PSPICE Diode Problem

"siliconmike" schrieb im Newsbeitrag news: snipped-for-privacy@75g2000cwc.googlegroups.com...

Hello Mike,

Recovery time means the reverse recovery time. Reverse recovery time is the time required to switch off.

Stimulate the diode with a forward current of 1A. Then switch to a negative voltage. Now look how long the current flows in the reverse direction. It's important to know the test setup if you want check against any number from the datasheet.

A possible test circuit: I_forward=1A, I_backward=1A Voltage source _/-\\_/-\\_.... +10V/-10V, 50us on, 100us period Series resistor with 9 Ohm Diode connected to resistor and GND(0V). Now you should get a few microseconds of turn-off delay. I checked this with a 1N4002 model.

Best regards, Helmut

PS: I use LTspice. It's an unlimited and free of charge SPICE simulator with GUI(schematic entry and waveform viewer).

This is the test circuit: "1N4002_test.asc" Just copy and paste it into a file named 1N4002_test.asc . Remove additional line feeds caused by the mail programs. Now you can open and run it with LTspice.

Version 4 SHEET 1 1352 680 WIRE -16 64 -128 64 WIRE 144 64 64 64 WIRE 512 64 144 64 WIRE -128 112 -128 64 WIRE 512 112 512 64 WIRE -128 240 -128 192 WIRE 512 240 512 176 WIRE 512 240 -128 240 WIRE -128 272 -128 240 FLAG -128 272 0 FLAG 144 64 IND1 SYMBOL diode 496 112 R0 SYMATTR InstName D1 SYMATTR Value DI_1N4002 SYMBOL res -32 80 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R1 SYMATTR Value 9 SYMBOL voltage -128 96 R0 SYMATTR InstName V1 SYMATTR Value PULSE(-10 11 1u 10n 10n 50u 100u) TEXT -144 384 Left 0 !.MODEL DI_1N4002 D ( IS=76.9p RS=42.0m BV=100 IBV=5.00u CJO=39.8p M=0.333 N=1.45 TT=4.32u ) TEXT -136 -24 Left 0 !.tran 0 300u 0 .01u TEXT -136 -64 Left 0 ;Plot I(D1) TEXT -144 344 Left 0 ;*SRC=1N4002;DI_1N4002;Diodes;Si; 100V 1.00A 3.00us Diodes, Inc. diode

I think your spice diode model only uses turn off delay, also it doesnt use the fall time wich is sometimes more of an issue when using soft recovery diodes or SRD.

Colin =^.^=

Find a better set of model parameters. Some have TT (transit time)unspecified (0) and others use 5.76 or 5.7 usec and Colin just posted one with TT=4.32usec.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

The latest PSpice diode.lib has TT=5.7us, but some time back there was NO TT specified, this defaults to zero.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

news: snipped-for-privacy@75g2000cwc.googlegroups.com...

But there is forward recovery time too. I just ran LTSpice. Looks decent. I'll take some days to check out your circuit. Thanks for the pointer.

CJO=39.8p M=0.333 N=1.45 TT=4.32u )

Diodes, Inc. diode

Use proportinal font. These are the diode params. As seen TT is 5.7uS.

D1N4748 D1N4007 D1N4001 IS 17.490000E-15 14.110000E-09 14.110000E-09 N 1.984 1.984 ISR 2.024000E-09 IKF 94.81 94.81 BV 22 1.500000E+03 75 IBV .16996 10.000000E-06 10.000000E-06 NBV 1.315 IBVL 7.007300E-15 NBVL 1.2735 RS 7.976 .03389 .03389 TT 5.700000E-06 5.700000E-06 CJO 49.000000E-12 25.890000E-12 25.890000E-12 VJ .75 .3245 .3245 M .2829 .44 .44 TBV1 840.910000E-06

I've posted the diode params in another post. Btw, I'm going to have to take some time to study your drawing regarding the high-side mosfet switch due to my inexperience in certain transistor configurations. I appreciate it though.

Mike

Feel free to ask questions.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Yes this stands for the Transit Time I beleive, however it seems there are different conventions for TT, it is also used as Transition Time for SRDs wich is different again, this confused me no end when I was trying to simulate SRDs.

Generaly it is the time taken for all the carriers that allow current flow in the PN junction to recombine wich is a random process. This cuases the 'turn off' delay.

However when the junction is initialy forward biased carriers are injected directly into the junction, the time this takes is very much smaller and so cunduction starts much more quickly, thus Turn on delay is usualy so short as to not be an issue and does not apear in the above model.

I beleive the effect of junction capacitance usualy makes turn on delay unoticable anyway.

Colin =^.^=

news: snipped-for-privacy@75g2000cwc.googlegroups.com...

I understand, it does show a pronounced reverse recovery time of about

4uS. What I'm wondering is that why is there no forward recovery period ?

When the diode turns on, the voltage across diode seems to go abruptly from -10V to 1V and the current from 0A to 11A.

In my case, the diode 1n4007 is used as a snubber parallel to a 40mH

12Ohms Inductor to which 12 volts are switched using a relay.

Therefore when the supply to the inductor is cut (assuming in a period of 1nS) , the diode turns on absorbing the current. But I'd like to focus my study on what happens "during the time" the diode turns on.

-Mike

The turn on and turn off actions of a PN junction diode are very different indeed.

Its like turning on a tap ... as soon as its on water flows imediatly, but as you turn it off it takes a while for the water to soak away.

If you imagine the water is actualy the charge carriers that permit conduction (in either direction) its a bit closer to whats realy going on.

The reason this turn off delay acts like this is that PN junction use minority charge carriers for conduction accros the barrier, and these stay in the junction untill an electron finds an empty hole or a hole finds a floating electron, they dont just simply disapear out of the terminals when you reverse the voltage.

A schotky diode however doesnt use minority carriers, and is therefroe a lot faster at turning off. as soon as you reverse the voltage they simply move out the elctrodes.

This is my simplified understanding of a very mathmatically complex process so somone correct me if im wrong please.

Colin =^.^=