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Quick Links Categories Recent Discussions. The only things being powered in the circuit is the stamp and the LCD.
LM2940ct 5.0 gets HOT quick.
The LM gets hot after a few min which isn’t nice. The burn your finger kind of hot. I have a 22uf cap between the output and ground as specified in the datasheet for stability. Is ths just because of the load placed on it due to the lcd?
Should I use some other voltage regulator? Comments 10 Comments sorted by Date Added Votes. Hi John, What is the input voltage to the regulator — can you measure it? The power in Watts being dissipated within the regulator is the voltage drop across the regulator times the current passing through it.
Do you know about how much output current you have? Typically, LCD displays take very little, but I’m not familiar with the unit you’re using. Does it have a backlight?
There is another possibility Did you take steps to obtain caps with appropriate ESR? I haven’t experienced it personally, but you could have an issue there that might result in overheating. Here’s a snip from p.
Larger values of output capacitance will give improved transient response. The ESR of the output capacitor will cause loop instability if it is too high or too low. The acceptable range of ESR plotted versus load current is shown in the graph below.
LMCT Datasheet(PDF) – National Semiconductor (TI)
It is essential that the output capacitor meet these requirements, or oscillations can result. If you aren’t running very much current, and your Vin isn’t too high, a small clip-on heat sink can datashdet reduce the regulator’s temperature. Hello, All I have is a cap between the output and ground at 22uf.
What are the caps on the BS2P40 demo board? I can’t find a schematic of it. That would work alright. It’s interesting that mine gets this hot when I have seen schematics using the datashee setup, with a 10uf cap even.
My input is 9V, I’m using the power supply that came with the P40 demo board.
LDO Voltage Regulator (5V 1A LM2940CT, drop 0.5V @0.5A)
I believe the data sheets show a 0. Keep in mind the adapter you have may be putting out more than 9 volts, or may not have a very clean output, both of which will make the regulator get hot. Also, remember the more voltage you have to drop and the more current you want to pull, the hotter the device will run. Another data sheet says 0.
Check your caps, it might be leaky. Another, does your LCD has backlights? Photos – easier uploading and sharing. Thank you for all the input. I will try it with the additional cap. Thanks, John In basicstamps yahoogroups. Many of the regulators require capacitance on the input and output to minimize oscillation.
Furthermore, hidden in the ap note the ones that I have seen is an admonition to have a minimum current load. Otherwise the output impedance is too high and it oscillates.
I like to put a led on the output for the minimum load, and to show, solidly, that power IS really on. Friday, December 05, Basic Stamp List Subject: Text in the Subject and Body of the message will be ignored.
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