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# MC34063A DC-DC Step-Up Converter Power Consumption?

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#### emaq

##### Member level 4
I have made a DC-DC step-up converter using MC34063A with following components
Ct=31 pF
Rsc=0.682 Ohm
Lmin=4 uH
Co=701 uF
R=180 Ohm
R1=1k R2=3k

and I used
for the design with following input parameters
Vin: 3V
Vout: 5V
Iout: 100mA
Vripple: 1mV(pp)
Fmin: 700kHz

The problem is the power consumption... at no load the current is about 4mA but as I start drawing 15mA @ 5V the total current reaches approx. 31mA.
I intend to use this converter for a low power application using a 3.6V lithium battery, but the converter current consumption of 16mA is beyond the budget.

How can I fix this problem?

Hi,

5V, 15mA output makes 75mW.

With the voltage drop of the catch diode included it may be 5.5V x 15mA = 82.5 mW.

82.5mW at 3.3V = 25mA

Now add the current for the Opamps and the complete control loop inside the IC, losses in the switching FET and losses in the coil...
Then 31mA is a typical value.

The output ripple of 1mV suggests that you need a constantly switching instead of power saving burst mode.

Sorry, there is not much to improve.
Use a synchronous rectifying controller and safe max 2mA, allow more output ripple, select a micro power converter IC and maybe save on other mA.

Klaus

Does this IC work very well at 700kHz? I thought the upper limit was about 150k?

the switching losses in the internal Darlington must be getting up there at 700k?...

The problem is the power consumption... at no load the current is about 4mA but as I start drawing 15mA @ 5V the total current reaches approx. 31mA.
I intend to use this converter for a low power application using a 3.6V lithium battery, but the converter current consumption of 16mA is beyond the budget.
The primary problem in your post is not considering law of energy conservation.

Conversion efficiency η = Pout/Pin = (Vout*Iout)/(Vin*Iin) can't be over unity. According to your measurement it's 80 %, better than I had guessed for cheap 34063 at 700 kHz.

With a modern low power boost converter IC, you might achieve 95% efficiency, but it's still 26 mA at 3V input.

sorry mc34063 is not for low power application....use one of the specific low power converter chips, linear.com do them, so do maxim, also ti.com...their datasheets brag about "low power" consumption so you should find them.

How can you fix the problem, more and or bigger batteries....

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