Need a simple 30V down to 24V 5A SMPS design

[Beowolf]

34063 mosfet

An simple and cheap design is needed...
Any suggestions?
I thought about using MC34063 with external MOSFET. Any suggestions?

I would be very happy not to use an heatsink...

 

[SmartBomb1979]

simple smps

Can you explain a little more about what you were thinking?

I believe the 34063 is a 1.5A device with an integrated switching FET, no?

 

[Beowolf]

5a current source

Yes, 34063 can handle 1.5A, but I need 5A, so I need an external switch. I know how to do it with NPN transistor, but with MOSFET it can be more efficient and heat less.

If anyone knows how to parallel two or more 34063s, that would be nice too, but not so efficient, becouse 34063 internaly use NPN darlington.

 

[A.Anand Srinivasan]

simple smps circuit

measure the input current to the IC when the output current is 1.5A... now put a resistance from the source to the IC input pin such that the voltage across the resistor is enough to turn on a pnp transistor(0.7-0.8V) when IC output current is 1.5A.... now connect a PNP power transistor with its emitter connected to source, base to IC input pin and collector to the IC output pin.... now the voltage is maintained by the regulator IC and the current exceeding 1.5A is taken care by the transistor....

 

[Beowolf]

switch-mode_power_supply_spice_cookbook-basso

I'm not shure that it's gonna work. You just described a way to use PNP with linear IC. There is a schematic in MC34063 how to use external NPN to boost current.

I was interested in replacing it with MOSFET.

 

[A.Anand Srinivasan]

+24v +5a +smps +schematic

the circuit that i'm talking about is

 

[Beowolf]

34063 apply design with external transistor

In second picture is how ON recomends it.
I want to replace it with MOSFET. How?

 

[A.Anand Srinivasan]

24v 5a linear regulator

replace the power transistor with a power MOSFET and take care that the resistor biases the mosfet in the saturation region.... we just need a external current source and since the drain and source are in points of fixed voltage the biasing work is made even simpler............

 

[PaulHolland]

mc34063 schematic

Hi, Use the LM2677 its a 5A SMPS buck regulator and has an internal MOSFET so only need some resistors capacitors and a coil !!... Look on internet or national for datasheet.

 

[mhtplsh]

mc34063 fet

The circuit of is very simple to use.
But don't draw more than 300 ma from the regulator IC with small heatsink.
Just use 2.2 ohm 1 watt resistor to be on safe side for switching 2N3055. Better use 2N 3055 metal TO-3 can as it is useful upto 15 amps. so nice for 5 amps.
If u don't want to use heatsink than use 2pcs. 2N3055 in parallel.

 

[PaulHolland]

34063 regulator

Seems everyone here is not reading !. The Guy is asking for a SMPS and NOT a linear regulator design !.

 

[Beowolf]

2n3055 smps application circuits

Thank you for your's observation. Furthermore, external switch of choice is MOSFET, not BJT.

 

[Rishi2530]

mc34063 external fet

hi

use ic 3842 plus a mosfet so that u can get better effiency and constant output.

 

[Beowolf]

24v design

Here is what I came up with.
What should be the correct value for R3?

 

[Beowolf]

mc34063 fet

I'm stuck with heating. The schematic I'm currently measuring is the above, R3 is 8K2, and instead of FET I'm using BC243.
In this picture You can see waveforms of base(2) and emitter(1) of the NPN switch transistor.
I'm concerned about the flat mid-point between ON and OFF state. Where does it come from and how to kill it ?

It is heating considerably with load current of only 400mA. Should I put LM311 in between to boost the transition or what?

Pls help, I'm on thin ice here....

 

[heyram123]

34063 mos application circuit

try this link for more smps design

**broken link removed**

 

[EricARG]

mc34063 30v

Mind that Mosfet is not "always" the best choice, a saturated BJT drop voltaje can be as low as 0.5v while handling 20Amp
To acomplish the same performance a msofet Rds should be 0.025 Ohms and only low voltaje mosfet have that.
Thats why IGBT are used for high voltage high current aplications.

 

[jsidev]

ao4407 mosfet

**broken link removed**

 

[roykyn]

mc34063a with external npn

i fount this circuit on my modem. but i clearly dont know how it works.the main doubt is that to turn on a P mos you require negative voltage but here its not available in the circuit or 0 volts would work i dont know.the mosfet used was 8 pin sop AO4407.the transistors and capacitors are smd so i dont know the value or part no.
the inductor is 150uH toroidal coil.