ok people, i'm new to Electro Tech here and i thought i would try out the forums and see how much people can help me with me next project!
anyways, my next project that i have is a buck-boost converter switch mode power supply. I'm going to be using it to supply both a positive and negative voltage for my 150 watt RMS power amp that i built (that's actually a bit underrated...it's closer to 170w RMS). The reason why i am choosing a switch mode supply vs using a transformer is because 1. space reasons 2. cost 3. weight and 4. i don't want the transformer's electric field induction into the wires of the amp
i have the basic outline for the buck-boost converter as shown here:
http://www.powerdesignersusa.com/InfoWeb/design_center/articles/DC-DC/dc_f5.gif
now, granted i will not be using a Bipolar transistor as my switch, but instead a power mosfet...in this case, a IRF640.
I understand the basic theory behind the buck-boost in that the output voltage is determined by the duty cycle of the PWM and you can get different output current and voltage ripple regulation by the selection of the inductor and capacitor values. I know about what continuous and discontinuous modes are (even tho i dont really know how to get the inductors to physically operate in those modes)...basically i know some theory about it.
Now i know basically how i want to build this (parameter wise) but the part i get confused on is component value selection...especially on the output inductor and capacitor. Here is what i want for the supply.
I'm going to be building two separate supplies, one with a negative output and the other with a positive output but the ratings will be the same.
-Power Rating: around 140 watts continuous per polarity
-Voltage Requirements: Mains 125vac input, 30vdc output
-Voltage Ripple: preferably less than 5% under load...i want to keep a steady power
-Output Current: 3A average, 6A peak
-Output Current Ripple: again, preferably less than 5%...but i don't know what is typical for a SMPS supply so i may be going a bit low...i have the ability to make my own inductors and measure their values at the frequency i will be running them at.
-Operating Frequency: probably somewhere between 40Khz and 80Khz
-Efficiency: anything above 75% sounds good to me
I don't think i am missing anything in the basic parameters, but if i am, then please tell me
now for my driver circuit for the mosfet, i'm not gonna be using any fancy chip, just the classic 555 timer connected for PWM. That will be driving the gate of the IRF640 for the switching, and then the rest of the buck-boost just kinda takes over from there.
As for the mosfet, i believe i have chosen a good mosfet for the job as it can handle 12A and 200v, which is more than enough than what the circuit will be requiring, including some headroom for spikes too... I have also gotten the P-Channel version of the mosfet, the IRF9640, for the construction of the positive polarity supply. a buck boost converter inverts the polarity of the original dc input so i'm gonna need a p-channel for when have the input at a negative voltage. I don't need to worry about the polarity of the gate drive circuit because on both versions of the mosfet, they can be driven from a positive or negative source.
The diodes i have selected are going to have to be paralleled because i haven't found any fast diodes that can handle some high current. the diodes are rated at 1000v and 3A, but i am going to parallel 3 of them together, each with their own resistor to help equal out the current "hogging" between the diodes. also i am considering placing them on a small heatsink..but that's only if they get warm under operation. They aren't anywhere close to being the fastest diodes on the market, but this is my first SMPS so i'm willing to sacrifice a little bit of speed and some efficiency just so i can get it working.
I'll be needing a little help with the negative to positive buck-boost, as i know the component arrangement will have to be slightly different because of the reversal of the polarities compared to the positive to negative one. Other than that, can anybody help me with my design? I hope i've been pretty thorough to give as many specs as i can think of that i want for this thing...i just need some more help and guidance in understanding the final design, cause the stuff they have on google for how to do this is ridiculously confusing mathematics to me..like college level stuff that i haven't even learned yet
Thanks for all the help!
Codex
anyways, my next project that i have is a buck-boost converter switch mode power supply. I'm going to be using it to supply both a positive and negative voltage for my 150 watt RMS power amp that i built (that's actually a bit underrated...it's closer to 170w RMS). The reason why i am choosing a switch mode supply vs using a transformer is because 1. space reasons 2. cost 3. weight and 4. i don't want the transformer's electric field induction into the wires of the amp
i have the basic outline for the buck-boost converter as shown here:
http://www.powerdesignersusa.com/InfoWeb/design_center/articles/DC-DC/dc_f5.gif
now, granted i will not be using a Bipolar transistor as my switch, but instead a power mosfet...in this case, a IRF640.
I understand the basic theory behind the buck-boost in that the output voltage is determined by the duty cycle of the PWM and you can get different output current and voltage ripple regulation by the selection of the inductor and capacitor values. I know about what continuous and discontinuous modes are (even tho i dont really know how to get the inductors to physically operate in those modes)...basically i know some theory about it.
Now i know basically how i want to build this (parameter wise) but the part i get confused on is component value selection...especially on the output inductor and capacitor. Here is what i want for the supply.
I'm going to be building two separate supplies, one with a negative output and the other with a positive output but the ratings will be the same.
-Power Rating: around 140 watts continuous per polarity
-Voltage Requirements: Mains 125vac input, 30vdc output
-Voltage Ripple: preferably less than 5% under load...i want to keep a steady power
-Output Current: 3A average, 6A peak
-Output Current Ripple: again, preferably less than 5%...but i don't know what is typical for a SMPS supply so i may be going a bit low...i have the ability to make my own inductors and measure their values at the frequency i will be running them at.
-Operating Frequency: probably somewhere between 40Khz and 80Khz
-Efficiency: anything above 75% sounds good to me
I don't think i am missing anything in the basic parameters, but if i am, then please tell me
now for my driver circuit for the mosfet, i'm not gonna be using any fancy chip, just the classic 555 timer connected for PWM. That will be driving the gate of the IRF640 for the switching, and then the rest of the buck-boost just kinda takes over from there.
As for the mosfet, i believe i have chosen a good mosfet for the job as it can handle 12A and 200v, which is more than enough than what the circuit will be requiring, including some headroom for spikes too... I have also gotten the P-Channel version of the mosfet, the IRF9640, for the construction of the positive polarity supply. a buck boost converter inverts the polarity of the original dc input so i'm gonna need a p-channel for when have the input at a negative voltage. I don't need to worry about the polarity of the gate drive circuit because on both versions of the mosfet, they can be driven from a positive or negative source.
The diodes i have selected are going to have to be paralleled because i haven't found any fast diodes that can handle some high current. the diodes are rated at 1000v and 3A, but i am going to parallel 3 of them together, each with their own resistor to help equal out the current "hogging" between the diodes. also i am considering placing them on a small heatsink..but that's only if they get warm under operation. They aren't anywhere close to being the fastest diodes on the market, but this is my first SMPS so i'm willing to sacrifice a little bit of speed and some efficiency just so i can get it working.
I'll be needing a little help with the negative to positive buck-boost, as i know the component arrangement will have to be slightly different because of the reversal of the polarities compared to the positive to negative one. Other than that, can anybody help me with my design? I hope i've been pretty thorough to give as many specs as i can think of that i want for this thing...i just need some more help and guidance in understanding the final design, cause the stuff they have on google for how to do this is ridiculously confusing mathematics to me..like college level stuff that i haven't even learned yet
Thanks for all the help!
Codex