Alternatives to Diodes

Thread Starter

Wendy

Joined Mar 24, 2008
22,239
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:

.......................................................Figure 1.png
................................................................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.

.......................................................Figure 2.png
................................................................Figure 2



Here is a design I was presented with:


........................................................Figure 3.png
...............................................................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

.............................................................Example 1.png

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.

.........................................Figure 4.png
...............................................................Figure 4



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



Discuss.
 
Last edited:

Thread Starter

Wendy

Joined Mar 24, 2008
22,239
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).
 
Last edited:

MrAl

Joined Jun 17, 2014
7,968
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.
 

Thread Starter

Wendy

Joined Mar 24, 2008
22,239
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.
 
Last edited:

MrAl

Joined Jun 17, 2014
7,968
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.
 
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