TNY 279 Chip gets hot

Hi Anand,

It is due to our thermal shutdown protection safety feature. It depends on the power loss on the TNY279, your heatsink, and environment. You can try to redesign the heatsink. If you are using TNY279 with its standard current limit, you may try to use TNY280 with a 1uF capacitor at BP/M pin to set the current limit to the same as TNY279's standard current limit.

Regards,

PI-Scotty

Thanks scotty.

By the way,right now we dont have plans of going with TNY280,as we have already procured TNY279 in bulk hoping that it would work.
We are using DIP Package.so how to dissipate using heat sink?
We just replaced the old TNY277 board with TNY279.
Is'nt it supposed to work with the same layout of that of TNY277.
Any hints on this.?

Regards,
Anand

Hello Anand,
The Tiny Switch family parts are designed to enable substitution of parts from a family in a given design with minimum changes.

The two important differences in the parts are the current limit and the RDS-On of the internal MOSFET.

When customers run into thermal shutdown problems, one easy way to resolve the problem is to use a higher device with the 1uF BP-pin capacitor which lowers the current limit to match the lower device thereby avoiding additional changes in the design. the lower MoSFET-Rds-ON reduces conduction losses and hence the temperature of the part.

If in your design, you are running into a thermal shutdown problem, I suggest the following approach:

1. Evaluate any opportunities for improving the efficiency of your design. The efficiency is dependent on the transformer design/construction, losses in the snubber, output rectifier and output capacitors(ESR) and any preloads.

Often the cause of thermal issues is the low efficiency of the power supply.

2. Evaluate the possibility of modifying the copper area on the board attached to the source pins of the TinySwitch (See Fig.15 of the datasheet)

3. If adding copper area is not an easy option at this time, consider use of a small copper or aluminium heatsink (often a small piece of metal is sufficient) soldered on the board next to the Tiny Switch source pins. Since this approach uses the vertical space, this does not need any significant board changes other than any slots or holes to attach the heatsink.

Regards

PI-Sarek

Both of them do work with the same layout
Since there is an issue of thermal shutdown on your board, I would advise(arbitrarily) to keep a bit larger area of the pad on the 4Source pins.

As your heat generated seems to be high, I would recommend to check up for the Trr of the output diode, efficiency lost on the clamping circuitry, reduce the capacitance value of the snubbers and check up for any core-saturation etc.