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DC (0-10V) input signal and isolation

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andyyau

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I need circuit for isolating a DC input signal (0-10V) which will be used to control the speed of motor. I know this can be done by a transformer, but I do not have the circuit?

Can anyone help?
 

Mr.Cool

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hi there;

it is true that you can use a transformer for electrical isolation. this is quite common technique for all sorts of applications.

simply place the transformer of 1:1 ratio between your PWM signal and your switching device.

however, there is a better solution. use Opto-coupler for isolation between each signal line. these components are FAR more efficient than transformers, cost much less, are smaller and easier to implement in projects instead of big bulky transformer(s). oh, and they cost a fraction of the cost of a transformer. :)
the negative side is that your circuit will require low power supply on the on the other side of isolation where as a trransforer does not.

in the end.. if you're original design was done properly you will have no need for isolation at all!

Mr.Cool
 

Gavran

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andyyau said:
I need circuit for isolating a DC input signal (0-10V) which will be used to control the speed of motor. I know this can be done by a transformer, but I do not have the circuit?

Can anyone help?
See HCNR200 (Hewlett Packard). Data sheet and application notes available on the web.
 

venz

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Hi,

Try the Infineon IL300 optocoupler.
There is a very usefull example in the datasheet.
I've used it to set the speed of a motor controller.
The circuit that generated the set signal had to be isolated from the motor controller for safety concerns.

The application can be a little difficult to understand at first, so just try it out on a breadboard first to figure out what values for the resistors and the OpAmps you need.

good luck.

Venz
 

7rots51

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Hi

This discrete methods are not good for new design ,try to use a component that do it ,there are many manufacturer that build isola*tion products,

see burrbr*own iso*lation products from www.t*i.com

check for IS*O122 or similar ICs they are suitable for you,see also www.ana*log.com isolation products .the products are very accurate and compact in size and reliable.
see also isol*oop by search in go*ogle or yah*oo.
 

Stark

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analog optocoupler

You can use (HP) now Agilent, HCPL788 .See website for datasheet an AN
Stark
 

goodboy_pl

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The solution is highly dependent on your control signal specifications:
1.if it is digital(for example output of cmos gates) use opto coupler.
2.if it is analog ,use infenion IL300.
Note:transformer is suitable for isolation ONLY for those signal that has not dc level,i.e. for control siganl MUST NOT be used!
for application like this one in which control signals are not very fast(i.e a few micro sec rise/fall time) low speed and low cost opto couplers are sufficient.(i.e. those with transistor/darlington output)
for higher speed (nano sec response) use schmitt trigger opto coupler which are expensive.
another note: usually special purpose isolators is not economic for conventional applications.
 

andyyau

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Many thanks for all your reply.

However, can anyone tell me the theory to use the transformer using PWM.

I am using an analog input signal of 0 to 10V DC. In what way the PWM signal can convert this analog voltage by the transformer?

Thanks!
 

MrEd

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Burr Brown has linear optocouplers for what you need, you can also get free samples straight from their website.

Cheers
MrEd
 

MrEd

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Sorry, I don't think they actually are optocouplers, I think it is an isolated OpAmp. Look for ISO124P.

Cheers
MrEd
 

7rots51

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The three most common types of isolation are:

• Magnetic Coupling. In this form of isolation, a transformer creates a barrier. The mechanical properties of the transformer dictate the amount of isolation, but in general, this method provides excellent protection against hazardous voltages, particularly transient voltages.

• Capacitive Coupling. Although this method requires the least amount of space to implement, capacitive coupling is not as effective at protecting against transient voltages as the other types of isolation.

• Optical Coupling. This method provides a physical barrier by creating a space inside the measurement device that hazardous voltages cannot cross and by using light to send information across the gap. Optical coupling is commonly used to provide isolation in digital devices because the on/off signal can easily be turned into light by optocouplers. Similar to magnetic coupling, optical coupling provides excellent protection against transient voltages.

In most cases, you’ll purchase a product that uses one of these methods to provide isolation. The technical details of how these methods are implemented at the design level are not as much of a concern as understanding how to interpret isolation specifications and determining if a product is adequate for your application.
 

marie65

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andyyau said:
Many thanks for all your reply.

However, can anyone tell me the theory to use the transformer using PWM.

I am using an analog input signal of 0 to 10V DC. In what way the PWM signal can convert this analog voltage by the transformer?

Thanks!
You can use a "voltage to frequency" IC (like AD654 or similar), a transformer and a "frequency to voltage" IC at the other side. Anyway I think that's more simple to use an isolation IC like ISO124 from Burr Brown (TI now, if I'm not wrong)
 

ahmedmedowahdan

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if i have only one voltage source what is the suitable method for isolation
 

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