Surge Protected Wide Range Input Power Supply using TNY280PN
I wanted some help with an existing product which uses TNY280PN. This product is already in production and we are getting failed units returned from field.
The reference design that we are already using is https://www.power.com/design-support/design-examples/di-152-3-w-ultra-wide-range-input-power-supply-industrials
We are using this reference design to power up the module with 24 VDC OR 240 VAC.
One of the issues that we are facing is that the Q2 transistor in this reference design is failing (Vce max = 400V). We suspect that this might be due to transient voltage surges. We are using a 320VAC / 510VAC MOV between the two input lines. Even this MOV probably wouldn't be able to safeguard the Q2 (which has Vce breakdown voltage of 400V). We were wondering how to protect both Q2, Q1 & U1 (which have a max drain voltage of 700V) against surges (without using a MOV with too less of rated voltage to avoid premature failure of it). Any suggestion recommended?
We also wanted to understand how is the minimum input voltage calculated to be 18V in this circuit.
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The schematic is more or less similar to the schematic in the reference design ( https://www.power.com/design-support/design-examples/di-152-3-w-ultra-wide-range-input-power-supply-industrials). Since my problem is with the design (requirement for higher surge protection), I am assuming layout is not needed at present.
I can't figure out the minimum input voltage calculation. All I could see was this: "The datasheet limit for minimum drain voltage to guarantee proper startup and functionality for U1 is 50 V. However, if a charging current is externally fed into the BYPASS pin, the chip can be powered externally and can start up and operate at lower input voltages". What is the correlation between lower operating voltage limit & amount of charging current. Why is the bias current set to 600uA? The datasheet seems to be silent about information about this bias current.
Hi sakjain92,
The bias current of 600uA came from 630uA typical DRAIN supply current (IS2) from the data sheet.
The device operates from the energy stored in the bypass capacitor.
The DRAIN pin supplies the BP voltage when there is no external bias.
For minimum input voltage calculation of the power rail, you may refer to PI Expert Online.
Hi sakjain92,
Can you send your schematic and layout?
The 18Vdc minimum input voltage is dependent on the device specs (current limit, maximum duty cycle, and etc) - as long as it is capable of providing the output power to the load.
The IC would work as long as the BP pin is biased properly.