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?
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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.