change components for flip flop circuit higher

The astable multivibrator is not a particularly appropriate circuit to use to drive an inductor. If you describe your whole project what you want to achieve, we can give much more specific advice.

 

OK, you have a toroid and you want to generate a magnetic field using one or two coils of wire so you can measure eddy currents. You want the injected magnetic field to alternate polarity at an adjustable frequency. You want the drive signal to be a bipolar square wave.

Your best option would be a circuit called an H-bridge. This can be powered from a single supply voltage and can generate a symmetrical, bipolar drive signal to the coil. You can drive the H-bridge from a square wave oscillator with variable frequency, and you have lots of options there.

I can recommend some components if you answer these questions.

What is the frequency range?
How much current do you want flowing in your coil?
What is the DC resistance of the coil?

 

Well, I'll give you some vague suggestions then. Check out the following H-bridge ICs:
http://www.digikey.com/product-detail/en/TA7291P(O)/TA7291PO-ND/1730026 (1A rated)
http://www.digikey.com/product-detail/en/BA6219B/BA6219B-ND/658358
http://www.digikey.com/product-detail/en/TLE5206-2S/TLE5206-2S-ND/1283081 (5A rated)

These are only three of a number of possibilities. I specifically chose THT parts because I don't know whether you can handle SMT. Here's a filter for the whole set of alternatives including SMT parts: http://www.digikey.com/product-sear...803c8,3fc0059&stock=1&quantity=1&pageSize=250

These ICs will drive the coil. You will need to limit the current according to the specification of the device you choose, by either adding a series resistor, or making sure that your coil's DC resistance is high enough to limit the current.

You need to provide control signals into the H-bridge IC. There are lots of options, including a 555 and a CD4046. If you need a duty cycle of exactly 50% (i.e. exactly equal positive and negative durations) you can use a flip-flop (e.g. half of a CD4027) to divide the oscillator frequency by two and provide true and complement outputs.

 

Actually the BA6219 isn't very easy to use; I shouldn't have suggested it. Here's a circuit that uses the Infineon TLE5206-2, which is rated for 5A output current.



U1 is a standard astable (oscillator) based on a 555. The frequency is determined by RT, which I've specified as a potentiometer so you can adjust it, and CT, and is roughly equal to 0.72 / (RT × CT).

The oscillator's output feeds the clock input of the first half of U2, a 74HC73 dual JK flip-flop, which divides the frequency by two to ensure exactly equal high and low times, and provides two complementary outputs which drive U4.

U3 is a 7805 linear regulator that provides a clean and steady 5V supply rail to U1 and U2. The supply rail to the right of U3 is noisy because of the heavy currents flowing in the coil; U3 prevents this noise from interfering with U1 and U2.

U4 is the H-bridge IC. It is driven with two complementary signals from U2 and it outputs drive coil L1 through current limiting resistor RSER. RSER plus the DC resistance of L1 must be high enough to prevent overcurrent in the output circuits of U4. Example values for RSER:

4.7Ω/50W (http://www.digikey.com/product-detail/en/6-1625984-4/A102171-ND/2056014) for a current of about 2.5A

6Ω/50W (http://www.digikey.com/product-detail/en/KAL50FB6R00/KAL50FB6R00-ND/1646199) for a current of about 2A

The LED is provided to indicate various types of errors that can be detected by U4. See the data sheet for more information.

All capacitors named CDn are decoupling capacitors and should be connected as close as possible to their relevant IC as directly as possible between the power and 0V pins.

 

No worries.

It depends on the frequency you want. Choose a frequency and calculate the cap using
f = 0.72 / (RT CT) or
CT = 0.72 / (f RT)

LOL Shall I PM you my address? LOL