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Non Inverting, Doubler or DC to DC

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Full Member level 6
Aug 1, 2009
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I am using a DAC with 5 V reference, so the output will vary from 0-5v

I need to drive a motor which needs 0-10v. I am still not sure about how much current the motor would need. Will know that by tomorrow but the feedback from the customers tech person is that it will be below 1.5amps.

Now the concern is what kind of circuit should i use, a non-inverting amplifier with gain of 2, a voltage doubler or a DC-DC boost converter.

DC-DC converter might not be the one that i should use, reason being most converters have min voltage requirement and motor requires voltage starting from 0v (rather 0.01 v min)

Just the non-inverting amplifier with a gain of 2, not sure, as the load (motor) can have some feedback.

Voltage doubler, i am not sure how much i can rely on this.

Even after the entire thing is designed, the output voltage to change with load. I generally find that without load the output is accurate but with load there are variations of 10%. I know it depends of load resistance. Can anyone shed some light on this and how i can work on these issues.

I will give you more details on the type of motor and its characteristics by tomorrow.


You can use a voltage follower to feed the motor. Or you can use a simple NPN transistor to boost the current to the motor so you won't fry the opamp ic.

You will need some sort of power amplifier running of a power supply greater then 10V (12V?). You will also need an op-amp to precede it to set the overall gain to 2 and to use it to gain some flexibility in negative feedback and linearising circuitry.
Do you hope that the motor's speed will accurately reflect the digital number at the DAC input?. If you do then you also need some form of speed transducer on the motors shaft coupled back to the op-amp. At low voltage = low speed the motor will be reluctant to start due to sticktion. Also the motors speed will vary with the mechanical load.

Also, be aware that:
- Motors need quite much current/power. If you plan using a voltage doubler made of diodes and capacitors, it will likely not work
- A power amplifier (linear amplifier) will be very little efficient, and thus wasting power a lot.
- The most efficient - but also most complex - circuitry would be based on a switchmode converter/controller. Or simply a pulse-width controlled on/off switch giving the required AVERAGE output voltage as a result of the on-time control
- When controlling reactive loads (inductance of the motor's windings and generated "back-emf"), one has to design in a way that the driver survives back-fed energy, spikes, and glitches which are generated.
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I dont think we need to worry for backemf, spikes etc, since the voltage from the microcontroller board goes to another board which is designed for motor control. This board requires 0-10v variation so that 0-100% speed of the motor can be controlled. I guess it is some sort of motor controller unit which inturn is being controlled by the DAC voltage.

Now the customers, technical person says that its some mA of current that is required. I am not sure about the exact value.

Need to check the datasheet of the motor controller, which again unfortunately is not available.

He told me some 25mA should be sufficient.

Sounds weird to do the project without proper specs, but since the person involved has changed the job and new person there has no much idea about the specs and requirement. And over that the deadline is fast approaching.

Anyways, at this point of time, i think a amplifier should be a good enough choice. I guess a non-inverting amplifier with gain of 2 followed by a voltage follower should be fine.

Any suggestions on this ??

since the voltage from the microcontroller board goes to another board which is designed for motor control.
some mA of current that is required
Sounds considerably different from 1.5 A stated in your first post. In this case, a single OP non-inverting amplifier would be just fine.

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