APPLICATION NOTE

®

HIGH FREQUENCIES DAMPER DIODES

AN874/0996 Ed : 2

B. RIVET

INTRODUCTION

The trend in new monitors is for ever increasing

switching frequencies of the horizontal deflection

stage : 64kHz ---> 110kHz.

SGS THOMSON has developed new 1500V

Damper

diodes

(DTV64D-DTV82D-DTV110D)

using a new silicon structure and a suitable lifetime

reduction process both optimized in order to

For

high

switching

frequencies,

the

key

parameters optimization of the damper diodes

becomes more and more critical. This application

note describes these key parameters and the

associated power losses.

KEY PARAMETERS OF THE DAMPER DIODE

The key parameters of a damper diode are the

Reverse recovery time : trr

The table in fig.1 gives the maximum reverse

recovery time for the three high frequency damper

diodes.

The application note "CHOICE OF DAMPER

DIODE FOR A HORIZONTAL DEFLECTION"

explains in detail the very particular mechanism of

the switching OFF losses (Poff) in the damper

diode. The maximum value of trr has been chosen

to be sure that the switching OFF losses in the

damper diode will be negligible.

This parameter fixes the value of the conduction

losses (Pcond) in the diode. This losses can be

estimated by :

Pcond

= Vto

Ip

2

δ = Rd

Ip

2

3

δ

Where :

Ip

: peak current in the diode

δ

: duty cycle of the conduction time

Vto

: Threshold voltage of the damper diode

Rd

: dynamical resistance of the

Example : With a DTV64D

Vto (typ.) = 0.89V

Rd

(typ.) = 35m

Ω

and

Ip = 6A

δ = 0.45

We find

Pcond =1.4W

This parameter has to be as low as possible in

order to reduce switching ON losses in the diode.

The peak forward voltage depends mainly on the

µs.

Fig.2 shows the current and voltage across the

diode when it turns on, in the following conditions :

µs Tj = 100°C with DTV64D,

DTV82D and DTV110D.

trr max

µs

DTV64D

135 ns

DTV82D

125 ns

DTV110D

115 ns

Fig.1: Maximum

reverse

recovery

time

of

DTV64D, DTV82D and DTV110D.

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