A friend of mine who runs an electronic shop wants to install an old cd-rom to be used as a stand alone cd-player in his truck. His problem was to find a suitable power supply for this purpose. A cd-rom uses 2 power supplies, 5 Volts which is used in its logic circuit and 12 Volts for its servos. With these parameters I needed to make a dual regulator that produces 5 Volts and 12 Volts output in one input voltage. Trucks usually uses 2 lead-acid batteries so that will be around 24 Volts.
The cd-rom uses around 1.5 Amperes of current for the 5 Volts and 2 Amperes for the 12 Volts. Considering all the needed parameters, using two 7805 regulators for the 5 Volt supply will suffice however we need higher current for the 12 Volts. Using an "old-school" technique, we will be utilizing one 7812 regulator but putting an additional transistor to beef up its current capacity up to 5 Amps. I know its an overkill but better safe than sorry.
The cd-rom uses around 1.5 Amperes of current for the 5 Volts and 2 Amperes for the 12 Volts. Considering all the needed parameters, using two 7805 regulators for the 5 Volt supply will suffice however we need higher current for the 12 Volts. Using an "old-school" technique, we will be utilizing one 7812 regulator but putting an additional transistor to beef up its current capacity up to 5 Amps. I know its an overkill but better safe than sorry.
Remove these ads by
Signing UpStep 1: PCB and Assembly
Component List:
IC1 and IC2 - 7805 series regulator
IC3 - 7812 series regulator
Q1 - MJ2955 NPN Transistor
R1 - 1 ohm / .5 watt resistor
R2 - 10 ohms / .5 watt resistor
C1 and C2 - 4700 uF / 16 Volts electrolytic capacitor
Heatsink
Using the diagram, make the PCB, you can see it in my previous blog. Put sufficient heatsink for all the IC's to maintain a normal heat.My PCB design for the diagram, this conforms with my plan to put all the regulators and transistor in one heatsink.I had bolted all heat generating components using only one heatsink, as you can see, the center is the MJ2955 transistor, two 7805's on the right side, and the 7812 on the left.Soldered all the components including the MOLEX connector for the CD-ROM and this project is ready for testing.
IC1 and IC2 - 7805 series regulator
IC3 - 7812 series regulator
Q1 - MJ2955 NPN Transistor
R1 - 1 ohm / .5 watt resistor
R2 - 10 ohms / .5 watt resistor
C1 and C2 - 4700 uF / 16 Volts electrolytic capacitor
Heatsink
Using the diagram, make the PCB, you can see it in my previous blog. Put sufficient heatsink for all the IC's to maintain a normal heat.My PCB design for the diagram, this conforms with my plan to put all the regulators and transistor in one heatsink.I had bolted all heat generating components using only one heatsink, as you can see, the center is the MJ2955 transistor, two 7805's on the right side, and the 7812 on the left.Soldered all the components including the MOLEX connector for the CD-ROM and this project is ready for testing.
Visit Our Store »
Go Pro Today »
A circuit to do what you want (a simple voltage regulator) is usually contained in any datasheet for a given device. You only need at most two capacitors to complete the circuit. Do a quick search for 78T05 data sheet.
A better more stable switching supply would be made by using an LM2576 switching regulator which will supply 3A but at higher efficiency and reduced heatsink size (or even no heatsink in many cases). They also have better current limiting and thermal shutdown features than linear regulators. The component count is a just a few more with a catch-diode, choke and two capacitors being needed to complete the circuit.
You're welcome.
You mean that if I take a car battery (12 volt, capable of delivering 1000 amps) and a headlight bulb (12 volt, 80 watt = 6.6 Amps) and connect one wire from the battery to the lamp, one wire between me and the bulb and finally a wire from me back to the battery - thus making a circuit between the bulb the battery and me - I would die? Sure....
There's not enough voltage to force any current thru your body since the body has a relatively high resistance. When you have learned about Ohms law you'll understand this.
The Electrical Safety Standards governmental agencies in most countries consider all voltages below 50 volts as harmless/safe due to the simple reason that there's normally no way of getting any harmful current through the body at those voltages.
http://users.tpg.com.au/pschamb/mpc.html
I would recommend using a dual switching power supply, such as an ISL6227. See: ISL6227 Datasheet. The switching power supply accepts an input voltage of up to 25V. All you need to do is provide the top and bottom FETs, output caps and biasing ciruitry.... I can do a write up and an example switching circuit if you'd like. This is a relatively simple task, though designing your first switching circuit might be a doozie.
The advantage to using switching power supplies is that you won't be dissipating an excess amount of power in the form of heat (as in the case with linear regulators). The ISL6227 has a dual supply output and can be set for the voltage that you are targeting for.