voltage level conversion- how to?

[ivar]

My MCU 's gpio pin can output 3 volts. I need to output 4.2 volts for a certain signal. The pin can toggle at a max of 10Khz.

I was wondering if i could use the 2N3904 switching transistor for this purpose and drive it from the gpio pin. I don't want to use a cmos-ttl converter chip because it's just one pin's voltage that i need to boost. Is this the right approach?

 

[keith1200rs]

That could be the right sort of idea, but we need more details. Have you a 4.2V supply or are you turning on an LED and have a 5V supply? What is the micro? Some have open drain outputs that are 5V tolerant. How much current do you need?

Keith

 

[ivar]

My MCU is a Samsung S3C8 series 8bit CMOS controller,and the board operates at 3 volts(I get this from a variable DC power supply).Consequently, the gpio pin cannot produce more than 3V.

The MCU has open drain outputs on some ports! I guess that means I can just use a pullup resistor to get the 4.2 volts.

In case i use a port pin not having pullups, is the 2N3904 a good choice?.I just need to send HIGH (>4.2V)and LOW (<0.4v) on the pin (communication protocol) and the current is not a factor.But the pin might switch at 10KHz.

 

[keith1200rs]

Unfortunately the S3C8 open drain outputs cannot be used above Vdd (some microcontrollers can) so you need to use a level shifter, such as a transistor, as you suggest or a small MOSFET with pull-up resistor.

Keith.