The Ultra Fast Recovery Diode Specifications

Ultra Fast Recovery Diode In Switch Mode Power Supply

Modern electronic equipment prefers to use switch mode power supply designed rather than linear power supply, thus switch mode power supplies requires ultra fast recovery diode at the secondary side to convert the high pulse ac voltage to dc voltage. If you use a general purpose diode such as the famous part number 1N5408 to replace the ultra fast recovery diode, the general purpose diode will burn in less than few seconds. Why? If you check from any semiconductor data books or even in the internet, an ultra fast recovery diode have the speed of 75 nanosecond (ns) or faster while the general purpose diode are quite slow which is in the microsecond!   

Even the replacement ultra fast recovery diode that have 50 ns different from the original specification, the diode may burn not in 1 hour time but in few seconds. Replacing the ultra fast recovery diodes in power supplies with original specification make the equipment last longer.

Ultra fast recovery diodes have specification quite similar to general purpose diode except that the speed is much more faster. Usually when you look at the specification of the ultra fast recover diode, you search for its peak reverse voltage (PRV), ampere and time (speed, normally in nano seconds). Always replace the ultra fast recovery diode with a spec that is the same or higher. The speed is very important and if possible find the exact speed or faster. For example, you can replace a 75ns diode with a 50ns or 35ns diode but you cannot substitute it with a 100 ns or 150 ns diode. 

A FUF5404 Is The Same As UF5404

If the speed is slower than the original one the diode will not last long and sometimes burnt immediately upon switch on the equipment. Testing the ultra fast recovery rectifier ust the same method when you check a general purpose diode. Set to time 10 kohm and it should have one reading using analog multimeter. Typical part number for ultra fast recovery diode are UF5404, HER305, 31DF6 and etc. The general purpose diode part number usually are 1N5408, 1N4007 and etc. When you want to buy ultra fast recovery diode from your local electronic distributors, be aware that they might give you a wrong part number. Most of the time when i asked for UF5408 they will give me 1N5408.

Both diode have the same voltage and ampere except the speed! Insist on the same ultra fast recovery rectifiers number. If you have those scrap monitor board in your work place you may also salvage the diode and use it. If you are in the field of monitor repairing, i have a tips for you. Since there are so many types of monitor designed in the market, quite often the monitor manufacturers used many different types of ultra fast recovery diode at the secondary section of the switch mode power supply and also in the B+ circuit. If you come across funny part number or those part number could not be found in your data book or in the internet, then i suggest you use UF5404. I've tested many monitors and this ultra fast recovery diode part number works perfectly fine.