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Voltage Divider Circuit problem!!


Guest bhemp1
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I have built a circuit that includes PIC and Chipcorder (5V), Stepper Motor Driver and audio amp(12V). I am trying to power all of them with an AC to DC power supply. When I hook the power supply to the circuit board the 12V IC's are fine, but the PIC and Chipcorder only get 1.4 volts when they are supposed to get 5V. WHen I hook all power up individually it works fine. I checked all grounds and powers. I endlessly checked my soldering and Orcad schematics. Resistance when measuring between + and - is in the range of 10 Mega ohms to 35 Mega ohms depending on where measurement is taken. Does anyone have any ideas on where to go from here. I am using voltage divider to supply both voltages. The calculations come out ok for the voltages, but somehwere I am loosing voltage. Even at 10 - 35 Mega ohms the load resistance I should have close to 5V. Thanks.

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I did try that and kept getting heat issues, but I will probably do that. YT2095 do you have any idea what the problem could be on the voltage divider? It has become a challenge to figure out why a simple voltage divider has become such a huge problem. I am using the voltage divider in another board in the same system with a PIC, stepper IC and some logic. This circuit works just fine. I am annoyed that I cannot figure it out. THanks.

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I'm not sure why your voltage divider isn't working. Could it be that the load is dynamic? In other words it draws different amounts of current depending on what is operating. If this is the case it's impossible to use a simple voltage divider.

 

You'll really do yourself some favors if you can seperate the control logic voltage supply from the dc stepper motor supply. All kinds of problematic noise can come back from that motor and eat-up your chips or make them do weird things. You'll probably hear the motor operating through you audio-amp as well. Best use some regulators to seperate them.

 

When you say heat, I assume your saying your regulator is getting warmer that you would like. One way to fix this would be to put a small valued resistor in series with your regulator. It won't reduce the total amount of heat made, but it will share it between the resistor and regulator. Don't forget to use a correctly rated resistor (wattage-wise) to disapate that heat.

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mayby if you have enough current in your source!

 

You could try a Current Deviding configuration.

 

that way you will have maxmimum volatage delivered to both but current will devide.

 

With in each parallel leg of you Current Devider you may need to step down voltage a bit.

 

I recomend trying to identify the load resistance of both object you are trying to connect.

 

Load resistance also playes a big factor in you voltage devision.

 

Total resistance = input resistance + load 1 + load 1 ... knowing this values will help you better design your voltage devider.

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I did try that and kept getting heat issues, but I will probably do that. YT2095 do you have any idea what the problem could be on the voltage divider? It has become a challenge to figure out why a simple voltage divider has become such a huge problem. I am using the voltage divider in another board in the same system with a PIC, stepper IC and some logic. This circuit works just fine. I am annoyed that I cannot figure it out. THanks.

 

I'm not sure it is possible to supply IC's with differing voltage requirements with the same power supply unless its regulated. I remember having a similar when I was designing some measurement circuitry. Instead of getting proper regulators, I just bogded up a couple of potential dividers. At one point I tried Zener diodes but then a couple of components started to heat up.

 

Unfortuantely I can't find any backing for this, and why lower supply IC's, suffer when higher supply IC's are added in. I can only guess that the sinking on the larger IC's, is taking current away from the perceived high resistance of the other network.

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Thanks everyone for the input. I used the lm7805 suggested earlier and it worked like a dream. Although I did try a different regulator a couple weeks ago, but with the same voltage issues and some heat problems. In the future I will always use the LM7805. Now I can start testing the PIC program. Yeah!!!

 

Thanks

bhemp1

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