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reverse breakdown voltage

Started by Bernhard Kuemel April 25, 2012
Hi seb!

I tried to measure the Vrbd of LEDs and found the resistance dropping:

Vr      R(MOhm)

3.18	244.6153846154
3.97	59.2537313433
4.23	48.6206896552
4.82	36.7938931298
5.65	27.5609756098
6.08	22.7715355805
7.61	16.295503212

I guess I have not reached the breakdown voltage and I need a power
supply with more voltage.

However, I wonder, what the definition of breakdown voltage is. Usually
you see the sharp increase in current at Vbd in the diode characteristic
curve. But isn't this a matter of zoom? When I use nA instead of mA on
the current axis the curve will look similar with the breakdown
(forward) voltage shifted towards 0. IMHO the curve will look exactly
the same if it's a purely exponential curve and you zoom in or out.

Or is there a voltage below which no impact ionization occurs and this
can be seen as lowest possible definition of Vbd? But I rather think
there is always a chance for a free electron to gain enough energy to
knock free another electron. It'll just never make an avalance through
the whole barrier below a certain voltage. OTOH if a single electron
travels through the barrier due to a low voltage and at the other side
it happens to get bounced around by the lattice atoms to enough energy
to kick free a second electron that's an avalanche that made it through
the whole barrier. So at any voltage there'll be avalanches and
avalanche current will increase (exponentially, I guess) over the whole
voltage range.

Then there's zener breakdown which I think is some kind of tunneling.

