Hi,
I have designed a SEPIC converter using the LM3478 with the following requirements:
Input Voltage : 3.1VDC - 16 VDC
Output Voltage : 5.3 VDC
Maximum Output Current: 1.1 A
I'm using uncoupled L1 and L2.
However I have a problem with current I can draw from the circuit especially in the lower voltages. Please see below summary table with various measurements:
Input Voltage | Output Voltage | Draw current |
Below the 3.3 V now working properly (output voltage is too low) | Less than 4 V | 200 mA |
3.3 V | 5.07 V | 200mA |
3.3 V | 4.4 V | 210 mA |
|
|
|
3.7 V | 5.07 V | 210 mA |
3.7 V | 5.07 V | 310 mA |
3.7 V | 5.07 V | 410 mA |
3.7 V | 4.37 V | 500 mA |
3.7 V | 3.90 V | 550 mA |
|
|
|
4.7 V | 5.07 V | 500 mA |
4.7 V | 5.07 V | 610 mA |
4.7 V | 4.32 V | 700 mA |
4.7 V | 3.89 V | 760 mA |
|
|
|
6.7 V | 5.07 V | 610 mA |
6.7 V | 5.07 V | 765 mA |
6.7 V | 5.07 V | 815 mA |
6.7 V | 4.43 V | 910 mA |
6.7 V | 3.86 V | 1010 mA |
|
|
|
10 V | 5.07 V | 720 mA |
10 V | 5.07 V | 820 mA |
10 V | 5.07 V | 920 mA |
10 V | 4.83 V | 1020mA |
10 V | 4.20 V | 1130 mA |
10 V | 3.92 V | 1170 mA |
|
|
|
13.3 V | 5.07 V | 870 mA |
13.3 V | 5.04 V | 1000 mA |
13.3 V | 4.81 V | 1100 mA |
13.3 V | 4.12 V | 1220 mA |
|
|
|
16 V | 5.04 V | 1000 mA |
16 V | 4.88 V | 1100 mA |
|
|
|
You can see from the table that for low voltages it can not provide sufficient current (1 A) but only 200 mA.
Please see attached schematic. I have very good level of ripple. The only problem is that it can not provide requested current with low input voltages. You help would be very appreciated.
Thank you in advance
Grazyna