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question on efficiency

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I think it will be greater. Because voltage drop on diode/transistor is smaller % of total voltage. Haven't used buck-boost, but buck or boost converters usually work better with bigger input voltage.
With bigger frequency you'll need smaller inductance. But transistor switching loses will increase. With smaller frequency you need more inductance, or it's core might saturate.

You can try to simulate it in any spice program

added:
There is graph voltage/efficiency for buck-boost controller from linear https://www.linear.com/solutions/1828
 
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Unusual question, it all depends on the design.

A buck/boost converter can have a higher or lower output voltage than the input, if the input and output were 12v then the purpose of the converter would probably be to electrically isolate the 2.

Generally speaking if you go higher in freq then the effeciency goes down, however like I said it depends on the design, its usually a toss up between physical size and cost and efficiency.
 
To add my two yen on dr. pepper's comment:

Engineering is the application of science to tradeoffs. Between size, efficiency, cost -and I will add- design effort.
Choose the parameters that really interest you, at the expense of the remaining.
 
This can be a very random question..What is the meaning of efficiency here?

If input voltage(power) is same as output voltage(power), it is 100% efficient?
 
No, it will never be 100% efficient. Even if input and output voltages are equal, output current is lesser than input. Why? Because transistor has resistance, inductor has it to, diode has voltage drop, and a controller ic require some power itself. So voltage drops on all those resistances when current is flowing, and heat is produced. Even if voltages are same, it needs little bit power(more current at input) only to compensate power loss on converter parts
efficiency = Pout/Pin * 100% = (Iout * Uout) / (Iin * Uin) * 100%
 
What we are saying is that the electronics within the converter wastes a little energy.
The converter put in very simple terms acts like a resistor energy wise (even though the o/p voltage can be higher than th ei/p) and wastes some energy as heat.
 
This can be a very random question..What is the meaning of efficiency here?

If input voltage(power) is same as output voltage(power), it is 100% efficient?
Voltage is not power, it is EMF.
Efficiency, as used here, is power efficiency and power is voltage times current.
 
This can be a very random question..What is the meaning of efficiency here?

If input voltage(power) is same as output voltage(power), it is 100% efficient?
voltage does not equal power.

Vin 12V X 1A, output 12V X 0.9A, 90%
Vin 12V X 1A, output 6V X 2A, 100%
Vin 12V 1A, output 1V X 9A, 90%
 
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