Could someone suggest a voltage follower with thermal protection (thermal shutdown)?
I see possible solutions:
- An LDO with external reference. I found only few of them, seems they are called tracking LDO and they are very rare and are hard to buy. Maybe I did a wrong search?
- Use a transistor with thermal shutdown. I found only one transistor in the entire internet and it's seem obsolete. Does such transistors exist?
- High current op-amp with thermal shutdown. I found only big expensive specialized devices of this type. Are there small, like SOT-23-6, and cheap op-amps of this type?
- Maybe it's possible to create a voltage follower using an op-amp and a regular adjustable LDO? How?
- Something else?
Please share your ideas. Thank you.
Just if you want a specific details: I need a voltage follower buffering 1.2-3.3V signal and powered from 5V supply. I want it to be able to provide up to 200mA of current at least for short period of time, typical consumption is about 30-50mA. Since my device is small and fitted in 10 x 8 x 3cm plastic box, I think, there is a possibility that under long lasting worst condition (200mA at 1.2V (i.e. 3.8V dropout)) the transistor of classic voltage follower could overheat. That is why I would like to have a solution with thermal shutdown.
Best Answer
It seems to me that it would be easier to create a solution that can withstand the 0.8 watts of heat, worst case continuous conditions than it would be to create a thermal shutdown. 0.8 watts isn't a lot in that size of case. It's mainly a matter of spreading the heat out so it's not concentrated. If the heat is spread out, it will more effectively dissipate through the plastic box. For that amount of heat, you could use a small heat sink, or simply put about 1 or 2 square inches of copper plane on the PCB.
But if you must have a thermal shutdown, I would go with option 4: An adjustable LDO with an Op-Amp. Have the output of the op-amp go through an RC filter then to the ADJ pin of the LDO. The RC filter would have to be tweaked to keep the whole thing stable while giving you the frequency response that you need. The inputs to the op-amp are the input and output voltages. This whole circuit is going to need tweaking depending on the op-amp, LDO, acceptable noise, etc. I highly recommend simulating it first. I don't see an option for attaching a file to this answer, otherwise I'd whip up a quick simulation and put the file here.