EEVblog Electronics Community Forum

Products => Test Equipment => Topic started by: abdulbadii on September 30, 2021, 03:45:07 am

Title: Purpose of D1 and D2
Post by: abdulbadii on September 30, 2021, 03:45:07 am

Would anyone please help out explain or show what is the purpose of D1 and D2 in circuit:

[attachimg=1]

Title: Re: Purpose of D1 and D2
Post by: bob91343 on September 30, 2021, 04:52:28 am

They clip the wave to about 0.7V peak, or 1.5V p-p.

Title: Re: Purpose of D1 and D2
Post by: TurboTom on September 30, 2021, 06:49:43 am

They are just for ESD protection and to safely discharge the DUT if someone attaches a charged cap to the tester. Voltage across the capacitor is unidirectional and very low (0.1V max). It's a very simple but still interesting instrument. In a practical setup, one of the voltage dividers (probably ideally R9/R10) should be adjustable to zero out the reading while no DUT is attached. The device will only work for (comparably) large capacitors (electrolytics) since it doesn't have a phase-sensitive rectifier and requires Zc to be much smaller than ESR to produce an accurate result.