WEBVTT 00:00.000 --> 00:10.866 The purpose of this assembly is to measure the threshold of diodes in operation 00:10.866 --> 00:18.771 The voltmeter displays 0.75 volts threshold; the intensity is 0.08 A 00:18.771 --> 00:28.645 The threshold measured with the multimeter is lower, the latter injects less than 1 mA against 80 mA here! 00:28.645 --> 00:39.211 I am increasing the intensity, here 0.72 A, 9 times more, the threshold has increased by 30%! 00:39.211 --> 00:54.766 Under 2 Amperes this time, one exceeds 1 Volt of threshold, the diode includes a resistance 00:54.766 --> 01:04.346 The threshold decreases because the diode heats, a characteristic common to many components! 01:04.346 --> 01:15.893 It drops back to 0.75 Volt at low intensity 01:15.893 --> 01:18.078 With a 25 Amp diode, the idle threshold is similar 01:18.078 --> 01:27.589 Under 2 amps the threshold has not increased so much! 01:27.589 --> 01:36.157 Normal: its internal resistance is lower because it is intended for a higher intensity 01:36.157 --> 01:45.378 New assembly with 2 diodes in parallel 01:45.378 --> 01:58.604 And the intensity in each diode is measured by an ammeter 01:58.604 --> 02:07.058 0.31 Amps supplied = about 0.19 + 0.16 A, the balance is correct but perfectible 02:07.058 --> 02:18.907 Under 2 A, the deviation is 20%: 1.1 Ampere against 0.9 A 02:18.907 --> 02:29.939 I will check the balancing of the wire lengths! 02:29.939 --> 02:40.746 The right diode uses 2 more lengths of wire (R circuit will be larger!) 02:40.746 --> 02:52.067 By moving a wire, I re-balance the lengths, what will it intensities? 02:52.067 --> 03:04.047 A little better but the worry has reversed ... The diodes have not been paired! 03:04.047 --> 03:14.624 Same day of manufacture and verification of load thresholds for a good pairing! 03:14.624 --> 03:19.213 I try other diodes ... 03:19.213 --> 03:23.972 Catastrophe! Yet diodes of the same references purchased at the same time! 03:23.972 --> 03:32.402 Here is 300% error! So paralleling is inoperative! 03:32.402 --> 03:38.326 I return with shunt resistors in series with the diodes 03:38.326 --> 03:53.371 The voltage drop under load is acceptable # 0.1 V, 10% more than the threshold 03:53.371 --> 04:03.946 The circuits are balanced ... 04:03.946 --> 04:17.118 We are already well! 04:17.118 --> 04:27.504 1.00 for 1.02:2% error against 20% without the resistors! 04:27.504 --> 04:38.418 These resistances increase the inclination and balance the diodes: see the course 04:38.418 --> 04:50.991 Note that these resistors are sometimes directly a circuit board track!