KA7500C application circuit

This buck converter/step down circuit is based on KA7500c SMPS controller chip,
the following circuit is from the reference design 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:

ka7500c circuit buck converter
ka7500 application circuit buck
KA7500 buck converter
KA7500 buck converter_1

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(η) calculated

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

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

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,  one of my friend Mr William helped me in selecting toroidal core, thanks to him.

Q1 , Q2  are2SB772 2SC4468 they are audio transistors, can be  used for switching applications, linear.



LM4755 amplifier

I built this amplifier for my iPod,  amp circuit based on LM4755 chip, stereo audio amp capable of delivering 11watt per channel of continues average power output to a 4Ω using a supply of 24V at 10% THD. It is designed for single supply operation.



  1. Wide supply range 9V-40V
  2. Drives 4Ω and 8Ω loads
  3. Integrated Mute Function
  4. Minimal External Components Needed
  5. Single Supply Operation
  6. Internal Current Limiting and Thermal Protection


Construction- DIY LM4755 amp

This amp, primarly used on my desk. So it needs to look good, for the enclosure  i used old dead CD-ROM case.


for  tone control and preamplifier I used OPA2134 (dual opamp) chip.

preamp is 1.5dB gain that works with single power supply. and the tone control to boost or reduce the particular audio frequencies,  simple RC filter circuit + preset/VR to control the Signal level of particular freq.



Pictures of my construction: