5v and 3.3v power supply for LCD and PIC

[bobledoux]

You could also buy a 3.3 volt LCD.

 

[cyrusthevirus]

Thanks for all of the advice. I think the best suggestion would be to use a regulated 5V supply and an LED to reduce the voltage to 3.3V. However I am going to take an easier way out and get a PIC which can handle 5v. This will also make driving my MOSFETs easier. Thanks for all of the advice.

 

[kchriste]

I think the best suggestion would be to use a regulated 5V supply and an LED to reduce the voltage to 3.3V.

In my opinion, that is the worst advice because:
The 3.3V would vary with current draw.
The LED won't drop exactly 1.7V and you'll have variations between LEDs of the same type.
A LED that can handle the current will cost more than a 3.3V LDO.
It would look just plain unprofessional.

However I am going to take an easier way out and get a PIC which can handle 5v.

Now THAT is the best advice of all!

 

[marcbarker]

regulated 5V supply and an LED to reduce the voltage to 3.3V.

Hey an advantage of an LED Vdropper, is you'll know immediately if you ever had an overload across the PIC's "2V to 3V3" supply, cos the LED would shine really bright, maybe even pop!

 

[smanches]

I run the 3.3v pics all the time with 5v components. Regulated 5v wall wart (old cell phone charger) then a regulator for the 3.3v.

Why go the diode route when 3.3v regulators are common and cheap? Do it right the first time. Only jury rig when you have to.

 

[cyrusthevirus]

Going back to the LCD everything I have read says to attach a 5V supply to the LCD on the VDD pin and 5V with a resistor to the LEDA pin. Do I have to limit the current to the VDD pin? According to the specs which are attached, the Logic current min is 1.5mA and the max is 3.0 mA.

 

[blueroomelectronics]

I run the 3.3v pics all the time with 5v components. Regulated 5v wall wart (old cell phone charger) then a regulator for the 3.3v.

Why go the diode route when 3.3v regulators are common and cheap? Do it right the first time. Only jury rig when you have to.

Same here. Those USB wall wart chargers are great for projects.

 

[cyrusthevirus]

Don't most of the USB wall warts put out 500mA? Isn't that too high for the 3.3v PICs? Maybe I am reading the specs wrong, but 500mA is too high for my PIC and all Microship PIC24s.

What about the LCD can that handle the 500mA?

 

[smanches]

Don't most of the USB wall warts put out 500mA? Isn't that too high for the 3.3v PICs? Maybe I am reading the specs wrong, but 500mA is too high for my PIC and all Microship PIC24s.

What about the LCD can that handle the 500mA?

Current is drawn from the circuit, not pushed into it. As long as the voltage is correct, it doesn't matter what the current rating is at all, as long as it's enough.

 

[cyrusthevirus]

Wow. I am learning alot. Kinda off topic, but related to current: Then why would an led blow if it is supplied with too much current? Is it because the led will continue to draw current to light the bulb unimpeded?

 

[marcbarker]

why would an led blow if it is supplied with too much current? Is it because the led will continue to draw current to light the bulb unimpeded?

With a light bulb, you present it with a voltage and it takes a current, depending on the wattage.

With an LED, you present it with an appropriate current and it drops a voltage, depending on the colour.