From: Bob Blick <bobblick@outlook.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Thu, 23 Jan 2020 13:28:50 -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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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 supp=
ly pump-up, depending on the speaker load and program material.

Best regards, Bob

________________________________________
From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> on behalf of Jason =
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 forward)

Hello everyone,

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.

Intuitively I am having trouble understanding why this should be. I
lack a decoupling capacitor on the supply line, but do have a zener.

I have attached a schematic of the circuit.

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.

--
Jason White

--=20
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