Akshaya. K
- Joined Jan 21, 2018
- 2
hello sir,.. i need to convert 230V ac into 5V dc with 1A current. so, what will the effective combinatons to make that circuit with needed combinations? help me with the exact block diagram,..please soon
Scope current L1 inductor at 5v 1.0 amps.
Same thing but at 1A. Frequency dropped a bit, closer to the 34063 oscillator freq of 26.2kHz, but still (just) triggering on the max current peaks. Current ripple now larger from approx 0.5A to 1.6A (average output 1A). Timing is still 20uS/hdiv but says 40uS on the screen as I had zoomed my h-axis (sorry).
Scope current L1 inductor at 5v 0.5 amps.
Here the L1 current has gone "discontinuous" meaning the L1 current is reduced to zero during the end of the off period, and has to start from 0 amps again during every on period. Typical of the regulation system used in a 34063 IC, the timing will "stutter" as needed to maintain Vout regulation at a steady 5.0v. This does not matter and the 34063 can be quite energy efficiency when "stuttering" in discontinuous mode like this. At less than 0.5 amps the stuttering can become very erratic looking, but this is all normal.
PFET drain/source voltage (main switching waveform).
(The PFET on period is the top of the waveform). Above you can see the PFET turnon (through a 10 ohm resistor) is nice and fast, It was about 0.07uS turnon time. However the turnoff is poor, because the turnoff is from a 560 ohm resistor and is slow at 0.8uS. This costs significant efficiency.
Using an external digital driver (like a 12v CMOS digital buffer/inverter chip?) to drive the PFET would improve turnoff time a lot and increase efficiency, but this was a test of using the simple datasheet example circuit with an external PFET (instead of the suggested external PNP) and as proof of concept it still works well enough.
5v DC output showing voltage ripple.
Because it is a switching regulator there will always be some ripple on the DC output voltage. This is shown when running at 5v 1.5A and the ripple is typical and acceptable enough at 30-35mV.
Improving efficiency.
This circuit was thrown together very quickly to show how to use a cheap common 34063 IC to get a high efficiency supply from 12v->5v DC at 0-1.5A or so. If you want to invest some effort it can be improved further;
1. My PFET is not a good choice, using a better PFET will give an easy 1% more efficiency, and would be the first choice.
2. The inductor is just an ordinary "off the shelf" type. A properly selected inductor or a good core hand wound for best performance could allow lower operating frequency and less current ripple, and maybe less DC ohms, and maybe pick up another 0.5% efficiency or so. (For lower operating freq CT should also be increased to 1.2nF or 1.5nF etc).
3. The PFET turnoff is too slow. Adding a cheap digital buffer IC could pick up 0.8-1.2% efficiency there from reduced switching losses and reduced loss from the 560 ohm resistor.
4. My PCB has very thin long tracks. Using a well designed PCB with thick short tracks for the main current paths might save 30 milliohms and give maybe 0.5% or more efficiency.
Bill of materials.
* 34063 SMPS 8pin IC (Fairchild/ON Semi/AIS etc, ie MC34063A or NCV34063A).
* 8pin IC socket (optional).
* PFET, rated more than double the input voltage and a few times the desired output current, preferably well under 0.1 ohm Rds on.
* Inductor L1 is a powdered iron toroid of 20-30 mm diameter, with thick wire >1.0mm preferred, 3A rated for a 1.5A capable supply. Value in the 150-470uH range, you may need to try a couple of different types. Ideally current ripple will be <50% at full output current.
* Schottky TO-220 dual 10A or dual 16A diode pack. Choose for low forward voltage, most brands are very good, parts can be found in any old PC PSU.
* 470-1000uF 35v electro cap.
* 1000uF 16-25v electro cap (25v will be larger and generally have a longer life).
* CT 1nF 25-50v ceramic or greencap.
* some 1/4W resistors; 560 ohm, 10 ohm, 6k8, 2k2.
* If you need a test load then a large 10W 4.7 ohm resistor will do.
Modifying the circuit for 12v car operation.
This circuit was designed for a car battery, generally 13.8v to 12.0v when running. If used in a car the circuit needs more protection as the Vin might be >15v at times. I would use a 100 ohm resistor instead of the 10 ohm resistor. Also a 13v zener diode across the 560 ohm resistor will add safety for the PFET. A 12v line filter might also be advised, they can be bought from auto stores.
Modifying the circuit for 24v operation.
Use 560 ohms instead of 10 ohms, so it now has two 560 ohm resistors. And again a 13v zener from PFET gate to source pin. With a 24v Vin you should use a higher inductor value and larger inductor core, 470uH and up are recommended.
Modifying the circuit for high output currents.
The circuit is meant for 5v out, 0-1.8A. It will do ok up to 2.5A just by changing the current limit resistor (at 2.5A the resitor should be 0.12 ohms or so).
Currents up to 5 amps or more should be ok, but use a larger inductor core size rated for more than the max amps you need, and again a larger inductor value helps >470uH is good. The diode pack will be fine, but the PFET should be rated for a few times more current than your max current. If needing 5A output I would use a 40-50v 60A TO-220 PFET which are a common size.
Changing output voltage.
Just change the 6k8 resistor, to change the output voltage to something other than 5.0v. Like most SMPS circuits it works best with roughly 2:1 Vin:Vout ratio, if using different ratios then again increasing the inductor value >470uH will help.
(end.)
