Boost converter schematics

[Halogrunt1234]

I am currently on a school project that a motor is powered by a 9v DC power supply. since the motor, which is supplied by the instructor and cannot be changed, has a maximum voltage of 12V, I want to make a DC-DC step up circuit that increases from 9V to 16V >=]

I will apprecciate any links or pictures that are supplied, and I can't use a transformer because the max weight is 2Lbs.

 

[Nigel Goodwin]

You need to provide many more details, to even see if it's possible - for example the type of battery used, and it's amp/hour rating, and the current requirements of the motor. Have you tried running the motor on 9V, to see how it performs?.

 

[cadstarsucks]

I am currently on a school project that a motor is powered by a 9v DC power supply. since the motor, which is supplied by the instructor and cannot be changed, has a maximum voltage of 12V, I want to make a DC-DC step up circuit that increases from 9V to 16V >=]

I will apprecciate any links or pictures that are supplied, and I can't use a transformer because the max weight is 2Lbs.

Actually you could use a transformer since size and weight go down as frequency goes up.

That being said, I have to assume you need a fairly big inductor, diode, and FET since you did not say how big the motor is. You need more the double the current the motor requires to go through the inductor. The actual size depends on operating frequency.

D.

 

[Papabravo]

The inductor in a boost converter to run a motor from will be the size and weight of a small transformer so I don't see that you've gained anything with that approach. What do you imagine that 16V will do for you that 9V will not? I'm just curious.

 

[bananasiong]

I'm not sure about this, isin't the current reduced if the voltage is boosted up?

 

[cadstarsucks]

The inductor in a boost converter to run a motor from will be the size and weight of a small transformer so I don't see that you've gained anything with that approach. What do you imagine that 16V will do for you that 9V will not? I'm just curious.

Actually one of these would most likely do the trick... They are on the average 10x20mm. At that size they could not weigh to much!

D.

 

[Papabravo]

One of the problems with switching regulators with small wimpy inductors is that they are not very stiff. This means that in the presence of a load transient, such as starting a motor, the voltage will sag noticeably before current can build up in the motor windings. This can be a disaster if there is a uP supply voltage that depends on the motor supply staying where it is supposed to be. An inductor with some ferite mass and some thicker wire than 30ga. magnet wire is generally required. In any case a 9V battery will be drained pretty quickly by a motor of any appreciable size.

 

[audioguru]

You want to smoke the motor?
You said its max voltage is 12V.
You want a supply voltage of 16V?

The voltage is increased 1/3rd above max. Then its current will also be increased 1/3rd above max. Then its power will be nearly doubled. The extra power makes smoke.

 

[cadstarsucks]

One of the problems with switching regulators with small wimpy inductors is that they are not very stiff. This means that in the presence of a load transient, such as starting a motor, the voltage will sag noticeably before current can build up in the motor windings. This can be a disaster if there is a uP supply voltage that depends on the motor supply staying where it is supposed to be. An inductor with some ferite mass and some thicker wire than 30ga. magnet wire is generally required. In any case a 9V battery will be drained pretty quickly by a motor of any appreciable size.

Actually that depends on the reaction time of the control loop. High frequency switchers can be designed to be very fast but that really does not matter since all you need to do is to isolate micro from it with a diode and capacitor.

D.

 

[Papabravo]

Actually that depends on the reaction time of the control loop. High frequency switchers can be designed to be very fast but that really does not matter since all you need to do is to isolate micro from it with a diode and capacitor.

D.

The control loop can do whatever it wants, but if the inductor is undersized and the load demands more current the voltage will sag.

 

[cadstarsucks]

The control loop can do whatever it wants, but if the inductor is undersized and the load demands more current the voltage will sag.

You raise the frequency and drop the inductor size. If you increase the load you have to decrease the inductor value and increase the current rating.

At 60Hz a 100VA transformer is huge. At 200KHz a 200W transformer can be the size of a 60Hz 2VA transformer. If you don't believe me go look it up.

D.

 

[infin]

why even step the voltage up just run it at max. depending on how your project is setup, you can easliy do it with timers and relays. Look at a LTC1872

 

[cadstarsucks]

I'm not sure about this, isin't the current reduced if the voltage is boosted up?

Yes... that just means you need to supply more current at the lower voltage to get the lower current at the higher voltage.

D.

 

[Halogrunt1234]

sorry for not providing good specs on the motor, the project itslef doesnt provide good specs. its about an inch in diameter, 12,150rpm, 6V-12V, and tiny. I cant find anything else on the motor. I am under the belief that increasing voltage may increase its revolution speed, and creating a small DC-DC boost will increase the voltage. I believe that the 9V power supply is stepped down from line power, if that helps any. my goal is to run as much power through this little motor as its tiny little coils can handle, without too much smoke..

I appreciate all the help you guys have given me already, and i will appreciate any other help you can give me. Happy valentines day too♥.

 

[Papabravo]

You raise the frequency and drop the inductor size. If you increase the load you have to decrease the inductor value and increase the current rating.

At 60Hz a 100VA transformer is huge. At 200KHz a 200W transformer can be the size of a 60Hz 2VA transformer. If you don't believe me go look it up.

D.

There is a limit to this process however. If you raise the frequency high enough inductors will become capacitors. Und tell me Herr Doktor how many SMPS haf you designed to run motors?

 

[cadstarsucks]

There is a limit to this process however. If you raise the frequency high enough inductors will become capacitors. Und tell me Herr Doktor how many SMPS haf you designed to run motors?

A few...the 3HP motor ran right off the rectified and filtered AC mains. Needless to say we were not expecting 3HP, that is just the motor that the customer had chosen.

Low frequency inductors do become capacitors...High frequency switchers have to use different inductors, low values and lower parasitic capacitance. Usually that means you can not use multiple layers right on top of each other. Real HF stuff is usually planar.

D.

 

[Papabravo]

A few...the 3HP motor ran right off the rectified and filtered AC mains. Needless to say we were not expecting 3HP, that is just the motor that the customer had chosen.

Low frequency inductors do become capacitors...High frequency switchers have to use different inductors, low values and lower parasitic capacitance. Usually that means you can not use multiple layers right on top of each other. Real HF stuff is usually planar.

D.

Well that is hardly a Switched Mode Power Supply (SMPS) now is it? RTDQ!

 

[cadstarsucks]

Well that is hardly a Switched Mode Power Supply (SMPS) now is it? RTDQ!

True...that was the PWM motor, the medical grade SMPS was to drive the displays on the equipment. Thanks to another engineer's paranoia about EMI, my 40W medical switcher design got downgraded to 10W. The planar ferrite was only 22x15x8mm and would handle 200W in a with a different drive circuit.

I put in an ST VIPER52, which would have supplied 40-45W with 5KV of isolation on that core, but the whiner talked the boss into telling me to knock it down from 200KHz to 50KHz. That should have been ok for 12V@1A but the primary ran to hot so we had to call it 12V@0.75A

At 200KHz I had a 2T secondary with 12T primary. At 50KHz I needed a 32T primary.

D.

 

[Hero999]

Some switchers run at frequencies of up to 3MHz, having said that I've had problems with lower frequency switchers being very noisy.

EMI is a real issue for switching regulators. I remember building a DCRCD and using a DC-DC converter module for to get +/-15V@50mA from 18-30V or 36V to 60V (depending on the model). When they tested it for EMI, they were prety supprised to discover emissions at 76MHz which is pretty high considering the switching frequency was only 300kHz. This wasn't my fault because, for a start no one gave me a specification for EMI and the DC-DC converter was an industrial standard off the shelf part, if I had know about this then I would've used a linear regulator power rail splitter for the 36V to 60V model and a charge pump converter for the 24V to 30V model.

 

[cadstarsucks]

Some switchers run at frequencies of up to 3MHz, having said that I've had problems with lower frequency switchers being very noisy.

EMI is a real issue for switching regulators. I remember building a DCRCD and using a DC-DC converter module for to get +/-15V@50mA from 18-30V or 36V to 60V (depending on the model). When they tested it for EMI, they were prety supprised to discover emissions at 76MHz which is pretty high considering the switching frequency was only 300kHz. This wasn't my fault because, for a start no one gave me a specification for EMI and the DC-DC converter was an industrial standard off the shelf part, if I had know about this then I would've used a linear regulator power rail splitter for the 36V to 60V model and a charge pump converter for the 24V to 30V model.

They can be. They really need to be properly layed out, bypassed, and snubbed. In addition they should use shielded or some other closed magnetic circuit inductors.

D.