LTspice: Trouble finding certain transistors, switches, and op-amps

Discussion in 'General Electronics Chat' started by Narwash, Jun 27, 2012.

  1. Narwash

    Thread Starter Member

    Jun 27, 2012
    Hi all,

    I'm kind of new to LTspice and was looking to model a decently large, 3 stage circuit. Figure the best way to learn is to jump in feet first.

    However, I'm having trouble finding the particular libraries for a CZ8320 RF amplifier, a 2N3570 high frequency transistor, a 2N222 high speed switch,, and LF356 OP-Amp.

    The circuit is from a relatively old schematic (1990) and I've done some googling for the correct libraries but I haven't had much luck.

    Thanks in advance for your help! :)
  2. absf

    Senior Member

    Dec 29, 2010
    Last edited: Jun 29, 2012
  3. Narwash

    Thread Starter Member

    Jun 27, 2012
    Sweet deal! I'll take a look. Thanks!
  4. Veracohr

    Well-Known Member

    Jan 3, 2011
    Are you aware you can construct your own component by entering specs? You don't necessarily have to find a library; if you have all the important specs from a datasheet you should be able to make a useable model. If you look through the LTSpice user manual it shows the parameters available for editing for each type of component.
    Narwash and absf like this.
  5. Narwash

    Thread Starter Member

    Jun 27, 2012
    Cool thanks. Been looking into that this morning. I'm having trouble converting data sheet parameters to spice parameters, however.

    From this forum I was reading, it seems like others have similar problems:

    After messing around with LTspice, the 2N222 npn transistor is already in the standard library. I was hoping to just modify a few of the parameters there to make a rough model of the 2N3570, but I'm not sure how to convert the parameters on the data sheet to those listed in the LTspice help file for bipolar transistors.

    Anyone have any ideas? Thanks!
  6. SgtWookie


    Jul 17, 2007
    It's most likely not worth the effort to try to model obsolete components, as even if you can find them, they will be prohibitively expensive.

    A much more productive approach is to compare the specifications of the old components, and look for equivalent or better-than parts that are currently available, that also have PSPICE models available.

    Keep in mind that PSPICE simulations just provide you with a starting point; you really have to build it using real components, and then troubleshoot it. The CZ8320 RF amp has a frequency range of kHz up to 1GHz. Once you start getting into hundreds of MHz, parasitics really start to come into play; a 47pF surface mount multilayer 0805 capacitor will measure close to 150pF at 500MHz.
    Narwash likes this.
  7. Narwash

    Thread Starter Member

    Jun 27, 2012
    That's true. Thanks for the advice.

    The operating frequencies of this circuit are 9 kHz to 50 MHz. I actually built the amplifier stage of this circuit (3 cascaded 2N3570 transistors in CE configuration) on a PCB and am just modeling the input and output stages with a 50 ohm resistor. I thought I would give the SPICE model another shot though. I'm hoping to replace this discrete element amplifier with an IC so that the circuit can perform the same function with a lower supply voltage. I was looking at the AD8651 from Analog Devices for this purpose. The game plan is to build both amplifier circuits (original with discrete elements and the new one with ICs) and show the same amplification at different supply voltages.

    I thought that the 2N222 switch and the CZ8320 RF amplifier would be okay as is. But on second thought, I should look into a modern replacement for the CZ8320.

    Thanks mucho!