1/5 AN1380 application note ? new family of damper and modulation diodes for horizontal deflection circuit july 2001 by b. rivet stmicroelectronics is introducing a new family of damper and modulation diodes for horizontal deflection circuits in tv and monitor applications. this application note will discuss the key parameters of the damper diode and its associated losses. a wide range of damper and modulation diodes will be outlined and some criteria will be given to select the appropriate component. introduction in order to understand the key parameters of the damper diode, it is interesting to refer back to the behaviour of a basic horizontal deflection circuit. the basic horizontal deflection circuit (without east-west correction) is shown in fig. 1 and the main current and voltage waveforms in fig. 2. 1.1 behaviour of the basic circuit of the hori- zontal deflection power stage 1. key parameters of damper diodes in basic horizontal deflection circuit b+ hv l i l v 0 v t c i c i d i t fig. 1: simplified diagram of the horizontal deflec- tion stage at t=t0 the transistor starts to turn on. the current in the line yoke and in the transistor is given by: () ii v/lt tl 0 == the voltage v t across the diode is equal to v cesat , the damper diode is blocked. i t i p i c i p -i p i l i p -i p i t i p v t t0 t1 t2 t0+t t t t t t t d t w off (di/dt) on v p w on v f v fp v cesat fig. 2: waveforms in the basic horizontal deflec- tion circuit
application note 2/5 at t=t1, the transistor turns off. the circuit be- comes resonant (v 0 -l-c), a high voltage appears across the diode (typically about 1100v). this is the reason why 1500v components are generally used. the current passes from i p to -i p . at t=t2, the voltage v t becomes negative and the damper diode starts to turn on. the current through the diode and the yoke is given by: () ii v/lt dp 0 =- at t0+t a new cycle starts. fig. 3 : current, voltage and switching energy in damper diode at turn on conduction losses can be calculated by: pv.i/2r.i/3 cond to p d p 2 =+ dd .. with () vi v r.i ff to d f =+ example: dtv1500m v to = 1.37v r d = 0.047 w i p =4a d = 0.45 p cond = 1.35w 1.2.1 forward voltage (v f ) and conduction losses (p cond ) 1.2 key parameters of damper diodes and their associated losses at t=t2, when the diode turns on, there is in the same time current and overvoltage across the di- ode (fig. 3) causing switching on energy: w on can be calculated by: wv.idt on tfr = 0 (fig. 3) and p w . f on on = example: dtv1500m in the conditions of fig.3 w on =14 m j p on = 0.98w at 70khz 1.2.2 peak forward voltage (v fp ) and turn on switching on losses (p on ) for high switching frequencies, this example shows that p on is high and v fp becomes a critical parameter. v fp increases with (di/dt) on . in this application, this parameter is mainly fixed by the layout and is generally lower than 100a/ m s. the new family of damper diodes uses new technology allowing a very low leakage current and negligible reverse losses in comparison with the other losses. 1.2.3 leakage current and reverse losses at t=t0, when the diode turns off, the reapplied voltage is low (v cesat of the transistor), and the corresponding switching energy w off is also very low (between t0 and t1). due to this low reapplied voltage,the damperdiode takes time to evacuate all these reverse recovery charges. for a given fre- quency, if trr is too high, there are always charges when the transistor turns off (at t1). in this situation the reverse recovery charge is evacuated over a high voltage inducing high switching energy w off (fig. 2). we can consider this as a critical fre quency f c . below f c ,w off is negligible (the damper diode has evacuated all the reverse recovery charges at t0). above f c , the switching energy increases very rapidly and can lead to a thermal runaway problem. this critical frequency depends not only on the reverse recovery time, but also on the operating junction temperature of the diode and v cesat . 1.2.4 reverse recovery time (trr) and turn off switching losses (p off )
