Common group problem and seperate supply

[vick5821]

Hey guys, recently I did one project where all the GND are connected together. Btw, this cause some problem to us. So I would like to ask if there is anyway to supply the voltage independantly from one input ? Using DC adapter, then step down to 12V and 6V using 7812 and 7806. Any suggestion ? You can view our circuit in the attachment below

Thank you

Attachement :

 

[vick5821]

I want the 9V cirrcuit to be an independant source to power up another circuit. Is it possible ?


Thank you

 

[TedA]

vick5821,

Here are some thoughts and questions for you.

What sort of problems have you experienced?

How many of these things are you making?

How much current does your fan draw? At 12V? At 9V?

Must the fan have as much as 12V for the higher speed; would 10V or so be enough?

Is there some sort of surge as the fan starts? What is the peak current as the fan starts on 12V?

What is the source of raw DC to the power jack?

Is the raw DC supply at the Power Jack reliably above 15 to 16V?

Is there ripple on the raw DC supply? How much?

Was there a reason to use relays to switch the fan?

Do you care if the relays chatter and buzz when the temperature is close to switching them on or off?

What sort of external 9V load do you want to power?

How much current will your external 9V load draw?

Does your external 9V load have some independent connection to ground?

Do you have a datasheet for the 7812? You need to look at parameters like "Line Regulation" and "Dropout Voltage".

Answering these questions may help you solve your problems yourself. Posting the answers will help other forum members to help you with better suggestions.

Ted

 

[Rleo6965]

I think you have to modify your 2 relay circuit. There's a possibility that both relay will turn on and +12V and +9V will be shorted together.

How about using 1 SPDT relay. Place the fan on Com terminal and +12V and +9V on NC and NO terminal.

Another option. This will solve your +9V independent source. Use LM317 variable regulator and make a circuit that will vary DC output from +12V into +9V. You can place shunt +12V zener to supply your comparator ic. and series resistor of zener will be connected to LM317 Vin. No need for
relay.

BTW congratulation. Your group was improving.

 

[vick5821]

How about using 1 SPDT relay. Place the fan on Com terminal and +12V and +9V on NC and NO terminal.

Your this idea is good.But how about when the comparator output is 0 ? Initally I want the fan to be off. When sense a lower temp, the DC fan will on will lower speed and when sense a higher temperature, the DC fan will switch on with higher speed.Ie 12V power up the fan.

Is it possible to do this ? I have to finalised my ccircuit soon. Hoope can help.

Thank you