# 30V pulse from transistor-inductor circuit

#### kyle7119

Joined Feb 11, 2011
84
I am trying to use to simulate this pulse:

I have designed the following circuit in LTSpice. However, I am struggling to get a larger voltage out of it. What can I add or adjust to get to 30V?

( I am measuring the voltage directly above L1 )

#### crutschow

Joined Mar 14, 2008
34,079
Put the inductor in series with the drain of the transistor, not the source.
What's the purpose of the diode?
It does nothing as shown.

#### AlbertHall

Joined Jun 4, 2014
12,332
Put the inductor in series with the drain of the transistor, not the source.
What's the purpose of the diode?
It does nothing as shown.
Moving the inductor will be able to produce a large positive going spike, but the negative spike will still be limited to the supply voltage.

#### AlbertHall

Joined Jun 4, 2014
12,332
To get 30V positive and negative going spikes, start with a 30V peak-to-peak square wave and feed that through a capacitor to a resistor to ground. You will the desired spikes across the resistor with the width of the spikes being set by the RC time constant.

#### ericgibbs

Joined Jan 29, 2010
18,679
hi k,
If you just want to simulate the pulse in LTS, this is one option.
E

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#### Alec_t

Joined Sep 17, 2013
14,238
.... and here's another option, which matches the oscillogram traces reasonably well for different rpms and load resistance.

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#### kyle7119

Joined Feb 11, 2011
84
I'm actually trying to make something that I can build and power with 12V. I was planning to feed it using a 555

#### Alec_t

Joined Sep 17, 2013
14,238
I'm actually trying to make something that I can build
For what purpose? If it's for automotive use, then the negative-going pulse portions are probably ignored/suppressed, so there's little point in generating those.

#### kyle7119

Joined Feb 11, 2011
84
For what purpose? If it's for automotive use, then the negative-going pulse portions are probably ignored/suppressed, so there's little point in generating those.
I built an engine monitor board for an experimental aircraft (using a Rotax 912 engine). I want to verify the tachometer "filter" circuit before I actually plug it into the aircraft. The circuit is supposed to limit the pulse to 5V. It works in steady state mode, but I want to verify it against high-voltage transients, both positive and negative.

D7 = BAT54S
D8 = PMEG4020ETP
D9 = PDZVTR4.3B

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#### eetech00

Joined Jun 8, 2013
3,824
Hmmm...Is this what your looking for?

The output shown is at 100Hz(6000RPM) but also works at 8.33Hz(500RPM). I'm thinking the clock generator could be made using a NE555 timer chip.

eT

#### kyle7119

Joined Feb 11, 2011
84
Hmmm...Is this what your looking for?

The output shown is at 100Hz(6000RPM) but also works at 8.33Hz(500RPM). I'm thinking the clock generator could be made using a NE555 timer chip.

eT
Thanks for the circuit, it gave me some ideas.

Here is a circuit that does the same thing with a +/- 12V supply. However, I'm still trying to figure out how to do this (1) without the -12V supply and (2) without the bipolar square wave