Need help - Voltage to Frequency converter

[bigjimcat]

I'm somewhat new to electronics and I need a device that will read either 0 - 5 volts and/or 5 - 0 volts, then convert it to PWM to control a motor's speed between 0 - 100% capacity. I also need to be able to adjust that power curve percentage. Can someone help me with this or is there someone who can design this cheaply and fast?

Thanks...i really need the help on this.

 

[Ubergeek63]

the short answer is that it can not be done... brushed motors get really flaky below 5%

the long answer is you need a full control loop with current as well as speed feedback.

what kind of motor? the easiest way is a switcher chip and a current sense amplifier.

negative slope on the control voltage, the motor voltage, and a negative slope on the current sense, all to a 2.5V feedback pin.

dan

 

[bigjimcat]

It will be connected to a brushless controller for a DC motor.

 

[Ubergeek63]

then you want a motor controller not a "voltage to frequency". a big one? most small ones can be driven by a simple ic controller. bigger ones need six BIG FETs and a lot of drive circuitry.

 

[Grossel]

then you want a motor controller not a "voltage to frequency". a big one? most small ones can be driven by a simple ic controller. bigger ones need six BIG FETs and a lot of drive circuitry.

IGBT transistors is the choice today I have heard.

 

[Hero999]

IBGTs are only good at high voltages >400V

For lower voltages MOSFETs are better.

 

[Ubergeek63]

IGBT transistors is the choice today I have heard.

depends on the voltage and frequency requirements and again, it was not specified.

IGBTs are good at high voltage high current apps at relatively low frequencies (the best of them can only hard switch between 100 and 200KHz).

We are currently switching our 110VAC DC motor boards to FETs. While it was once thought that IGBTs would be a panacea, they keep playing leap frog with the FET developement. The current leaders at up to 300V are FETs. Of course we are looking at everything, with qty price being a major player. There are better parts, but not under $5 and this FET is only $2.

Dan