Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Need to Mod this Circuit

Status
Not open for further replies.

biggy238

New Member
I need a way to modify this circuit so that the Duty Cycle can be changed with an input DC voltage of 19mV to 25mV.

The input will be from a K-Type thermocouple and %5 duty cycle will need to correlate to 19mV with 95% being had by 25mV in.

I found this online, and even if I can't make the input work, I can still use this as a manual controller. I just wanted to present it and find out if it can be done.

My skills are fairly limited. I can build this easily, which played a part in choosing it for my basis.

Thank you for any ideas.
 

Attachments

  • PWM Schematic.JPG
    PWM Schematic.JPG
    32.1 KB · Views: 225
Last edited:
You haven't mentioned what frequency you require.

A 555 timer isn't the way to do it.

Firstly you need to use an amplifier to boost the voltage to something useable, for example 1.9V to 2.5V.

A couple of comparators can do this.

You need a triangle wave generator generating 2.5V - 1.9V plus 10% which is 0.66V with (2.5+2.5)/2 = 3.15V of DC bias.

Use a comparator to compare the signal to the triangle wave.

The circuit attached will work but it needs a good rail to rail op-amp which needs to be fast if you want a reasonably high frequency. It's possible to use a comparator but you need 1k pull up resistors on the output and a compensation capacitor on the amplifier.

I'd recommend using a comparator like the LM393 for the oscillator and comparator and an op-amp like the LM358 for the amplifier. Of course you could use an LM399 for both but it won't make a very good amplifier.
 

Attachments

  • Thermocouple PWM.GIF
    Thermocouple PWM.GIF
    4 KB · Views: 328
Last edited:
Wow

Well... it will take me a while to digest. My skills are novice at best.

The frequency on the other circuit was 100hz. Supposedly a good frequency for starting dc motors.

Is that an LM393 or an LM339?


I liked the simplicity of the other circuit.

I should also mention this will be driving a 12v, 7 amp Dc pump motor in a vehicle.

Edit: I looked at the schematic, unless you can show me what components and how to wire them, I don't have the knowledge of available small components to select what is necessary and how to apply them. I can research all that you've given me and learn how they operate... just more time than i had intended to invest.

I do appreciate your help greatly
 
Last edited:
Question

This symbol? Also, Vin would be input from the thermocouple, The other lead of the thermocouple would need to be attatched to V- on the control?

I'm also curious about the 5v and 0V above and below what I think is a comparator?

Go easy on me... I'm trying :eek:)
 

Attachments

  • PWM Question.GIF
    PWM Question.GIF
    2.6 KB · Views: 186
Last edited:
The circuit posted needs to be run from a stable 5V power supply in order to ensure that 19mV to 25mV corresponds to roughly 5% to 95% duty cycle.

The symbol you highlighted is the 0V referance, most of the time it means the negative terminal of the battery but it could mean the positive terminal.

Perhaps the forum software won't let you post your replies because they contain links which nubes are banned from posting as an anti-spam measure.
 
I'm having trouble out of the forum. It won't let me see the new posts until after I reply with something. I've never had trouble before.

No way around the 5V supply? The variable nature of automobile voltage might be a problem then..
 
Last edited:
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top