Electronic – Is this H bridge circuit viable

I suggest you study this other H-Bridge.

It gives you braking as you want (besides going forward, in reverse and coasting). But, in my opinion, the nicest feature about that bridge is that it doesn't allow dangerous input combinations that short battery contacts, like the situation you experienced with your circuit.

The trick in this h-brigde I mentioned is that it cleverly uses 3 control signals to turn on the diagonal transistors (to move the motor forward and in reverse) without ever letting you turn both vertical transistors (both left, both right or all four transistors) at once, preventing you from shorting the battery contacts.

The circuit brakes the motor by shorting both of its contacts to the battery ground. It does it by turning on both lower-left and lower-right transistors, while turning off the upper ones. It also lets your motor to coast, by turning off all four transistors. The circuit also isolates the motor circuit from the MCU using opto-couplers, which may be helpful to protect your MCU.

You could probably change your circuit to add these features of the h-bridge I mentioned, but I don't know for sure. Maybe some more experienced user can help you with that. I can't. But, as far as I can tell, you would have to add one control pin, add two more 2N5551 transistors and change the way all four 2N5551 bases are wired. But make sure you read and understand the concepts in the page I mentioned above, so that you can evaluate whether the concept will work with your transistors and circuit. If you are unsure, try building the circuit of the h-bridge I mentioned just the way it is, as the author made a decent effort to select the appropriate components for his circuit.

I've done that. See my attempt at building the mentioned h-bridge in this question of mine. It works pretty well.

I think your circuit looks good. Although you made the common mistake of placing the PMOS symbols upside-down. The source of the PMOS should be on top for this kind of circuit. Also, put a bypass capacitor on the VDD pin of the IC.

If you won't be switching Q1 and Q3 very fast, R6 and R8 can be fairly large. 10k is probably fine. They'll turn on fast, but turn off slowly. The gate resistors on Q5 and Q6 aren't strictly necessary, but don't hurt and may prevent large current spikes from the uC pins. A small value (100 or less) is sufficient.

A few other suggestions:

1. Assuming you're controlling everything with GPIO pins from a microcontroller, Q5 and Q6 will need to be logic-level FETs compatible with your logic voltage (5V, 3.3V, whatever).

2. Put pull-downs at HI-A and HI-B. That'll prevent the gates of Q5 and Q6 from floating during initial power-up and accidentally turning on Q1 and Q3 momentarily.

3. Similarly, put pull-downs on the gates of Q2 and Q4 in case the TC427 floats its pins momentarily on power-up.

4. It's a good idea to put a capacitor (0.1uF is enough) between the 12V rail and the gates of Q1 and Q3. When the 12V first comes up, the gate capacitance of Q1 and Q3 will hold the voltage on the gates low until enough current has flowed through the resistors and into the gate. That may cause Q1 and Q3 to turn on momentarily. The capacitor will force the gate voltage to follow the 12V rail as it comes online and prevent that from happening.

5. MOSFETs do not turn off instantaneously. So if you, for example, turn on Q1 and turn off Q2 in the same instruction cycle in your firmware, Q2 may stay on for a few extra milliseconds and cause a shoot-through condition. Therefore, write your code with small delays between switching instructions. Better yet, use a micocontroller that has an H-bridge driver peripheral with built-in delays.