4050 Burnout in Motor Circuit

Thread Starter

BobbyTheD

Joined Mar 10, 2016
36
Hi all -
I'm using the attached circuit to drive a motor. What I'm noticing is that the 4050 chip frequency "gives up" and I get a steady "on" voltage, instead of the expected PWM pulses.
One small difference is that I'm not using a 1N5817 Schottky Diode on the motor - is it possible that the flyback current is reaching the 4050?
 

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LowQCab

Joined Nov 6, 2012
2,171
A CD4050B, even a stack of them, ( ~180ma ..... maybe ),
are not adequate to switch roughly ~4nf at any Frequency greater than maybe ~2khz.

Also, not all CD4050B Chips are created equal, some have an "un-buffered" Output,
and some have an "Open-Collector" Output.

You need a proper Gate-Driver for a High-Current-FET,
such as ........ https://www.digikey.com/en/products/detail/microchip-technology/TC4421AVAT/857570


Also, Back-EMF is rarely a problem, as long as You have
some kind of a Diode across the Motor Terminals.
The bugga-boo that causes real problems is RFI-Hash from the Motor-Brushes,
which scoff at old dumb Diodes and blast right through and smoke various parts.

A variety of sizes of Ceramic-Capacitors soldered directly across the Motor Terminals,
and from each Motor-Terminal to the Motor-Case/Ground will "sometimes" be adequate.
( 100nf, 10nf, 1nf, )
A Common-Mode-Choke, mounted close to the Motor can help, ( must be rated for Max Motor-Current ).
Ferrite-Beads over the Motor Supply Wires can also help.
Always twist the Wires supplying the Motor, this will reduce radiated-RF-Noise.
This RFI-"Hash" may easily go up into the Gigahertz range, and can be very frustrating to get rid of.
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Thread Starter

BobbyTheD

Joined Mar 10, 2016
36
Thanks, @LowQCab - this is some great information.
As such, I'm thinking I might need to scrap the circuit and start over.
Is there anything you would recommend for building a solid circuit for driving small motors at various speeds and directions?
 

LowQCab

Joined Nov 6, 2012
2,171
For Motors that demand less than 8 Locked-Rotor-Amps, ( LRA ),
I like the idea of simply using 2 very stout FET-Gate-Driver-Chips to make a Full-Bridge Circuit.
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Low Power Motor Control External PWM 1 FLAT  .png
 
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