switch mode power supply

[sarahkarigan]

hello,

how does a buck boost converter work? Is it possible to build a cct with the output voltage being boosted then bucked after a short period of time but with the same current limit. can this be done w/o the use of mcu and transformer? thanks for the help.

 

[MikeMl]

Buck implies a voltage step-down. Boost implies a voltage step-up. Buck/Boost means it can do either as required to keep the output voltage constant even as the input voltage sags lower than the output...

SMPSupplies usually regulate the output voltage; and current-limit only to protect themselves. There are SMPS that regulate current (LED drivers, for example), so their output voltage changes to maintain a constant-current.

 

[bychon]

Let's see..a buck-boost converter without a controller or a transformer, that has both constant voltage and current. I don't think so. Perhaps you could be a bit clearer in your description. I think I'm not understanding you.

 

[smanches]

You could build one without a microcontroller, although in my opinion it would be much more work. You can still have current limiting. But you CANNOT build one without a coil or transformer.

All SMPS require three things to work. Switch (transistor), coil or transformer, and a diode. You cannot build one without those three basic things.

 

[sarahkarigan]

For switch mode power supply, there are buck-boost converter, sepic converter, flyback converter and cuk converter, they all can buck and boost an input. how does one determine which converter to be used in his or her design? thank you

 

[misterT]

I like this IC: **broken link removed**

What do you mean by the 'same current limit' in: "voltage being boosted then bucked after a short period of time but with the same current limit".

 

[Claude Abraham]

A buck-boost requires a simple inductor, not a transformer. It also requires 1 or 2 diodes (inverting or non-inverting topology), 1 or 2 power switches (inv or non-inv), and a PWM control IC. I recommend the UCC28C42/43/40 family. They are peak current mode controlled, which gives a buck-boost higher speed than voltage mode control can give. My paper from 2006, published in EDN, discusses buck-boost in detail. It is attached. BR.

 

[Hero999]

A buck-boost converter, inverts the polarity so the input maybe positive but the output is negative.
Buck?boost converter - Wikipedia, the free encyclopedia

 

[sarahkarigan]

Thanks for the replies.
there are two error amplifiers in TL494 pwm controller chip. is it common for both error amplifiers to be used at the same time? how does it work then? thanks

 

[sahu]

A buck-boost requires a simple inductor, not a transformer. It also requires 1 or 2 diodes (inverting or non-inverting topology), 1 or 2 power switches (inv or non-inv), and a PWM control IC. I recommend the UCC28C42/43/40 family. They are peak current mode controlled, which gives a buck-boost higher speed than voltage mode control can give. My paper from 2006, published in EDN, discusses buck-boost in detail. It is attached. BR.

i want smps based on pic micro controller (220ac i\p+ bridgh rect.+ high volt tronsisotor+ freriod transfommer ) it posibol.