I have a beginner question please. I am trying to design a circuit to latch and unlatch a dual coil 4PDT relay with a SPDT toggle switch. The circuit will be battery operated so to save power I am using a latching relay.
I intend using a 556 timer to provide two monostables to pulse the reset or set coils on the relay depending on the position of the toggle switch. I have got most of the way researching and building how I might possibly do this and have the timer circuit flashing LEDS with ~50mS pulses no problem.
I am however unclear about how to protect the 556 from the relay coil back emf without degrading the switching speed of the relay. I have seen plenty of examples of using a single diode flyback in parallel with the coil but as I understand it this will delay collapse of the coil magnetic field and delay the speed and forcefulness of the armature operation. To keep switching speed snappy, would it be possible to use 36V zeners (D5 and D6) in the configuration shown? I am thinking that D1 and D2 should block 36V reversed (1N40004 good for 400V I think), and block any circuit developing through the 556. However the ground 0V rail is still connected to the -ve ends of the coils. Am I right in thinking that no voltage will develop here as far as the 556 is concerned (i.e. remains at 0v as the coil winds down). I will link to schematic of my proposed circuit here...
http://pict.co.uk/556_RD_with_Relay.gif
Apologies if this is a really dumb question, but if anyone can offer any learned clarification I would be most grateful.
John
I intend using a 556 timer to provide two monostables to pulse the reset or set coils on the relay depending on the position of the toggle switch. I have got most of the way researching and building how I might possibly do this and have the timer circuit flashing LEDS with ~50mS pulses no problem.
I am however unclear about how to protect the 556 from the relay coil back emf without degrading the switching speed of the relay. I have seen plenty of examples of using a single diode flyback in parallel with the coil but as I understand it this will delay collapse of the coil magnetic field and delay the speed and forcefulness of the armature operation. To keep switching speed snappy, would it be possible to use 36V zeners (D5 and D6) in the configuration shown? I am thinking that D1 and D2 should block 36V reversed (1N40004 good for 400V I think), and block any circuit developing through the 556. However the ground 0V rail is still connected to the -ve ends of the coils. Am I right in thinking that no voltage will develop here as far as the 556 is concerned (i.e. remains at 0v as the coil winds down). I will link to schematic of my proposed circuit here...
http://pict.co.uk/556_RD_with_Relay.gif
Apologies if this is a really dumb question, but if anyone can offer any learned clarification I would be most grateful.
John