I have a device (a printer) which will work on 7.2V and requires about 2.5 amps. I need to design a circuit that will supply the voltage only when required. Hence i decided to use a transistor for the switching. I am not too sure which transistor to use. Can anybody kindly suggest me the option for the same. Or for that matter, will a simple switching circuit actually work for this configuration?
You have the transistor connected as an emitter-follower instead of as a switch. Its datasheet shows a max saturation voltage loss of 1.2V if its current is 3A and with a base current of 375mA.
With a current of 2.5A then its output is about 6.2V if it has a base current of 250mA.
For a base current of 250mA the 1k base resistor needs 250V across it and VDM ON will need to be about +257V.
To make things clear. I need to provide 7.2V, about 3 Amps to a device (a printer head). This should not be continuous as the head will heat up. The controller will control this by use of a circuit that i have shown. The controller used is LPC1768 and this works on 3.3V Logic
Since the above discussions show that I am not doing it the right way. I am also thinking of having a P Channel MOSFET which will inturn be driven by a PNP Transistor. (This was also suggested in one of the forum, although i am not sure the exact parts that i could use)
IRF9540 p channel mosfet will do the job, putting the gate to 0V will turn it on, putting the gate to VCC will turn it off, if you need reversed logic use a 2N7000 n chanel mosfet as an inverter
@Thunderchild Is this what you are suggesting. Let me also see if the component is available locally. Meanwhile a small schematic will be very helpful.
source of the IRF9540 does to VCC the drain to the load, a resistor goes from gate to source. The gate of the IRF9540 is connected to the drain of the 2N7000, the source of the 2N7000 goes to GND, the gate of the 2N7000 is connected to your drive circuitry. you may want a resistor from the gate of the 2N7000 to ground.
I am trying the schematic with the circuit description, you told me. I will post once i am done. Meanwhile what do you mean by collector for 2N7000. Its a MOSFET. I guess it is drain that you meant. Kindly clarify