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using MC34063 for 6V to [email protected]

audioguru

Well-Known Member
Most Helpful Member
nikhil arora said:
how can we design power supply using MC34063 for boosting 6V to 12V and provides [email protected]
How can you make anything without looking at the datasheet???

The datasheets from Motorola and from ST Micro show how to do it with an external pass transistor to handle the current.
 

nikhil arora

New Member
sir i have seen the datasheet they have given two ways .
I have to connect the NPN transistor and a resistor from base to ground.

But the datasheets are not explaining. all the other things according to design would change.

I think atleast I should change Co to larger value as current is more.

I can use BD139 transistor and 3.3K transistor at its base

what about Rsc it would remain same to extenal npn transistor

I going to read datasheet again.
 

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audioguru

Well-Known Member
Most Helpful Member
ON Semi 's datasheet has a table with formulas for the parts values. They also have two excellent Applications Notes about the MC34063 IC.
 

justDIY

Active Member
The cool thing about a lot of these integerated switchers is they're not real sensative to the actual components you use ... just take what you have available and build in on a breadboard, you'll be supprised that it works.

sure, having the actual proper components means higher efficiency and lower ripple, but you can worry about that once you get the prototype working.

I deff like the ON versions of datasheets for a lot of the components TI has ... I wonder how they both have similar products like that. However, TI offers free simulators for a lot of those chips, which can answer more questions than a datasheet sometimes.
 

nikhil arora

New Member
thanks for giving me confidence
I have tested one ckt and have succeed in it.

I would like to ask which is more better linear or switching in general sense.
As switching will give rise to switching noise also
and linear will only dissipate.
 

justDIY

Active Member
one is better than the other, depending on application

for low to very low power (under say 100mA), linear is good because it's quiet and small and simple

for high power (say 500mA and up), switching is good because it doesn't waste a lot of power as heat

some exotic switching regs have built in linear's ... so when the current demand is very low, the switcher shuts down and the linear takes over.
 

nikhil arora

New Member
I have designed the following step up conveter

the only things which are differing are
1>
For Rsc I have used a short wire
2>
I have used 50uH of inductor even I am not sure of its value.
I have inductors but I cannot read their values.
I got 50 by using parallel combination of 100uH but I am not sure they are 100uH or what.

3>Instead of MBR1645
I am uisng 1N5822

Input voltage is 6.4V from a SLA battery. 4.2AH marking

NOW the problem is
1>
when I am connecting a load which just takes 300mA to 400mA the voltages fall from 12V to 6.8V or so
2>
without ouput capacitor and load the voltage at ouput is constant 12V
but when i connect a 2200uF/35V capacitor the voltage fluctuates a little and voltage drop to 11.6 to 11.7Vs
I think this is what they called they need less ESR of capacitor
 

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justDIY

Active Member
try a bigger inductor, and make sure it's a power inductor, and not an RF choke

the only 'critical' parts I've run into on these things, is (A) the switch itself and (B) the output capacitor ... you're probably right about the ESR of your 2200uF cap being too high

also, it could be your piece of wire for the osc resistor has the clock running too fast, and the switch and/or diode can't handle it?

also, where is the 6v coming from ... do you have sufficient input capacitance?
 

nikhil arora

New Member
try a bigger inductor, and make sure it's a power inductor, and not an RF choke
I donot know whether it is Rf choke but it is like a 1/2W resistor with color band markings.
I donot know it power handling capacity.

My output falls when i connect load which draws 250mA, and
I burned out one cylindrical shaped sealed inductor on which just rosy was written.




the only 'critical' parts I've run into on these things, is (A) the switch itself and (B) the output capacitor ... you're probably right about the ESR of your 2200uF cap being too high
i am using IRF540 and a 2200uF electrolytic capcitor.
When i connect 2200uf capacitor the output falls from 12V to 11.5V and there are little oscillation in output. output constantly varies from 11V to 11.6V



also, it could be your piece of wire for the osc resistor has the clock running too fast, and the switch and/or diode can't handle it?
its Rsc resistor for current limmiting lesser it is more current u can draw before ic shutdowns it self.



also, where is the 6v coming from ... do you have sufficient input capacitance?
the input is from battery 6V,4.2Ah and i have connected 1000uF at input.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
nikhil arora said:
try a bigger inductor, and make sure it's a power inductor, and not an RF choke
I donot know whether it is Rf choke but it is like a 1/2W resistor with color band markings.
I donot know it power handling capacity.
That's a RF choke, completely unsuitable for you purpose!.

BTW, don't post diagrams as JPEG's, use GIF or PNG instead, far better quality and smaller as well - only use JPEG for photos as intended.
 

nikhil arora

New Member
how the inductor for dc/dc look like

I have few more inductors
which are again in shape of resistor but size is near to 1W.
and few inductors which i have look like completely sealed cylindrical they are round like capacitors. notting written on them not even bands.
just they are purple, orange, pink, red etc.

I have searched net and got they are called radial and axial inductors and I have both of them.

I am looking for the inductor values ranging from 10uH to 47uH.

so which type of inductor should I use
 

justDIY

Active Member
nikhil arora said:
I donot know whether it is Rf choke but it is like a 1/2W resistor with color band markings. I donot know it power handling capacity.
Like Nigel has said, this is an rf choke ... a "power inductor" is usually wound on a torrid or bobbin core, and is larger than an rf choke ... here are some pictures (mainly surface mount) http://images.google.com/images?q=power+inductor ... you can see a power inductor I wound myself in this picture ... it's the green torrid with white wire wrapped around it

i am using IRF540 and a 2200uF electrolytic capcitor.
The IRF540 is a high voltage medium current transistor, rated for between 80 to 100 volts ... and as such, requires substantial gate drive Vgs of at least 20v ... most likely your smps controller is not able to drive the switch fully on. You need a "logic level" mosfet, something with a much lowr Vgs requirement ... IRLR, IRLU, IRL, etc... these are all logic level parts compatible transistors, and don't take 20 volts on the gate, instead they generally take under 10, some as low as 1.8

For the output stage, use a lot of smaller caps in parallel instead of one big cap, this will help to reduce your ESR

the input is from battery 6V,4.2Ah and i have connected 1000uF at input.
that sounds fine, again, use smaller caps in larger numbers, try something like four 100uf in parallel
 

justDIY

Active Member
i've read so many SMPS datasheets lately, they've all merged together in my head! :shock:

anyway, reading the mc34063a sheet again, I see that both TI and ON recommend the use of an NPN (or PNP) BJT transistor, not a FET.

Looking at the internal diagram, I can see why - the chip doesn't have a "gate drive" totempole, instead, its just a darlington transistor

so, I'd recommend trying something like a medium power darlington... like a TIP31, TIP100, etc... find yourself an NPN in a to-220 package, and plug it into your breadboard, see what happens!
 

Hero999

Banned

justDIY

Active Member
nikhil arora said:
how the inductor for dc/dc look like
I have few more inductors
(snip)
so which type of inductor should I use
if you have any dead computers laying around, or anything that would have a power supply in it, you could harvest inductors from them.

I harvested a bunch of nice inductors from old motherboards, and there are big inductors in the ATX power supply
 

nikhil arora

New Member
I have got other darlingtons like BD679 and I will try to find other darlington matching for what u suggested.
 

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