TOP233
Posted by: tolos
on
Hello, we are using TOP233 for the 5VSB in an AC/DC power supply. The switch is used in "line-sensing for under-over voltage and DCmax reduction" with Pin-M connected via resistors to a bulk voltage with nominal 400V. A higher rate of destroyed TOP233 on field suggests changing to "current limit reduction with line voltage" mode. So here are my questions: 1. What are the voltages VBG, VTP ans VT shown in the datasheet and how are they created? 2. What is the calculation for the RLS resistor? When picking RIL resistor value uppon diagramm on page 30 of datasheet there is no information about RLS. 3. Do you think Overshoot while switching can lead to problems witn over-under voltage function?
Best regards
Tolos
Hi Tolos,
Thank you for choosing Power Integrations.
Here are the answers to your questions:
1. VBG, VTP, and VT are voltages which are generated inside the silicon. These are drive voltages to the internal switches.
2. For the RLS calculation, you may refer to Figure 14 on page 12. Vuv and Vov will be according to your requirements and Iuv and Iov is 50uAtyp and 225uAtyp respectively. You have to take note though that the total current will be divided between RLS and RIL. The ratio of which will depend on your resistor values.
3. You can calculate this RIL independent of the RLS. My suggestion is you choose the initial value for RIL using the chart on page 30 then proceeed on calculating RLS taking into consideration Iuv and Iov current thresholds.
4. The over/undervoltage function is there to protect the power supply. Instances of over/undervoltage while switching would cause the power supply to stop switching to protect the power supply.