Datasheet

Datasheet

28/34

BD9271KUT

TSZ02201-0F1F0C100260-1-2

27.Feb.2015 Rev.004

www.rohm.com

TSZ22111・15・001

2. About the Clamp Circuit

In BD9271KUT, the absolute maximum voltage of D pin which is connected to the drain of external MOSFET is 40V. Due to it is

necessary to raise the power supply voltage according to the VF of the used LED bar, the voltage of D pin maybe exceed the

absolute maximum when PWM is LOW. In this case, in order to secure the absolute maximum voltage of the D pin, it is

necessary to set up a clamp circuit at the drain side of the NMOSFET.

Zener Diode can be used as a solution for clamp circuit. We use the Diode of 36V (EDZ36B:ROHM) which has a lower Zener

voltage than the absolute maximum voltage. About the LED, for example, in case of the LED which needs 3.5V for lighting, 2V

cannot light it. For this, the method by using the Zener Diode is applicable when the LED supply voltage is under 80V.

When use this clamp circuit, please guarantee the absolute maximum voltage of NOMOS is lower than the absolute maximum

voltage of the clamp circuit.

When the LED supply voltage is over 80V, we can use the FET for clamp circuit. In this case, clamped power supply for FET

gate voltage is necessary, for example, if VCC of BD9271KUT is 12V, it can be used.

In this case, the absolute maximum voltage is the clamp voltage.

Clamp circuit example

using Zener Diode

Clamp circuit example

using MOSFET

Figure 27. Clamp Circuit example using Zener Diode

Figure 28. Clamp Circuit example using MOS FET