Quick Question about protection diodes

[2camjohn]

I ran out of signal diodes so I used an LED instead of a protection diode.

The diode protects a transistor from its inductive load (coil of a relay).

The problem is the transistor only works intermittently.

Could this be caused by using an LED instead of a normal diode?


Cheers

 

[Styx]

YES!!!!!!

LED are special case diodes, their reverse blocking is only in the order of 5V, anything more and they avalanch

 

[Optikon]

I ran out of signal diodes so I used an LED instead of a protection diode.

The diode protects a transistor from its inductive load (coil of a relay).

The problem is the transistor only works intermittently.

Could this be caused by using an LED instead of a normal diode?


Cheers

Get rid of the LED.. if you absolutely cannot find a diode (not even in the scrap pile?) at least use a transistor connected as a diode! You can do this with bipolars or Fet types... if you use a bipolar, don't use the base emitter junction though because it will breakdown at around 7V more like a zener diode than a normal one.

Also keep in mind, diodes made like this are not fast, they have recovery times on the order of hundreds of nanoseconds..so it might STILL not be good enough for you, but you can try it!