Bernhard
On Apr 25, 1:49=A0pm, Bernhard Kuemel <bernh...@bksys.at> wrote:
> Hi seb! > > I tried to measure the Vrbd of LEDs and found the resistance dropping: > > Vr =A0 =A0 =A0R(MOhm) > > 3.18 =A0 =A0244.6153846154 > 3.97 =A0 =A059.2537313433 > 4.23 =A0 =A048.6206896552 > 4.82 =A0 =A036.7938931298 > 5.65 =A0 =A027.5609756098 > 6.08 =A0 =A022.7715355805 > 7.61 =A0 =A016.295503212
Oh no didn't you lose credit in school for too many digits! :^) I stuck a red LED backwards with a 100k ohm resistor is series... at about 24V I got all these 'beautiful' RC spikes. ~ 1 volt peak, rc time ~20us. Cranking up the voltage more and it was noise everywhere, on a DC background. (I was monitoring the voltage across the resistor.) Any reason you need to know this? George H.
> > I guess I have not reached the breakdown voltage and I need a power > supply with more voltage. > > However, I wonder, what the definition of breakdown voltage is. Usually > you see the sharp increase in current at Vbd in the diode characteristic > curve. But isn't this a matter of zoom? When I use nA instead of mA on > the current axis the curve will look similar with the breakdown > (forward) voltage shifted towards 0. IMHO the curve will look exactly > the same if it's a purely exponential curve and you zoom in or out. > > Or is there a voltage below which no impact ionization occurs and this > can be seen as lowest possible definition of Vbd? But I rather think > there is always a chance for a free electron to gain enough energy to > knock free another electron. It'll just never make an avalance through > the whole barrier below a certain voltage. OTOH if a single electron > travels through the barrier due to a low voltage and at the other side > it happens to get bounced around by the lattice atoms to enough energy > to kick free a second electron that's an avalanche that made it through > the whole barrier. So at any voltage there'll be avalanches and > avalanche current will increase (exponentially, I guess) over the whole > voltage range. > > Then there's zener breakdown which I think is some kind of tunneling. > > Bernhard
On 04/25/2012 09:38 PM, George Herold wrote:
> On Apr 25, 1:49 pm, Bernhard Kuemel <bernh...@bksys.at> wrote: >> Hi seb! >> >> I tried to measure the Vrbd of LEDs and found the resistance dropping: >> >> Vr R(MOhm) >> >> 3.18 244.6153846154 >> 3.97 59.2537313433 >> 4.23 48.6206896552 >> 4.82 36.7938931298 >> 5.65 27.5609756098 >> 6.08 22.7715355805 >> 7.61 16.295503212 > > Oh no didn't you lose credit in school for too many digits! > :^)
I don't remember. I never gave too many digits when I was in school :). I thought about trimming it, but nah, not worth the trouble :).
> I stuck a red LED backwards with a 100k ohm resistor is series... at > about 24V I got all these 'beautiful' RC spikes. ~ 1 volt peak, rc > time ~20us. Cranking up the voltage more and it was noise everywhere, > on a DC background. (I was monitoring the voltage across the > resistor.)
RC? What C? RC spikes? 1V at the resistor and 23V at the diode doesn't look like a huge breakdown. Maybe I'll really connect a rectifier to 230V and do: 325V - -LED+ - 10MOhm (input resistance of multimeter) - 0V
> Any reason you need to know this?
Mostly curiosity. I have various LEDs here, including 3 Cree XP-G R5 cool white, which are specified as 5V reverse voltage. Bernhard
Bernhard Kuemel wrote:
> Hi seb! > > I tried to measure the Vrbd of LEDs and found the resistance dropping: > > Vr R(MOhm) > > 3.18 244.6153846154 > 3.97 59.2537313433 > 4.23 48.6206896552 > 4.82 36.7938931298 > 5.65 27.5609756098 > 6.08 22.7715355805 > 7.61 16.295503212 > > I guess I have not reached the breakdown voltage and I need a power > supply with more voltage. > > However, I wonder, what the definition of breakdown voltage is. Usually > you see the sharp increase in current at Vbd in the diode characteristic > curve. But isn't this a matter of zoom? When I use nA instead of mA on > the current axis the curve will look similar with the breakdown > (forward) voltage shifted towards 0. IMHO the curve will look exactly > the same if it's a purely exponential curve and you zoom in or out. > > Or is there a voltage below which no impact ionization occurs and this > can be seen as lowest possible definition of Vbd? But I rather think > there is always a chance for a free electron to gain enough energy to > knock free another electron. It'll just never make an avalance through > the whole barrier below a certain voltage. OTOH if a single electron > travels through the barrier due to a low voltage and at the other side > it happens to get bounced around by the lattice atoms to enough energy > to kick free a second electron that's an avalanche that made it through > the whole barrier. So at any voltage there'll be avalanches and > avalanche current will increase (exponentially, I guess) over the whole > voltage range. > > Then there's zener breakdown which I think is some kind of tunneling. > > Bernhard
Did you also subject the LED to various light sources concentrated on the package while doing this? Might be interesting on the results differences. Jamie
On Wed, 25 Apr 2012 19:49:31 +0200, Bernhard Kuemel
<bernhard@bksys.at> wrote:

>Hi seb! > >I tried to measure the Vrbd of LEDs and found the resistance dropping: > >Vr R(MOhm) > >3.18 244.6153846154 >3.97 59.2537313433 >4.23 48.6206896552 >4.82 36.7938931298 >5.65 27.5609756098 >6.08 22.7715355805 >7.61 16.295503212 > >I guess I have not reached the breakdown voltage and I need a power >supply with more voltage. > >However, I wonder, what the definition of breakdown voltage is.
--- Generally, it's defined as the minimum voltage required to force a certain reverse current through the LED. -- JF
On Wed, 25 Apr 2012 17:39:42 -0400, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charte

