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Load control using PWM and temperature sensor

udhaya

Feb 26, 2016
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Hai friends,

I want some clarification or ideas regarding load control.

Am using LM35 temperature sensor and depends upon the output of LM35 need to control the 24v load,my requirement is depends on the temperature on and off the load,when temperature below 45 degree on the load and above 75 degree off the load, i want using PWM but it operates on 5v only how to control the load using pwm please help me on this, if possible let me know the circuit diagram.

Thanks in advance .
 

udhaya

Feb 26, 2016
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Thanks Harald kapp,

For control the load your suggestion is nice and i want the temperature dependent circuit how to set minimum temperature set point and maximum set point(using comparator or integrator)please send me the circuit diagram.
 

Harald Kapp

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You'll need a voltage controlled PWM generator. Your favorite search engine will turn up many circuits on the internet. You may have to match the output voltage of the sensor to the input voltage range of the PWM generator using some kind of amplification or attenuation.
 

udhaya

Feb 26, 2016
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am searched in google but did not get the circuit how to set minimum and maximum value of temperature am beginner, you have a lot of experience in electronics circuit could you please help me on this.
 

udhaya

Feb 26, 2016
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Hello Harald kapp,

I have used 2n2222a transistor to drive the 24v load but initially it works but once switch off and then switch on the supply means that transistor not work at all, can you please refer any other transistor or any options waiting for your valuable comments.
 

Harald Kapp

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Show us a circuit diagram with driver circuit, load, voltages etc.
 

Harald Kapp

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This is incomplete: where is the power transistor (driver circuit)? Where is the load?
 

udhaya

Feb 26, 2016
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Here by attached the circuit diagram
 

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Harald Kapp

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I can see no reason why this circuit should not work.
What do you mean by
once switch off and then switch on the supply means transistor not work at all
- Does the 555 operate correctly?
- Is there a base current into the 2N2222 in this case?
- Does the load still work when you connect it directly to 24V (by the way: what is your load? A motor, a lamp, LEDs?)
 

udhaya

Feb 26, 2016
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I mean that as per the circuit diagram 2N2222 works fine at one time only after that its not worked.
555 time worked properly so that the base of 2N2222 also triggered as 12v dc by 555 pwm, am checked with multimeter.
load am used as lamp normally it works when connect direct 24v.
 

udhaya

Feb 26, 2016
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Is there any possible to use other transistor, instead of 2N2222 ?
 

Harald Kapp

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Any NPN with suitable voltage and current rating.

Note that if you use an incandescent lamp (tungsten, halogen) the inrush current when the lamp is cold is many times (>10*) higher than the operating current when the lamp is cold. In your case this amounts to over 5A!.
The transistor needs to be abble to withstand that current.
 

udhaya

Feb 26, 2016
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In above circuit light is replace with heater(low voltage), depend on the heat need to change the pwm output, like if we set upper limit is 65degree and lower limit is 40degree output is less than 40 degree means switch on the load,above 65 degree means switch off the load please help me on this you have lot of experience in electronics am waiting for your valuable comments if any circuit there please share.
 

Harald Kapp

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if any circuit there please share.
The circuit is o.k. You need to select the components (transistor) to match the power requirements of the load. A heater also has a much higher inrush current (similar to an incandescant lamp) tan the rated operating current.

It is not very comon to operate a heater using PWM. A heater typically has a rather slow response to changes in the power supplied to it. In electrical terms it is a "low pass" with a very low corner frequency. Therefore instead of a PWM signal a heater is usually controlled by a two-level controller (also known as on-off controller or bang-bang controller):
  • tempertaure too high -> turn heater off
  • temperature too low -> turn heater on
You can then use e.g. a relay to manage the high power requirements of the heater.
 

udhaya

Feb 26, 2016
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Hai Haralad,

Using IRF 740B N channel MOSFET the functions is working,
The problem is am giving 12 v in to the drain, when trigger the pwm input to the gate the drain gives voltage 12v (using multimeter able to see the voltage) but cannot turn on the even LED,what s the problem in this case,can you give some suggestion.
 

Harald Kapp

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am giving 12 v in to the drain, when trigger the pwm input to the gate the drain gives voltage 12v
Sorry, I do not understand this. When the drain is connected to 12V, it will be at 12V regardless of the gate voltage.

Again: show a schematic circuit diagram.
 

udhaya

Feb 26, 2016
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Schematic diagram is same as am sent earlier(load 24v am changed into 12v) instead of transistor replaced with IRF 740B N channel MOSFET load is 12V that is connected with load(drain),Gate is connected with PWM pulse,Sourse is connected with ground.
 

Alec_t

Jul 7, 2015
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If Vcc=5V the 555 may be struggling to output 4V. With Vgs=4V that particular FET won't be turned on fully. You need either (a) a 'logic-level' rated FET or (b) Vcc increased to, say, 12V.
 
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