Most frequently asked questions for beginners - Revision history

DennisChi: Specify default value of Vh for Schmitt devices.

2024-02-08T17:58:55Z

Specify default value of Vh for Schmitt devices.

Analogspiceman: /* How can I add subcircuits to LTspice? */ corrected spelling of LTspice and SPICE

2019-11-03T19:08:32Z

‎How can I add subcircuits to LTspice?: corrected spelling of LTspice and SPICE

Lewispaul: /* Why is the current going the wrong way in a resistor? */

2013-01-20T07:07:03Z

‎Why is the current going the wrong way in a resistor?

Lewispaul at 20:35, 15 January 2013

2013-01-15T20:35:44Z

Lewispaul: /* How can I add subcircuits to LTspice? */

2012-07-07T04:05:20Z

‎How can I add subcircuits to LTspice?

Lewispaul: /* How can I add subcircuits to LTspice? */ Added link "Adding a LM741 Op Amp Model to LTSpice"

2011-10-02T18:06:52Z

‎How can I add subcircuits to LTspice?: Added link "Adding a LM741 Op Amp Model to LTSpice"

Lewispaul: Add DISQUS for comments

2011-09-21T00:13:17Z

Add DISQUS for comments

Lewispaul2: /* How can I add subcircuits to LTspice? */

2009-09-13T03:55:27Z

‎How can I add subcircuits to LTspice?

Lewispaul2: /* How can I add subcircuits to LTspice? */

2009-09-12T02:28:11Z

‎How can I add subcircuits to LTspice?

Lewispaul2: /* How can I add subcircuits to LTspice? */

2009-09-11T21:08:33Z

‎How can I add subcircuits to LTspice?

@@ Line 109: / Line 109: @@
 *SpiceLine2: Td=5n Trise=3n
-Schmitt devices have the threshold and hysteresis parameters Vt and Vh instead of Ref.  Vup=Vt+Vh Vdn=Vt-Vh.
+Schmitt devices have the threshold and hysteresis parameters Vt and Vh instead of Ref.  Vup=Vt+Vh Vdn=Vt-Vh. The default Vh is 25 mV.
 {{#widget:DISQUS

@@ Line 42: / Line 42: @@
   Links
-  Links -> Spice Courseware And Tutorials
+  Links -> SPICE Courseware And Tutorials
   There is another document about symbols and models in our Files section.
@@ Line 85: / Line 85: @@
 You can also make this op-amp a permanent addition to your component selections. See  [[Components_Library#Opamps]]<br>
-Here is an external link as well - [http://jeastham.blogspot.com/2009/10/adding-lm741-op-amp-model-to-ltspice.html Adding a LM741 Op Amp Model to LTSpice ]
+Here is an external link as well - [http://jeastham.blogspot.com/2009/10/adding-lm741-op-amp-model-to-ltspice.html Adding a LM741 Op Amp Model to LTspice ]
 ==== I have a pulse source in my schematic with zero transition times.&nbsp; LTspice only shows slow transition times of 2ns.&nbsp; What's going on here? ====

@@ Line 24: / Line 24: @@
 ==== Why is the current going the wrong way in a resistor? ====
-LTspice has to pick a reference current direction, and it can only be one way.  Think of it like the current convention used in [http://en.wikipedia.org/wiki/Kirchhoff%27s_circuit_laws Kirchhoff's circuit laws].  Simply rotate your resistor 180 degrees in the schematic and the current will be to your liking.
+LTspice has to pick a reference current direction, and it can only be one way.  Think of it like the current convention used in [http://en.wikipedia.org/wiki/Kirchhoff%27s_circuit_laws Kirchhoff's circuit laws].  Simply rotate your resistor 180 degrees in the schematic and the current will be to your liking.  '''Alternate:''' Download [[File:Res.asy]] and place in your /lib/sym folder.  This symbol has a small arrow indicating the defined way current flows.
 ==== How can I add intrinsic device models (BJTs, FETs, etc.) to LTspice? ====

← Older revision		Revision as of 20:35, 15 January 2013
Line 21:		Line 21:

	It is not possible to use copy and paste in the symbol editor.  Symbol files are ascii text.  Merge the text as described in [http://tech.groups.yahoo.com/group/LTspice/message/7201?threaded=1&l=1 message 7201] in the LTspice Yahoo Group.		It is not possible to use copy and paste in the symbol editor.  Symbol files are ascii text.  Merge the text as described in [http://tech.groups.yahoo.com/group/LTspice/message/7201?threaded=1&l=1 message 7201] in the LTspice Yahoo Group.
		+
		+	==== Why is the current going the wrong way in a resistor? ====
		+
		+	LTspice has to pick a reference current direction, and it can only be one way. Think of it like the current convention used in [http://en.wikipedia.org/wiki/Kirchhoff%27s_circuit_laws Kirchhoff's circuit laws]. Simply rotate your resistor 180 degrees in the schematic and the current will be to your liking.

