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Is there something better than an H-bridge to drive two motors using the ATmega8 with a 7V power supply?

My teacher said the H-bridge overheats and is bad. Is there a better solution? For instance: creating my own BJT circuit?

JYelton
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Napster
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    A better H-bridge. – Ignacio Vazquez-Abrams May 29 '14 at 19:52
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    I agree with @Ignacio, but to make anything useful out of this question we need to know which bridge you are using and which one overheats, so we can compare and suggest anything better. Also, knowing something more about your motors may help. – Ricardo May 29 '14 at 20:01
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    It may be that the **particular** H-bridge you are using is not suitable for operation with 7V or the motor current requirement. As Ignacio says - look for a better one - they do exist. – JIm Dearden May 29 '14 at 20:09
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    Try this dude http://electronics.stackexchange.com/questions/108686/what-h-bridge-drivers-are-preferred-for-applications-controlling-a-low-voltage-m it's all about the BJT H bridges and how much better the MOSFET ones are. – Andy aka May 29 '14 at 20:19

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If the motor has a certain coil resistance then any switch to be cool must be much lower resistance. I would start by measuring coil resistance then choose a bridge or transistor with an equivalent resistance <5% for a ballpark figure. Thus temperature rise is measured by thermal resistance x Watts and power is I^2*R.

So if a motor say has a coil resistance of 1 Ohm for 7A max at 7V then the bridge or switch ought to be around 50 milliohms with wiggle room depending on heatsink for 2.5Watt dissipation or more with higher resistance, such as 100 milliohms bridge *7A^2= 5W requires a bigger heatsink.

For more details on understanding motor power read http://www.ti.com/lit/an/slva505/slva505.pdf

Consider an inrush current limiter Polyfuse. It is also cheap insurance for a stalled motor often used or windshield wiper and power window motors. Lots of references on this site.