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pulse output

eTech

Active Member
I had already written which relay it was in post number 7.
this is what I wrote:
"I need it to drive single coil bistable relays.
in these relays the current flows in both directions. ".
what does this sentence mean?
"snd we are now teaching"
I didn't know I was in school :D, who is the pupil ?
the first circuit you propose is made for double coil bistable relays with a common terminal.
I don't like the second circuit. when the coil of the relay has to discharge it is found in front of two resistors in series which in total make 94 ohm more when the transistor is in saturation most of the current goes on the resistance.
I have only one driving channel coming from the cd40193 and not two, otherwise I would have used a full H bridge which are specially designed for this purpose.
if I insist on the single coil bistable relay there is a reason.
:confused:So why not use the latching relay driver in post #17?
You won't need a split supply.
 

arivel

Member
to be honest I haven't looked at what the two flip flops of your complex scheme do.
on the second it says toggle and that I know what it does. you were kind to me and I don't mean to be rude but I don't see a way to discharge the surge surge generated by the relay coil.
the impulse is generated by the two capacitors placed on the base of the push pull transistor pairs but being capacitors the impulse does not have a rectangular shape.
 

gophert

Well-Known Member
Most Helpful Member
I had already written which relay it was in post number 7.
this is what I wrote:
"I need it to drive single coil bistable relays.
in these relays the current flows in both directions. ".
what does this sentence mean?
"snd we are now teaching"
I didn't know I was in school :D, who is the pupil ?
the first circuit you propose is made for double coil bistable relays with a common terminal.
I don't like the second circuit. when the coil of the relay has to discharge it is found in front of two resistors in series which in total make 94 ohm more when the transistor is in saturation most of the current goes on the resistance.
I have only one driving channel coming from the cd40193 and not two, otherwise I would have used a full H bridge which are specially designed for this purpose.
if I insist on the single coil bistable relay there is a reason.
You need to do the math again (and analyze the circuit), there is only ever 47 additional ohms (in the configurations shown) in series with the coil. You'll have to calculate the right resistor size for your voltage and coil current. This IS a very common way to drive a single coil latch relay since it is only pulsing for a very short period of time.
If you are driving with a cd40193, then it can operate from 3 to 18volts. Also, you can simply use a darlington transistor to avoid loading your cd40193 too much.
 

eTech

Active Member
to be honest I haven't looked at what the two flip flops of your complex scheme do.
on the second it says toggle and that I know what it does. you were kind to me and I don't mean to be rude but I don't see a way to discharge the surge surge generated by the relay coil.
the impulse is generated by the two capacitors placed on the base of the push pull transistor pairs but being capacitors the impulse does not have a rectangular shape.
the capacitor impulse does not need to be rectangular. Only high enough and long enough to trigger the push/pull pair for the required time. The inductive transient is easily handled by placing a pair of diodes across each side of the relay coil.

I don’t mean to be rude either, but this is simpler than creating a split supply that isn’t needed.
 

arivel

Member
the capacitor impulse does not need to be rectangular. Only high enough and long enough to trigger the push/pull pair for the required time. The inductive transient is easily handled by placing a pair of diodes across each side of the relay coil.

I don’t mean to be rude either, but this is simpler than creating a split supply that isn’t needed.
"by placing a pair of diodes across each side of the relay coil "

I do not think so
 

gophert

Well-Known Member
Most Helpful Member
I do not think so
Why does a pair of diodes across a coil work for every relay-driving circuit In the world except your circuit? How is your problem exceptional?

99% of the times someone comes here with a "unique problem", it becomes a standard problem when the original poster learns a bit more and resolves his/her knowledge gap or misconception of the problem.

Millions of people have managed to engage and disengage single coil relays - there are many thousands to millions of circuit options on a simple google search. There are also dedicated ICs that can do this (internal design is very similar to the two--troansistor+two-resistor designs I posted above or an internal H-bridge.

Note that the two-transistor+two-resistor design is just a super simple, minimalist design of an H-bridge.
 

eTech

Active Member
"by placing a pair of diodes across each side of the relay coil "

I do not think so
this is a common method to surpress back emf for single coil latching relays that works.

obviously (and unfortunately) you will not except any solutions other than your own (and much excellent help from others has been offered) so I will end attempting to help.

good luck with your project.
 

throbscottle

Well-Known Member
Here's another version of the 2 transistor circuit. https://www.edn.com/drive-a-single-coil-latching-relay-without-an-h-bridge-circuit/.
You could use a variant of a window comparator to drive the two high inputs from your high/low control signal. As others have pointed out, feed the signal via capacitors to get pulses. They don't need to be rectangular, merely long enough.
(Edit - I might be missing something here, but surely it's enough to just invert one of the inputs? No comparator needed!)
 
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