Why do some dc-dc buck or boost converters do not have the switching frequency value in their datasheet?
For example: Link does not have switching frequency ?
Is it possible to get power dissipation of a dc-dc boost converter?
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2\$\begingroup\$ It's not fixed. Page 4 shows you a graph of switching frequency vs load current for a given set of components. \$\endgroup\$– FinbarrMay 24 at 10:38
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\$\begingroup\$ That's a tricky part since it's not a fixed frequency switcher but a constant time switcher. Getting (better, estimating) the dissipation is a whole art in itself since everything in the converter heats up. Usually you focus on the switch but diode, inductor and even the current sensor can fill up your thermal budget. \$\endgroup\$– Lorenzo MarcantonioMay 24 at 14:31
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1 Answer
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Try this: -
The device you linked is a constant ripple hysteretic converter and therefore the lower the load current, the lower the switching frequency: -
As you can see, the ripple voltage is constant pretty much across all load currents and, this supports the fact that switching frequency is proportional to load current: -
Is it possible to get power dissipation of a dc-dc boost converter?
Most converter data sheets allow this to be found. From the above data sheet this graph can be used to find power dissipation: -
So, with an output (load) current of (say) 20 mA and an output voltage of 24 volts, the efficiency from the graph is 80%. The output power is 20 mA x 24 volts = 0.48 watts therefore, the input power is 0.48/0.8 = 0.6 watts.
This means that the losses in the circuit are 0.6 watts minus 0.48 watts = 0.12 watts.
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\$\begingroup\$ Thank you for the answer. With the last graph attached, can you tell me how to find the power dissipation from it? \$\endgroup\$– NewbieMay 24 at 11:29
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\$\begingroup\$ @Newbie - detail added to my answer at the bottom. \$\endgroup\$– Andy akaMay 24 at 11:35
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\$\begingroup\$ Thank you for the detail. So, can we take this 0.12W in your example as the power dissipation of the IC? \$\endgroup\$– NewbieMay 24 at 13:03
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\$\begingroup\$ @Newbie I would say yes although they may have accounted for some power dissipation in the inductor in the efficiency figure but, no matter, if you want to be sure about whether the chip gets too warm, it's better to err on the cautious side and assume all the 0.12 watt is dissipated by the chip. \$\endgroup\$– Andy akaMay 24 at 13:08