MT494MT - Page 1
Forum section: electronics / repair

author: csaba911
author_rank: Newbie
timestamp: July 27, 2021, 02:24:25 pm
content: Hi everyone, first postneed helpLooking for pinout/datasheet/schematic for MT494FP (not Ti's 494)Want to increase over voltage shut down from 15.5V to 16.5V hopping its not internally determined and some external voltage divider values can be changed to achieve it.The chip used in a DC-AC (12v-120v) 150W inverter, the battery bank 16.4V fully charged so the inverter shut down seconds after power up.Thanks in advance..Steve

author: csaba911
author_rank: Newbie
timestamp: July 27, 2021, 02:29:33 pm
content: Some pictures might help, pin 1&16 output to the Fet’s, pin5 GND, pin12 VCC (from 7805)

author: Zero999
author_rank: Super Contributor
timestamp: July 27, 2021, 03:35:51 pm
content: Are you sure all of the components can tolerate 16.5V, without smoking?It's possible the over/under-voltage circuit is elsewhere. Are there any comparator ICs on the board?

author: csaba911
author_rank: Newbie
timestamp: July 27, 2021, 07:51:30 pm
content: Yes, input caps are 25V, 78L05 30VTried up to 24V nothing smoking or overheating but output shuts down at 16.5V

author: csaba911
author_rank: Newbie
timestamp: July 27, 2021, 07:53:11 pm
content: Some transition for the gate driver, 431 ref and 1 8.3V zener diode

author: csaba911
author_rank: Newbie
timestamp: July 27, 2021, 08:09:28 pm
content: Top right dot-8 is a buck converter for the USB charger. I don’t think that’s shutting down the ac output

author: fourtytwo42
author_rank: Super Contributor
timestamp: July 27, 2021, 08:19:28 pm
content: What's the product data sheet say ?Something external like a silicon diode might work, OK it's a power loss.Usually these things blow up before stopping working so that's unusual.Cannot find any chip data so could be custom or re-marked.

author: fzabkar
author_rank: Super Contributor
timestamp: July 27, 2021, 08:39:42 pm
content: This chip is very old ...https://mirrorservice.org/sites/www.bitsavers.org/components/mitsubishi/_dataBooks/1987_General_Purpose_ICs.pdfThere is an M5T494P,FP on page 218.Alsohttps://www.semiee.com/file/EOL2/Mitsumi-M5T494.pdf(M5T494P,FP,GP -- Mitsubishi, not Mitsumi)

author: csaba911
author_rank: Newbie
timestamp: July 27, 2021, 10:26:40 pm
content: Unfortunately that data sheets not for this chip, my pin 5 is definitely ground 0.1ohm to input wire negative.The output is pin 1 & 16, pin 4 goes low during shutdown but pulling high (100 ohm) will not starting it up again, pin 11 probably over current protection (latching, need power down before recovery)

author: csaba911
author_rank: Newbie
timestamp: July 27, 2021, 10:35:25 pm
content: The buck converter for the USB use TMI2243B, doesn't have over voltage shut down output pin.

author: fourtytwo42
author_rank: Super Contributor
timestamp: July 28, 2021, 01:48:10 am
content: Quote from: fzabkar on July 27, 2021, 08:39:42 pmWell doneA copy of a TL494 no less and certainly no overvoltage lockout, nor does any other SMPS control chip that I have ever come across.P.S. OP Once more can you identify the product please (weblink or make/model etc).

author: csaba911
author_rank: Newbie
timestamp: July 28, 2021, 04:57:09 am
content: Not much information from the vendor.

author: perieanuo
author_rank: Frequent Contributor
timestamp: July 28, 2021, 05:09:55 am
content: hi, if tl431 magic word appeared, did you try to play a little bit with his output? this would definitively allow you to modify output voltage

author: csaba911
author_rank: Newbie
timestamp: July 28, 2021, 06:08:50 am
content: pin13, 320mv for normal operation, shut down at 400mvadded 33k across the original res and now its operational all the way to 17.3V, prefect for the 16.8 fresh fully charged battery, the under voltage cutoff raised from 9.6V to 11.02V what is ok with me as the bottom end of the battery doesn't have much capacity.

author: fourtytwo42
author_rank: Super Contributor
timestamp: July 28, 2021, 10:45:17 am
content: Quote from: csaba911 on July 28, 2021, 06:08:50 amWell done, result! Good bit of detective work & reverse engineering

author: fourtytwo42
author_rank: Super Contributor
timestamp: July 28, 2021, 10:47:38 am
content: Quote from: csaba911 on July 28, 2021, 04:57:09 amOMG nothing to go on there, good job you persevered with the RE

author: Zero999
author_rank: Super Contributor
timestamp: July 28, 2021, 11:09:53 am
content: Quote from: fourtytwo42 on July 28, 2021, 10:45:17 amIt's a shame the identity of the IC is still a mystery.