application note 3/5 power losses frequency p = f(v , f) on fp p = f(v , i ) cond f p p = f(f ) off c p <<<< rev f = f(trr, v t, t ) c cesa j fig. 4: main features of the different losses the higher the v cesat, the higher f c (the diode evacuating these charges more quickly). in a de- flection design it is important to have a negligible w off (to keep the junction temperature under control). this is the reason why stmicroelectronics has developed damper di- odes with a low reverse recovery time. the fig. 4 summarizes the main features of the different losses as follows: n p on are proportional to v fp and f n p cond depend on v f (v t0 ,r d ), i p and d n p rev are negligible n p off are negligible for ff c n f c depends on trr, t j ,v cesat 2. st damper family in new monitor designs, horizontal deflection frequency is becoming higher and higher. in a conventional 15 inches monitor, the maximum frequency can be higher than 70khz, and in a high end monitor this frequency can reach 130khz. this evolution has led stmicroelectronics to develop a new family of damper diodes with very good dynamical parameters (low v fp and trr). the new st damper diodes have a low trr in order to get a higher critical frequency (f c ). this new technology allows v fp to be reduced and as a consequence, the turn on switching losses are also reduced. the table in fig. 5 shows the four different types of damper diode: the l, m, h and uh families with their key parameters. every device is available in to-220ac, to-220fpac and isowatt220ac. v f max (6a, 125 c) (v) trr max (1a, 50a/ m s 30v, 25 c) (ns) v fp typ (6a, 80a/ m s 100 c) (v) v rm (v) dtv1500l (4a) 1.5 170 (4a) 28 1500 dtv1500m 1.65 135 21 1500 dtv1500h 1.7 125 18 1500 dtv1500uh 1.3 125 12 1500 fig. 5: key parameters of the different damper diodes for tv and 14, 15, 17 inches monitors the damper diode is generally associated with a modulation diode for east-west correction fig. 6.
application note 4/5 stmicroelectronics offers an axial modulation diode stth306 and a dmv family dmv1500l, dmv1500m, dmv1500h. the dmv1500x device is a damper diode with a modulation diode in an isolated to-220 package. electrical parameters of the damper diode are the same as the dtv1500l, dtv1500m, and dtv1500h respectively. the modulation di- ode is a 600v device with very good dynamical parameters (low trr and v fp ). the main parameters of the modulation diode are: trr max (1a, 50a/ m s, 30v, 25 c)=50ns v fmax (3a, 125 c)=1.4v v fpmax (3a, 80a/ m s, 100 c)=8v generally, monitor manufacturers have the following rule to design damper and modulation diodes: the case temperature of the device has to be lower than 100 c for a room temperature equal to 40 c. a very common question is: is it possible to use a damper or a modulation diode with a peak current i p higher than the average current (i f(av) ) given in the datasheet? the answer is yes. the only limitations are the i f(rms) value and the oper- ating junction temperature. with the rule t case <100 c, there is generally no problem when using these components with an i p higher than i f(av) . fig. 7 shows the device generally used versus tv and monitor size. b+ ht dmv1500x fig. 6: basic circuit of the horizontal deflection circuit with east-west correction 14o 15o 17o 19o >19o monitor tv dtv1500uh dtv1500h dmv1500h dtv1500m dmv1500m dtv1500l dmv1500l stth306 high end low end fig. 7: damper and modulation diode versus tv and monitor size stmicroelectronics has developed an optimized family of damper and modulation diodes specifically for tv and monitor applications. with the horizontal deflection frequency becoming higher and higher, st has developed devices with very good dynamical parameters (low trr and v fp ). st offers a wide range of damper and modula- tion diodes allowing the designer to choose an appropriate performance-cost solution. conclusion
application note 5/5 information furnished is believed to be accurate and reliable. however, stmicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of stmicroelectronics. specifications mentioned in this publication are subject to change without notice. this publication supersedes and replaces all information previously supplied. stmicroelectronics products are not authorized for use as critical components in life support devices or systems without express written ap- proval of stmicroelectronics. the st logo is a registered trademark of stmicroelectronics ? 2001 stmicroelectronics - printed in italy - all rights reserved. stmicroelectronics group of companies australia - brazil - china - finland - france - germany - hong kong - india - italy - japan - malaysia malta - morocco - singapore - spain - sweden - switzerland - united kingdom - u.s.a. http://www.st.com
|
