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Voltage Regulator 12 - 5volt

ThomsCircuit

Active Member
Power source is a wall wart 12V 1A
My circuit requires the full 12V but the touch sensor in this circuit (TTP223) needs just 5v.
The datasheet on the TTP says the following
~Operating voltage 2.0V~5.5V
~Operating current @VDD=3V, no load
~At low power mode typical 1.5uA, maximum 3.0uA
id like to use a voltage regulator like LF33 but one that outputs 5volts not 3.3volts. I understand the datasheet says it will work at 3.3 volts but i have read that the TTP works better at 5volts. Can you help me find a suitable component that will supply the TTP223 the voltage and current it requires? I would also need some help with the capacitors needed at the input and output.
Im sorry i dont know much but i am trying. I do know that these IC's get hot. I am hoping that if the IC has a fixed output, the right caps are used, and that its drawing very little current it will be safe enough to use.
Im attaching my schematic. so you can see where everything is.
Umbrella - Project-1.png
 

ThomsCircuit

Active Member
A 78L05 should be enough
Thank you Pommie. Very nice to hear from you.

OK great! Only 100ma needed to control the TTP.
As for the bypass capacitors Ill be good using the recommended .33uf and 0.1uf?
Do you recommend the shunt diode 1N4001 across input and output as well?

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I see this 78l05 works as a current limiter as well. See sample.
Screenshot 2022-05-15 at 20-33-20 UA78L00 Series Positive-Voltage Linear Regulators datasheet ...png

Does this example fix the current based on the resistor used. and will it maintain that same current regardless of the voltage applied to the input? Id like to use it to power an LED on my Buck converter project.
 

Pommie

Well-Known Member
Most Helpful Member
Sorry, I read your initial post as max current for the TTP as 30mA.
At 100mA it'll probably overheat.
However, I don't think that chip will take anything near 100mA and probably only a few milliamps.
Couldn't find it in the datasheet.

If you use it as a constant current source then the input voltage needs to be 5+Vf of LED + Vdropout(appears to be 2V) so in excess of 9V.
The resistor should drop 5V (assuming 78L05) at the required current.
Note, heating could be a problem if the input voltage is too high.
It is also very inefficient so not for battery operation.

Mike.
 

ThomsCircuit

Active Member
Sorry, I read your initial post as max current for the TTP as 30mA.
At 100mA it'll probably overheat.
However, I don't think that chip will take anything near 100mA and probably only a few milliamps.
Couldn't find it in the datasheet.
No im incorrect. My comment about the 100ma was in reference a parameter of the 78L05.
Your assumption that 30ma is required to drive the TTP is accurate. I am the one who has no idea what it requires. I only know that since it is an IC with a max voltage of 5.5volts it could not be much.

If you use it as a constant current source then the input voltage needs to be 5+Vf of LED + Vdropout(appears to be 2V) so in excess of 9V.
The resistor should drop 5V (assuming 78L05) at the required current.
Note, heating could be a problem if the input voltage is too high.
It is also very inefficient so not for battery operation.
And i assume as long as it has power applied at the input it will remain active. Meaning if i toggle the TTP and it turns off the circuit the input is still getting 12 volts and the IC remains hot so it makes sense that it would drain a battery quickly. To address this i briefly read about an IC that could regulate the voltage and be placed in standby mode accessed via a feedback pin.
 

ThomsCircuit

Active Member
I added the IC to my circuit. and created a pour to connect the ground pads together.
Observation:
the PCB has 4 pads. 3 have pin assignments but the large pad has no assignment. Is that a heat sink?
78L05.png
 

Pommie

Well-Known Member
Most Helpful Member
In EasyEDA there are two SMD devices a SOT-89-4 and a SOT-89-3.
Here are the footprints,
sot89.png

I suggest you find a datasheet for the actual device you are using and see if the 4th pin is connected - in the above the two horizontally aligned center pins are both connected to ground.
I think they are internally connected so the device is actually a 3 pin device.
In the diagram above the either footprint could be used for either device!!

Mike.
 

ThomsCircuit

Active Member
I think they are internally connected so the device is actually a 3 pin device.
In the diagram above the either footprint could be used for either device!!
I agree. Thought of that this morning. It is indeed a 3 pin device. In reality if i applied solder to the pin pad it would flow to the isolated pad. I was concerned as it was not attached to a net in the PCB so i attached it to ground and the pour applied the needed spokes.
Im still very much at the early stage of learning so id be waiting for the parts to be delivered before i submit the board to the FAB house.
Thank you Pommie
78L05-PCB 3PIN.png
 

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