role of optocoupler for biasing drain of amplifiers - Page 1
Forum section: electronics / projects

author: john23
author_rank: Frequent Contributor
timestamp: April 17, 2024, 04:42:03 pm
content: Hello,In the diagram sown below I have a MOSFET called NDT3055L, the mosfet sends the current into the Qorvo TGA2590-CP drain.When we test the circuit the source of the mosfet is basically floating although when I will connect the amplifier to source then the QORVO amplifier will introduce a load to the source of the mosfet.Somehow the optocoupler helps with the transition of the state when we don't have QORVO amplifier load on the source of the MOSFET.What is the role of the optocoupler in this situation?I'll be glad to have some analog design logic behind putting this component in this position.Thanks.https://www.ti.com/lit/ds/symlink/ucc5304.pdf?ts=1713292114392TGA2590-CP - Qorvowww.qorvo.comwww.qorvo.com

author: xvr
author_rank: Frequent Contributor
timestamp: April 17, 2024, 05:43:13 pm
content: There is no optocoupler in this schema. UCC5304 is an isolated driver, but not optocoupler.As for using it here at all - it used to decouple ground of schema from Source of MOSFET. MOSFET controlled by voltage, applied between Source and Gate. Original signal to control MOSFET based to ground of all schema, but MOSFET Source has floating potential relatively ground, so control signal can not be directly passed to MOSFET Gate.UCC5304 rebased this control signal to MOSFET Source - it used as ground potential on output (isolated) side of UCC5304.BTW - there is no supply attached to isolated side of UCC5304 in schema. I think something was forgotten

author: john23
author_rank: Frequent Contributor
timestamp: April 18, 2024, 12:37:54 pm
content: Hello XVR, an updated version is attached of the schematics.Why do we connect floating ground to a place where we would get the amplifier connected.The TGA 2590 amplifier will be the load the mosfet source(when we connect them together)What is the logic of connecting floating ground there?Thanks."it used to decouple ground of schema from Source of MOSFET"

author: xvr
author_rank: Frequent Contributor
timestamp: April 18, 2024, 12:54:21 pm
content: > an updated version is attached of the schematics.Floating power still unconnected. You should connect right Vdd of UCxxx to +24V net.> What is the logic of connecting floating ground there?Output of UCCxxx should be referenced again Source of MOSFET - this is the way how NOSFET works (it controlled by Gate-Source voltage).And doesn't matter what else is connected to MOSFET Source.

author: moffy
author_rank: Super Contributor
timestamp: April 18, 2024, 02:11:49 pm
content: I think you need a diode from +24V to Vdd, because the source shifts up to +24V when the MOSFET is on, but +24V exceeds the maximum voltage of the UCC5304, and is also too high for MOSFET gates. You probably need a zener in series with the diode to drop the voltage down to say 15V. I also think you need some moderate value resistor from your floating ground to ground otherwise there will be no current path to charge the driver IC supply unless the opamp can provide that path.

author: RFDx
author_rank: Regular Contributor
timestamp: April 18, 2024, 02:56:48 pm
content: Quote from: john23 on April 18, 2024, 12:37:54 pmYes, power supply (VDD) for the isolated side still missing, as is the bootstrap diode. The bootstrap capacitor (multiple values in parallel) ist also rather high. Is there a reason for that? How are you charging the bootstrapping capacitor the first time you turn the driver on? Maybe also tell something about what you are trying to achive here, not just how you wanna do it.

author: john23
author_rank: Frequent Contributor
timestamp: April 18, 2024, 05:08:52 pm
content: Hello ,I am learning the principles of circuit,I only know that its supposed to drive a power amplifier TGA 2590 .regarding your question two extended schematics photos are attached the node is call VIZ and GIZ and its connected to DB02S2415A component as shown in another picture .Yes of course the mosfter is opened and closed by the Vgs>Vt condition, however what i have inner logical conflict when on one hand we put "floating" Ground.But on the other hand we the source is not connected to ground it could be connected to power amplifier and the draing of power amplifier is the load and not plain ground.So how this virtual ground helps us here?Thanks."Output of UCCxxx should be referenced again Source of MOSFET - this is the way how NOSFET works (it controlled by Gate-Source voltage)""BTW - there is no supply attached to isolated side of UCC5304 in schema. I think something was forgotten"https://www.mouser.co.il/datasheet/2/632/DS_DB02S_D-3106392.pdf

author: xvr
author_rank: Frequent Contributor
timestamp: April 18, 2024, 05:16:41 pm
content: > But on the other hand we the source is not connected to ground it could be connected to power amplifier and the draing of power amplifier is the load and not plain ground.We have 2 power sources in schema and 2 different not intersected set of Power/Ground.One is a whole schema Power source and Ground, and second - your VIZ and GIZ nodes. They also Power and Ground, but different.So there is no any conflicts - top amplifier connection is a ground in one power domain (isolated) and nothing in another (main).

