 W silicon zener diode – BKC International Electronics
Because it rises as per the quote you must have an unstable power source of 5V and this is rising as you increase the load resistance. Andy aka k 10 I set up the standard test circuit shown below.
Post as a guest Name. If you include the dynamic resistance in the model, you must use a lower voltage for the ideal zener. You may be on right but it sure makes working out the correct resistor value a chore. Null 4, 10 22 Dqtasheet my experience, low-voltage zeners anything below 5V all seem to have a very soft ‘knee’ and not particularly ‘vertical’ current-vs-voltage curve.
Double check this supply. Both Zeners came from separate suppliers. First this stated in the question: How much current will th load require?