Cheap step down switching power supply - Info

[Boncuk]

Hi All,

here is a chip which might not be generally known.

It's the L4971 (8-pin DIP) and L4917D (16-pin SO) step down regulator from "ST".

Here are the schematic and a PCB design (using the L4971) for any desired output voltage from 3.3 to 24 at 1.5A.

Details are contained in the schematic. The PCB is single sided and measures 2X1.55inches.

Perform "Ratsnest" for the ground fill for proper function.

(Eagle files will be provided free after PMing your email address.)

Cheers

Boncuk

 

[MrAl]

Hello,

Not too bad i guess, look a little higher priced though for 1.5 amp output. Do you have a specific reason for bringing this chip to mind?

 

[Boncuk]

Not any specific reason, but thinking about it for high power LEDs, 10W+ will certainly be a good idea.

Boncuk

 

[4pyros]

Look here https://www.anglia-lighting.com/st/VIPER%20STUFF/LIGHTING/LED/STEVAL-ILL008V1/AN/AN1941.pdf Its a farly common chip for cell chargers and stuff. Andy

 

[Boncuk]

Look here https://www.anglia-lighting.com/st/VIPER%20STUFF/LIGHTING/LED/STEVAL-ILL008V1/AN/AN1941.pdf Its a farly common chip for cell chargers and stuff. Andy

Thanks your input.

I was thinking of high power LEDs, e.g. 10W requiring Uf=16V, If=700mA, 20W - Uf=16V and If=1.400mA and 50W - Uf=28V and If=1750mA.

They have one thing in common: They aren't toys.

Boncuk

 

[crutschow]

The best type of converter for LEDs has a constant-current output, not constant-voltage output, for highest efficiency, since you don't need any series resistor, with its power loss.

 

[Mr RB]

It doesn't appear to have current limiting built in. If you use a MC34063 it has facility to connect a current set resistor and you can run it as a current regulated buck, it's a cheap chip and needs less parts count, but if you use the internal switch it's linited to under 1 amp LED current.

 

[MrAl]

Hello,

MrRB, yes that's the chip i was talking about in another thread. Hard to get a good clean output but with an LED who cares

 

[crutschow]

If you use a MC34063 it has facility to connect a current set resistor and you can run it as a current regulated buck, it's a cheap chip and needs less parts count, but if you use the internal switch it's linited to under 1 amp LED current.

It is an older chip and uses a bipolar transistor in a Darlington connection for the switch transistor. This means, unless you have a higher bias voltage than the normal input supply, the switch saturation voltage is about 1V. This will reduce the efficiency somewhat as compared to those switching regulators that use MOSFETs which will typically have an "on" voltage well below 1V.