to improve converter

[fifahaywire]

hi again,

some might know that i previously had problems with my buck converter. but now it's working and i even tried to extend it to a synchronous buck and it worked as well. the problem is, i was wondering how can i improve the output and efficiency of the converter.

someone posted this post awhile ago https://www.electro-tech-online.com/attachments/buck-jpg.3360/
i did ask why is there resistance of R2 and R3 but no reply. i hope u guys can help me

& my circuit is exactly as attached.

View attachment 62033

L = 1mH
C = 22uF
Rload = 150 ohms

 

[Diver300]

R2 and R3 are to make sure that both MOSFETs turn off when the PWM isn't driving them.

 

[fifahaywire]

R2 and R3 are to make sure that both MOSFETs turn off when the PWM isn't driving them.

do you think i need them? this is my circuit together with the PWM signal.
**broken link removed**
those are really large resistors right?

 

[alec_t]

those are really large resistors right?

They don't have to be physically large, if that's what you mean. They dissipate very little power.

 

[ronsimpson]

this is my circuit together with the PWM signal.
**broken link removed**
those are really large resistors right?

What is wrong? Are the parts hot? You want better efficiency? Are you really using a IGBT at 20 volts?
As stated last week: dump the IGBT and get a MOSFET! Use a Schottky diode!

 

[fifahaywire]

They don't have to be physically large, if that's what you mean. They dissipate very little power.

not physically. i mean the values

What is wrong? Are the parts hot? You want better efficiency? Are you really using a IGBT at 20 volts?
As stated last week: dump the IGBT and get a MOSFET! Use a Schottky diode!

i'm actually having a bridge rectifier with filter before the converter from 240Vac. the 20V is just for trial for the converter. so i think i probably need an IGBT, right?

 

[ronsimpson]

It is a good idea to start with a bench supply and not the 240VAC.

 

[fifahaywire]

what do u mean by a bench supply?

 

[ronsimpson]

It is good to start out with a current limited power source.

 

[simonbramble]

Just one point to be aware of: a switched mode power supply has a ramped current input (as the inductor current ramps up). So for , say, an average input current of 1A, you will probably need a peak input current of 3A. Set the current limit on your supply accordingly. Here is my tutorial on buck converters and some of the waveforms around the circuit:
http://www.simonbramble.co.uk/dc_dc_converter_design/buck_converter/buck_converter_design.htm

 

[ronsimpson]

Just one point to be aware of: a switched mode power supply has a ramped current input (as the inductor current ramps up). So for , say, an average input current of 1A, you will probably need a peak input current of 3A. Set the current limit on your supply accordingly. Here is my tutorial on buck converters and some of the waveforms around the circuit:[/URL]

The current ramp depends on inductance and time. In one of your examples; the average current is 5A, the ramp is from 4.5 to 5.5A.
It is possible to have 1A average and 3A peak.
This all depends on the inductor.

Hopefully the PWM has enough capacitance to do averaging. The bench supply has a large capacitance. Your bench power supply should have current limit, but with all the capacitance around it will probably not see "the 3 amp peak" and it can not respond at the switching frequency. I believe, with the 1A/3A example a 2A supply will work fine and maybe 1.5A.