Serin serout problem

[lerameur]

Hey , I just realize that after running my receiving circuit for a minute or so , he Lm7805 gets very hot, Is this normal ?. on my sending circuit it stays cool.
I have on the receiving, an lcd, the receiving RF module, a Pic16F877a and an H-Bridge.. The H bridge is running directly from the battery for the Vs. everything is battery operated

[keithdoxey]

Hey , I just realize that after running my receiving circuit for a minute or so , he Lm7805 gets very hot, Is this normal ?. on my sending circuit it stays cool.
I have on the receiving, an lcd, the receiving RF module, a Pic16F877a and an H-Bridge.. The H bridge is running directly from the battery for the Vs. everything is battery operated

Does the LCD have a backlight ?

If so, try running it from the unregulated power supply after increasing the resistor accordingly.

[lerameur]

yes it does have a backlioght.
The supply is a 12v battery cannot put that directly on thebattery

[keithdoxey]

yes it does have a backlioght.
The supply is a 12v battery cannot put that directly on thebattery

Do you have a series resistor between your 5v supply and the LCD backlight?

If not it will be drawing excessive current which will definately be why the 7805 is cooking.

If you do have a resistor, then increase its value and drive the backlight from the 12v supply. Search for threads about "backlight", one just resurfaced in the last couple of days.

[lerameur]

i have a potenetiometer between the 5 v and the LCD, I swiched to the 12v with the pot, and the LCD is finished

[keithdoxey]

i have a potenetiometer between the 5 v and the LCD, I swiched to the 12v with the pot, and the LCD is finished

Sorry to hear that you toasted the LCD but I didnt suggest running the LCD from the 12v supply.... just the backlight.

If you had read the other threads about this you would see the reason behind it. The LCD only takes a couple of milliamps but the backlight takes 50-80mA which is a lot of extra for the regulator to handle.

The backlight doesnt need a regulated supply, just a current limited one hence the use of a series resistor which you calculate according to the forward voltage of the backlight , the required current through the backlight and the maximum voltage of the unregulated supply.

[lerameur]

a ok , i get it,
By the way , anybody knows why My h_bridge, L298N get really really hot even with a heat sink and just 1.8 amp ?and yes it is connected to the 12v battery. Getting hot, and its not working anymore...