Which fly-back protection diode to use?

[thecritic]

I want to use this mosfet irfz44n, to drive a highly inductive load, (Coils of a coilgun). Which fly-back protection diode do you recommend.
(I will be using 12V system and the coils will draw around 6A).

 

[MikeMl]

Since your coil is basically an air-core coil, it has much less inductance than say a relay or a solenoid. The diode has to carry the coil current, but only for a few msec. Even a nominal 1A 1N400X will handle a 6A pulse provided it happens less than a few times per second. Look at the data sheet. It shows the derating from the non-recurring max pulse based on how frequently it happens...

 

[thecritic]

Thanks for the response, Mike.
Since the coils would have an iron rod (moving through them), I thought they had high inductance. And also because they produced deadly sparks when connecting via bare wires, I thought they need good fly-back protection.
I am going to use 1n4007 then.

 

[MikeMl]

The peak reverse voltage across the diode is the applied voltage to coil, so even a 1N4001 will likely work.

 

[Speakerguy]

Look for a rating of Ifsm. Make sure it's above your coil current.

 

[thecritic]

1n4000 series are rated for 30A Ifsm.
Are 1n4000 series capable of quicly conduction in the forward direction, so that the mosfet won't experience any spikes? When do i need to use fast diodes such as 1N4148?

 

[MikeMl]

The 1N4148 is a small-signal diode, not a rectifier. If you think you need a rectifier that turns on faster than a 1N400X, use a 1A Schottky.

 

[thecritic]

hi mike,
sorry to ask basic electronics, but whats the difference between rectifier diode & small signal diode? (I thought they are distinguished by there current capacity and response time) and why do I need rectifier diode here?
The datasheet says that 1N4148 is a high speed diode. (I have been using it for fly-back protection from relays, in several of my circuits)

 

[ronv]

The 4148 is only good for 2 amps peak, the 4001 30 amps, or for a dime more you can use a 1N5818 (25 amp schottky).