author: moffy
author_rank: Super Contributor
timestamp: April 18, 2024, 11:12:37 pm
content: There you go, an isolated 15V supply for the MOSFET driver, just what was needed.Think of the MOSFET as a resistor with one terminal connected to the +24V. When the driver is 'off' the resistance is very high, when the driver is 'on' the resistance is very low, since the driver is referenced to the source of the MOSFET and it now has a floating supply it is happy.P.S. They could have used a P channel MOSFET and saved quite a bit in complexity and cost.

author: xvr
author_rank: Frequent Contributor
timestamp: April 19, 2024, 07:57:23 am
content: Why just not use SSR? Unstead of MOSFET and all circuit that now controll it?

author: RFDx
author_rank: Regular Contributor
timestamp: April 19, 2024, 08:00:33 am
content: Quote from: john23 on April 18, 2024, 05:08:52 pmNow it makes sense.Quote from: john23 on April 18, 2024, 05:08:52 pmThe source of the N-MOSFET has to vary between 0V (MMIC amp off) and 24V (MMIC amp on). In order to do that, the gate of the MOSFET needs to be driven with 0V (for off) or at least 10V (for on), referenced to the level at the source of the MOSFET. If you connect the ground pin (VSS) of the isolated driver to the source terminal of the transistor it becomes a floating ground because it moves up and down (0<->24V, referenced to real ground), depending on the MMIC amp being on or off.The driver itself is isolated (floating) from the rest of the circuit and is supplied from an isolated voltage source (15 V DC/DC converter) connected between the VDD (floating supply) and VSS (floating ground) pins of the driver. The gate-source Voltage Vgs of the MOSFET alternates between ~0V (amp off) and ~15V (amp on). Referenced to real ground, the gate voltage of the MOSFET will measure ~0V (for amp off) and ~39V (24V+15V) (for amp on).

author: john23
author_rank: Frequent Contributor
timestamp: April 19, 2024, 06:57:29 pm
content: Hello RDFX,I am used to this of voltages always with reference to some poing gnd.When we want to mosfet to be ON we have to put at least 10V Vgs.we have DB02S2415A which gets as input 24V and -12V while the output is Viz and Giz which are refrenced to gnd of the supply of the component.Then those two voltage are connected to the UCC5304 out and VSS1.what is the logic of connecting the output of the DB02S2415A to the output of the UCC5304?Is it a logical error in the schematics or there is some logic for doing this?THanks.

author: xvr
author_rank: Frequent Contributor
timestamp: April 19, 2024, 07:02:24 pm
content: This is not output of UCCxxx, this is its power

author: john23
author_rank: Frequent Contributor
timestamp: April 19, 2024, 07:42:31 pm
content: Hello XVR, Yes i understnad so my GND reference point of the UCC5304 is basicly the gnd of the DB02S2415A .Given the datasheet shwon below how do i know what voltages will come out of pin7 OUT and pin 5 GND?https://www.ti.com/lit/ds/symlink/ucc5304.pdf?ts=1713493999921&ref_url=https%253A%252F%252Fwww.google.com%252F

author: xvr
author_rank: Frequent Contributor
timestamp: April 19, 2024, 08:05:58 pm
content: Page 3. Pin table.OUT 7 O Output of driver. Connect to the gate of the FET or IGBT.So, this is outputVDD 8 P Secondary-side power for driver.VSS 5, 6 P Ground for secondary-side driver.So, pin 8 is isolated power and pins 5 and 6 - isolated ground

author: RFDx
author_rank: Regular Contributor
timestamp: April 19, 2024, 11:07:10 pm
content: Quote from: john23 on April 19, 2024, 06:57:29 pmThat is correct. I have attached a simplified circuit with a similar optocoupler type driver which should make things clearer. The load (think MMIC amp) is shown here as a simple 50 Ohm resistor. When turned on, the gate-source voltage Vgs in this case is 13.4V (37.4-24V). All voltage probes are referenced to real ground. When the load is turned off all voltages and currents are zero.

author: john23
author_rank: Frequent Contributor
timestamp: April 20, 2024, 05:40:24 am
content: Hello XVR, i ment what is the exact voltage on the out pin7 and Vss pin 5?Where in the datasheet they say what exact voltages i should expet on those pins.what pulse should i use to test this component in simulation?Thanks.https://www.ti.com/lit/ds/symlink/ucc5304.pdf?ts=1713493999921&ref_url=https%253A%252F%252Fwww.google.com%252FThanks.