> Bernhard > Did you also subject the LED to various light sources concentrated on >the package while doing this? Might be interesting on the results >differences.
--- Hardly germane. -- JF
On Apr 25, 5:39=A0pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
> Bernhard Kuemel wrote: > > Hi seb! > > > I tried to measure the Vrbd of LEDs and found the resistance dropping: > > > Vr =A0 =A0 =A0R(MOhm) > > > 3.18 =A0 =A0 =A0 244.6153846154 > > 3.97 =A0 =A0 =A0 59.2537313433 > > 4.23 =A0 =A0 =A0 48.6206896552 > > 4.82 =A0 =A0 =A0 36.7938931298 > > 5.65 =A0 =A0 =A0 27.5609756098 > > 6.08 =A0 =A0 =A0 22.7715355805 > > 7.61 =A0 =A0 =A0 16.295503212 > > > I guess I have not reached the breakdown voltage and I need a power > > supply with more voltage. > > > However, I wonder, what the definition of breakdown voltage is. Usually > > you see the sharp increase in current at Vbd in the diode characteristi=
c
> > curve. But isn't this a matter of zoom? When I use nA instead of mA on > > the current axis the curve will look similar with the breakdown > > (forward) voltage shifted towards 0. IMHO the curve will look exactly > > the same if it's a purely exponential curve and you zoom in or out. > > > Or is there a voltage below which no impact ionization occurs and this > > can be seen as lowest possible definition of Vbd? But I rather think > > there is always a chance for a free electron to gain enough energy to > > knock free another electron. It'll just never make an avalance through > > the whole barrier below a certain voltage. OTOH if a single electron > > travels through the barrier due to a low voltage and at the other side > > it happens to get bounced around by the lattice atoms to enough energy > > to kick free a second electron that's an avalanche that made it through > > the whole barrier. So at any voltage there'll be avalanches and > > avalanche current will increase (exponentially, I guess) over the whole > > voltage range. > > > Then there's zener breakdown which I think is some kind of tunneling. > > > Bernhard > > =A0 =A0Did you also subject the LED to various light sources concentrated=
on
> the package while doing this? =A0Might be interesting on the results > differences.
Yeah I did, When you biased it right to the breakdown region you could definitely see the effect of sticking an light up to it. Try it. Everyone's got a red 5mm LED, 100k ohm and ~30V power supply. George H.
> > =A0 Jamie- Hide quoted text - > > - Show quoted text -
On Apr 25, 5:14=A0pm, Bernhard Kuemel <bernh...@bksys.at> wrote:
> On 04/25/2012 09:38 PM, George Herold wrote: > > > > > > > On Apr 25, 1:49 pm, Bernhard Kuemel <bernh...@bksys.at> wrote: > >> Hi seb! > > >> I tried to measure the Vrbd of LEDs and found the resistance dropping: > > >> Vr =A0 =A0 =A0R(MOhm) > > >> 3.18 =A0 =A0244.6153846154 > >> 3.97 =A0 =A059.2537313433 > >> 4.23 =A0 =A048.6206896552 > >> 4.82 =A0 =A036.7938931298 > >> 5.65 =A0 =A027.5609756098 > >> 6.08 =A0 =A022.7715355805 > >> 7.61 =A0 =A016.295503212 > > > Oh no didn't you lose credit in school for too many digits! > > =A0 :^) > > I don't remember. I never gave too many digits when I was in school :). > I thought about trimming it, but nah, not worth the trouble :). > > > I stuck a red LED backwards with a 100k ohm resistor is series... at > > about 24V I got all these 'beautiful' RC spikes. =A0 ~ 1 volt peak, rc > > time ~20us. =A0Cranking up the voltage more and it was noise everywhere=
,
> > on a DC background. =A0(I was monitoring the voltage across the > > resistor.) > > RC? What C? RC spikes? 1V at the resistor and 23V at the diode doesn't > look like a huge breakdown. Maybe I'll really connect a rectifier to > 230V and do: > > 325V - -LED+ - 10MOhm (input resistance of multimeter) - 0V > > > Any reason you need to know this? > > Mostly curiosity. I have various LEDs here, including 3 Cree XP-G R5 > cool white, which are specified as 5V reverse voltage. > > Bernhard- Hide quoted text - > > - Show quoted text -
The voltage across the 100k R looked like <----peak here about 1 volt |\ | -\ | - \ <--- that's an exponential decay...sorta | -- -------+ \ --------- ^----2/3 (1/e) time constant about 20 us. Those came at random times... more of them with the light on... avalanche break down. Kinda fun, thanks. George H.
George Herold wrote:

