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5 volt PWM


#1

I need to do some PWM control of a pump for variable speed control and the voltage level needs to reach 5 volts not 3.3. I did some PWM test on the UC5550 and FEZ and the max is 3.3 volts. I recall seeing that the FEZ outputs are 5V tolerant. Is there any quick way to get a 5 volt PWM with the FEZ? For a regular digital output on the FEZ how would I get 5 volts? The IORef pin reads 3.3 volts.

Long term, I will be using the UC5550, not FEZ. What external circuity would be recommended to get from 3.3 to 5 on PWM for an industrial application? I will be in the 1 kHz to 1.5 KHz range. Thanks!


#2

I would look at a device like SN74LVC1G07, which has an Open Drain output to be used as a voltage level shifter by simply connecting a pull-up resistor to 5 volts.

There is a extensive family of this type of device from Texas Instruments, rated for High Reliability, Automotive, temperature ranges, and some even have a Schmitt trigger on the input.

http://www.ti.com/product/SN74LVC1G07

Regards
Phil


#3

You should never connect a pump to your FEZ, or any microcontroller directly. Look online on how you would control a relay fro example. You need a circuit that consists of a transistor and a diode. There are also chips that do that. In this image ( that I found online) VCC is your 5V. Replace the relay coil with your pump/solenoid/anything :slight_smile:

image


#4

The pump is powered separately through an external 24 vdc supply. The PWM is just as a control circuit for speed control.

How do I get the FEZ to GPIO to be 5 volt tolerant instead of the default 3.3?


#5

Fez INPUTS are 5v tolerant. Nowhere would you have seen a modern micro that can output at higher than VCC. Fez and most if not all GHI devices runs VCC at 3v3


#6

and since your reply and mine arrived at the same time, to be clear the I part of a GPIO is 5v tolerant already, no change. For the O part, you need to work with the 3v3 you have and control something else that will produce 5v.


#7

Thanks for the clarification.


#8

Hi Gus:

mattc mentioned that he had a variable speed controller, hence my simple level shifter solution was offered.

Regards
Phil


#9

You are right