KA7500C buck converter - Page 1
Forum section: electronics / projects

author: viswesh
author_rank: Newbie
timestamp: August 22, 2016, 08:15:09 am
content: This buck converter/step down is based on KA7500c SMPS controller chip,the following circuit is from the reference designhttp://www.ti.com/lit/an/slva001e/slva001e.pdfyou 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) calculatedn = output power/input power = 5×5.75/18×2n = 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 3wattL1, 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

author: station240
author_rank: Unknown
timestamp: August 22, 2016, 03:21:35 pm
content: 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.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 22, 2016, 06:00:30 pm
content: D1 goesbeforethe 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

author: viswesh
author_rank: Newbie
timestamp: August 22, 2016, 06:19:17 pm
content: Quote from: T3sl4co1l on August 22, 2016, 06:00:30 pmSir,really thanks , modified now.really thanks sir

author: tatus1969
author_rank: Super Contributor
timestamp: August 22, 2016, 07:46:10 pm
content: 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.htmlp.s. R3 is probably underrated for 40V operation. At ~ 12.5% duty cycle (40V -> 5V) it'll have ~ 0.35W.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 23, 2016, 01:17:24 am
content: 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...Tim

author: viswesh
author_rank: Newbie
timestamp: August 23, 2016, 01:49:26 am
content: Quote from: blueskull on August 23, 2016, 01:39:49 amthanks yes sir, I had few chips lying around on my bench so I did built with the parts i have.