Lambda diode - Page 1
Forum section: electronics / projects

author: temperance
author_rank: Super Contributor
timestamp: June 06, 2025, 12:00:08 am
content: I just came across something called a lambda diode. This is a circuit made with 2 JFET's connected together which show a resistance graph similar to that of a tunnel diode.https://en.wikipedia.org/wiki/Lambda_diodeSome practical circuits with lambda diodes:https://www.cxi1.co.uk/Theory/neg_resistance/negres.htmI don't need this but I find it interesting.

author: RoGeorge
author_rank: Super Contributor
timestamp: June 06, 2025, 07:45:08 am
content: Nice!A reversed BJT (with C and E swapped) also shows negative resistance. Certainly can make an oscillator, not sure if anybody tried a regenerative receiver with reversed BJT.https://www.eevblog.com/forum/beginners/why-when-this-transistor-appears-to-be-reversed-does-this-circuit-work/msg5923648/#msg5923648https://www.eevblog.com/forum/testgear/fooln-around-with-dso-awg/msg4422982/#msg4422982

author: temperance
author_rank: Super Contributor
timestamp: June 06, 2025, 09:41:23 am
content: Thanks RoGeorge for the interesting links.

author: LaserSteve
author_rank: Super Contributor
timestamp: June 06, 2025, 03:26:21 pm
content: Please enjoy the link and attachment. This is one component that I wish was back in serial production. You can do this with paired discrete parts. There are a ton of bipolar and fet variations. Using these parts as oscillators can reach well into VHF if done properly.https://www.qsl.net/vk5br/NegativeResistance/NegResDipMeter.htmRecently this combination has been rediscovered for memory elements and low battery indicators.Steve

author: Alex Nikitin
author_rank: Super Contributor
timestamp: June 06, 2025, 03:43:07 pm
content: That brings back some old memories. I've used this configuration (made from two discrete JFETs, obviously) in the RF oscillator circuit of the super heterodyne SW radio receiver I've built around 1978 (I think).CheersAlex

author: Grandchuck
author_rank: Super Contributor
timestamp: June 06, 2025, 05:12:58 pm
content: mawyatt just posted this:https://www.eevblog.com/forum/testgear/fooln-around-with-dso-awg/msg5939296/#msg5939296

author: TimFox
author_rank: Super Contributor
timestamp: June 06, 2025, 05:40:35 pm
content: I've fooled around with an interesting vacuum-tube circuit, the "transitron", to build voltage-tunable HF oscillators.The first 6AS6 dual-control pentode (basically a 6AK5 with the suppressor grid modified to function as a second control grid) is the oscillator: the transitron circuit generates a negative conductance that is connected in parallel with the LC tuned circuit.A second 6AS6 connected as a "reactance modulator" to the same tuned circuit makes voltage-controlled capacitance (or inductance) in parallel with the LC circuit to change its frequency; the control voltage goes to the suppressor grid to change the transconductance of the pentode.Transitron:https://books.google.com/books?id=e_oZ69GAuxAC&pg=PA79&lpg=PA79&dq=transitron+oscillator&source=bl&ots=v-nK1uhV3n&sig=ACfU3U0HN6HCz8jiyvgkR2MbEeWDbD7lig&hl=en&sa=X&ved=2ahUKEwioksu7yZr7AhUBpokEHfQlBvQ4ChDoAXoECBAQAw#v=onepage&q=transitron%20oscillator&f=falseReactance modulator:https://www.one-electron.com/Archives/Radio/RadioFM_Tech/Hund%201942%20Reactance%20Tubes%20in%20FM%20Applications.pdfThe transitron tube circuit replaced the earlier "dynatron" circuit that exploited the secondary emission problem with a tetrode, when the plate voltage was lower than the screen-grid voltage.However, the dynatron was sensitive to the condition of the plate itself, which changed its secondary emission charactistics.The transitron uses a pentode, which suppresses the secondary electron emission, and depends on well-controlled control characteristics of the suppressor and screen grids.

author: temperance
author_rank: Super Contributor
timestamp: June 06, 2025, 06:25:21 pm
content: Now I must order some JFET's...

author: coppercone2
author_rank: Super Contributor
timestamp: June 06, 2025, 08:49:15 pm
content: an answer to peak tunnel diode? but the voltage is too high. 6V :'(

author: TimFox
author_rank: Super Contributor
timestamp: June 06, 2025, 09:05:56 pm
content: Quote from: coppercone2 on June 06, 2025, 08:49:15 pmLooking at the various discrete-circuit examples quoted above, the peak voltage varies considerably from design to design.

author: coppercone2
author_rank: Super Contributor
timestamp: June 06, 2025, 09:18:20 pm
content: the tunnel diode is 60mVI am almost amazed with how 'hot' quantum is, there is no tunnel diodes anymore (quantum device)I guess it needs to be shiny to be popular (laser)

author: temperance
author_rank: Super Contributor
timestamp: June 06, 2025, 09:31:11 pm
content: QuoteNo, and that wasn't the point.

author: MariuszD
author_rank: Regular Contributor
timestamp: June 07, 2025, 10:11:06 am
content: This circuit with bipolar transistors also exhibits negative resistance.https://www.edn.com/simple-5-component-oscillator-works-below-0-8v/

author: tggzzz
author_rank: Super Contributor
timestamp: June 07, 2025, 10:42:26 am
content: Quote from: MariuszD on June 07, 2025, 10:11:06 amAnd the author is on this forum, currently with 4447 posts