Diode equal

Discussion in 'The Projects Forum' started by Redstone2, Jan 11, 2011.

Oct 21, 2010
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Hello,
I need help finding an equal to a BYW98 diode. The application is for a 24 volt, 4 ampere (maximum) dc motor controller. Attached is the circuit diagram.
Would a Schottky diode work in this application?
Thanks for any ideas.
Sincerely,
Tom

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2. SgtWookie Expert

Jul 17, 2007
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Redstone2 likes this.

Oct 21, 2010
20
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Hello,

Finally got everything together, assembled, the motor controller and the microprocessor, and tested last night. There was no joy but no smoke, so not so bad. The code was checked = ok, the microcontroller checked: PWM=OK, logic flip-flop for bi-direction=OK, voltage=OK.

I think the diodes purchased are no good. I'm complete novice, so I tried the test with battery found here http://www.allaboutcircuits.com/vol_3/chpt_3/2.html . The readings, with a 9 volt battery, are: test set-up as shown = 0.5 volts; text has another test "Connecting the diode backwards to this testing circuit will simply result in the voltmeter indicating the full voltage of the battery" this version of the test = 8.3 volts.

I also did a simple test with a multimeter: Measure the voltage through the diode with a 9-volt battery. No matter the orientation of the diode the meter read battery voltage. This confuses me, should the voltage be 0 in one of the two directions?

Attached are two images. One across the diode, the other at motor terminals.

Thanks for any pointers and/or ideas on the problem.

Kind Regards,
Tom

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• 20120115_Motor_Terminals.jpg
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Dec 26, 2010
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The 1N5822 is a Schottky diode with a relatively high leakage current, specified at 2mA at 25C. See datasheet: http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00001626.pdf

This may result in the reverse connection tests showing such results, which do not necessarily indicate a problem.

Ordinary silicon PN diodes might have leakage currents around a thousand times less - and for some smaller devices the leakage would be lower still. The simple diode tests should give clearer indications with devices like these.