author: john23
author_rank: Frequent Contributor
timestamp: April 20, 2024, 06:40:48 am
content: Hello RDFX,could you give intuition regarding the diode in this stucrture?How it functiones?Thanks."Yes, power supply (VDD) for the isolated side still missing, as is the bootstrap diode. The bootstrap capacitor (multiple values in parallel) ist also rather high. Is there a reason for that? How are you charging the bootstrapping capacitor the first time you turn the driver on? Maybe also tell something about what you are trying to achive here, not just how you wanna do it."

author: xvr
author_rank: Frequent Contributor
timestamp: April 20, 2024, 08:37:33 am
content: > i ment what is the exact voltage on the out pin7 and Vss pin 5?When UCCxxx in turned on state voltage in pin 7 will be the same as on pin 8 (Vcc). You also can measure voltage BETWEEN pins 5 and 7 - it will be isolated side supply voltage.Measuring any of them relative whole schema ground meanless, because all MOSFET control circuit floating with the Source potential of MOSFET.So datasheet also lack of this numbers - they have no any physical meaning (except for maximum isolation voltage - difference between any primary net potential and secondary should not exceed it)In your circuit Source of MOSFET (in turned on state) will bring to +24V

author: RFDx
author_rank: Regular Contributor
timestamp: April 20, 2024, 12:17:18 pm
content: Quote from: john23 on April 20, 2024, 06:40:48 amThe bootstrap diode and capacitor are irrelevant because the goal is to turn the MMIC amp continuously (static) on/off. At least I'm guessing that is the case.I mentioned the diode/capacitor before I knew there is a DC/DC converter to supply the floating driver.

author: john23
author_rank: Frequent Contributor
timestamp: April 20, 2024, 02:46:09 pm
content: Hello , i was told that i don't need R4u Du1 C4Uon the MOSFET gate. The UCC5304 is an active pull-down device, they wont turn the MOSFET off any quicker.Could you reccomend me a strtucture will indeed help switching this mosfet i could try and simulate it in LTSPICE.

author: xvr
author_rank: Frequent Contributor
timestamp: April 20, 2024, 02:51:25 pm
content: > Could you reccomend me a strtucture will indeed help switching this mosfetHow fast you need to switch MOSFET? If you don't need nanoseconds times you can use MUCH simpler circuit

author: john23
author_rank: Frequent Contributor
timestamp: April 20, 2024, 06:05:01 pm
content: Hello XVR,Its for learning puposes.Could you reccomend me very fast configuration and normal configuration :-)So i could simulate them?Thanks.

author: xvr
author_rank: Frequent Contributor
timestamp: April 20, 2024, 06:19:01 pm
content: Very fast is a your current one (without R4, R4u, R6u, Du1 and C4u).Normal is a one where UCC5304 and DB02S2415A replaced by TLP3905 (or by some analog of it)It's internal LED connected (via resistor) directly to input control circuit and output directly to S-G of MOSFET

author: john23
author_rank: Frequent Contributor
timestamp: April 22, 2024, 02:36:09 pm
content: Hello XVR i have simulated the driver components as shown in the photos below.In the datasheet they present a structure shown in the lask link photo, it very similar to my schematics.Could you give an intuition regarding how the diode and resistor act ?Why this structure is irrlevant for my mosfet controll of switching?https://ibb.co/HBq9LTZhttps://ibb.co/64MC3b5https://ibb.co/1KR6vmm

author: xvr
author_rank: Frequent Contributor
timestamp: April 22, 2024, 05:02:38 pm
content: That is absolutely the same as your initial schematic (just used 2 channel isolator).> Could you give an intuition regarding how the diode and resistor act ?They control open/close timings for MOSFET (almost the same as your initial schematic, but without capacitor)You can safely drop all of them (just put small resistor, something about 20-200 Ohm, directly between output of UCC and MOSFET Gate)

author: john23
author_rank: Frequent Contributor
timestamp: April 23, 2024, 11:50:31 am
content: Hello ,according to the datasheet (photo shown in the link)I have to put 20V on the drain(which is the source of the NDT3055L mosfet) of the TGA2590 power amplifier that means i need to put20V on the source of the mosfet.You said that its a floating voltage without reference ,how do i make sure i have 20V on the source of the mosfet (drain of TGA2590) as shown in the diagram below.Thanks.https://www.qorvo.com/products/p/TGA2590-CPhttps://ibb.co/SfNRtJyhttps://ibb.co/xgF5VL0

author: xvr
author_rank: Frequent Contributor
timestamp: April 23, 2024, 12:00:57 pm
content: Schematic is definitely wrong,Remove V2 and connect VSSa/VSSB directly to Source of U2Now V1 is your floating power, V4 - logic power, V5 - TGA2590 power.

