Multiple Output Voltage Level In Single Product Using Link Switch LNK6776V
Dear all,
I want to obtained the controlled variable out put voltage using link switch LNK6776V in a single product.
The controller variable output voltage are as follow,
- 9Vdc
- 12Vdc
- 15Vdc
- 19Vdc
To obtained these, calculation of feedback resistance is obtained as bellow (See Fig.1),
- For 9 Vdc R10 = 11.4kΩ
- For 12 Vdc R10 = 8kΩ
- For 15 Vdc R10 = 6kΩ
- For 19 Vdc R10 = 4.65kΩ
When I replace the resistance R10 as specified in above, I get proper voltage.
- There is no voltage ripple in output
- The output voltage is regulated in either variation of input supply voltage or change the load (no load to full load of 15W)
To obtained the similar voltage level in smart way, I am using the microcontroller, optocoupler and resistance combination is presented in Fig. 1 (In Circled). However, under this condition I am getting some problems as bellow,
- Output voltage is non-regulated, it varies with variation in input supply voltage
Note: for example, to obtained 9Vdc at no load I get output as (Vo = 9Vdc At input of 85Vac, Vo = 11Vdc at input of 230Vac and Vo = 12.5Vdc at input of 257Vac).
- There is ripple in output voltage as presented in Fig. 2.
Files
| Attachment | Size |
|---|---|
| Fig. 1.png | 66.3 KB |
| Fig. 2.png | 200.27 KB |
Comments
Hi Jedidiah,
Thanks for reply.
When, I connect the optocoupler circuit with resistance to provide optimum resistance on the feedback terminal of the LNK6776V. And when i connect the voltage prob across feedback resistance then problem are resolved. It may be possible die to noise cancelation by oscilloscope.
Again to to remove the noise i have tired to increase the capacitance across feedback resistance and not connect the voltage prob, the problem remains same.
Other things is that after 2-3 time testing it with opto circuit, the switch LNK6776V get damaged.
Kindly suggest any solution to resolve this problem.
Thanks and Regards
Pemendra Kumar Pardhi
Hi,
Can you share your layout? What capacitance value did you added across feedback resistance?
Can you also share which part of the IC got damaged (Drain to Source damaged? feeback pin damaged?, etc....)
Do you have Drain to Source measurement of LNK6776V when the output is at 19V with highest input voltage.
Regards,
Jedidiah
Hi,
As you have stated, when you use the typical resistor change for R10, the output voltage is fine. It seems the optocoupler you added in the circuitry is distorting the signal seen on FB pin.
Regards,
Jedidiah