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TOP250YN low control voltage

Posted by: reidw on Thu, 06/24/2021

I recently replaced a TOP250YN in an amplifier with a TOP250YN flyback topology, nearly identical to Figure 41 on Page 20 of the TOP242/250 datasheet (https://www.power.com/sites/default/files/product-docs/top242.250.pdf)

the main difference in the circuit is that R1 (4.7M) is not in this schematic and C5 and R5 are flipped (C5 on top touching Pin C and R5 below touching Pin S). when the amplifier was working prior, i measured 6.1V on Pin C of the TOP250YN and it was providing all the correct voltages necessary on the output. i put in a brand new TOP250YN and now nothing happens. Pin C only goes to 5.4v and does not hit the 5.8v DC necessary to turn on the device. the output voltage on the flyback transformer only goes to 16v DC when it normally would reach 360v DC when it was operating correctly last time. is my new TOP250YN defective? or do i need to modify the circuit to make this work? 

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Submitted by PI-Wrench on Fri, 06/25/2021

The TOPSwitch may be defective. It may also be a counterfeit device. What are the P/N, date code, and lot code on your replacement IC?

Submitted by reidw on Fri, 06/25/2021

the IC is from Power Integration and was purchased through Digi-Key. the IC has the following stamped codes on it.
2049
TOP250YN
8Z296A

what should i do...do i need to purchase another TOP250YN? digikey and mouser are both currently out of stock. are you guys able to send me one? is there a replacement IC i could use as a substitute like a TOP252?

the IC is from Power Integration and was purchased through Digi-Key. the IC has the following stamped codes on it.
2049
TOP250YN
8Z296A

what should i do...do i need to purchase another TOP250YN? digikey and mouser are both currently out of stock. are you guys able to send me one? is there a replacement IC i could use as a substitute like a TOP252?

Submitted by PI-Wrench on Mon, 06/28/2021

You can try contacting PI customer service with your issue. It might be also a good idea to contact Digi-Key and let them know you have a defective IC.

i reached out to digi key, they sent me a replacement part. i just installed it and now im getting the same values as the last IC i just put in, which makes me think that the TOP250YN is not defective since 2 are testing identical. below is a hand-drawn schematic of the exact circuit as well as some DC voltages taken. i also have attached two oscope photos of Pin C&F as well as on Pin X. according to the spec sheet, it looks similar. what seems odd is that Pin C&F have a DC voltage of 5.4v, but if you factor in the oscope probe of the AC peak and portion, it would reach 5.9v. does anything on this circuit look right or wrong? are there any other measurements i need to take? also, note that the two other outputs from the Flyback transformer are supposed to reach 300V DC and 6.5v DC. but all i measued now was 16.2v and 0.43v DC. 

 

Any help would be appreciated.

첨부 파일 파일 크기
drawn schematic of circuit and DC voltages 699.92 KB
Oscope probe of Pin X 953.68 KB
Oscope probe of Pin C&F 942.72 KB
Submitted by PI-Wrench on Tue, 07/06/2021

You might want to try replacing some of the components connected to the TOPswitch control pin, starting with the 47 uF capacitor. If this has been damaged by the original failure event that prompted replacing the TOPSwitch, it might be shunting current to ground and not allowing the control pin to charge to sufficient voltage to allow the TOPSwitch to start.

I am assuming that the original TOPSwitch in the circuit broke in some fashion. Often, when this happens, you get a drain to source short. When the bond wires for the source pin then fail open due to the fault current (which has the authority of a charged bulk capacitor behind it), you can then have fault current coming out of the control pin, as the device is shorted inside and the control pin is the only available path for the fault current to reach ground until the control pin bond wire in turn opens. This can damage components connected to the control pin, such as the 47uF cap and maybe even the optocoupler output transistor.