# Confusion with figuring out voltage regulator maximum input voltage

I will use this 12V voltage regulator which in my case marked as MC7812ABT and TO−220 package. And I want to use it for a 12V 16mA load where it will regulate 24V supply to 12V. In the datasheet there is a section which confuses me:

There is 19V, 27V and 30V ect. mentioned. In my case the output will be 12V, can the input voltage be 24V?

• Yes, you can use it Vin max = 35V
– G36
Apr 6, 2020 at 11:04

For maximum input, refer to the "Maximum Ratings" section. In your case, as you have a 12 V part (MC7812ABT), VI-max=35 V.

The electrical characteristics table specifies behaviour under certain conditions. In this case, the Output Voltage is specified to be in the range 12 V (+-0.5 V) for VI = [14.8..27] V. It does not specify the output for e.g. VI=VI-max and you'd have to measure that yourself.

Note that your screenshot refers to another part, not MC7812ABT as you said you are using.

### Update:

Your part is a 12 V part, which can be found in the table of all parts (ordering information). This is why you look at the "5.0 - 18 V" maximum rating, not the "24 V" one. Which tells you 35 V is the maximum.

The 221A is your case code. Here, I'm a bit lost too why they call it 221AB sometimes and sometimes 221A. Luckily in this case though, there is no difference between the cases, regarding the max input voltage.

• What is 221A? And in my screenshot MC7812AB is the closest thing in the datasheet to MC7812ABT. I dont understand the method to conclude what makes the result as 35V in my case. Could you explain it more explicitly? Apr 8, 2020 at 21:41
• Sure - pleae see my updated answer. Your screenshot shows the table for MC7812B, not MC7812AB, but the difference is marginal. Apr 9, 2020 at 16:23