Hi
I'm not very experienced but I've build astable multivibrator using CD4047 with option to turn on by LOW signal on the pin 4 (IC is very easy to use and has nice features)
However the problem is that when generator outputs are turned off the Q pin is still HIGH. Is there a way to avoid it ? If not, do you know similar IC with dual square wave output which can be stopped and all outputs drop to LOW state (to turn off connected mosfets)

 

Welcome to AAC!

When discussing circuits, it's best to post a schematic so we can better understand what you're describing.

Have you tried using reset (possibly labeled EXT RESET)?

 

Yes, I checked RESET pin also. Here is what I tested. Both circuits works fine and stop CD4047 oscillation at pin OSC (pin13) and pin 10 (Q) but pin 11 is always set to HIGH :-(

 

pin 10 (Q) but pin 11 is always set to HIGH

Pin 10 is the Q output and pin 11 is Q#. If Q is LOW then, by definition, Q# must be HIGH.

 

You could use a quad NAND gate, CD4011B. The oscillator is uses two of the gates as in the circuit below. Set the frequency by changing C1 and/or R1. When enable is high the oscillator will run. The outputs of the two gates will be antiphase like the CD4047. When enable is low the oscillator will be stopped and both outputs will be high. You can use the other two gates in the chip as inverters to invert (and buffer) both outputs so they will be low when the oscillator is stopped.

 

Thank you, I will surely check it. Would it have also the same frequency stability as CD4047 ?

 

I don't know. The '4047 should be better as ir was designed for the purpose, but I don't think the NAND version will be far behind.
https://www.fairchildsemi.com/application-notes/AN/AN-118.pdf

 

Would it have also the same frequency stability as CD4047 ?

With respect to what? Temperature? Supply voltage? Part to part?

Also note that two inverter oscillators aren't guaranteed to oscillate. For example, if C1 was sufficiently small...

 

Also note that two inverter oscillators aren't guaranteed to oscillate. For example, if C1 was sufficiently small...

The '4047 oscillator circuit used a 100n timing capacitor so that isn't going to be a problem.

 

I mean stability with respect to temperature (mainly) and power supply voltage (sealed lead acid battery with voltage between 14 and 12V).

 

Another possibility would be to use the '4047 but then feed the two outputs through a pair of AND gates. Connect the other two inputs of the AND gates to your enable. When the enable is low so will be the AND gate outputs. When enable is high the AND gate outputs will follow the '4047 outputs.

 

I like the method with AND gates. Unfortunately I can't find any IC in my collection working with 12V.I don't have currently CD4081. :-( May I ask if the workaround I think about it would work ? I will use the P-Channel mosfet to steer +24V to the inverter (which is using CD4047 and two N-Channel mosfets). Something like in the new schematic. Would it work ?

 

No. If the input to R2 stays high both Q1 and M1 will be left turned on.
You could use the transistor with an N channel MOSFET (put the zener between the gate and source od the MOSFET) and connect the transformer between drain and +24V.

 

Sorry, I think I was not quite precise
R2 should be 1k of course (mistake) and is connected to Arduino which is used to start/stop this simple inverter based on cd4047.

I wonder if additionally to shuting down cd4047 I could turn off the positive rail going into the transformer using p-channel mosfet ,driven by 2n2222 from the same pin of Arduino. This is the purpose of last circuit.
In other words - to prevent n-mosfet connected to pin Q# from overburn ( because stopped cd4047 leave this pin in HIGH state) I would like to disconnect +24 V rail (like presented in last schematic) . Is this very uncommon or it should work ?

 

OIC. Yes, that would work. I think it is OK as it is but I would swap D1 and R1. That way the zener will protect the MOSFET gate if something unexpected happens.

 

If this is driving an inverter is frequency stability really an issue?

 

I don't know. It is experiment to learn higher frequencies with ferrite toroid. I suspect on frequency depends the output voltage.
P.S. Yes, I know I should use TL494 or SG3525 but I need to check something simple. Anyway,that's complicated. It has no voltage feedback loop, so I suppose stable frequency is the only way to get kind of stable output voltage (for planned load <30W)