Microcontroller - Controlled SMPS

[Jon Wilder]

Hi all. Out of curiosity, in an SMPS circuit using a microcontroller to generate the switching signal, what would supply 5V initially to start the microcontroller until it's generating the switching signal in an SMPS?

 

[alec_t]

A battery-pack?

 

[KeepItSimpleStupid]

For an AC operated device you might find a 2-3 Watt always online switching supply. For other stuff that has a "real power switch" the mains are usually recified and sometimes a small amount of power comes from say a Zener regulator. Still others might use a rechargeable battery (The PC) or a coin cell.

 

[Nigel Goodwin]

Hi all. Out of curiosity, in an SMPS circuit using a microcontroller to generate the switching signal, what would supply 5V initially to start the microcontroller until it's generating the switching signal in an SMPS?

Doesn't matter if it's micro based or not, it still needs something to power it before it starts. There are various different schemes, such as capacitors to give it a 'kick' (they go high ESR, O/C, and stop the PSU working), or high value resistors (these go high and O/C - again, stopping it from working). If you've repaired TV's over the past 30 years you would be MORE than familiar with them

There are usually called start-up or kick-start components, and normally only operate in the few hundred milliseconds before the PSU proper takes over.

 

[dr pepper]

I concur with nige on that one, older pc supplies were similar, nowadays theres a seperate chipfor the 5v standby power, usually a tny264.

A cap/resistor/zener typical transformerless supply could be used, power the chip through a diode at a little lower voltage than the main supply so that the diode gets reversed biased and shut off once main power is on.

The only problem with either metod is isolation from the mains, there ae systems that self start and still be isolated but they start to get tricky.

I've coded smps routines for the pic for nixie clocks, originally with feedback control, but then I dropped feedback as it wasnt necessary, nice touch to have a brightness control in software.