author: john23
author_rank: Frequent Contributor
timestamp: April 23, 2024, 04:02:27 pm
content: Hello, As i understand the component We have on the input Vcci_0 and INA pint which we get inputand the output which is desided low level from VSSA and high level from VDDA ,we can see it in the basic functionality of photo 1 link.If i Understand correctly your words we need to connect the mosfe gate and source to the mosfet .In photo two i got a very high current(which says that my Vds and Vgs are too high),but we see that the mosfet opens.In photo 3 I have connected the simulation as you told me ,but unfortunetly its not converging and freezes.Why my simulation is freezes when i tried the configuration you reccomended?Thanks.LTSPICE simulation is attached and NDT3055L lib link spice model file.photo 1:https://ibb.co/6Jn2h0Nphoto 2:https://ibb.co/DKzMdXrNDT3055L spice model:https://www.onsemi.com/download/models/lib/ndt3055l.libUCC212 spice model link:http://www.ti.com/litv/zip/slum649

author: xvr
author_rank: Frequent Contributor
timestamp: April 23, 2024, 04:12:18 pm
content: Something very strange with your MOSFET connection. It has 2 pins for Drain, so on schematic 2 pins should be short. On your schema all 4 pins connected to different circuits. I can't say who is who on Spice model - there is no pin names, only Spice node numbers

author: john23
author_rank: Frequent Contributor
timestamp: April 23, 2024, 04:33:25 pm
content: Hello XVR, I have tried to connect other mosfet but connecting VSS as you said just gives me very bad gliching result.A schematics is shown below is it the proper way i should connect the driver to a mosfet?Thanks.

author: xvr
author_rank: Frequent Contributor
timestamp: April 23, 2024, 04:38:04 pm
content: Yes, connection is right, but result is very strangeLow pin of V1 should be connected to MOSFET source as well.Try to add small resistor in gate of MOSFET (20 Ohm will be enough)

author: john23
author_rank: Frequent Contributor
timestamp: April 23, 2024, 04:55:38 pm
content: Hello , the problem is that i dont know the exact power amplifier TGA2590 drain voltage if we connect it this way.I need exactly 20V to know how it by the datasheet.

author: xvr
author_rank: Frequent Contributor
timestamp: April 23, 2024, 04:57:44 pm
content: Power amplifier supply voltage has no relation to connection of V1. It will be defined by V5BTW. Why not use P channel MOSFET? All isolated drivers and floating power supplies will gone avay.

author: john23
author_rank: Frequent Contributor
timestamp: April 27, 2024, 09:04:43 am
content: Hello , There is a logical problemThe source of the mosfet is connected to the drain of the amplifier.The source of the mosfet is something floating :-)I need the source to be 20V because its the drain of the amplifier.So either my schemtics is wrong and source of the mosfet is not connected to drain of the amplifier?How do i make sure i get 20V to the drain of the amplifier?

author: xvr
author_rank: Frequent Contributor
timestamp: April 27, 2024, 09:49:51 am
content: That is exactly DB02S2415A used for. You still need it to power floating side of schematicIt"s V1 in Spice model

author: john23
author_rank: Frequent Contributor
timestamp: April 27, 2024, 09:57:34 am
content: Hello XVR,DB02S2415A outputs 15V voltage difference between the gate and the source of the mosfet(floating).I need a solid 20V on the drain of the TGA2590 power amplifier with respect to the source of the power amplifier.How the DB02S2415A does that?Can you please draw so i could understand?For the mosfet i understood the 15V difference floating ,but how it helps us put 20V with respect to the TGA2590 source?Thanks.

author: xvr
author_rank: Frequent Contributor
timestamp: April 27, 2024, 10:08:37 am
content: You need separate voltage source for it. It was labeled +24V in your first schematic

author: john23
author_rank: Frequent Contributor
timestamp: April 27, 2024, 10:17:53 am
content: Hello , there is a basic confusion I have.We have a mosfet with 24V drain its VGS i getting plugged with 15V floating from DB02S2415A floating difference.But in my configuration as you see the drain of the power amplifier is the source of the mosfet.So on one side we have the floating value of GIZ but on the other hand you said i should connect to the same node 24V to 20V converter I will try to build.So we are connecting two different voltage potentials on the same node.Arent they going to conflict which other?Thanks.

