Usually an IR signal generated from a TV remote control is about 40kHz. You can create 40kHz modulated IR wave by making a 40kHz square wave using a simple 555 timer. And this 555 timer operates using DC power supply.
If you want to performe single function such as turning something ON or OFF you can employ dc current.
When you use square wave (40-50kHz)?
If you want to code more than one function then you have to use a carrier (square wave) and modulate this carrier with a code; you will use unique code for each funtion.
Supply:
For dc control the diode current will be about 20mA dc.
For "square wave" control you will have to supply in same cases 100 or even 200mA in pulses to achieve the same average output power (range) as for dc current.
this circuit can generate 38 or 40Khz squire wave which normally available IR receivers can detect.
Give Vcc to pin 8 and mC output pin to 4 .
Whenever you set that output pin of mC to 1 ,IR will be emitted and your receiver will detect and will give a low in its output.
The rest may be done through coding.
i know that IR trasnmitter with AC signal will have long radiation and good light immunity... but not sharp enought.... with DC signal we will have a sharp, short signal..