I am trying to understand how a dual motor controller works. It drives two DC motors with support for running the motors in the opposite direction, as well as stopping them. Looking at the board I spotted two FDS4953 Dual P-Channel mosfets, presumably one for each motor, as well as a transistor. Their schematic shows that each is comprised of two mosfets. How is the board able to achive this with just two mosfets per motor?
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1\$\begingroup\$ you linked the driver datasheet instead of the module schematic \$\endgroup\$– jsotolaAug 15, 2020 at 19:03
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1\$\begingroup\$ it may be a case of false advertising ... the module can drive two motors unidirectionally or it can drive one motor bidirectionally if you make connections only at the terminal blocks on the module ... off-board connections would be required for bidirectional control of two motors \$\endgroup\$– jsotolaAug 15, 2020 at 19:08
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1\$\begingroup\$ @jsoola:: I don't have the circuit schematic; that's why I asked the question. \$\endgroup\$– Dionysis SpinellisAug 15, 2020 at 21:24
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1\$\begingroup\$ @jsotola: Regarding your second comment, an example program on the maker's site microbot.it/sketches/Dual_DC_Motor_Driver_4A_V3_test_sketch.ino shows simultaneous control of both motors using two potentiometers (this was also useful as i was not sure whether i could drive the motor using a pwm signal). \$\endgroup\$– Dionysis SpinellisAug 15, 2020 at 21:34
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1\$\begingroup\$ "Looking at the board I spotted two FDS4953 Dual P-Channel mosfets" - evidence? \$\endgroup\$– Bruce AbbottAug 15, 2020 at 21:54
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2 Answers
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How is the board able to achive this with just two mosfets per motor?
It doesn't. The board actually has two Allegro MicroSystems A4953 DMOS PWM motor drivers. Here's a photo of the IC:-
answered Aug 17, 2020 at 9:38
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\$\begingroup\$ Indeed, this is clearly supported by the single pair of supply inputs and the truth table given which is that of a full bridge per motor. \$\endgroup\$ Aug 17, 2020 at 10:22
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\$\begingroup\$ Thank you very mush! The picture of the board was not very clear and i could only make out the "4953" part. This coincidentally also matched the "FDS4953" mosfets but the one you found looks like the right one. \$\endgroup\$ Aug 17, 2020 at 22:22
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How is the board able to achive this with just two mosfets per motor?
And
Looking at the board I spotted two FDS4953 Dual P-Channel mosfets
Right on the front page is the hint to how it does this: -
The Dual DC Motor Driver 4A V3 allows to indipendently drive two DC motors, controlling both velocity and direction. The minimum supply voltage allowed is 7V, so you can use also two-cell LiPo batteries (7.4V) that grant small dimensions and low weight characteristics.
Wrong voltage corrected below
Ignoring the spelling (I'm certainly no expert), it suggests using two 3.7 volt batteries in series and this means that one motor wire can terminate to the battery midpoint. This means that one MOSFET can pull the remaining motor wire up to 7.4 volts (applying +3.7 volts to get forward motion) whilst the other MOSFET can pull it down to 0 volts (applying -3.7 volts to get reverse direction): -
answered Aug 15, 2020 at 18:55
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1\$\begingroup\$ Thank you! I think the reference to the two cell 7.4 volts means two 3.7 LiPo cells connected in series to drive the board, rather than center tapping two 7.4 batteries. Also the board's input power terminal provides only two screw inputs, rather than three. \$\endgroup\$ Aug 15, 2020 at 21:26
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2\$\begingroup\$ @DionysisSpinellis Yes I got the voltage stated incorrectly but my point is still valid. At the series junction of the two batteries is where one wire on the motor makes a connection. The other connection on the motor connects to the half bridge output hence, the motor can be driven forwards, backwards or anywhere in between. Do you follow? \$\endgroup\$– Andy akaAug 15, 2020 at 21:51
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1\$\begingroup\$ @tlfong01 does the added picture help? \$\endgroup\$– Andy akaAug 16, 2020 at 8:54
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1\$\begingroup\$ Think of the motor as a loudspeaker and the two MOSFETs as a push pull output stage in an audio power amplifier. Does that help? \$\endgroup\$– Andy akaAug 16, 2020 at 9:13
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1\$\begingroup\$ That'll be "complementary" and not "complimentary" @tlfong01 \$\endgroup\$– Andy akaAug 16, 2020 at 13:23
