Mosfet Replacement - Page 1
Forum section: electronics / repair

author: 2X
author_rank: Frequent Contributor
timestamp: March 01, 2025, 03:19:59 pm
content: Hi,I have the HAT2226R mosfet shorted and I can’t find the same one to buy it. After searching I found the SIHJ240N60E-T1-GE3 where have the most critical characteristics (in my opinion) except of the ID current where in SIHJ240N60E-T1-GE3 is much bigger. The PCB have short circuit the protection, so if a mosfet short-circuit the protection circuit is engaged and no power anymore… if there was not a short circuit protection I believe a mosfet with much bigger ID value would be a risk of something else to burn out instead of damaged itself… or am I wrong?Also, in the most sites on the parametric search I found the Qg (Total Gate Charge) parameter/value. I can’t understand exactly what is the purpose of this parameter and if it is critical. Could you tell me if the Qg value is critical and what is the practical use of it?HAT2226R red colour valuesSIHJ240N60E-T1-GE3 green colour valuesVdss =600V/600VId =0.1A/12AVgs =+-30V/+-30VRDSON =35ohm/0.208ohmVGSth =3-5V/3-5Vtdon =34ns/15nstdoff =57ns/26nsQg =3.1nC/15nC

author: Slh
author_rank: Regular Contributor
timestamp: March 01, 2025, 05:03:58 pm
content: Qg being 5 times higher will slow the switch on for the same gate driver circuit. This will result higher losses if it's something like a buck converter.What's the circuit?I often find that when the MOSFET dies, you also looe the gate driver.

author: 2X
author_rank: Frequent Contributor
timestamp: March 01, 2025, 05:15:17 pm
content: Quote from: Slh on March 01, 2025, 05:03:58 pmThe circuit is a buck converter with the IC MAX15046.https://www.analog.com/media/en/technical-documentation/data-sheets/max15046-max15046b.pdfWhy the Qg being 5 times will slow the switch ON time? The switch ON time isn't depended from the tdon time (34ns/15ns)?

author: 2X
author_rank: Frequent Contributor
timestamp: March 01, 2025, 05:54:55 pm
content: I found also the below (STD3LN80K5) with Qg slide smaller. Would you beleive it is more suitable?HAT2226R red colour valuesSTD3LN80K5 green colour valuesVdss =600V/800VId =0.1A/2AVgs =+-30V/+-30VRDSON =35ohm/2.75ohmVGSth =3-5V/3-5Vtdon =34ns/6.2nstdoff =57ns/30nsQg =3.1nC/2.63nC

author: PCB.Wiz
author_rank: Super Contributor
timestamp: March 01, 2025, 10:26:49 pm
content: Quote from: 2X on March 01, 2025, 05:54:55 pmThat is a closer match to your original part, but note that failed, and it is strange to use a 600V 35 Ohm FET in a 24V Buck regulator?What is your load current, and what FETs does the MAX15046 suggest using as suitable?

author: 2X
author_rank: Frequent Contributor
timestamp: March 02, 2025, 08:46:23 am
content: Quote from: PCB.Wiz on March 01, 2025, 10:26:49 pmI believe it is failed because the fan inside the enclosure was dead and there was no cooling.

author: tooki
author_rank: Super Contributor
timestamp: March 02, 2025, 11:36:51 am
content: Quote from: Slh on March 01, 2025, 05:03:58 pmIf Rds(on) is significantly lower than the original, it simply won’t matter, as the losses will still be lower even if it dwells in the not-fully-on state for a few ns longer.(As an example: So many modern MOSFETs have insanely low Rds(on) that, for example, a modern non-logic-level MOSFET can have a much lower Rds(on) when driven by 3.3V logic than older ones designed for 3.3V gate drive!)

author: tooki
author_rank: Super Contributor
timestamp: March 02, 2025, 11:37:45 am
content: Quote from: 2X on March 02, 2025, 08:46:23 amPCB.Wiz asked you two very good questions. Answer them.

author: 2X
author_rank: Frequent Contributor
timestamp: March 02, 2025, 12:20:48 pm
content: Quote from: tooki on March 02, 2025, 11:37:45 amThe MAX15046 suggest the below values as very critical (attached picture). The load current is 60mA.HAT2226RCrss = 0.4pF@f=1MHzQgd = 2.3nC @Id=100mAThe below have lower Crss & Qgd values from the HAT2226R where I beleive is better.STD3LN80K5Crss = 0.1pF@f=1MHz, Vds=100V, Vgs=0V (the HAT2226R don't specify the values of Vds & Vgs)Qgd = 1.53nC @Id=2A, Vdd=640V, Vgs=10V (the HAT2226R don't specify the values of Vdd & Vgs)What are MOSFETs? – MOSFET Parasitic Capacitance and Its Temperature Characteristichttps://techweb.rohm.com/product/power-device/si/4873/Total Gate Chargehttps://www.rohm.com/electronics-basics/transistors/tr_what10

author: tooki
author_rank: Super Contributor
timestamp: March 02, 2025, 02:42:21 pm
content: Can you please share the actual schematic of the actual circuit (with model name of the product, if applicable), as well as everything you know about the converter’s input and output voltages, currents, what supply and load it’s being used with, etc.Because it doesn’t make sense so far. A 600V MOSFET in a low-voltage circuit makes no sense. The MOSFET running hot with just a 60mA load makes no sense. Etc.

author: 2X
author_rank: Frequent Contributor
timestamp: March 02, 2025, 03:01:17 pm
content: Quote from: tooki on March 02, 2025, 02:42:21 pmUnfortunatelly I don't have a schematic of this power supply (only If I would make one... it is over 2 layer PCB), but I found out the source of heating problem I beleive. The resistor on this gate driver was originally 4.7ohm and I measured it 56ohm, so the mosfet didn't turn "fully ON" and consiquently the RDSon didn't low causing heat because of the higher losses. This power supply is from an automatic corn sheller machine.Quote from: tooki on March 02, 2025, 02:42:21 pmIndeed it is very strange the selection of a mosfet with so big Vdss... but I found on another place on PCB where have the same step down converter and gives out 3.3V to have the same mosfet. Maybe the high Vdss is just a coincidence. The input voltage of the power supply is 230Vrms.