Question about measuring voltage of forward biased diode

[misha82]

A silicon diode, when it is forward biased there is a drop of .7v. but when we use multimeter to measure this drop across diode, it gives zero reading show a short ckt. why?:?:

 

[yjkwon57]

Re: Diode

Hi~~

Because the current level used to detect the diode is very low. For the diode forward bias voltage drop to be about 0.7 V, the current level is relatively much higher.

Bye~~

 

[Borber]

Re: Diode

Usual DVM on diode test position when you measure ordinary Si diode forward voltage drop should show a voltage of about 500 mV. Significantly different readings shows that diode is defective.

 

[dirace]

Re: Diode

If you make the messurment like this and you get 0V then your diode is short circuited and you need another one.

 

[rectifier]

Re: Diode

The analog multimeter don't show any deflection because it is not able to bias the diode alone but the digital multimeter with diode tester can give the result ...

 

[hasitri]

Re: Diode

think of a basin n jug concept.
basin --> network
jug --> diode
water --> current
force of water --> voltage


now, the jug is kept in basin which both are empty (just imagine). u supposed to fill the basin thru jug. i.e., u keep the water pipe into jug. as soon as the jug fills completely, water overflows into the basin and basin space starts to fill with water.
** water does'nt goes into basin untill unless first filled completely by jug.

the same is the case with voltage ax diode also. the diode need to be forced bya min of 0.7 V(si) to allow the current to be passed thru it.
** the diode is empty, which must fist be given a +ve 0.7 volts

 

[electronics_kumar]

Re: Diode

wonderful ..highly commendable job by hasitri.....
nice hasitri

 

[e_eja]

Re: Diode

Because multi meter has high load therefore current flowing through diode less then current required for diode to conduct (.07 V)

 

[A.Anand Srinivasan]

Re: Diode

you say it is a short circuit but try the resistance using a really sensitive multimeter then you can understand that is nearly an open circuit

 

[gunsuresh]

Re: Diode

since the diode is in open its current should be zero. hence it does not show the bias reading on the voltmeter