# DC DC boost converter design

Discussion in 'General Electronics Chat' started by S_adnan, Jul 29, 2010.

Jul 28, 2010
9
1
I am making a Wind turbine power plant prototype for my project work

My generator is DC.actually its DC motor but it can be used as gen.1900 rpm rated with 24V and 2.5 A current.Problem is not all time wind gives enough rpm.But the charge controller i am using takes 24V constant to charge lead acid battery.so i need a DC DC booster.i will control the pulse width via micro controller.

My basic design is attached here.

using this equ i took min l value. i used min load current 2A and D i used when the worst case voltage is found as i got 7V and have to boost to 24V.

C=D/(2*f*R) here R is the load.

My problems are

1.while simulation i saw output voltage is dependent on L value.for safety i used 980uH that's greater than min L value and D=0.5 always.I saw it can perfectly boost 7 to 24 but while if 24V is given it gives 53V instead of 48V.

2.Output is very much depended on R value.If i use R=100 ohm it gives good result.But if i use R=500 ohm it cant even boost 7V to 14V for D=0.5,instead it gives 11V.

3.In lab i used this circuit to test but the IRF840 cant switch in 40K.whats the problem?

4.I burned 2 IRF840 though i used protection diode.but in lab source i used only 10V and 2A current.why IRF840 burns?

that's a lengthy post.But please someone help me.

• ###### my_design.jpg
File size:
168.5 KB
Views:
818
ahmedkh likes this.
2. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,990
1,115
Well I think its impassible to do in this circuit.
First of all for Vin_min = 7V and Vout = 24V you need
D = (24 - 7)/24 = 0.7 = 70%.
And for I_out=2A you need more then I_in = I_out / (1 - D) = 6.8A input current

Last edited: Jul 29, 2010

Jul 28, 2010
9
1
Thanks.

can u tell whether this circuit will give 2.5A even in 7V?or should i check this thing?

If i suppose 2.5A current regardless voltage value than i can insert min load current 0.73A according this equ. and if i select L value using this min I then will it work.However simulation is ideal.why this circuit don't work even in simulation(i used proteus and pspice)?

what should i do?please give some suggestion.

Thanks

4. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,990
1,115
For Vin = 7V and Io = 0.7A ---> L = 133uH --> D ≈ 70% for CCM for F=40KHz
And you need some IC which will be decrease the duty cycle if Vin rising
http://schmidt-walter.eit.h-da.de/smps_e/aww_smps_e.html

PS. And if you put this numbers in to the simulation it will work quite well

5. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,990
1,115
You should check it first.

Jul 28, 2010
9
1
this is really a good site for calculation.

I checked my design suggested by this site L value.only i added a load of R=100 ohm unless it the circuit becomes unstable as its open ckt voltage continues to rise.

Check the attachments.still is standing on the failure edge.sorry to disturb again.but its really bothering me.

Thanks again

File size:
148 KB
Views:
286
File size:
209.1 KB
Views:
190
7. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,990
1,115
You must change your duty cycle in simulation to get correct result.
And in this site calculator you enter 5V for Vin_min

File size:
1.2 KB
Views:
55
File size:
11.4 KB
Views:
180
File size:
32.9 KB
Views:
91
8. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
Why are you using an IRF840 500v MOSFET when you only need one rated for Vdss=30v? You're paying a penalty of high gate charge (65nC) and high Rds(on) (0.85 Ohms). You could use a MOSFET with a much lower Vdss rating, and in return you will have a much lower Rds(on), higher Id, and Qg; easily improving ratings by an order of magnitude.

You're trying to drive the gate using an optocoupler. Your gate charge/discharge times will be VERY long, so your MOSFET will spend most of it's brief life in linear mode where it is dissipating power as heat. That is, right before the smoke makes a hasty exit.

You need to improve your gate drive. There are dedicated gate optodrivers, but you need to have enough voltage to run them in the first place. If you don't absolutely have to have optoisolators, there are dedicated gate driver ICs which will improve switching times enormously. If you're planning on switching at speeds over a few kHz, you'll need something like that.

Jul 28, 2010
9
1
It works jony130 with some problem.

see the attachment 1&2(done with)

Second is the L value that determined for 7-24V is same as 10-24V as expected but the duty cycle shown in figure for 7-24V simulate perfect res while the duty cycle for 10-24v doesn't.

other value also doesn't work.why is this?

