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Offline markm6164

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Identify this diode
« on: February 18, 2017, 04:24:47 AM »
Hi, i'm an auto electrician and i have just bought a Snap on test light from eBay. Its a LED test light EECT4H and the 4 diodes on the PCB are blown. Can anyone help me identify them. I have included the datasheet for the light and pictures of the diode and a diagram i did of the circuit. I believe the diode is size SOD323 if that is correct and i'm not sure if the diode is a standard diode or a zener as the lamp works at 6-12v?

Many thanks
« Last Edit: February 18, 2017, 04:28:01 AM by markm6164 »
 

Offline Armadillo

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Re: Identify this diode
« Reply #1 on: February 18, 2017, 05:05:13 AM »
I think is a BAV16W/1N4148W fast switching diode in SOD123 case.
« Last Edit: February 18, 2017, 05:27:23 AM by Armadillo »
 

Online Ian.M

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Re: Identify this diode
« Reply #2 on: February 18, 2017, 05:09:49 AM »
The application is totally non-critical. Any silicon diode rated at >100mA If and >50V, in the same package and pinout could be substituted.
 

Offline Armadillo

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Re: Identify this diode
« Reply #3 on: February 18, 2017, 05:20:49 AM »
Wow! $39 for a piece of low current 20mA LED test pen... that's  :phew: expensive.!
Yeap, you will need the smd parts to fit into the space and justify the cost of this test pen.

 

Offline markm6164

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Re: Identify this diode
« Reply #4 on: February 18, 2017, 05:38:39 AM »
Thanks for the replies everyone.  :-+
 

Online Ian.M

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Re: Identify this diode
« Reply #5 on: February 18, 2017, 05:50:58 AM »
Substitute a two pin bicolour LED, and remove and bypass the diode bridge and you'll have upgraded it to indicate polarity.
 

Offline james_s

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Re: Identify this diode
« Reply #6 on: February 18, 2017, 06:38:59 AM »
That's a bridge rectifier, as someone else said, not critical at all. Just pick up any standard diodes that will physically fit. Probably want a PIV of at least 50V but most will have at least that.
 

Offline grifftech

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Re: Identify this diode
« Reply #7 on: February 18, 2017, 08:11:52 AM »
buy one from harbor freight
 

Offline darrellg

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Re: Identify this diode
« Reply #8 on: February 18, 2017, 09:38:56 AM »
Wow! $39 for a piece of low current 20mA LED test pen... that's  :phew: expensive.!
Yeap, you will need the smd parts to fit into the space and justify the cost of this test pen.
That's $2 for the tester and $37 to have the Snap-on name printed on the outside.
 

Offline Bushougoma

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Re: Identify this diode
« Reply #9 on: February 18, 2017, 11:50:36 AM »
As others have said a standard 1N4148 or the like diode can be substituted.

The current through that LED (based on the resistor) is around 20 milliamps tops (slightly less due to the 2 diode voltage drop from the bridge rectifier).

They put the bridge rectifier there so the test light wouldn't be polarity sensitive (like it's incandescent counterpart). It also prevents the LED from becoming reverse biased (most LEDs have a max reverse voltage of 5 volts) a fully charged battery can easily exceed this.
« Last Edit: February 19, 2017, 07:36:37 AM by Bushougoma »
 

Offline james_s

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Re: Identify this diode
« Reply #10 on: February 18, 2017, 06:52:16 PM »
I made a test light using almost exactly that same circuit when I was about 10 years old. I used parts I salvaged from a broken portable stereo and housed it in a Bic pen with a sewing needle as a probe. I used it for probably another 10 years until I lost it. Amazing that SnapOn can get so much for something so simple. I made a similarly built one with a neon indicator for 120V, not sure what happened to that one either.
 

Offline Bushougoma

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Re: Identify this diode
« Reply #11 on: February 19, 2017, 07:36:01 AM »
The reason most mechanics buy their stuff is the no nonsense exchange policy if you break it the tool truck guy will replace it no questions asked. You pay for that in the purchase price.

I don't believe that applies to their electronic equipment though.
 

Offline Armadillo

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Re: Identify this diode
« Reply #12 on: February 19, 2017, 08:17:27 AM »
The reason most mechanics buy their stuff is the no nonsense exchange policy if you break it the tool truck guy will replace it no questions asked. You pay for that in the purchase price.

I don't believe that applies to their electronic equipment though.

Then, may I ask, why the need to be here the first place?
 

Offline Bushougoma

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Re: Identify this diode
« Reply #13 on: February 19, 2017, 08:59:02 AM »
I don't believe that applies to their electronic equipment though.

 ;)
 


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