Generating 5V power from 3.3V powered PIC

[Andy_123]

Have a small project with PIC 18F66J60 / Ethernet connection
It is powered by batteries and 3.3V/200mA generated by TPS60120

I need to add 5V LCD, so is it possible to generate 5V /30mA using PWM output and inductor?
For now I am using TPS60140, but would like to simplify whole thing.
I know I can use TL2775 and few external components as well

The goal is to cut the cost for small batch (~25 pcs)

Point me to the righ direction please.

 

[blueroomelectronics]

Yes you could build a boost converter with PWM, there are a few companies making 3.3V LCD displays like www.topwaydisplay.com

 

[Hero999]

What's the battery voltage?

You can use a flyback inductor circuit to generate higher voltages but you need some feedback to stop it from rising to too high.

Does the microcontroller have an ADC pin?

You might also be able to use the comparator to cut the pulses when it gets to 5.01V and start them when it drops below 4.99V which would give 2mV of ripple.

 

[bananasiong]

How about charge pump with only diodes and caps via one output pin?

 

[Andy_123]

@blueroomelectronics:
I have to use a small display that fits in specific box (16x2 LCD 60mm wide max), if you can point me to a 3.3V display, I can use it

@Hero999:
It uses 2xAA batteries, TPS60120 generates 3.3V, TPS60140 generates 5V.
PIC has available ADC pin, and I am looking if someone already has design
PWM->inductror -> load-> feedback to ADC

@bananasiong:
this will be another option, but I need about 30mA, will it work? Can you point me to a working schematics please.

Like I said I have TPS60140 with 4 capacitors working, but trying to reduce cost.

 

[blueroomelectronics]

This page has 16x2 3V (3.3V) displays.
**broken link removed**

 

[Andy_123]

This page has 16x2 3V (3.3V) displays.
**broken link removed**

None of 3V LCDs one this page are less than 60mm wide

 

[blueroomelectronics]

What LCD do you have?

 

[bananasiong]

What type of LCD you use that consume that much current? I've used one which draw only 3 mA that I can directly power from the PIC.

 

[Andy_123]

https://www.hantronix.com/down/16216ls.pdf

53mm wide

Should I try to run it from 3.3V?

 

[bananasiong]

I mean I was using 5 V. 3.3 V most probably won't work.

 

[blueroomelectronics]

Just a thought, the ENC28J60 chews through power when the Ethernet is running, the LCD backlight will also burn through power. You power source is only 200ma have you measured it, is it enough?

 

[Andy_123]

Right now I have 80 mm LCD in different box, no backlight and it uses few mA only
Adding backlight makes it power hungry.

 

[bananasiong]

Hi,
I think this is enough for a few mA. Try with a load resistor first.

 

[Andy_123]

Just a thought, the ENC28J60 chews through power when the Ethernet is running, the LCD backlight will also burn through power. You power source is only 200ma have you measured it, is it enough?

I am not using ENC28, I am using 18F66J60 and TYP value is 180mA and TPS60120 works just fine - device typically used for just a couple minutes once in a while and TPS can handle short overloads up to 300mA.
As of today LCD uses own regulator directly from the battery.
But you are right: adding LCD to 3.3V source may be too much for TPS60120.

 

[blueroomelectronics]

Wired Ethernet is an odd choice for battery power? After all AC connectors and wired Ethernet connectors are usually in the same room.
Have you looked at USB?

 

[Andy_123]

Nothing strange - this is a handheld setup/tester device for indistrial Ethernet devices.
It used were PC and power are not available.
Must have batteries.

I am not sure why you mentioned USB? This is Ethernet ....

 

[blueroomelectronics]

Ahh, I never thought of that. Neat.

 

[jpanhalt]

The Max1680/1681 and ICL7660 can be configured as positive voltage doublers using only capacitors and diodes.
John

 

[Andy_123]

Switching gears a little, but still same issue:
do I need to put 3v-5v buffer between PIC and LCD?
https://www.hantronix.com/down/16216ls.pdf

It looks like LCD inputs can handle 3.3V levels
I am only writing to LCD, I am not reading anything.

I was planning to use 74HCT541, but may be I don't need it?

LCD will have 5V power, PIC 3.3V