In an effort to protect your products, switching power supply manufactures use many safety features. Sometimes these features can trip when it does not seem like they should have and then a perfectly good power supply can be uninstalled unnecessarily.
OVP - Over Voltage Protection is the most common culprit in these situations. OVP is a legacy from old linear power supplies that had a common failure mode of burning out the output regulator and then delivering much more than their rated voltage... This is an unlikely scenario in switching models however the circuit remains. There is more than one way to accomplish OVP but most circuits turn off the PWM chip when an over voltage event occurs. Lets say that you are working on a 5 volt power supply but to make up for line losses or to meet a special requirement you turn up the voltage to 5.4. The set OVP voltage may be as low as 5.6 volts. Some power supplies track the set voltage and raise the limit accordingly others do not. If the voltage is turned up to 5.6 during the installation or if there is a spike caused by loose connection, power surge, etc the unit could go into OVP. Now that the switching chip is turned off the capacitors have full charge but they are not being drained to the load since the power supply has essentially latched off. The OVP will not reset until the capacitors have drained below a set point. In most cases you will need to remove the AC power and wait ~2-5 minutes for the power supply drain the caps and reset. Meanwhile turn down the voltage potentiometer a bit and double check the connections on the power supply. Once the power supply has had a few minutes, it should operate as normal. A word of caution, if the fuse is blown in a switching power supply, the power supply has been damaged and you should not replace the fuse. This seems contrary to logic, however switching power supplies have over current limit to eliminate the conventional function of a fuse. Fuses are only used to prevent "catastrophic failure". (read fire). If you have an application that is causing you problems, we can help you work through your technical issues. 813-996-5230
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