dc-dc converter

[erkanyigiter]

how can i convert 12V DC input to 24V DC output. it also must deliver up to 5A. i have searched but not found an IC. is there anybody who can help me?

[dyarker]

Excuse me?!?! Is this 24V for the same project that's in 2 other threads (discussions)?<p>That means you want to take the car's 12V, pump it to 24V, for the purpose of charging the car's 12V at a constant current?????????????????<p>Are Ron and windmill beating each other up in the other thread for perpetual motion machine ? <p>[ October 12, 2004: Message edited by: Dale Y ]</p>

[erkanyigiter]

the real project is that:
i have a power supply who supplies 24V from 220VAC and i want to charge my 12V battery with it. but also i want to use the charger in my car, so if i am at car and so if i can't use my power supply, i want to charge my battery with "12V car battery".
i mean, it will be compatible with 220 VAC and also 12V DC. is it clear?<p>[ October 12, 2004: Message edited by: yigiter ]</p>

[dyarker]

My opinion is that 24V and all extra circuitry in thread "Current source" is over-kill. Remember thread SLA battery charger? The car recharges it's own battery just fine on 13.5V to 14.8V. You said you're going to use a microcontroller. So monitor current with a 0.1 Ohm resistor in series, one op amp to translate the voltage across that resistor to 0V to 5V, to feed an ADC on the microcontroller. Monitor the battery voltage through a voltage divider to another ADC. A DAC on the microcontroller drives a couple transistors that regulates the current to the battery.<p>---------------------------------------------<p>If you really want to step-up 12VDC to 24VDC, you're going to need some kind of switching supply. The manufactured DC to DC converters I found are step down only, plus expensive. Building is possible if you can rewind a toriod transformer from an old PC power supply.<p>Another way to go is get a 12VDC to 220VAC inverter to power your existing 24V supply from the car's 12V. Jameco sells a 150W 120VAC inverter for $30. You should be able to find a 220VAC model for about 50MTL.<p>Cheers,

[erkanyigiter]

i have found a datasheet about National's LM2588. it is a 5A flyback converter and you can use it as a boost regulator. it has a circuit drawing for 12V to 24V boost regulator (Figure 38)but it is for 1A current. maybe you can help me to increase current value for 5A. it has not got any information about current adjustment.

[dyarker]

Got the spec sheet, I'll take a look.

[dyarker]

In figure 38 the 5A max output of the IC is used during "on-time" to store energy in the inductor. The IC by itself can't output more the 1A average at 24V.<p>To get 5A:<p>Replace 33uH inductor with 6.6uH, 7A to 10A, I think. The inductor must 5 times lower value so 5 times more current can flow during the same on-time.<p>Connect emitter of 30A PNP transistor to point between inductor and schottky(sp?) diode where fig 38 shows IC pin 5 connected.<p>Connect collector of PNP to ground.<p>Base of PNP through resistor to pin 5. Value of resistor depends on current gain of the transistor.<p>Change schottky(sp?) diode to 25A to 30A part.<p>Increase Cout1 to 5000uF low ESR.<p>-----------------------------------------
Getting it to work will be hard. Switching 25A at 100KHz is not a job for beginners. Using just any old length of wire to connect to the big transistor on it's heatsink can cause voltage spikes in bad places. Destroying the IC and power transistor. A properly layed out printed circuit will work. But, most circuit board blanks don't have thick enough copper to carry 25A on reasonable width traces.<p>That's why I suggested buying a 12VDC to 220VAC inverter.
----------------------------------<p>Anyway, I thought the battery you want to charge needed less than 1A?<p>C U L -