EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: jonovid on September 29, 2018, 10:52:01 pm
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my particular problem
I have some mini dc motor & gearbox units. the specifications are 1 to 2 volts.
the H bridge chip I would like to use is a BA6218 as I have a lot of them.
but the BA6218 H bridge is 5 volts.
BA6218 datasheet
https://4donline.ihs.com/images/VipMasterIC/IC/ROHM/ROHMS04491/ROHMS04491-1.pdf?hkey=EF798316E3902B6ED9A73243A3159BB0 (https://4donline.ihs.com/images/VipMasterIC/IC/ROHM/ROHMS04491/ROHMS04491-1.pdf?hkey=EF798316E3902B6ED9A73243A3159BB0)
one gearbox unit I would like to use, but it only uses 1.5 volts.
if i just add resistance in series with the dc motor and the BA6218 H bridge.
so the BA6218 runs at 5 volts. but the dc motor only gets 1.5 volts.
currents are less then 100Mma. efficiency will be low , so will this work?
have not seen this particular problem in any H bridge circuit for dc motor control.
dc motors are to control mini jack screws in a DIY lens focus assembly.
BA6218 H bridge is to be used with TTL 5 volts logic & limit switches - Arduino control.
mechanically controlling zoom and a DIY lens focus assembly. is by rotary encoders
here is one I have one particular 1990s video-cam lens assembly I would like to use, as all the gears are already in a working assembly. in one unit , just add a new video image sensor to the back. as the bolt hole sizes are standard image sensor pcb mount. see image \/ , this unit came from a 3 volt dc video-cam assembly.
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Using a resistor will limit torque because the voltage will drop with load on the motor. That may or may not be a problem for this application.
A pair of 2.7 V Zeners in series (opposite polarity) instead of the resistor would greatly reduce the low torque problem.
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You're already going to lose 1.2-1.8V internally. That is, given a 5V supply, the most you can expect to see on the output is 3.8V. Look at spec for "Output Saturation Voltage" and note that the spec is for just 200 mA. If the current is higher, the VCEsat will be higher.
If you plan to use PWM, just make sure you never go to 100% on. In the case of the 1.5V motor, limit the PWM to 1.5 / (5.0-1.2) or 40%.
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There is a good chance it will operate well enough at a lower supply voltage than listed in the datasheet. The logic inputs will not care. Try it.