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The Projects Forum Working on an electronics project and would like some suggestions, help or critiques? If you would like to comment or assist others with their projects, this is the place to do it.

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Old 01-24-2011, 04:37 PM
alexilla alexilla is offline
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Default Variable Voltage Controller

I need some suggestions on creating a power supply that is capable of varying voltage from near zero to 120vac at about 3A and is capable of accepting a milliamp signal from a controller IC. I need a very quick response time for partial load to full load voltage. This is for varying the voltage on an electrical resistance heater coil that has to maintain a set airflow temperature through a tube. As the airflow varies from none to high flow, the coil voltage has to continuously adjust to maintain the temperature set point and to avoid damaging the coil when the airflow is minimal. ie... low airflow, low coil voltage; high airflow, high coil voltage. Any help would be greatly appreciated. Thank you.
Alex
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Old 01-24-2011, 05:27 PM
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beenthere beenthere is offline
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The resistance heater will operate on DC as well as AC, and with DC you can use a form of PWM to control the heat. Otherwise, you can use a TRIAC to control current.

That milliamp level signal will almost certainly need amplification. Can you post the schematic?
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Old 01-24-2011, 06:58 PM
wayneh wayneh is offline
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Quote:
Originally Posted by alexilla View Post
...accepting a milliamp signal ...
That's a unit of measure, not an amount. Do you mean in the hundreds of mA (probably usable without amplification), or single digits (needs amplification)?

I agree that PWM control of a MOSFET "switch" would be a good option here to control a DC heater, with the PWM being controlled by the controller voltage.

The old-school approach is a variac under thermostatic control.
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