fan assisted 5v switching regulator

[takao21203]

This is the latest revision, using a 7805 to generate 7v supply for the fan (adjustable),
and the LM2576 is mounted on a cooling fan grid.

12 volts is from small electronic transformer.

I have not used this technology before, only recently ordered some cooling fans,
originally for POWER LEDs.

It's important to keep the wires very short, and the coil must match, or voltage will drop down,
if current is increased. The coil I use here is rated for high currents. Originally it had pins for PCB,
I removed them

This chip has output rating of 3 Amps.

[ABSF]

This is the latest revision, using a 7805 to generate 7v supply for the fan (adjustable),
and the LM2576 is mounted on a cooling fan grid.

12 volts is from small electronic transformer.

I have not used this technology before, only recently ordered some cooling fans,
originally for POWER LEDs.

It's important to keep the wires very short, and the coil must match, or voltage will drop down,
if current is increased. The coil I use here is rated for high currents. Originally it had pins for PCB,
I removed them

This chip has output rating of 3 Amps.

I have used LM2577 and 2575. 2577 for step-up while 2575 steps down. My LM2577 is really hot, it burnt the plastic casing of the inductor. The heat sink was also very hot. Luckily there was over current protection built in, or else my 3577 should have toasted. I never though of using a fan because the switcher was used inside the high-wattage LED lamp. It steps up DC 12V to 24V used by the led lamp.

Was your 3A measured on the output or input side?

Allen

[takao21203]

It's the chip's rating for the output side.

I never used this way of mounting a chip to aluminium substrate before.
Because if there is high temperature, connection is not secure.
But small fans are good at removing heat!
Otherwise, a clip system must be used, or screws (a lot of effort to drill holes into metal).
I have not seen much experience with the circuit, the other one I built remains totally cool (12v -> 3.3v).

All these chips need cooling at higher current don't let them become too hot (bad for electrolytic capacitor).

I don't know if this circuit can reach full 3 Amps however the coil is large enough for that.

There are some PCBs on eBay they also don't have a cooling grid they can't use full current or get too hot!

This fan only costed 99 cents + $1.25 shipping, was a little bent (the aluminium fins) so the fan would not spin,
but possible to correct it.

[kl84]

I have a question. Is it possible to produce 5V output with 5-12V input? The Vin may be come from 12V DC adaptor or 5V USB supply. A slight voltage drop below 5V is acceptable when 5V input is used, but I wonder can buck converter achieves this requirement?

[takao21203]

I don't think so. USB isn't always full 5 volts as well.
You have to try maybe you can get 4 volts for small currents,
but this buck regulator won't work for 3 Amps using 5v input.

And why would you want to, USB sockets are only used for 5 volts, you can connect it to the output?

Do you have a concrete schematics?

[takao21203]

I have a question. Is it possible to produce 5V output with 5-12V input? The Vin may be come from 12V DC adaptor or 5V USB supply. A slight voltage drop below 5V is acceptable when 5V input is used, but I wonder can buck converter achieves this requirement?

For this I think a bypass MOSFET would be used, and the switcher disabled as well for low voltage.

If in doubt, build a test circuit and see how much it works to give current at low voltage.