Author Topic: KA7500C buck converter  (Read 5293 times)

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Offline visweshTopic starter

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KA7500C buck converter
« on: August 22, 2016, 08:15:09 am »
This buck converter/step down  is based on KA7500c SMPS controller chip,
the following circuit is from the reference design http://www.ti.com/lit/an/slva001e/slva001e.pdf you can find the details of the circuit and calculations from the document. This is one of the application circuit built around with KA7500C, this buck converter  can suply a load current of 5.75Ampere at 5V we could also use  TL494 or KA7500c both are same in operation/ratings. The recommended operating voltage range is 7V to 40V DC and the power source i am using for this is a old laptop power supply adapter rated 18V,3.7A. , however the maximum input current the circuit draws is 2A at full load.

circuit diagram:






buck converter can supply load current of 5.75A at 5V and the short circuit current is 7Ampere.  the maximum output is 5V×5.75A, the ripple voltage at max power out is 94mV and input power is 18V×2A and the efficiency(n) calculated

n = output power/input power = 5×5.75/18×2
n = 79.86%

Note: C1,C2,C3 are the low ESR <= 50milli ohms electrolytic capacitors add 2 of 100nF,50V rated ceramic capacitors in parallel to C1,C2,C3, to reduce the high frequency noise.

all resistors are 1/4 watt rated except R13 which is 3watt

L1,  FS-1RN series toroidal cores made from iron powder (26) for creating inductors, FS-1RN core or similar  you can get this one from old desktop PSU’s. here is a useful link of toroids, http://toroids.info/

Q1 , Q2  are2SB772 2SC4468 they are audio transistors, can be used for switching applications, linear. isolate the tab of transistors and schottky diode with mica/silicone insulator
« Last Edit: August 22, 2016, 06:17:59 pm by viswesh »
 
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Offline station240

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Re: KA7500C buck converter
« Reply #1 on: August 22, 2016, 03:21:35 pm »
Neat, I might actually have all the parts to build this also.
First have to finish what I have on the breadboard at the moment.
 
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Offline T3sl4co1l

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Re: KA7500C buck converter
« Reply #2 on: August 22, 2016, 06:00:30 pm »
D1 goes before the inductor!

Note that this is a voltage mode converter, without compensation, and without inside loop current control.  It will happily destroy transistors if you look away from it for too long. Be careful. :)

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 

Offline visweshTopic starter

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Re: KA7500C buck converter
« Reply #3 on: August 22, 2016, 06:19:17 pm »
D1 goes before the inductor!

Note that this is a voltage mode converter, without compensation, and without inside loop current control.  It will happily destroy transistors if you look away from it for too long. Be careful. :)

Tim
Sir,really thanks , modified now. 
really thanks sir
 

Offline tatus1969

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Re: KA7500C buck converter
« Reply #4 on: August 22, 2016, 07:46:10 pm »
I wonder if this is really worth the effort (except of course for experimenting/learning) when there are these available, for example:

http://www.hobbyking.com/hobbyking/store/__10313__Turnigy_5A_8_40v_SBEC_for_Lipo.html


p.s. R3 is probably underrated for 40V operation. At ~ 12.5% duty cycle (40V -> 5V) it'll have ~ 0.35W.
« Last Edit: August 22, 2016, 07:51:40 pm by tatus1969 »
We Are The Watt - Resistance Is Futile!
 

Offline T3sl4co1l

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Re: KA7500C buck converter
« Reply #5 on: August 23, 2016, 01:17:24 am »
What is "interference free"?

As it's not an FCC Part 15 certification, or even a CE self-certification, I can only begin to speculate... :-DD

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 

Offline visweshTopic starter

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Re: KA7500C buck converter
« Reply #6 on: August 23, 2016, 01:49:26 am »
Good job, but why? There are some fully integrated converters (i.e. LMZ31710) can do twice better than this (12A/15A current limit, 10A nominal output), occupying 10*10*4mm space, with higher efficiency, lower noise and more stable control loop.
Unless you are looking for absolutely cheapest BOM, there is really no sense to use a 20 years old chip with a single (not even sync rectification) 20 years old FET BJT.
  thanks yes sir, I had few chips lying around on my bench so I did built with the parts i have. 
 


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