> On Apr 25, 5:39 pm, Jamie > <jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote: > >>Bernhard Kuemel wrote: >> >>>Hi seb! >> >>>I tried to measure the Vrbd of LEDs and found the resistance dropping: >> >>>Vr R(MOhm) >> >>>3.18 244.6153846154 >>>3.97 59.2537313433 >>>4.23 48.6206896552 >>>4.82 36.7938931298 >>>5.65 27.5609756098 >>>6.08 22.7715355805 >>>7.61 16.295503212 >> >>>I guess I have not reached the breakdown voltage and I need a power >>>supply with more voltage. >> >>>However, I wonder, what the definition of breakdown voltage is. Usually >>>you see the sharp increase in current at Vbd in the diode characteristic >>>curve. But isn't this a matter of zoom? When I use nA instead of mA on >>>the current axis the curve will look similar with the breakdown >>>(forward) voltage shifted towards 0. IMHO the curve will look exactly >>>the same if it's a purely exponential curve and you zoom in or out. >> >>>Or is there a voltage below which no impact ionization occurs and this >>>can be seen as lowest possible definition of Vbd? But I rather think >>>there is always a chance for a free electron to gain enough energy to >>>knock free another electron. It'll just never make an avalance through >>>the whole barrier below a certain voltage. OTOH if a single electron >>>travels through the barrier due to a low voltage and at the other side >>>it happens to get bounced around by the lattice atoms to enough energy >>>to kick free a second electron that's an avalanche that made it through >>>the whole barrier. So at any voltage there'll be avalanches and >>>avalanche current will increase (exponentially, I guess) over the whole >>>voltage range. >> >>>Then there's zener breakdown which I think is some kind of tunneling. >> >>>Bernhard >> >> Did you also subject the LED to various light sources concentrated on >>the package while doing this? Might be interesting on the results >>differences. > > > Yeah I did, When you biased it right to the breakdown region you > could definitely see the effect of sticking an light up to it. Try > it. Everyone's got a red 5mm LED, 100k ohm and ~30V power supply. > > George H. > >> Jamie- Hide quoted text - >> >>- Show quoted text - > >
Oh, I've already done this not to long ago when I was pondering on an idea. How ever, I am trying to see where you are getting the noise from? When I did it, all I saw on the scope was a PV effect at 1 uA, it could've been more, been a while. I used my over head light which is nothing more than a incandescent 52 watt. I did see the 120 hz in the signal, too, when getting the exposure to where I was getting 50% forward biasing voltage for that LED. But I was able to get over 1 V as a PV with out any biasing, just the LED on the leads. It would make for a nice photo detector in a pinch though if you have the hi-z circuit for it. I guess if one was to have a few LED's in series with HV applied and wait for a few photons to stop by for visit it would then act as a photo multiplier and push things a long, thus giving you a very sensitive detector. Or at least I think it would :) I'll have to set that experiment up again at work, this time using the Lecroy maybe and see if I can see anything I may have missed before. Jamie
On 04/25/2012 11:14 PM, Bernhard Kuemel wrote:
> > 325V - -LED+ - 10MOhm (input resistance of multimeter) - 0V
Hmm, the DMM showed the full input voltage. No voltage drop due to the LED. IIRC before that I tried the LED in forward direction and got some voltage drop. However, after trying the reverse direction the behaviour was the same in either direction. No light, except for a short flash when I closed the circuit. The DMM showed ca. 330 mV diode drop and 445 Ohm resistance, both in each direction. I was convinced the LED was dead, but when hooked up normally it was still shining without appearant loss in brightness. Ohh, I also had a 10uF film capacitor across the input voltage. Bernhard