author: xvr
author_rank: Frequent Contributor
timestamp: April 27, 2024, 10:36:14 am
content: You don't need 24V, it should be 20V. This is a amplifier power. You didn't specify power voltage for amplifier in first post, but label it as +24V, so I decided that your amplifier powered by 24V.There are 3 voltage source in scheme in total: logic side power supply, floating power supply (from DC/DC) and amplifier power supply. That is all, bo more power supplies (no any +24V)

author: john23
author_rank: Frequent Contributor
timestamp: April 27, 2024, 10:58:41 am
content: Could you please draw the mosfet and amplifier with the devices ?I am having trouble to imagine your words.

author: xvr
author_rank: Frequent Contributor
timestamp: April 27, 2024, 12:04:42 pm
content: Your overall schematic is very over-complicated. You need just P channel MOSFET, one NPN bipolar transistor and a couple of resistors.I will draw schematic...All resistors values are taken approximately.Q1 - your power MOSFET. Should have DrainToSource breakdown voltage > 20V. GateToSource also >20V. RDSon will determine voltage drop and power dissipation on MOSFET.Q2 - any NPN transistor with CE > 20V and high enough Ic (100mA or more will be enough) - it will define turn on time of schematic. R2 limit Ic of Q2.R1 used to discharge Q1 Gate, it will determine turn off time.R3 determine Ib of Q2. Should be low enough to ensure Ic (with minimum h21e of Q2

author: john23
author_rank: Frequent Contributor
timestamp: April 28, 2024, 01:31:38 pm
content: Hello I am trying to solve this riddle :-)As shown in the diagram The output of DB02S2415A difference is 15V , this floating voltage supply goes into UCC5304DWVR which creates again a floating voltage for NDT3055L NMOS.This floating voltage opens the NMOS and current goes threw from drain to source.The problem starts with the parts that is not present in the schematics.I need to connect TGA2590 power amplifier to J4 node. It needs 20V on the drain.How do i make sure i have the desired 20V on that node and get the current of the NDT3055L(which was opened by the floating voltage of UCC5304DWVR)?If there is some method i could use? because this floating voltage is confusing. i am used to this of voltage where each node has exact voltage with respect to some reference.From the LTSPICE model I need some how to make 24V into 20V and make it pulsating open and close like the V2 because currently forsing steady 20V which is not good. is athere something that could be done?Thanks.

author: xvr
author_rank: Frequent Contributor
timestamp: April 28, 2024, 01:51:44 pm
content: In LTSpice schematic you again connect all 4 pins of MOSFET to different nets. I guess that one of them directly shot some MOSFET terminal to ground. There should not be.As for 20V - power for your amplifier should be connected to terminal that in your schematic labeled 'After relay. 24V (ar)'. I don't know what relay was connected ant where, but definitely here should be connected just plain +20V.Noany +24V from any relay should be used in final schematic.In LTSpace change voltage of V1 to +20V and remove V3> because this floating voltage is confusing. i am used to this of voltage where each node has exact voltage with respect to some reference.Yes, but for flying voltage will be another reference - not common ground, as for all others.If you want to see voltage on MOSFET gate set a probe toV(Gate)-V(Souce)

author: john23
author_rank: Frequent Contributor
timestamp: April 28, 2024, 04:21:52 pm
content: Hello XVR, in the case below i conected two power amplifiers.each of them needs to be 20V and 6A , and i get them by tuning the system with Vgs and Vds.Is there a way to improve the circuit so my Vds of the power amplifier could be tuned ?Thanks.

author: xvr
author_rank: Frequent Contributor
timestamp: April 28, 2024, 04:40:33 pm
content: QuoteI'm not quite understand. You want to turn on/off 2 amplifier in parallel? On control both individually?In any case Vgs and Vds is internals of switching schema and do not directly affect connected load (amplifiers). What you want to get?

author: john23
author_rank: Frequent Contributor
timestamp: April 28, 2024, 04:44:56 pm
content: Hello XVR, I have 5 amplifier i need to power.Single and two pairs.I want both to be able to power a single amplifier and a pair from a single Vds and Vgs.For that i need to tune the bias for my single amplifier and to tune sepratly for the pair.Is there a clever way to tune to Vgs and Vds .Its basicly a thing of a load.

author: xvr
author_rank: Frequent Contributor
timestamp: April 28, 2024, 05:02:44 pm
content: > For that i need to tune the bias for my single amplifier and to tune sepratly for the pair.Nothing. Your schematic do not depends of amplifier current (6A for single, 12A for pair), only for amplifier voltage. Voltage the same for both single and pair.But you need 3 identical channel (including DC/DC and UCC) for control 3 independent subcircuit (1 single + 2 pair)PS. Consider P channel MOSFETS from my previous post - your current schematic became monstrousPPS. Your currently selected MOSFET do not fit to your requirement: only 4A of Id and large Rdsonn - 0.1Ohm. Consider something more powerfull

author: john23
author_rank: Frequent Contributor
timestamp: April 28, 2024, 05:49:00 pm
content: Hello XVR, Could you please reccomend me a PMOS model i could use?Also , I have attached the two plots from NDT3055L mosfet.How do you see that its problematics , from the Vds sweep i can have 20A.How do you see thats its limited to only 4A?Thanks.

