If you want a complete solution, look at a VNH2SP30-E - Automotive Fully Integrated H-Bridge Motor Driver, made by ST Microelectronics.

Somewhat difficult to use for a hobbyist, as they are surface mount devices and require a good part of the PCB to serve as a heat sink area. However, they're rated for 3x the voltage and 10x+ the current that you require. Studying up on the basic theory of operation should give you better ideas on how to build an H-bridge.

 

The text on the four resistors each says "200 ohm".
The text in the transistors just says "TIP120".
The text above the single resistor just says "LOAD"
The text for the logics one "74LS04" and four "74LS07"'s.
The 2 diodes are "1N5401"

I'm used to AutoCad where you can zoom in on components and bring them to full screen.

 

I don't think 74LS07's are available anymore. 7407's might be available.
They have open-collector outputs; they require pull-up resistors in order to provide a current source.
The way you have them wired now, nothing would happen; the transistors would never conduct.

The 200 Ohm resistors should be replaced with wire. Then 330 Ohm pull-up resistors need to be added to 12V.

7407's can sink up to 40mA. I=E/R, as R=E/I, so Rpullup = 12/0.04A, or 300 Ohms. To lighten the load on the IC, I arbitrarily increased the size of the pullup resistor by 10%.

Even then, if you're going to use transistors, you'll need to use PNPs for the high side. They don't make PNP Darlingtons anymore that I know of. [eta] I don't know what in the world I was thinking when I typed that previous sentence; they most certainly do still make PNP Darlingtons. TIP125-TIP127, TIP135-TIP137, TIP145-TIP147 are just a few examples.
NPN Darlingtons would not work for the high side of an H-bridge, unless you had another voltage supply that was higher than 12v.

For MOSFET H-bridges, there are driver ICs that allow the use of N-ch (N channel) MOSFETS for both the high side and the low side of an H-bridge. N-ch MOSFETS are preferred due to their much lower Rds(on).

 

Mouser site says they have them in stock.
I'll try to send you a Datasheet.

 

Mouser also has the ST Microelectronics IC that I previously mentioned.

Look at an L298 dual full-bridge driver IC. Many manufacturers make them.

Relatively cheap, and has just about everything inside of them that you need for this circuit.

 

It appears that the L298 is designed to do what I need. I may go that route.
By the way, I have modified that drawing and will send it to you again. Although I probably wont use it I would like your opinion on whether it would work. See if I understand the principle of the transistors.

I have to be leaving for the evening but will check back tomorrow to see if you replied. Don't worry about hurting my feelings. I can take it.

Thanks

 

The tiny parts on the schematic are half a kilometer apart so i cropped the schematic and zoomed in on it.
It cannot be seen. Here is part of it:

 

It appears that the L298 is designed to do what I need. I may go that route.

Integrated solutions are usually the least expensive and most trouble-free way to go, if you can find something that fits the specifications.

However, it is also a good idea to be aware of the technology behind the integrated solution.

By the way, I have modified that drawing and will send it to you again. Although I probably wont use it I would like your opinion on whether it would work. See if I understand the principle of the transistors.

You probably missed my last post. No, it won't work. The 74xx07 buffers have open-collector outputs; they need pull-up resistors rather than your current limiting resistors.

Additionally, Darlingtons won't work well on the high side of an H-bridge, which is basically what you're trying to make. They will be voltage followers, and you'll lose between 0.6v and 1.4v due to the double voltage drop across the two emitters. You would have to bring the base of the Darlingtons a couple volts higher than the 12v Vcc in order to supply enough current to saturate it.

An MJ3955 is the PNP complement to a 2N3055. You could "roll your own" PNP Darlington by driving an MJ3955 with a 2N2907, as you could "roll your own" NPN Darlington using a 2N2222 with a 2N3055. However, an integrated H-bridge would be so much more efficient that it isn't worth your time and money, unless you really want to experiment.

I have to be leaving for the evening but will check back tomorrow to see if you replied. Don't worry about hurting my feelings. I can take it.

I'm not worried about hurting people's feelings. People wasting money and energy - now that gripes me.

 

The tiny parts on the schematic are half a kilometer apart so i cropped the schematic and zoomed in on it.
It cannot be seen. Here is part of it:

I completely agree with your assessment; although our OP's last circuit post was much better.

Placing the components much closer together would help a great deal to improve the readability. As things are now, the components are so far apart that it would be virtually impossible to reduce the entire schematic to the point where you could both view all of the components, and read the specifications of said components.

Reduce the white space. Sometimes it enhances readability, but in this case, it's done to great excess.

 

click on the "go advanced" button below the text reply box.
Then click on the "manage attachment" button near the bottom.
It's best to use .png format for things such as schematics; they will be compact and not distorted.

sir i'm muni i've also tried the way. There are 3 columns to upload from computer, i've selected the required file (word document) and then uploaded it. Even on final check i couldn't find my attachment. What should i do afteer uploading the file?.

 

sir i'm muni i've also tried the way. There are 3 columns to upload from computer, i've selected the required file (word document) and then uploaded it. Even on final check i couldn't find my attachment. What should i do afteer uploading the file?.

Word ".doc" documents are not the preferred method for uploading files. They are very slow to load/view on many people's computers. They can contain viruses. .doc files may be too large to attach; there are size limits for each type of file.

.png type files can be very compact. They are preferred because they don't become "blurred" like .jpg and .gif type files do.

Try converting your Word document to a .png file.
1) Bring up your document in Word or WordPad.
2) Size it as necessary for good legibility.
3) Do a screen print by holding down the Ctrl key and tapping the PrintScreen key.
4) Start MS Paint.
5) Paste the image into Paint by pressing Ctrl+V or selecting Edit/Paste from the menu.
6) File/Save As...
Give it a name, and select .png for the file type.