# VOLTAGE DIVIDER

#### noblevirk

Joined Oct 24, 2004
1
HI
FRIENDS CAN ANY ONE GUIDE ME TO DESIGN A VOLTAGE DIVIDER WHICH CAN CONVERTE 24V TO 9V OUTPUT. I DONOT A KNOW ANY OF THE RESISTOR VALUE .BUT I HAVE TO KEEP THE COST MININMUM.(HINT: LOW RESISTENCE TOLERENCE, AND HIGH POWER RATING DRIVE THE RESISTOR COSTS UP.!)

#### mozikluv

Joined Jan 22, 2004
1,437
hi,

one of your best approach is using an IC regulator like the LM7809 tied to a heatsink having to drop about 15v and capable of handling 1.5A.

a voltage divider circuit will also do using this formula:

Vo = ( Vin x R2 ) / R1 + R2 P = I x R

#### Perion

Joined Oct 12, 2004
43
Hi,

First of all - just check out http://www.tpub.com/neets/book1/chapter3/1-35.htm for a good example of the calculation you are looking for. It's real simple (if you have a constant load).

BTW: Power = I x I x R
That is, current (amps) squared times resistance (ohms)

Remember:
You need to know in advance what your load device's current will be at 9 volts in order to calculate proper values for R1 and R2 that will result in 9 volts to the load AFTER connecting it across the divider resistor. You also need to know how much the load current will vary during its normal operation and how much your 9 volt supply is allowed vary.

To the degree that your load current will vary, the stablility of your 9 volts supply will decrease. This effect can be minimized to a degree by a suitable combination of R1 and R2 but you won't be able to eliminate it and it will complicate your calculations. For example, you will have to decide, based on your load device's voltage requirements, whether to use its normal max or min operating current, in choosing R1 and R2. Or, maybe using some estimated average current would be a better choice. You may have to play with several scenarios to see which works best for your requirements. If the load current varies to the point that you can't find suitable R1 and R2 values that will keep the 9 volts as stable as it needs to be then you have no choice but to use some form of voltage regulation instead of just a divider.

Perion