1n4148 forward voltage vs current graph - Electronic Circuits Projects Diagrams Free

gjpollitt · 22nd August 2005, 07:58 PM

Looking at the datasheet with forward voltage of 1v there should be around 170ma

On my test circuit I have 10vdc supply limited to 200ma, series resistor of 470 ohms and then the 1n4148 diode.

My question is why am I only measuring 20mA ? I have a voltage of .95 across the diode which suggests I should be getting at least 100ma.

Thanks
Graham

Phasor · 22nd August 2005, 08:55 PM

Small calculation:

(10V {psu voltage} - 0.95V {diode Vf} ) / 470 ohms = 0.0193A = 19.3mA.

Your series resistor is too high a resistance to allow 100mA from a 10V supply. Try reducing it to 82 ohms or so.

audioguru · 22nd August 2005, 10:39 PM

Maybe you expect the diode to generate 100mA? Then try it without your 10V supply. :lol: :lol:

k7elp60 · 24th August 2005, 01:29 AM

I think you may be looking at it in a wrong way. The forward voltage drop is specified with a average current. This voltage drop can vary with temperature. In fact the older version of the 1N4148 the 1N914 has been used as a temperature sensor on occasion by monitoring the forward voltage with a specified current flowing thru it. I also remember seeing a circuit or two that used the forward voltage of this type of diode as a voltage reference source.

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22nd August 2005, 07:58 PM	(permalink)
gjpollitt	1n4148 forward voltage vs current graph Looking at the datasheet with forward voltage of 1v there should be around 170ma On my test circuit I have 10vdc supply limited to 200ma, series resistor of 470 ohms and then the 1n4148 diode. My question is why am I only measuring 20mA ? I have a voltage of .95 across the diode which suggests I should be getting at least 100ma. Thanks Graham

22nd August 2005, 08:55 PM	(permalink)
Phasor	Small calculation: (10V {psu voltage} - 0.95V {diode Vf} ) / 470 ohms = 0.0193A = 19.3mA. Your series resistor is too high a resistance to allow 100mA from a 10V supply. Try reducing it to 82 ohms or so.

22nd August 2005, 10:39 PM	(permalink)
audioguru	Maybe you expect the diode to generate 100mA? Then try it without your 10V supply. :lol: :lol: __________________ Uncle $crooge

24th August 2005, 01:29 AM	(permalink)
k7elp60	I think you may be looking at it in a wrong way. The forward voltage drop is specified with a average current. This voltage drop can vary with temperature. In fact the older version of the 1N4148 the 1N914 has been used as a temperature sensor on occasion by monitoring the forward voltage with a specified current flowing thru it. I also remember seeing a circuit or two that used the forward voltage of this type of diode as a voltage reference source. __________________ The great thing about electronics is unlimited ways to do the job. The only limit is one\'s imagination. I generally think my way is best. Show me a different way. I have an open mind.