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Author Topic: do i need LM7812 as regulator FOR 12 VOLT POWER SUPPLY?  (Read 3913 times)

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Offline louisTopic starter

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do i need LM7812 as regulator FOR 12 VOLT POWER SUPPLY?
« on: January 09, 2009, 11:53:17 PM »
hi Sr

MY CIRCUIT IS  (http://www.uoguelph.ca/~antoon/circ/relay61.html)

require 12 volt dc. if i connect it to power supply (12 volt) and add variable resistor so it will be exactly 12 volt .

it is ok ? or i need add LM7812 as regulator

                                                            thank you

Offline hgordon

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Re: do i need LM7812 as regulator FOR 12 VOLT POWER SUPPLY?
« Reply #1 on: January 10, 2009, 12:58:45 AM »
Dropout voltage for an LM78xx regulator is around 2V, meaning that you need at least a 14V supply to get 12V from an LM7812.  Your circuit is probably fine without a regulator.
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Offline want2learn

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Re: do i need LM7812 as regulator FOR 12 VOLT POWER SUPPLY?
« Reply #2 on: January 10, 2009, 01:20:37 AM »
Don't use a regulator or variable resistor, your circuit is fine without it. A variable resistor to regulate supply to a whole circuit in general is a bad idea and wastes battery power.

Also as the pack voltage changes when discharging the voltage supply to your board will change, you would need to manually adjust the resistor frequently
« Last Edit: January 10, 2009, 05:03:08 AM by want2learn »
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Offline louisTopic starter

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Re: do i need LM7812 as regulator FOR 12 VOLT POWER SUPPLY?
« Reply #3 on: January 10, 2009, 10:59:20 PM »
but if i connect directly to my circuit i afraid the circuit will burn  :'( since i measure the power supply only it said 17 volt or it is going to be stable to 12 volt once i connect to my circuit above

                                                      thank you for your help

Offline Soeren

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Re: do i need LM7812 as regulator FOR 12 VOLT POWER SUPPLY?
« Reply #4 on: January 10, 2009, 11:30:08 PM »
Hi,

When loaded, the voltage will drop some (not that the circuit in question draws all that much current when the relay is not energized).

The IC CMOS4001 can handle up to 18V (absolute maximum, not for regular use though).

A 12V relay won't like 17V for a very long time, but if you have the relay, mount the diode (D3) directly on the relay terminals  and use the relay for a load while you measure the voltage - a few seconds won't kill it.
Or, you could load the supply with a 12V lamp of an appropriate wattage and take the measure.

Post the measurement here for added help.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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