JAJSH60 データシート

JAJSH60A april 2019 – december 2020 UC1825B-SP

PRODUCTION DATA

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）

HKT|16
- MCDF014A
KGD|0

サーマルパッド・メカニカル・データ

発注情報

8.2.1.3 RCD and Diode Clamp

For the UC1825BEVM-CVAL a resistor and capacitor in combination with a diode was used to clamp the voltage of the switch node. The resistor and capacitor is generally a value that is found through testing, but starting values can be obtained. To figure out the resistor and capacitor needed for the RCD clamp, one must first decide how much the node is allowed to overshoot. The equation for finding the voltage of the clamp is Equation 30.

Equation 30.

V_{c l a m p} = K_{c l a m p} \times N_{p s} \times (V_{o u t} + V_{D i o d e})

Note that K_clamp is recommended to be 1.5 as this will allow for only around 50% overshoot. Knowing the parasitic inductance of the transformer and how much the RCD clamp voltage is allowed to change over the switching cycle, can allow one to figuring out starting values for the resistor and capacitor using Equation 31 and Equation 32.

Equation 31.

R_{c l a m p} = \frac{{V_{c l a m p}}^{2}}{\frac{1}{2} \times L_{l e a k a g e} \times {I_{P r i P e a k}}^{2} \times \frac{V_{c l a m p}}{V_{c l a m p} - N_{p s} \times (V_{o u t} + V_{D i o d e})} \times f_{o s c}}

Equation 32.

C_{c l a m p} = \frac{V_{c l a m p}}{Δ V_{c l a m p} \times V_{c l a m p} \times R_{c l a m p} \times f_{o s c}}

A starting value of 10% is generally used for ΔV_clamp.