If you need a relay to operate a device, the current taken by the device will be considerable while the current taken by a relay is very small. Our CMOS relays require 5mA @5v.
The awkwardness of using a latching relay is not worth the effort.
If you need a relay to operate a device, the current taken by the device will be considerable while the current taken by a relay is very small. Our CMOS relays require 5mA @5v.
The awkwardness of using a latching relay is not worth the effort.
If the current is over 15 amps, it would be better to use a MOSFET. Currents over 10 amp cause a lot of trouble with contacts. You get welding and pitting.
Alphadog, see the attached. It will not harm your I/O. In sleep mode your I/O retains the mode and state that is set before entering sleep mode. At power-up, your I/O is set to input mode with no pull-ups, so all bridge transistors will be off. You should put reversed biased diodes across each of the four transistors to protect the transistors against counter-EMF from the relay coil when it is turned off.
Alphadog, see the attached. It will not harm your I/O. In sleep mode your I/O retains the mode and state that is set before entering sleep mode. At power-up, your I/O is set to input mode with no pull-ups, so all bridge transistors will be off. You should put reversed biased diodes across each of the four transistors to protect the transistors against counter-EMF from the relay coil when it is turned off.
Your simulation results are not the same as mine. Check that your bridge transistors have a gain (hfe) of at least 20 at collector curent of 200 mA, preferably more.
The Fairchild datasheet for PN2222 says the maximum Vce(sat) at 500mA is 1.0V. Typical is less than 300mV (see Fig. 2).
I found a Philips datasheet that says max Vce(sat) for 2N2222 is 1.6V.
The simpler circuit (presented above) will need base resistors on the PNP transistors to keep them turned off as the bases are floating at the moment (say 4k7 from base to positive).
The 10uH choke will not be needed as this value will not have any effect in this situation. The 25R (27R) resistor will reduce the back emf from the (relay) coil.
The transistors may have to be up-rated to take the current.