[SOLVED] Resistor values for HCPL2630

[jmx66]

Hi all,

I have some queries about resistor values, if someone could reply it would be great....

In fact, i need to drive an IR2130 with optocoupler outputs.


Data for HCPL2630:

If maxi = 15 mA High level
If maxi = 250 µA Low level
Vf = 1,5 V

Data about MC33035:

Bottom drive output: ( pin 19 , 20 , 21 )
H: 12,9 13 V
L : 2V Maxi


I want to know , for using MC33035 top drive output , best choice from Choice A or Choice B?

About , now MC33035 Bottom drive outputs , I made ohm's law and found these results:

R1 = 1150 Ohm HCPL led: Vf =1,5 V
R2 = 50 Ohm If = 10 mA


I added 1N4148 to be lower than 250 µA for Low level .

( With diode voltage drop about 1V )

Is schematic " Choice C " a good idea, or not needed to add 1N4148?

If only R = 1500 Ohm.

( 2-1,5) 1500 = 333 µA


Other question about HCPL2630 supply:
Mandatory to use a dc/dc converter or 7805 output will do the job ?

Thanks a lot.

jm

 

[svhb]

15mA is the maximum recommended operating LED current, you can go down to 6.3mA. But 10mA should be a good compromise.

I should go for option B, where you can calculate the resistors that the opto for sure not turns on by the 33035 output leakage (and some margin). Take for example 0.5mA will generate less than 1V --> R2 ~ 2kOhm. Then calculate R1 for the on state current of minimum 10mA --> Vf led = 1.8V max at 10mA, so we need an extra 0.9mA, say 1mA that will flow through R2 --> 15V - mc33035 output saturation max - Vfopto max = 15-1.5-1.8 = 11.7 --> 11.7/11mA = 1063 ~ 1kOhm.

For the bottom drive, use the same technique, if you choose r1 and r2 properly, you don't need the extra diode.

For the dcdc-converter. It all depends on the total current needed on the 5V on your secondary side. calculate first the power dissipation in the 7805, and then decide to go for dcdc-converter if you can not get rid of the heat (or if you have very strict total efficiency targets)

stefaan

 

[jmx66]

Hi,

Thanks a lot for your fast and clear reply.

Not seen leakage for MC33035....

Best regards.

jm

 

[svhb]

For example on the second line of the datasheet-snippet:



It's near to nothing, but you better prepared...


Stefaan