PWM and PFM advantages ? differences in Boost converter apps

[mengghee]

pwm advantages

hiye,

can anybody tell me what are the advantages and disadvantages between pwm and pfm in boost converter ? thank you

 

[Miguel Gaspar]

advantages of pwm

PWM easy to implement, noise inmunity and frequency band limited.
pfm is more complex and it has a variable frequency band.

 

[ls000rhb]

pwm boost converter

PWM maybe low frequency!!!not limited by technology level!!also maybe low power design stragety!!!

 

[zackyman]

pfm boost converter

what is a pfm?

 

[jonneylu]

pfm pwm

pfm is pulse frequence modulator

 

[liuyonggen_1]

boost converter pfm pulse skipping mode

PWM control need Error amplifier, PFM control only need comparators.
maybe the feedback stability of PFM is better than that of PWM.

 

[Willt]

advantage of pulse width modulation

PWM ~
adv:
- fixed frequency (good for applications which need to aviod certain frequency band)
disadv:
low efficiency in light load condition

PFM ~
adv:
- higher efficiency in light load condition
- easy to implement cos no error amplifier is involved
disadv:
- wide frequency band (noise)

Hope it helps ~

 

[liuyonggen_1]

frequence boost converter

does someone know another control technique "pulse skipping modulation(PSM)" proposed by UESTC in china?

 

[alec82]

difference pwm&pfm

hi
enybody can explain more about pfm?

 

[liuyonggen_1]

pfm pwm advantage

PFM use some discrete duty cycles to get a stable output voltage.
PWM use continuous duty cycles to stabilize the output voltage.

 

[mss]

voltage and freq control adv/disadv

PSM and PFM same.

 

[tekno1]

psm pwm site:www.edaboard.com

Willt's explanation is the right one, others I could not make any sense.

PFM basicaly skippes pulses (on cycles) when load is light. So name pulse frequency means because pulses skipped frequency of pulses changes between max and a minimum just to compansate for leakages at the output.

PWM does not skip pulses but makes on time shorter (pulse with is modulated) to accomadate light loads. So pulse frequency is constant but duty cycle varies.

PFM is simler to design, PWM has more circuitry.

As for different technologies: One can combine these two in one topology by switching the operation mode -- i.e. heavy load PWM, Light load PFM. There are many variaties and implementations of PFM and PWM also.

 

[Nimer]

pwm controller boost converter variable frequency

pwm is brtter generally for the fact that it produces less emi .

 

[mss]

advantages and disadvatages of pwm

Usualy for low current (<300mA) uses PFM. But remember about limitation currents passed thru power PMOS or NMOS.

 

[cesczhang]

PWM is more complex, for it need a error-amp, when duty-cycle is larger than 0.5, it need slope compensation, it can work at both current mode and voltage mode.the efficiency is high at heavy load and dcrease at light load.
PFM ? I am not sure, but it need not a error-AMP. you just need to monitoring inductor's current. and it features high efficiency at light load
hope it is helpful

 

[zeldazzz]

I am also learning how to design PFM mode boost. can anyone help suggest how to compensate the regular PFM loop. since the comparator is used how to do the loop stability analysis? Thank you.