MC34063A: MC34063A, 3.7V to 12V boost converter with 200mA output current

Hello Dilrosh,

The engineer responsible for this device is out of the office. He should respond Monday.

-Garrett

Dear Garrett,

Good Day..!!!

Awaiting for the reply.

Regards,

Dilrosh

I don’t think this device can support 200ma, because of the voltage drop of the internal NPN is too large. The reasonable output current should be less than 100ma. I would suggest tps61089 for your application.

Dear Jasper Li,

But it is said that (in datasheet) the maximum switching current is 1.5A then why it is limit to 100mA?

Hi Dilrosh,

1. Can you tell the value of Rsc (resistor between Ipk (6) and Vin (7) ) used in your circuit

2. Can you post the specs of the inductor used, put a link to the datasheet if its a COTS inductor

3. If possible, can you also post a waveform on the Ipk pin

Thanks and Regards,

Avish

Dear Avish,

1. Can you tell the value of Rsc (resistor between Ipk (6) and Vin (7) ) used in your circuit : 0.15 Ohm

2. Can you post the specs of the inductor used, put a link to the datasheet if its a COTS inductor 

  https://www.mouser.in/ProductDetail/Bourns/SRR1210- 271M?qs=%2Fha2pyFadugwAu%252BkJMGkW%252Bbjmbyf3Q4LqBzF9ImD9h2jcINGoH6UQA%3D%3D

Regards,

Dilrosh

Dear Avish,

Can you please help me with the design? I tried a lot of combinations and couldn't able to draw more than 100mA in any case.

Regards

Dilrosh

Hi Dilrosh,

Would be glad to help. Can you put the exact schematic and the BOM for verification or should I start from scratch?

Thanks and Regards,

Avish

Dear Avish,

One of our project has been delayed because of this issue. I already shared the schematic with you and I experimented with a lot of values in Rsc, R & inductor but couldn't succeeded. If you can  start from the scratch you can go ahead.

Regards,

Dilrosh

i'll get back by tomorrow

Dear Avish,

Awaiting for your reply.

Dear Jasper Li,

Thanks for your comments

As I followed the design procedure for 100 mA output current still I unable to draw the same from the circuit. If I load for 80mA then voltage drops from 12V to 10.2V. As per the design I got the inductance value of 15uH but when is mounted the same the output voltage I got was 5V and I replaced with 220uH then I got the desired output. What will be the issue with the inductor?

Regards,

Dilrosh

Exactly, the Ipk is given by 2Iout/(1-D) which is >2.6A!!

HI,

There's no issue with the inductor value. Re-check the design, some of the parameters are beyond the permissible limits.

Thanks,

Hi,

The device might not be able to meet your specs. Re-check the design, some of the parameters are beyond the permissible limits.

Thanks,

Dear Avish,

With the same chip I designed for 120V output with 2mA current. The schematic is given below.  In this circuit also unable to draw the current of 2mA.     What is your point on this circuit?

Hi Dilrosh,

could you share me the schematic and layout of the current circuit?

Dear Li,

Good Day....!!!!

Correct values

C56 : 330pF

FB2 : 470uH

Regards

Dilrosh

Hi Dilrosh,

what I said is the circuit of the 3.7V to 12V project? not 120V output project.

I would like to focus on 12V firstly to avoid any misunderstanding. 

Dear Li,

Please find the schematic below

Regards 

Dilrosh

Dear Li,

Please find the schematic below

Regards 

Dilrosh

Avish Gupta said:

Hi Dilrosh,

Another fundamental flaw,

Vcc = 3.3V

Vsat = 1-1.3V

Vdiode = 0.4 - 1V

Vth = 1 - 3V

To turn on the FET, Vgs>Vth

and vgs = vcc-vsat-vdiode which may or may not be sufficient  depending on component variances.

best case vgs you can achieve is 1.9V, worst case 1V

Thanks,

Avish

Moreover, the Rdson is 50ohms even at vgs of 10V

Dear Avish,

I tried with 170mA output current also, but in that stage also I unable to draw the current needed. So by typical application circuit what twill be the maximum output current I can drew from the IC with input voltage (3.7V)  and output voltage 12V.

Regards,

Dilrosh

Hi Dilrosh,

the value of the Rsc should be 0.22ohm. there should be 10uF ceramic in the output  in parallel with the Co.

what is the part number of the inductor and the Co? also please share me the PCB layout.

Hi Dilrosh,

Sorry, some miscalculations from my end. The current wont go as high as 2.6A. I was accidentally putting 22 instead of 12 in my calculator. Sorry for that.

If I take 90% efficiency and take the switch current peak to be 1.5A( limit), then my output current would be 200mA.

But again, at 1.5A, the inductor you mentioned would tend to saturate thereby requiring a higher switch current.

I'm so sorry for my miscalculations, make sure that your inductor doesn't saturate and check typical efficiency values of mc34063.

Thanks,

Avish

Hi Dilrosh,

Any update about this case? thanks