Finding the Values of the Snubber Circuit The recovery current of a diode, as shown in Figure 17.17, is IR = 20 A and the circuit inductance is L = 50 H. The input voltage is Vs = 220 V. If it is necessary to limit the peak transient voltage to 1.5 times the input voltage, determine

Question

Finding the Values of the Snubber Circuit

The recovery current of a diode, as shown in Figure 17.17, is [latex]I_R = 20 A[/latex] and the circuit inductance is [latex]L = 50 µH[/latex]. The input voltage is [latex]V_s = 220 V[/latex]. If it is necessary to limit the peak transient voltage to 1.5 times the input voltage, determine (a) the optimum value of current factor [latex]α_o[/latex], (b) the optimum damping factor [latex]δ_o [/latex], (c) the snubber capacitance C, (d) the snubber resistance R, (e) the average [latex]dv/dt[/latex], and (f) the initial reverse voltage.

Accepted Answer

[latex]I_R = 20 A, L = 50 \mu H, V_s = 220 V[/latex], and [latex]V_p = 1.5 imes 220 = 330 V[/latex]. For [latex]V_p/V_s = 1.5[/latex], Figure 17.19 gives:

a. The optimum current factor [latex]d_o = 0.75[/latex].

b. The optimum damping factor [latex]δ_o = 0.4[/latex].

c. From Eq. (17.20),

[latex]d=\frac{I_R}{V_s}\sqrt{\frac{L}{C} } =\frac{I_R}{I_p}[/latex] (17.20)

the snubber capacitance (with [latex]d = d_o[/latex]) is

[latex]C=L\left[\frac{I_R}{dV_s} ight]^2 [/latex] (17.24)

[latex] =50\left[\frac{20}{0.75 imes 220} ight]^2=0.735 \mu F[/latex]

d. From Eq. (17.15),

[latex]\delta =\frac{\alpha }{\omega _0}=\frac{R}{2}\sqrt{\frac{C}{L} }[/latex] (17.15)

the snubber resistance is

[latex]R=2\delta \sqrt{\frac{L}{C} }[/latex] (17.25)

[latex]=2 imes 0.4\sqrt{\frac{50}{0.735} }=6.6\Omega [/latex]

e. From Eq. (17.14),

[latex]\omega _0=\frac{1}{\sqrt{LC} }[/latex] (17.14)

[latex]\omega _0=\frac{10^6}{\sqrt{50 imes 0.735} }=164,957 rad/s [/latex]

From Figure 17.19,

[latex]\frac{d_v/dt}{V_s\omega _0}=0.88 [/latex]

or

[latex]\frac{d_v}{dt}= 0.88 V_s\omega _0 = 0.88 imes 220 imes 164,957 = 31.9 V/\mu s[/latex]

f. From Eq. (17.18),

[latex]v(t = 0) = RI_R[/latex] (17.18)

the initial reverse voltage is

[latex]v(t = 0)= 6.6 × 20 = 132 V[/latex]

Question 17.3: Finding the Values of the Snubber Circuit The recovery curre...

This Question has been Answered.

Already have an account?

Login

Related Answered Questions