author: xvr
author_rank: Frequent Contributor
timestamp: April 28, 2024, 06:22:11 pm
content: > How do you see thats its limited to only 4A?It stated in its datasheet. LTSpice do not take in account physical limits of devices which it  simulate.> Could you please reccomend me a PMOS model i could use?You should firstly select REAL transistor, by its real parameters. Ids and Rdson firstly.What maximum voltage drop on MOSFET you can tolerate? 0.1V (0.5% of Supply Voltage for AMP) will be acceptable?And what budget limit for MOSFET? High power MOSFETs can be expensiveSISS65DN-T1-GE3 (0.8 euro on Digikey). Gate maximum voltage is 20V , so additional zener should be used to protect GateFDS6681Z (1.49 euro). Gate maximum 25V, no zener needed

author: john23
author_rank: Frequent Contributor
timestamp: April 28, 2024, 06:46:02 pm
content: Hello XVR, I saw in the datasheet tacle attached that its 4A is continues 25A when pulsed .What are the pulse limitation for this N MOSFET because 25A is very high?https://www.mouser.com/datasheet/2/308/1/NDT3055L_D-2317585.pdfThanks.

author: xvr
author_rank: Frequent Contributor
timestamp: April 28, 2024, 06:58:18 pm
content: Do you turn on power for amplifiers only for milliseconds? Or you will turn them on more o less permanently?See Figure 9 in datasheet .You should look on permanent Id, not pulsed

author: john23
author_rank: Frequent Contributor
timestamp: April 29, 2024, 05:19:07 am
content: Hello XVR, You said i should put a zenner diode .did you meen in parralel to the power supply? becuase i had negative power supplyand it solved the problem :-)Regarding what you said for pulse and heat.In the datashet there is a plot figure 11 attached.suppuse i have 1sec period and 50% duty cycle.t1=0.5sec so r(t) is 0.5R_JA=110 C/W *0.5 =55C/WWhat is Tj-TA in the plot? how do i know what temperature rise the mosfet can handle?https://www.mouser.com/datasheet/2/308/1/NDT3055L_D-2317585.pdf

author: xvr
author_rank: Frequent Contributor
timestamp: April 29, 2024, 09:21:45 am
content: > You said i should put a zenner diode .did you meen in parralel to the power supply?No. In series with R2 in my schematicAs for temperature raise, it calaculated as power, dissipated in MOSFET multiplayed by Temperature resistance (55W/C by your calculations). Power dissipation is I^2*RdsonGraph in question shows changes of Temperature resistance via pulse characteristics.Tja & Tjc are temperature resistancies from chip junction to ambient (this is case of bare chip in air) and for chip junction to case (this is variant of chip attached to ideal heatsink)As you understand there is no such thing as ideal heatsink, so in later case you shoul add Temperature resistance of heatsink itself to Tjc to get real value

author: john23
author_rank: Frequent Contributor
timestamp: April 29, 2024, 11:06:38 am
content: Hello XVR,could you give a practical numerical example with Tja & Tjc expression so i could see in what cases my MOSFET will be burned?Thanks.

author: xvr
author_rank: Frequent Contributor
timestamp: April 29, 2024, 12:10:07 pm
content: Ok, lets start from NDT3055LCalculate for worst case 2 amp in parallel with steady on state. We have 12A load.Rdson = 0.1OHm, so Voltage Drop on transistor is 12*0.1 = 1.2V, This is 6% of 20V, this is more than 5% of amplifier tolerance (as far as I remember) - transistor can't be used in this configurationLet's try to calculate for 6A load.Voltage drop is 6*0.1=0.6V. This is 3%, so your power supply should provide 20V +5%/-2% (quite tight but possible).Power dissipation on transistor: P = I*V = 6*0.6 = 3.6W. This is quite a lot for smd chip without heatsink.Temperature raise: P*Tja = 3.6*42 = 151C. Die temperature is 151 + 25 (ambient) = 176C. This is more than 150C maximum. So, transistor can't be used.Now, let's try to evaluate for pulsed mode (2s cycle 50% duty cycle). By Figure 11 give coefficient 0.5 to Tj.So, Tja will be 21, Die temperature is 3.6*21+25 = 100.6. In limits, but still too hot. Each 10 degrees of temperature raise reduce life time of transistor by 2 times.And relaying for pulsed mode also dangerous - if some amplifier will be turned on for more than some time (10-100s approximately) transistor will be burned out.Now check SiSS65DN.Rdson = 4.6mOhm. Voltage drop (12A load) is 12*4.6e-3 = 55mV. Almost negligible from point of view of power supply for Amplifier.P = 12*55e-3 = 0.66W. Max T raise 0.66*25 = 16.5C. Quite cold.PS. 25 is worst case for Tja (from datasheet). But it specified for mounting on PCB with 1" copper area and for pulse less than 10s. DS do not contain information for steady state. But there is a large reserve in power and temperature, so steady state should not be a problem.

