From: Brent Brown <brent@eds.co.nz>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Thu, 23 Jan 2020 14:15:18 -0800
Subject: Re: [EE] H-Bridge supply voltage spike only in "reverse" (not
 forward)
Thread-Topic: [EE] H-Bridge supply voltage spike only in "reverse" (not
 forward)
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Add to that, brushed DC motors can have the brush positions optimised for o=
ne=20
direction, in which case reverse direction is slightly different.

Still hard to decipher what's going on from waveforms though. Does the moto=
r=20
actually run fwd/rev ok... speed/torque ok? Could you run it with a moderat=
e=20
resistive load instead of a motor and check everything... rule out back-EMF=
 and=20
prove the MOSFET bridge and drivers are behaving correctly (or not).

On 23 Jan 2020 at 21:28, Bob Blick wrote:

> Hi Jason, Back-EMF from the motor can pump the supply up. Why it
> would do it only in reverse is a bit of a mystery though. Having a
> big-enough bulk capacitor on an H-bridge supply is always a
> requirement when driving an inductive load. Class-D audio power
> amplifiers also sometimes have the same problem of supply pump-up,
> depending on the speaker load and program material.=20
>=20
> Best regards, Bob
>=20
> ________________________________________
> From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> on behalf of Jaso=
n White=20
> Sent: Thursday, January 23, 2020 11:04 AM
> To: Microcontroller discussion list - Public.
> Subject: [EE] H-Bridge supply voltage spike only in "reverse" (not forwar=
d)
>=20
> Hello everyone,
>=20
> I am encountering the following. The supply voltage line to my
> H-Bridge is rising only when the H-Bridge is running a motor in
> "reverse." In forward the supply voltage is unaffected.
>=20
> Intuitively I am having trouble understanding why this should be. I
> lack a decoupling capacitor on the supply line, but do have a zener.
>=20
> I have attached a schematic of the circuit.
>=20
> I will send the forward and reverse waveforms in two follow up emails
> to avoid hitting the file size attachment limits.The waveforms will
> show supply voltage and voltage across the H-Bridge.
>=20
> --
> Jason White
>=20
> --=20
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
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