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

 

Sure. You could use something like a 1N5822; Mouser carries them. 3A, 40V, $0.19/ea.
http://www.mouser.com/ProductDetail...=sGAEpiMZZMuIUjt4yeP9c4vDnG6dExKEWTjW6pdAawU=

 

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

 

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.

 

Thank you. Makes sense now; the meter was measuring the voltage with the 2mA leakage.
Using the test from volume 3, the diode tests good; V(f) is on target.
Now to find the problem.

Thanks for your reply.

Tom