author: john23
author_rank: Frequent Contributor
timestamp: May 04, 2024, 11:18:48 am
content: Hello XVR,siss65dn sounds great,however I need to use CGHV1A250F power amplifier.regarding being able to handle rise and fall times.As you can see in te attached photo they put very very large capacitors.suppose for the drain i will only put 1uF + 470pF.I=CdV/dtC=470pfdV=45Vdt=100nsecso 1470pF*45V/10ns=6.6A which is possible with this great mosfet.The problem with this new CGHV1A250F amplifier the it needs 45V on the Vds to function.However siss65dn PMOS has tottaly different .Even if we needed 12A for example from this mosfet :-) how can connect this mosfet with the new amplifier so each one of them will get the bias it needs for proper functionality?Thanks.https://www.alldatasheet.com/datasheet-pdf/pdf/1673867/WOLFSPEED/CGHV1A250F.htmlhttps://www.mouser.co.il/ProductDetail/Vishay-Semiconductors/SISS65DN-T1-GE3?qs=gTYE2QTfZfRTVNwOG%2FwJeQ%3D%3D&_gl=1*1ew6q0n*_ga*MTc3OTc5NzEwMS4xNzE0MzE3MTU5*_ga_15W4STQT4T*MTcxNDgxNzUzNi41LjAuMTcxNDgxNzU0MS41NS4wLjA.

author: xvr
author_rank: Frequent Contributor
timestamp: May 04, 2024, 11:37:56 am
content: CGHV is not amplifier, it's just a transistor. You don't need to gate power to it - just removing of input signal is enough to turn it off.If you still need to switch power you will need mosfet with more Vds voltage.As for 339uF capacitor it can be placed BEFORE switching MOSFET

author: john23
author_rank: Frequent Contributor
timestamp: May 04, 2024, 11:42:29 am
content: In page 13 diagram I need to put Vgg and Vdd,In page 14 they say even a procedure.How do i connect this PMOS to the CGHV1 transistor so they can work together in the previos configuration of mosfet current goint into the drain of the CGHV1A250F?What i the logic so they will bias together properly?Thanks.https://pdf1.alldatasheet.com/datasheet-pdf/download/1673867/WOLFSPEED/CGHV1A250F.html

author: xvr
author_rank: Frequent Contributor
timestamp: May 04, 2024, 04:37:55 pm
content: > How do i connect this PMOS to the CGHV1 transistor so they can work together in the previos configuration of mosfet current goint into the drain of the CGHV1A250F?You should place MOSFET between C18 '+' pin (Source) and top point of W1 (Drain).> What i the logic so they will bias together properly?Bias you should commutate independently by another circuit.In terms of schedule on page 14 MOSFET on/off is a '3. Apply nominal drain voltage (Vd)' and '3. Turn off drain voltage (Vd)'

author: john23
author_rank: Frequent Contributor
timestamp: May 04, 2024, 07:27:33 pm
content: Hello XVR , i have made the simulation of the PMOS model but for PMOS i need negative Vds so i get negative voltage on the CGHV1A250F.My driver gate voltage node was switched in order to open the SiSS65DN.How do i get positive voltage on CGHV1A250F when my PMOS drain of SiSS65DN needs to be negative?Thanks.

author: xvr
author_rank: Frequent Contributor
timestamp: May 04, 2024, 07:46:40 pm
content: Your schema is wrong again. Take a look at my original schema in post 41

author: john23
author_rank: Frequent Contributor
timestamp: May 05, 2024, 06:57:33 pm
content: Hello XVR, i am trying to solve the equations for PMOS current threw the drain.I drew the currents on the attached photo.Von suppose its 5V for mathematical purposes :-)how do i know the voltage potential at the collector of the bjt? so i could find the voltage at the gate of the PMOS afterwardsThanks.Von-Ib*R3-Vbe=0Ib=(Von-Vbe)/R3Ic=beta*Ib=beta*(Von-Vbe)/R320-(R1+R2)*Ic=V_bjt_collector

