Part Difference.. 1N4002 vs. 1N4004

[msurdin]

Hey Guys

I am wondering the difference between the 2 different parts. I was reccomended the 2 as replacements for a rat I am building. What can you guys tell me about the 2?


Thanks Guys

Matt

[R.G.]

The only significant difference is that the 1N4002 is a 100V breakdown part; I think the 4004 is 400V. Otherwise, too little difference to worry about.

[msurdin]

Does one have more headroom or anything?

Thanks for the help!

[CGDARK]

Does one have more headroom or anything?

Thanks for the help!

The characteristic that make a diode more or less prone to distort is the forward voltage and don't think the breakdown voltage will do anything with this:

Forward Voltage:
LED = between 1.5V to 2.4V
1N400x series =1.1V
1N4148 = 1V max.
1N34 = less than 1V (0.60V)
(these values may vary depending on the manufacturer and other factors)

CG

[msurdin]

Is that any LED?

[GibsonGM]

Most LEDs have forward voltages from 1.5v to 2.4 volts.   In other words, the voltage that will 'turn them on' and make then start to conduct.  It varies by color, composition, and manufacturer....you can measure it with the diode setting on your DMM.

[R O Tiree]

The purpose of the 1N400x diode in the stock Rat circuit is polarity protection. A lot of circuits have something like a 1N4148, or similar, reverse biased across the battery so that if you accidentally connect the battery the wrong way round, current flows through the diode, not through your circuit. Even 9V connected the wrong way round will kill an op-amp after not many seconds.

Sadly, a 1N4148 is a small signal diode and cannot dissipate very much current for very long without blowing. If it fails to a short circuit, you just get a hot battery. If, however, it fails to open circuit, then 9V the wrong way is now fed to your circuit. In short (sorry - another bad pun) these little diodes can stand the battery snap being brushed over the wrong terminals of the battery for a split second without damage ("Oops - wrong way..."), but no more than that.

The 1N400x series is made of sterner stuff, as they can handle a relatively large current (1.0A). Where the Rat circuit scores is as follows:

See the 47 Ohm resistor? It's connected between the battery +ve terminal and the rest of the circuit. All current has to go through it first. Now, connect the battery the wrong way round and you have about a 0.7V drop across the diode and 8.3V across the 47R. Since the diode is strapped across the rest of the circuit, all the circuit sees is 0.7V the wrong way, not 9V. 0.7V will not fry anything. Clever, hey?

Only one word of caution, though... The power dissipated in that resistor is nearly 1.5W. A 1/4W resistor just won't cope if the power is applied for more than a few seconds - long enough in most circumstances to go, "Doh! Silly me" and swap the battery round. I always use a 2W resistor in there, just in case someone persists in applying the wrong polarity through a power supply, as it will cope with the power dissipation.

BTW, the normal Vf for 1N400x series is 0.65V - 0.7V, not 1.1V, which is the max instantaneous Vf at 1.0A DC.

Max DC reverse voltage ratings for the 1N4001 is 50V and, as RG says, the higher numbered ones go up to silly numbers.

So, a 1N4001 is already more than 5 times over-rated on both voltage and also current - 0.18A (max 1.0A). No need to go higher than that but it won't do any harm at all if you just want to get rid of it out of your parts box.

If you're planning on using them to replace the clipping diodes then, again, it won't do any harm, you'll have exactly the same 0.65V or so passing a tiny, tiny current... The whole circuit only uses 7.8mA, so what's going through those diodes will be a very small proportion of that. As to how they'll sound, 1N4001 appears to have a harder "switch-on" than 1N4148 when comparing datasheets, so I'd hazard a guess that the distortion will be even harder than a "normal" clip-to-ground arrangement.

[CGDARK]

BTW, the normal Vf for 1N400x series is 0.65V - 0.7V, not 1.1V, which is the max instantaneous Vf at 1.0A DC.

You are right I and I knew that (I don't konw what I was thinking), but when I took a fast look at the data sheets, for some reason I forgot and looked at the wrong row/column.

CG