I don't have a very good knowledge of electrical engineering yet but I'm working on it. I will like to know as simple as possible, how can i drive a latching relay that needs about 70-90mA if the raspberry pi can only deliver about 40mA. I need to find a relay that can handle home appliances but can be controlled by the raspberry pi.
One solution (of many) is to use the Raspberry Pi GPIO pin to drive a logic-level MOSFET.
The GPIO only needs to sink/source enough current to turn the MOSFET on and off. The 10k resistor is there to keep the MOSFET in a defined state if the GPIO goes high-impedance. The diode across the coil clamps the reverse EMF generated when the coil is switched off, protecting the rest of the circuitry.
(It is up to you to choose an appropriate MOSFET and diode; the examples shown are for illustration only.)