Recently Someone showed me an alternative to using a diode in this thread . I will test the idea, when I was a new tech over 40 years ago someone suggested this concept:

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................................................................Figure 1

It was total bullcorn. I got 0.7V Vf drop when I got around to testing it. It does make a dandy reference for a constant source however where other model of a transistor is used (transistor as a voltage controlled device), it is not the most stable constant current out there, but it works.

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................................................................Figure 2



Here is a design I was presented with:


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...............................................................Figure 3



Looking at it I can see how it works. I will test it and return the results here.



I use diodes as an occasional voltage reference, but since Vf is temperature dependent. I prefer to use the LM317 and its cousins as a voltage regulator/reference. I can see how Figure 3 is supposed to work, but having been fooled by Figure 1, I am looking forward to testing it, possibly to destruction.



It has obvious limitations, it cannot be used in a diode bridge for power supplies, only in areas where there is already a DC power supply in use. It should make a dandy detector for a powered AM crystal radio. The power is again a necessary requirement. But if you have an audio amplifier, then it might be of use. Time will tell.



Other diodes

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Schottky and germanium diodes both drop 0.3V for a Vf. I am told Figure 1 has no voltage drop, I’ll find out. So here is the test setup (Figure 4), to find out what Figure 1 specifications are.

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...............................................................Figure 4



I am interested if there are any other alternatives out there I may have never heard of.



Discuss.

 

Guys I apologize I started this thread then got distracted and called away from the computer. So I moderated it, finished the drawings still in my head, erased all the confused replies to my screw up, then wrote this apology and was going to unmoderated this thread (except @JohnInTX beat me to it).

 

Hi,

Long time ago i experimented with DC biasing a regular Si diode for use in AM detection.
It worked well because if the diode is partly biased then when a low level AC signal comes along it gets more easily detected.
The only part i never got around to doing was to stabilize the DC level which would have eliminated manual adjustment.

 

I started using Schottky diodes late in my career, the are the best diodes for the application of AM detector I've found to date.

I'm still trying to figure out a good P/N for Figure 3. I prefer discrete components w/ leads.

 

I started using Schottky diodes late in my career, the are the best diodes for the application of AM detector I've found to date.

I'm still trying to figure out a good P/N for Figure 3. I prefer discrete components.

Hi,

You can bias any diode and get the effect. It effectively lowers the forward voltage required for detecting the low level AC signal.

 

The technology actually has a name: https://en.wikipedia.org/wiki/Active_rectification