Thanks

File size:
194.8 KB
Views:
287
File size:
193.3 KB
Views:
276
File size:
184.9 KB
Views:
135
• ###### Ckt_para_for_10Vtest.jpg
File size:
167.6 KB
Views:
211

Jul 28, 2010
9
1
What should i use for gate Drive? YOU SAID " There are dedicated gate optodrivers, but you need to have enough voltage to run them in the first place." but i want to run this via microcontroller.so there's no scope of enough voltage facility.

Can u propose some gate driver ICs for high speed switching?

Thanks for MOSFET problem.Pls suggest some other MOSFET that i can use.I live in Bangladesh so here's not all MOSFET are available.so give 2/3 specimen of ur MOSFET suggestion

Jul 28, 2010
9
1
Thanks

draft4.asc which soft will open this?I have also posted another reply.please comment on that.

Thanks again

Jul 28, 2010
9
1
Thanks again

How i open this draft4.asc?By which software?

Feb 17, 2009
3,990
1,115

Feb 17, 2009
3,990
1,115
15. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
Here are some; you'll have to figure out what you can get locally. Since I'm in the States, I can find multiple suppliers for any of these.

I don't know if MicroChip Direct ships to Bangladesh, but if they do, they carry a number of different gate driver IC's.

FAN3121,FAN3122 - Single 9A High Speed Low Side Gate Driver
FOD3120 - 2.5A Optoisolator Gate Driver
FOD3150 - 1A Optocoupler Gate Driver
FOD3180 - 2A Output Optocoupler Gate Driver
HCNW-3120-000E - OPTOCOUPLER, 2.5A, GATE DRIVE I-O
HCPL-3120, HCNW3120 - 2.5A Output Current IGBT Gate Drive Optocoupler
ICL7667 - Dual Power MOSFET Driver
IR2101, IR2102 - High and Low Side Driver (see IRS2101, IRS2102)
IR2110 - High and low side driver
IR2301 - High and Low Side Driver
IR4426, IR4227, IR4228 - Dual Low-Side Driver
L6387E - HV Hi-Lo Side Driver Half H driver DIP
LM5112 - Tiny 7A MOSFET gate driver
LT1160,LT1162 - Half- or Full-Bridge N-Channel Power MOSFET Drivers
LT1161 - Quad High-Side Gate Driver w Drain Sense
LT1336 - Half-Bridge N-Channel Power MOSFET Driver with Boost Regulator
LTC4444 - High Voltage Synchronous N-Channel MOSFET Driver
LTC4447 - High Speed Synchronous N-Channel MOSFET Driver
MC34152, MC33152, NCV33152 - High Speed Dual MOSFET Drivers
MCP14628 - 2A Synchronous Buck Power MOSFET Driver
MIC4421, MIC4422 - 9A Peak Low-Side MOSFET Driver
NCP4423, NCP4424, NCP4425 - 3A Dual High-Speed MOSFET Drivers
TC429 - 6A Single High-Speed CMOS power MOSFET driver
TC4421, TC4422 - 9A Gate Drivers
TC4423, TC4424, TC4425 - 3A Dual High-Speed Power MOSFET Drivers
TC4423A,TC4424A,TC4425A - Low Side MOSFET Drivers
TC4426, TC4427, TC4428 - 1.5A Dual High-Speed Power MOSFET Drivers
TC4431, TC4432 - 1.5A high side high-speed 30v MOSFET drivers
TC4467, TC4468, TC4469 - Logic-Input CMOS Quad 1.5A Drivers
TC4467,TC4468,TC4469 - Logic Input Quad 1.2A Drivers
TC4467,TC4468,TC4469 - Logic-Input CMOS Quad Drivers
TLP250 - TRANSISTOR INVERTER FOR AIR CONDITIONER IGBT GATE DRIVE
TPS2811,TPS2812,TPS2814,TPS2815 - Dual High-Speed MOSFET Drivers
UC1710,UC2710,UC3710 - High Current FET driver
UCC27323, UCC27324, UCC27325 - Dual 4A Peak High Speed Low Side Power MOSFET Drivers

Here are some:

FDC655BN - Logic level power SMD MOSFET (Vdss=30,Rdson=33m,Id=6.3)
FDR858P - P-Ch, Logic Level, MOSFET (Vdss=-30V, Rdson=28m,Id=-8)
HP4410 - N-Ch Logic Level Power MOSFET (Vdss=30,Rdson=13.5m,Id=10)
HUF76131SK8 - N-Ch Logic Level Power MOSFET (Vdss=30,Rdson=13m,Id=10)
IPD50N03S2-07 - N-ch Power MOSFET (Vds=30,Rdson=7.3m,Id=50)
IRF1503 - N-ch power MOSFET (Vdss=30,Rdson=3.3m,Id=75)
IRF3703 - Power MOSFET(Vdss=30V, Rds(on)max=2.8mohm, Id=210A)
IRF7468 - SMPS MOSFET (Vdss=40,Rdson=0.0155,Id=9.4)
IRF7821 - N-ch Logic Level Power MOSFET (Vdss=30,Rdson=9m,Id=11,Qg=9.3)
IRL2203N - N-ch MOSFET (Vdss=30,Rdson=7m,Id=116)
IRL3713 - SMPS MOSFET (Vdss=30,Rdson=.003,Id=260)
IRL3803 - Logic level N-ch power MOSFET (Vdss=30,Rdson=6m,Id=140)
IRLB8748pbf - N-ch Logic Level power MOSFET (Vdss=30,Rdson=4.8m,Id=78)
IRLML5203 - P-ch Logic Level Power MOSFET (Vgss=30,Rdson=98m,Id=3)
IRLR7807Z - N-ch logic level Power MOSFET (Vdss=30, Rdson=13.8m, Id=30)
IRLR7821, IRLU7821 - N-ch logic level power MOSFET (Vdss=30,Rdson=10m,Id=65)
IRLR8721,IRLU8721 - N-ch LL power MOSFET (Vdss=30,Rdson=8.4m,Id=30,Qg=8.5nC)
NDS9936 - Dual N-ch logic level MOSFETs (Vdss=30,Rdsn=.05,Id=5)
NTD4863N - N-ch power MOSFET (Vdss=25,Rdson=9.3m,Id=49) DPAK
RJK0301 - Logic level N-ch MOSFET (Vdss=30,Rdson=2.3m,Id=60)
RJK0305 - Logic level N-ch power MOSFET (Vdss=30,Rdson=6.7m,Id=30)
Si4174DY - N-ch power MOSFET (Vdss=30,Rdson=9.5m,13m,Id=17,14.5,Qg=8nC)
STD17NF03L - N-ch power MOSFET (Vdss=30,Rdson=38m,Id=17)
STP27N3lH5 - N-ch logic level MOSFET (Vdss=30,Rdson=14m,Id=27)
STP80NF03L - N-ch power MOSFET (Vdss=30,Rdson=4m,Id=80)
STV300NH02L - N-ch PowerSO-10 MOSFET (Vdss=24,Rds(on)=0.8m,Id=280A)
SUM110P04-05 - P-ch Power MOSFET (Vds=40,Rdson=5m,Id=110)

Jul 28, 2010
9
1
I understood.I can change the duty cycle via micro controller programming but it will now become lot problematic.

However in Boost design consideration there is nothing on load dependency except the time of charging and discharging of capacitor.can u tell me why is this difference?

However how can i detect load variation?should i have to measure current through load?Any better solution of detection of load change.My output wont Detroit with load increase or decrease.And practically i am giving this output to charge controller which will charge the lead acid battery.So should i instead measure the transfer load of charger circuit and design the booster with that load value?

Thanks for circuit view.It works for various input while load constant.

Thanks again

Jul 28, 2010
9
1
Thanks

I will try search these the next days.I think i will have at least 1 of them as u given many options.

I will be in touch.Thanks again

18. ### ahmedkh New Member

Oct 29, 2014
2
1

ahmed kh likes this.
19. ### ahmedkh New Member

Oct 29, 2014
2
1
hello
please i need a help i have been used buck-boost converted my problem when i change the load the output voltage is also change i design the circuit at 2 A and the input voltage is 6V and output is 12 so i could not reach at 12V at load 2 A .
and buck converter is working well can reach at 2A and the output as a constant at 12V.
my regards