The problem of TNY178D input peak current
I designed a circuit using TNY178D and during the testing process, I found that the current limiting value for different loads is 100mA. If the load is heavy, it will enter an automatic restart state. However, its current value still turns off the MOSFET at 100mA, which is significantly different from the 500mA given in the manual. What may be the reason for this?
Comments
Hello, I designed a 48VDC input and output a current of 12V 1A.
In the TNY-LT datasheet, the minimum drain voltage is listed at 50VDC. That is likely your problem. The IC is designed to run from standard AC line voltages with suitable rectification and filtering, not as a general purpose DC-DC converter chip.
You may want to consider using DPA-Switch instead for this application.
That's probably still insufficient input voltage to provide the power you are looking for The TNY178 is probably operating at max peak current, but still unable to deliver the needed power. A lot of will depend n your transformer design - if your reflected output voltage (VOR) is too high, the IC will duty cycle limit, again limiting the available output power..
If you use DPASwitch instead, you can achieve your output power goal with 48V input, as this IC was designed for relatively low input voltage DC-DC applications. The TNY-LT is not designed to provide the output power you are looking for at such low input voltage.
Attached is a PDF file with a DPASwitch design that will deliver the power you need at 48V input. You can use the design software at power.com to change the transformer core type if necessary.
| Attachment | Size |
|---|---|
| DPASwitch_Fly_12V_1A.pdf | 653.45 KB |
Just for your information, I was working with the PIXLS design software to find a solution for your output power requirements using TNY-LT, and PIXLS is stating a minimum DC input voltage of 70VDC to achieve your output power requirement.
Quite possibly because you need to update to the latest version. I have Version 10.3.8.1 resident in my computer, and it has TNY-LT.
What output voltage and current target are you using for your design? If you are using a diode that is too slow for either the output or the bias winding, this can trigger current limiting. Can you post a readable schematic for your design for review?