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I'm using a BTS7960 H-bridge to regulate a fuel pump´s RPM. Currently, I'm facing the challenge of extreme heat production. I think the reason is an inaccurate PWM-input signal (picture below.)

Background information:

My goal is to use a high current fuel pump in a car with on demand fuel supply. To regulate the RPM, the car has installed an OEM fuel pump module. When using a high current fuel pump in combination with the original fuel pump module, the module is getting hot & shutting off.

This gives us the reason for using the H-bridge: BTS7960 can operate >40A, the original module < 15A.

Currently I am using the PWM output signal of the OEM module (which was originally intended for the pump,) using a voltage divider to bringing this signal from 12 to 5V and use it as PWM input signal for the BTS7960.

The BTS7960 is connected to the car battery and directly to the fuel pump (both + and ground.) This gives us the ability to run 100% of the load via the BTS7960 and decouple the OEM module.

Voltage at the fuel pump/ OEM module:

Voltage at Fuelpump// OEM Module

PWM input signal. Measured at the PWM pin of the H-bridge. Base is voltage at the fuel pump with the OEM module:

PWM Input Signal. Measured at PWM Pin of H bridge. Base ist Voltage at fuelpump with OEM Module

Voltage at the fuel pump: Voltage at Fuelpump // H Bridge

How would you proceed to clean up the PWM signal?

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    \$\begingroup\$ Can you please provide a schematic? Probably the values of the voltage divider resistors are far to big \$\endgroup\$
    – Jens
    Commented Jun 18, 2022 at 20:26
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    \$\begingroup\$ A voltage divider is not the best way to reduce the signal level. That's probably where the slanting slopes and rounded shoulders are coming from. \$\endgroup\$
    – JRE
    Commented Jun 18, 2022 at 20:45
  • \$\begingroup\$ @Jens of course, gonna send the schematic in some hours. \$\endgroup\$
    – Gustav
    Commented Jun 20, 2022 at 14:06
  • \$\begingroup\$ @JRE Alright, what is a better way for reducing a PWM Signal level? \$\endgroup\$
    – Gustav
    Commented Jun 20, 2022 at 14:06
  • \$\begingroup\$ How much current does the pump use, and how is the BTS chip cooled? \$\endgroup\$
    – bobflux
    Commented Jun 25, 2022 at 19:04

1 Answer 1

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Between the [14V by 50us] square wave out from the OEM controller and the voltage divider output [5V by 50us] going in to the BTS, there is a lot of distortion happening.

The BTS7960 has cmos schmitt trigger logic inputs so it cleans up the input itself, triggering at about half way up or down the [5V by 50us] of that distorted square wave, which produces the reduced width output pulses of 15us ON & 35us OFF. I'd look at improving the logic input wiring by ensuring that the ground reference between them is valid by using a dedicated ground wire then using a twisted pair or shielded cable.

The way you are driving it at the moment it is applying 15us full power On followed by 35us active braking (with slowly decaying inductive voltage), very good for making heat. As the motor only ever turns one way I'd suggest using the half driver 'backwards' by setting the turning direction via the PWM input and applying the pulses into the enable pin. This will supply 15us periods of full power On followed by fast decay coasting periods of 35us. With very little heating.

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  • \$\begingroup\$ Thanks for the advice, I tried like you mentioned: PWM input pin (right direction) constant to 5V and connecting the PWM input signal to the enable pin (right direction). The BTS7960 is still getting very hot. I found out, that it’s necessary to also power up the left-direction-enable pin by 5V. Without 5V at this pin, the pump does not start running. Should it be like this? Do you have any idea, what else could be improved? Image \$\endgroup\$
    – Gustav
    Commented Jun 25, 2022 at 16:41
  • \$\begingroup\$ @MISC {624698, TITLE = {Cleaning PWM input signal to reduce heating of H-bridge}, AUTHOR = {Bruce Gennette (electronics.stackexchange.com/users/316349/bruce-gennette)}, HOWPUBLISHED = {Electrical Engineering Stack Exchange}, NOTE = {URL:electronics.stackexchange.com/q/624698 (version: 2022-06-23)}, EPRINT = {electronics.stackexchange.com/q/624698}, URL = {electronics.stackexchange.com/q/624698} } Do you have any further tips, which I can try out? \$\endgroup\$
    – Gustav
    Commented Jul 7, 2022 at 4:41

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