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Power Supply Diode Problem


The circuit elements you identify as either possibly faulted or properly functioning can be wires, traces, and connections as well as components. The maximum, non-regulated output can exceed the safe output rating of power supply components. Because the transistors operate as switches they dissipate little power. Put a light bulb in series with the AC mains line to prevent damage when first powering up a SMPS. http://macland.net/power-supply/power-supply-atx-2-0-any-suggestions-as-to-a-power-supply.php

Inductor L1 fails open: no voltage across load, no current through load, no current through rest of secondary-side components, little current through primary winding. The most likely scenario is that with a 0.9A holding current your fault current will be 4.5A however the LM2675 will be limiting the current using its internal current limit to Back to top. 5.2 Voltage and current Regulator Circuits. 5.2.0 How a voltage regulator works and what it does. Such a capacitor may show good using an ohmmeter but will blow fuses and diodes when the power is turned on. https://www.mikesarcade.com/cgi-bin/spies.cgi?action=url&type=info&page=psrepair.txt

Power Supply Repair Guide

If they are not cylindrical anymore, are "inflated", have a dome-shaped top or bottom side (instead of being flat) or have leaked they're faulty. The bridge rectifier can also be used for translating a DC input of unknown or arbitrary polarity into an output of known polarity. Even with a power system properly grounded, problems can develop from an EMI producing source creating a voltage potential in the grounding circuit.

  • Smaller power supplies sometimes rely on natural convection, but larger equipment requires forced air or water cooling.
  • Incidentally, the method of building a project (such as a power supply) in a step-by-step fashion rather than all at once, saves a lot of time and effort when things go
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  • The output voltage is supposed to be 15 volts DC, but instead it is actually outputting nothing at all (zero volts): The technician measures 120 volts AC between test points TP1
  • If your SMPS has a regulator IC, try to find it's datasheet on the internet: many SMPS have a schematic diagram very similar to the examples reported in the datasheets.
  • It regulates the voltage by reducing it by the amount required to hold it at some preset value.

Be sure to spend plenty of time in class with your students developing efficient and logical diagnostic procedures, as this will assist them greatly in their careers. If Q1 and Q2 were replaced by a power FET R6 could be very large and the limiter would work quite well. Browse other questions tagged diodes switch-mode-power-supply failure or ask your own question. Troubleshooting & Repairing Switch Mode Power Supplies To discharge the capacitors, don't short them with the screwdriver, use a suitable resistor instead (a few kΩ and a few Watts) connected to two insulated probes like the one of

Question 13 What will be the consequence of one diode failing open in the bridge rectifier of a single-phase power supply? Computer Power Supply Repair Based on this voltage measurement and the knowledge that there is reduced DC output voltage, identify two possible faults that could account for the problem and all measured values in this Back to Fun with Transistors. The diode has a huge copper plane around its pads so I don't think that overcurrent destroyed the diode. –Andre Oct 29 '13 at 10:43 add a comment| Your Answer

Since SMPS can fail in a lot of different ways, you may still not find the right hint in this page, but I truly hope you'll find here useful information and Power Supply Repair Guide Free Download Draw the schematic diagram for the circuit to be analyzed. Notes: It is important for students to understand where this equation comes from. The horizontal line on the waveform is the assumed level of the noninverting input.

Computer Power Supply Repair

Electronic feedback circuitry is usually faster than the switching of mechanical relays and contactors and during the switching instant, the power supply is operated without sensing the output. Very dangerous for technicians to work on. Power Supply Repair Guide Environment Power supplies contain heat producing components: transformers, inductors, power semiconductors, and the like. Power Supply Troubleshooting & Repair Notes: A question such as this is best discussed while viewing the schematic diagram for a bridge rectifier.

Because only one half of the input waveform reaches the output, it is only 50% efficient if used for power transfer. this contact form Advertisement Home/Diodes/Power Diodes and Rectifiers Power Diodes and Rectifiers In the previous tutorials we saw that a semiconductor signal diode will only conduct current in one direction from its anode to I have never seen a vacuum tube power supply that was protected by a current limiting circuit. I always choose the higher temperature because they last longer. Computer Power Supply Repair Manual

If your input can really go to 40V then your schottky should be 60V rated or at least 50V rated. From that point on, the relatively low impedance of the diode keeps the voltage across the diode at that value. Thus, R1 is carrying the DC plus the AC components of current. have a peek here Besides making sure that electrical connections do not exceed manufacturers’ ratings, placement of cables can be critical.

Powering it off-line with a small external DC power supply and checking for pulses on the transistor base (or gate) is a good idea. Power Supply Repair Guide Pdf Should we always specify ID attribute in HTML? Reveal answer Hide answer XL = 0.0377 Ω (each) XC = 120.6 kΩ (each) Notes: Ask your students how they determined the identity of this filter.

Almost all of the AC component of current in R1 flows back to the center-tap through C2.

The light blue capacitor in this picture is the high voltage capacitor connecting the low voltage ground with the mains ground. If the regulator is air cooled and the air passage becomes clogged with dust as it is guaranteed to do, The regulator will overheat and shut down. A full wave rectifier, figure 6.5(b) achieves two peaks per cycle and this is the best that can be done with single-phase input. Power Supply Repair Service Reveal answer Hide answer I’ll let you and your classmates figure out some possibilities here!

Follow-up question: with regard to the troubleshooting technique, this technician seems to have started from one end of the circuit and moved incrementally toward the other, checking voltage at almost every Trace the shape of the input current waveform, given the output voltage waveform and magnetizing current waveform (dotted line) shown here: The non-filtered DC output waveform is still shown as a Transformer secondary winding fails open: no voltage or current on secondary side of circuit after C1 discharges through load, little current through primary winding. http://macland.net/power-supply/power-flashes-when-i-flip-the-power-supply-switch.php The output voltage of this circuit cannot be adjusted below the voltage of the VR tube plus about 50 volts.

Blocking ventilation openings can obviously cause equipment failure. Notes: Troubleshooting scenarios are always good for stimulating class discussion. Questions such as this should be followed (eventually) by other questions asking students to identify likely faults based on measurements. Every year Magna-Power Electronics receives support calls that a customer's power supply has failed because of connection to the wrong AC mains voltage.

During each "negative" half cycle of the AC sinusoidal input waveform, the diode is reverse biased as the anode is negative with respect to the cathode. Privacy Policy Contact Troubleshooting switch mode power supplies Introduction Switch mode power supplies (SMPS) are now standard for the majority of our home appliances. If a capacitor is placed in parallel with a VR tube it will form a relaxation oscillator just like the neon lamp type we used to build for science fair projects. If the output voltage, emitter of Q1, tries to decrease due to an increase in load or a decrease in line voltage the voltage at the base of Q2 will decrease

I don't the reason pls help me out from this problem.