author: xvr
author_rank: Frequent Contributor
timestamp: May 05, 2024, 07:31:28 pm
content: Voltage on MOSFET Gate swing from zero (when BJT is open) and to Vdd (when it closed). Voltage drop on R2 considered negligible and can be assumed as zero. Purpose of R2 is reduce current surge when BJT opened, because MOSFET Gate is a capacitor and without R2 its churge current is not limited. R1 used to bring Gate voltage to zero when BJT is closed and to provide path to discharge Gate capacitor.If MOSFET maximum Gate voltage is lover than Vdd additional TVS should be placed in series with R2 to reduce Gate voltage to allowed limit. R1 in this case used to provide minimal stabilization current to TVSBJT used in on-off mode, turned off completely when control voltage iz zero and be in saturation when control voltage is at logical high. Base resistor selected to be low enough to ensure saturation with minimum h21e and maximum allowed BJT collector current. R2 also should limit this current to maximum of BJT. Current assumed as Vdd/R2

author: john23
author_rank: Frequent Contributor
timestamp: May 06, 2024, 08:34:47 am
content: Hello xvr,I have found NPN which is Ic=100mA Vce=30V shown below.regarding the compatibility between the SISS65DN and CGHV1A250FI need to put 45V of the drain of the CGHV1A250F while the Vds of the PMOS can only have -30 Vds .what Voltage source to put on the mosfet so i'll have +45 at the drain of CGHV1A250F?Thanks.NPN datasheet:https://www.nexperia.com/products/automotive-qualified-products-aec-q100-q101/automotive-bipolar-transistors/general-purpose-bipolar-transistors/transistors-single-npn/BC848B.htmlPMOS:https://pdf1.alldatasheet.com/datasheet-pdf/download/1377290/VISHAY/SISS65DN.html

author: xvr
author_rank: Frequent Contributor
timestamp: May 06, 2024, 08:38:33 am
content: You need another NPN and MOSFET - rated for 50V or more

author: john23
author_rank: Frequent Contributor
timestamp: May 06, 2024, 08:16:01 pm
content: Hello XVR, I have fount the si7461dp PMos shown below .From datasheet of CGHV1A250F figure 7 I need 14A and 45V for each transisor.can they work together?What source voltage to use in the diagram you reccomended?why did you says that my NPN also needs to be 50V rating on VCE?Thanks.https://www.vishay.com/docs/72567/si7461dp.pdfhttps://pdf1.alldatasheet.com/datasheet-pdf/download/1673867/WOLFSPEED/CGHV1A250F.html

author: xvr
author_rank: Frequent Contributor
timestamp: May 06, 2024, 08:39:03 pm
content: Steady state drain current of SIxxx is not enough (8.6A in best case). You need 14A. And Rdson is quite large. 11mOhm (vs 4 of previous version) But you can use a 2-3 pcs in parallel.NPN BJT should be able to handle full Vdd, because at start of turn-on process Gate-Source of MOSFET can be considered as fully discharged capacitor. This capacitor plugged in series with CE junction of BJT to Vdd. So CE junction will see full Vdd voltage (voltage drop on R2 can be disregarded)

author: john23
author_rank: Frequent Contributor
timestamp: June 30, 2024, 10:08:00 am
content: Hello XVR,regarding what you reccomended.I have removed those.What about the decoupling capacitors Cu5 Cu5c3UC2u which are at pin8 of the VCC are they nessesary?I dont know that configuration to use.can you reccomend something?"Very fast is a your current one (without R4, R4u, R6u, Du1 and C4u).Normal is a one where UCC5304 and DB02S2415A replaced by TLP3905 (or by some analog of it)It's internal LED connected (via resistor) directly to input control circuit and output directly to S-G of MOSFET"

author: xvr
author_rank: Frequent Contributor
timestamp: June 30, 2024, 10:13:11 am
content: Decoupling capacitors you mentioned are a part of standart powering scheme of UCC IC. If you still use it you definitely need decoupling capacitors.

author: john23
author_rank: Frequent Contributor
timestamp: June 30, 2024, 12:30:54 pm
content: Hello,In the data sheet they say to put a decoupling capacitor as close as possible.They don specify how much and the values.I know decoupling capactiors are intended to be low impedance and filter noises and i need to do AC responce.but in general ,what do you reccomend to use for UCC5304?Thanks.https://www.ti.com/lit/ds/symlink/ucc5304.pdf?ts=1719732264818&ref_url=https%253A%252F%252Fwww.mouser.com%252F

author: xvr
author_rank: Frequent Contributor
timestamp: June 30, 2024, 12:50:16 pm
content: One standart for decoupling: 0.1-1.0 uF. And one for MOSFET charge current supply reservoir - about 10uF I think