Blown AC/DC Converter IC - HELP - Page 1
Forum section: electronics / general

author: bigjoncoop
author_rank: Regular Contributor
timestamp: March 31, 2024, 07:08:22 am
content: Overview:Ive got a Ryobi 6 port charger and it suddenly stopped working. No signs of life at all... After dismantling it i found there was a blown IC on the A/C side of the board. (board pics attached)The blown IC is a "TOP267EG" (AC/DC Converters Integrated Off-Line Switcher) According to the datasheet (datasheet attached) it has a output voltage of 19v.(The TOP267EG incorporates a 725 V power MOSFET, high-voltage switched current source, multi-mode PWM control, oscillator, thermal shutdown circuit, fault protection and other control circuitry onto a monolithic device)Main Question:Since this IC just outputs 19v which then gets fed to the DC side of the PCB, couldn't I just use my own power supply that has a 19v output and connect it to the output pad of that IC?I don't see why this wouldn't work unless the PCB has a way of monitoring that IC and can tell if it is not functioning properly...Regardless though it shouldn't hurt if I connect a 19v supply to the output pad and see what happens correct?

author: Ian.M
author_rank: Super Contributor
timestamp: March 31, 2024, 08:44:33 am
content: Wrong. If you actually read the datasheet instead of just looking at the first page (which doesn't mention 19V), and take the parametric info on your supplier's product page with a pinch of salt, you will realise that the output voltage of a TOP267 based PSU can be more or less whatever you want, defined by external components, e.g. the transformer winding ratios, the components connected to its control pin, and if optocoupler feedback is used, the components driving the optocoupler. You've also misidentified where the PSU section of the charger's DC output is - the point you've picked is in the mains live section of the board, and attempting to connect 19V DC there will do nothing good. At best it wont work and at worst it will burn more of the board and make it unrepairable.You appear to be a long way from developing the competences required to safely and effectively repaire this sort of equipment. Studying this should point you in the right direction:https://www.repairfaq.org/sam/smpsfaq.htm

author: bigjoncoop
author_rank: Regular Contributor
timestamp: March 31, 2024, 11:17:00 am
content: Wow thank you so much, that was so helpful...Yes you are absolutely correct, the first page of the data sheet does not mention 19v. It is mentioned numerous times throughout the datasheet, as well as in the sample circuit diagrams, and so does the distributors details on this particular IC.I have done a good amount of research on SMPS designs that use this sort of IC, including the data sheet itself and from what I gathered this IC mainly controls / monitors the current consumption and regulates the output voltage in order to provide a steady 19v output...That is how I came up with the assumption that I could provide 19v where the drain of that IC connects.Now I might be incorrect... now if that's the case I would appreciate some guidance.Thx

author: Ian.M
author_rank: Super Contributor
timestamp: March 31, 2024, 12:15:20 pm
content: Let me make it a little bit clearer. A TOP267 doesn't output 19V, it doesn't even output a voltage! What it actually outputs is a variable duty cycle PWM via its internal power N-MOSFET output transistor, which connects the pins Drain and Source during its on time. This is normally connected to the low side of the primary of a switching (flyback) transformer, and the other end of the primary is powered by a HV DC bus supplied with either direct full wave rectified mains or via boost PFC, so typically around 170V DC in north America (unless a voltage doubling rectifier is used) and up to about 360V worldwide. The transformer needs precisely pulsed primary current to work. Connecting 19V DC at best wont work, and at worst will burn out the primary and various other primary side components.The TOP267's Control pin receives feedback from the secondary side of the switching transformer via an optocoupler (six pin IC bridging the L shaped slot in the board a bit to the left of the TOP267EG location you highlighted in orange on your second photo), to precisely regulate the output voltage or put it in standby. The output voltage is determined by the transformer winding ratio and the complex secondary side circuit driving the optocoupler. Your charger appears to have two secondary side voltage rails, one high power, supplied via D201 on the heatsink (top left) ad the other a low current auxiliary supply, almost certainly for the charger control chips, via D202 to the left of the top edge of the switching transformer (big yellow taped transformer in middle of board).Therefore supplying a single DC voltage, even in the right place on the secondary side, won't make it work. Also Dewalt 18V batteries need more than 19V to charge them. They are 5S LiPO packs so charge to around 20.5V. How much extra voltage the charging circuit needs is anyone's guess. The auxiliary supply is probably much lower, I guess somewhere in the 3.3V to 12V range. Get either wrong, and at best you'll let the magic smoke out, but if you are close, but not quite right there is a risk it may not detect full charge correctly resulting in a damaged battery and possible house fire!

author: amyk
author_rank: Super Contributor
timestamp: April 01, 2024, 12:16:43 am
content: I recommend replacing the IC and then plugging it into a surge protector.These single-chip SMPSs tend to be very sensitive to mains surges and die semi-regularly as a result; there's plenty of other products using them which fail in the same way, as a look through the repair forums here will show.

author: Ian.M
author_rank: Super Contributor
timestamp: April 01, 2024, 03:05:17 am
content: Trouble is: In a typical application, there are a lot of resistors, capacitors, diodes etc. associated with the TOP267EG, and they all need to be checked, as there is no way to know which of its pins got transiently connected as its die fused, and any pins that shorted to the drain will have had their associated components overvoltaged. Its especially important to check small electrolytics and low-ohm resistors.The typical result of missing a bad part round a SMPS integrated switch IC is the new IC immediately going BANG! Sometimes you get lucky and it just doesn't work, giving you a second chance to fault find . . . .

author: David_AVD
author_rank: Super Contributor
timestamp: April 01, 2024, 03:10:57 am
content: Testing it with an old incandescent lamp in series (look up "dim bulb tester") is advised after repairing most SMPS boards.Checking all the parts around the blown IC is good advice. I've also seen SMPS chips seemingly fail due to the main filter cap going very low capacitance / high ESR.