about h-bridge diode


I'm planning to make h-bridge with p-ch mosfet and n-ch mosfet.(mosfetis n-ch irf1405 and p-ch irf4905) And want to drive solednoid not a moter. solenoid is 200turn and 0.7ohm. will driven at 24V.

Anyway I want to select 4 diode using at H-bridge circuit but I don't know which one is proper to my project. So, Could you tell me proper diode's max current,voltage or other things that I have to reference.

You don't need diodes when using a MOSFET bridge because power MOSFETs all have body-diodes.

BTW the max current and voltage are the max current of the load, the max supply voltage x a safety factor.


When I don't attach diode,just using transistor's diode, Doesn't it dangerous to transistors?

That article is wrong, the MOSFET body diode can be relied upon to handle any current you can throw at the MOSFET in normal use - if in doubt look at the datasheet, its always characterized there.

You can add external schottky diodes with lower forward voltages to reduce switching losses, as in the circuit they give which is extremely high current so reducing losses is important.

BTW normally solenoids don't need bidirectional drive - are you sure you need an H-bridge.

Note that one subtlety of MOSFET H-bridges is that the diode of each MOSFET protects its partner, not itself, so if you drop down to a single MOSFET for one-way driving, you must add a free-wheel diode across the load - the diode in the MOSFET is not useful in this case.