matching output voltage of the sequencer to VG1 of PMA5-83-2W+ - Page 1
Forum section: electronics / projects

author: john23
author_rank: Frequent Contributor
timestamp: September 09, 2024, 02:37:53 pm
content: Hello ,As you can see in the last stage of the schematics presented below, I have succeeded in converting the -12V into a -2.5 as shown below.I used a comparator with constant voltage which is passing M12 signal, then using TL431 i converted -12V to -2.5V.I know that choosing comparator is because we want low impedance.How can i know according to the datasheet if this signal will fit good the component?Full LTspice simulation is attached.https://www.minicircuits.com/pdfs/PMA5-83-2W+.pdf

author: RFDx
author_rank: Regular Contributor
timestamp: September 10, 2024, 04:55:10 pm
content: An op amp in inverting configuration would already be sufficient to generate -2V for VG1 from a stable, positive voltage.After initially applying -2V (-2.5V is probably OK too) to VG1 during the power-on sequence, you have to raise it in the second to last step of the sequence to about -0.8V to get the amplifier into class-A operation with a typ. drain current of Id=400mA. How is that gonna happen with your solution based on a comparator and voltage reference?

author: john23
author_rank: Frequent Contributor
timestamp: September 11, 2024, 06:54:26 am
content: Hello ,I used the method below to bias Vg1 input of PMA5-83-2W link below.I assumed my Vg1 input is high Z so 1 put 1Mohm resistor as the load for the circuit you helped me to build.Is it a correct assumption?Ltspice files are attached.Thanks.https://www.minicircuits.com/pdfs/PMA5-83-2W+.pdf

author: john23
author_rank: Frequent Contributor
timestamp: September 11, 2024, 01:24:24 pm
content: Hello , I have built a circuit that supposed to supply -2.5V to PMA5-83-2W+ Vg1.as you can see at 800 Ohm load i get -2.5V and 9mA current.Basickly the Vg1 needs to have as much current as it needs.In my circuit I have a TLV3701 comparator and TL431 reference voltage.Given the attached simulation and photos from the datasheet table PMA5-83-2W+ Vg1.How can i KNow that there will not be any current supply problem for the Vg1 input?LTspice file is attached.Thanks.TL431:https://www.ti.com/lit/ds/symlink/tl431.pdf?ts=1726014140885&ref_url=https%253A%252F%252Fwww.google.com%252FTLV3701:https://www.ti.com/lit/ds/symlink/tlv3701.pdf?ts=1726060732336&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTLV3701

author: ftg
author_rank: Frequent Contributor
timestamp: September 11, 2024, 01:51:07 pm
content: Quote from: john23 on September 11, 2024, 01:24:24 pmAccording to the PMA5-83-2W+ datasheet, the gate 1 input bias current is maximum of 4mA, with typical gate input bias current being 15µA.The absolute maximum input bias current is 4.5mA, if you can supply that, then it should always have more than enough.https://www.minicircuits.com/pdfs/PMA5-83-2W+.pdfI have attached the relevant numbers from the datasheet, to save the effort of opening the datasheet.

author: john23
author_rank: Frequent Contributor
timestamp: September 11, 2024, 06:14:09 pm
content: Ok so we need to supply 4mA at most.I was told that TL431 cannot sוppךy this amount of current.I need it to supply -2.5V.What current can it supply when its -2.5V on the anode?Thanks.TL431:https://www.ti.com/lit/ds/symlink/tl431.pdf?ts=1726014140885&ref_url=https%253A%252F%252Fwww.google.com%252F

author: eutectique
author_rank: Frequent Contributor
timestamp: September 11, 2024, 08:22:23 pm
content: Quote from: john23 on September 11, 2024, 06:14:09 pmTell that person to read the data sheet.

author: john23
author_rank: Frequent Contributor
timestamp: September 12, 2024, 06:11:22 am
content: Hello,I need to supply My Vdd 400mA , I need to supply Vg1 and Vg2 at most 4mAThe load is a very dinamic thing we cant be sure what load my PMA5-83-2W+will create on the circuit.I need to supply the Vdd with 12V and 400mAWhat is the proper way to test the ability to Source current for the VDD.LTSpice files are attached.https://www.minicircuits.com/pdfs/PMA5-83-2W+.pdf