TOP242-250 - OV / UV Protection
I am experiencing problems at the moment where the TOP242 is going into auto-restart mode when short interruptions to the supply occur. This is causing problems with certain functionality of my product.
The problem is occurring because I didn't have the UV protection enabled (OV is enabled). By enabling UV it solves this problem, but creates another. The voltage range of my supply is 60 -300VAC. If I fit a 2M resistor to the line sense pin it gives me a turn on of 71VAC and 315VAC OV protection. I've played with the resistor value and the best fit would be 1.7M that would give me a turn on of 61V and OV protection of 268V. This still does not cover the range of the supply.
How can I extend the range of the UV / OV protection? Has anyone done this previously?
Comments
I am also working on this issue,
Thanks PI_Crusher for your response, though I am not sure it fully answers our question, If I can ask it in a different way.
We wish to have both U/V and O/V enabled.
The range of supply can be 60 - 300Vac,
i.e. we expect turn on of 60V and O/V protection at 300V.
By playing with the values of resistor and possibly the zener diode is it possible to create this scenario?
I am trying to get a final solution for the power supply to have both U/V and O/V protection with a voltage range of 85Vdc (60Vac) to 424Vdc (300Vac). So I would like the TOP switch to switch on before 85Vdc and off after 450Vdc.
I have messed with the resistor values and found that by using a 1.5M resistance I can lower the turn on to below 85V. However; this decreases the turn off to about 380Vdc which is unacceptable.
The proposed solution is to disable the O/V protection. Figure 18 which calls for a 6.2V zener. Is there a specific zener that you would recommend? as my model of this does not seem to show the properties one would expect. (BZX84C6V2L). Is there any more information you can offer about the O/V function that would help me understand?
I am trying to find a solution to my overall issue by using Figure 18 and a variety of resistor and zener values.
For example if I use a primary resistor of 1.5M a secondary resistor of 22K with a 4.7V 1N750 zener, I am almost able to model the properties I wish for.
Any assistance in this matter is greatly appreciated.
Ellis
Hello Scotty,
You just have to check the data sheet, see http://www.powerint.com/sites/default/files/product-docs/top242.250.pdf page 15. I would advise you to use figure 18 for under-voltage protection only. If you must keep the over-voltage protection too, then add an extra resistor from V+ to M pin (or L). You have to adjust the extra resistor (2meg for starting) for desired over-voltage limit, and check the relation from figure 18 for under-voltage limit, but take into account the equivalent serial-parallel connection for the three resistors (ignore the existing 6.2V zenner for under-voltage case).
Cheers,
PI_Crusher