	==== How can I add intrinsic device models (BJTs, FETs, etc.) to LTspice? ====		==== How can I add intrinsic device models (BJTs, FETs, etc.) to LTspice? ====

@@ Line 67: / Line 67: @@
 This section of the asy file gives the location and the same information as opening the .asy file in LTspice.  So it's your preference which approach you take.
-An excerpt from the subcircuit we want to use is listed below in its original form: [http://www.national.com/models/spice/LM/LMH6642.MOD Source of the SPICE model from National Semiconductor]
+An excerpt from the subcircuit we want to use is listed below in its original form: [http://ltwiki.org/images/f/fa/LMH6642.MOD Source of the SPICE model from National Semiconductor]
 <pre>
 * PINOUT ORDER -IN +IN VCC VEE OUT
@@ Line 77: / Line 77: @@
 Saving the opamp2.asy file in LTspice as Opamp2(In+ In- reversed).asy, right-clicking the pins as indicated above, then reversing the pin orders on the input produces this file [[File:Opamp2(In+ In- reversed).asy]]  Note:  You have to close and reopen LTspice so that this symbol is available.
 <br>
-Finally, we can add our new opamp2 to a test circuit and try it.  We have to save the model [http://www.national.com/models/spice/LM/LMH6642.MOD Source of the SPICE model] to the same directory as our test file.  Next, we can place the component in our circuit, the new Opamp2(In+ In- reversed).  Right clicking on the modified opamp2 component, we put LMH6642 as the Value.  This name must ''exactly'' match the subcircuit name in LMH6642.MOD.  Then we add an include statement on the test file, .include LMH6642.mod.
+Finally, we can add our new opamp2 to a test circuit and try it.  We have to save the model [http://ltwiki.org/images/f/fa/LMH6642.MOD Source of the SPICE model] to the same directory as our test file.  Next, we can place the component in our circuit, the new Opamp2(In+ In- reversed).  Right clicking on the modified opamp2 component, we put LMH6642 as the Value.  This name must ''exactly'' match the subcircuit name in LMH6642.MOD.  Then we add an include statement on the test file, .include LMH6642.mod.
 The test circuit is here: [[File:LMH6642 test opamp2(+-).asc]]

← Older revision		Revision as of 00:13, 21 September 2011
Line 105:		Line 105:

	Schmitt devices have the threshold and hysteresis parameters Vt and Vh instead of Ref. Vup=Vt+Vh Vdn=Vt-Vh.		Schmitt devices have the threshold and hysteresis parameters Vt and Vh instead of Ref. Vup=Vt+Vh Vdn=Vt-Vh.
		+
		+	{{#widget:DISQUS
		+	\|id=ltwiki
		+	\|uniqid={{PAGENAME}}
		+	\|url={{fullurl:{{PAGENAME}}}}
		+	}}

@@ Line 73: / Line 73: @@
 .SUBCKT LMH6642 2 3 7 4 6
 </pre>
-So, we either have to modify the symbol or the subcircuit.  Given the provisions of the model, that it cannot be modified AND there would be other subcircuits that have the same netlist order, i.e. IN+ and IN- reversed, the choice is to make a new symbol and save it under 'Opamps' as is opamp2.
+So, we either have to modify the symbol or the subcircuit.  Given the provisions of the model, that it cannot be modified (see Copyright) AND there would be other subcircuits that have the same netlist order, i.e. IN+ and IN- reversed, the choice is to make a new symbol and save it under 'Opamps', the same folder as opamp2.
-Saving the file in LTspice as Opamp2(In+ In- reversed).asy, then right-clicking the pins as indicated above, then reversing the pin orders on the input produces this file [[File:Opamp2(In+ In- reversed).asy]]  Note:  You have to close and reopen LTspice so that this symbol is available.
+Saving the opamp2.asy file in LTspice as Opamp2(In+ In- reversed).asy, right-clicking the pins as indicated above, then reversing the pin orders on the input produces this file [[File:Opamp2(In+ In- reversed).asy]]  Note:  You have to close and reopen LTspice so that this symbol is available.
 <br>
-Finally, we can add our new opamp2 to a test circuit and try it.  We have to save the model [http://www.national.com/models/spice/LM/LMH6642.MOD Source of the SPICE model] to the same directory as our test file.  Then we add an include statement on the test file, .include LMH6642.mod.
+Finally, we can add our new opamp2 to a test circuit and try it.  We have to save the model [http://www.national.com/models/spice/LM/LMH6642.MOD Source of the SPICE model] to the same directory as our test file.  Next, we can place the component in our circuit, the new Opamp2(In+ In- reversed).  Right clicking on the modified opamp2 component, we put LMH6642 as the Value.  This name must ''exactly'' match the subcircuit name in LMH6642.MOD.  Then we add an include statement on the test file, .include LMH6642.mod.
 The test circuit is here: [[File:LMH6642 test opamp2(+-).asc]]