Dynamic Braking MOSFET Control Circuit
The way you normally (or often) achieve what you want is by letting the braking current charge back into the power-supply raising the voltage on the supply, what you then do is you put an over-voltage-protection circuit on the supply which will bypass/sink current to ground if the voltage on the supply exceeds the intended voltage (in your case 48v). here is a very crude exsample of how this can be accomplished.







simulate this circuit &ndash; Schematic created using CircuitLab

This exsample is made using a half-bridge output, when the voltage at the output exceeds the supply voltage the diode across the top FET allows the power to run back into the supply, If the supply voltage increases to more than 48v the zener will start conducting and will dissapate the extra power in the zener and in the resistor in series. this is a very crude way to clamp the supply voltage to gnd in the case of an overvoltage and it can be done much better but this is just to give you an idea of how it is done.