STEL12H24 RBleed Calculation

[OTwin38BoH]

On the STEL12H24, but am not sure about the calculation for Rbleed:

I am designing a 12V system.

RBLEED [kΩ] = VIN / 20 – Rb (min)

Rb would be about 95Ω (from Figure 14 in the datasheet)

That would make Rbleed 12/(20-95) = -160Ω (negative makes no sense)

But according to Table 2, Rbleed is minimum of 560?

Can you clarify this please?

[Peter BENSCH]

Welcome @OTwin38BoH, to the community!

I am sorry that the formula in the data sheet, section 6.3, might be somewhat misleading. In the formula, the resistances are calculated in kohms, the voltage in volts and the current (the 20) in mA. In addition, there is no bracket around 20 - Rb(min), so VIN/20 must be calculated first.

For your values:

• VIN = 12V
• Rb = 95ohms = 0.095kohms

this results in (I have put a bracket around the division for clarity):

Rbleed = (12V/20mA) - 0.095kohms = 0.6kohms - 0.095kohms = 0.515kohms or 515ohms

Does it answer your question?

Regards
/Peter

[OTwin38BoH]

Thanks for responding. making the datasheet more clear would help a lot.

So the calculated 516 Ohms being less than the specification of 560 Ohms min, I would assume I should still stay above 560, but somewhere in that range?

Kind regards,
Kevin

 

[Peter BENSCH]

Correct.