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Looking for transistors that can do the job...

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Externet

Well-Known Member
Hi all.

Looking for which transistors could match the requierements:

NPN
Vce between 99 and 200 V
Ic between 499 mA and 1 A
Ft between 49 and 180 MHz
TO220 if possible

No matter if low gain, it is only to linearly invert (gain 1) a 25 Vpp sawtooth signal riding on top of 50 Vdc as common emitter amplifier buffer.

If anyone has a spare to sell, or trade with whatever you need, fine.

A simulation on a simple Multisim works fine when chosing an 'ideal' transistor, but does not perforn selecting a couple of candidates in its humble library.
 
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What do you mean Ic between 500mA and 1A?

What's the maximum current you need to amplify?

The same question applies to the voltage and transition frequency. You normally specify the maximum voltages, currents in your circuit, then choose a transistor which exceeds the ratings. The Ft is the frequency at which the gain becomes unity so you need to stay well below it.

More importantly you haven't specified the Hfe?

Yesterday someone wanted to find a replacement for an odd transistor which was within the ranges you've listed, here's what I found for them:

The transistor's datasheet:
https://www.electro-tech-online.com/custompdfs/2010/04/7767.pdf

Possible replacements:

**broken link removed**
2SC2238 pdf, 2SC2238 description, 2SC2238 datasheets, 2SC2238 view ::: ALLDATASHEET :::

Digi-Key - 2SC59930Q-ND (Manufacturer - 2SC59930Q)
Discrete | Maintenance and Discontinued Types | Semiconductors | Panasonic Industrial Solutions Global

Anyway, please post a schematic.
 
Thanks for responding, Hero

Any current capability of the device between 0.5A and 1A should provide enough headroom and safety margin.
The maximum current that the load can draw is 300mA, expected to be typical 100mA

The voltage supply for the circuit is 87V. Any device capable of handling over 100V will provide headroom and safety margin.

Ft maximum in operation is 30MHz; typically 10 MHz. Any device capable of 50 MHz will provide headroom and safety margin.

hfe not stated. The signal just needs inverting at the same exact level it is fed to the transistor, no gain wanted.

I will look at your links. Am sorry am unable to post the simulation schematic; browsing the web for a similar but not exact; this plain :

File:Common emitter amplifier.svg - Wikipedia, the free encyclopedia

Without capacitors Ce; Cout; Cin, direct feed to base on a 18K series resistor, direct output from the collector node. Rc = Re = 1K ; V+ =87V ; Vin = Vout = 25V pp sawtooth riding on +50V dc

Edited, added ---> Checked at your suggested devices, look good.

Edited, added ---> the schematic of the simulation is closer to the one here:

https://www.electronicsteacher.com/experiments/discrete-semiconductors/common-emitter-amplifier.php

After the paragraph "Instructions" with no potentiometer. Rb=18 K ; Rc = Re = 1K on 'ideal' transistor
 
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Why can't you post the schematic?

The second circuit isn't intended as a practical circuit, it won't be very stable and will have lots of distortion.

A transistor with an ft of 50MHz won't amplify a 30MHz signal much.

Ever considered a cascode amplifier?
 
Hi Hero.
Sorry, unable to capture the Multisim simulator screen. Old version, or limited features, or do not know how to. The project is :

Waveforms 62 and 63:

https://i588.photobucket.com/albums/ss323/Innernet/62and63.png

I have 62 alive, 63 is dead. I want to attempt to replicate a mirror waveform "63" with a simple inverting circuit fed tapping from existing pin 9 waveform "62" as only resource I can think of to restore life to my oscilloscope by disconnecting output pin 4 of a malfunctioning U800 -unobtainable IC- and insert instead the inverted to feed R804 for the minus horizontal deflection plate V900.

https://i588.photobucket.com/albums/ss323/Innernet/U800.png.

Not considered the cascode amplifier at all. NO amplification desired. Just inversion
 
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Hi Hero.
Sorry, unable to capture the Multisim simulator screen. Old version, or limited features, or do not know how to.
Have you tried pressing the print screen key?

Failing that, take a picture of the monitor with a digital camera but please crop and scale the image to a sensible resolution before posting it.
 
Once you press the Print Screen key, you screen picture will be in the clipboard. Then open paint or GIMP, and paste it in there. Then you can save it as a jpg or png. (Please no bmps!)
 
Half managed to print and scan and upload the simple simulation.
The component labels faintly show.

Rb=10K; Rc=1K; Re=0.8K; Rload=10K; Vsupply=87V

**broken link removed**

With the 'ideal' transistor, it inverts as desired, nice and neat. Real life is very different.
 
The circuit is wrong but that's the least of your worries, you need to learn how to use the simulation software before you can simulate it properly.

It appears you're using Electronics Workbench which I also have. The only difference is you've got your set to US symbols, mine is set to EU.

To copy the circuit to the clipboard, select copy as bitmap from the edit menu, see attachment below.
EWB copy1 bmp..PNG

The mouse cursor will then turn into a cross, hold down the left button, drag over the area you want to copy and release the left button. If you get it wrong, you'll have to start from the beginning.
EWB copy2 bmp..PNG

To paste into MS Paint, select paste from the edit menu, see screenshot below. Then save it in PNG format. If you don't know how to start MS Paint or save files using it, ask me and I'll post a tutorial.
Paste paint..PNG

I'm assuming you're using XP or Windows 2000 and not Vista.
 
power transistors have less t.frequency ,huh?
then y use it? hero, a MOSFET can do it huh?
 
You can get high frequency power transistors, some of the ones I linked to in my first reply thread will do.

I'm not completely sure what he is trying to do, it's obviously a common emitter amplifier but it's not right.

The circuit could probably be redesigned to use a MOSFET but there are BJTs which will do.
 
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Well the frequency of that waveform is only 333Hz so the amplifier doesn't need a large bandwidth, probably only up to 10kHz to account or the higher frequency harmonics?

A common emitter amplifier with Re = Rc will give a gain of -1 (inverting) but you've not said what the source and load impedances are so I can't tell you what resistor values to use.

Does it have to be DC coupled?

Do you have a service manual for the 'scope?

Do you know what the unobtainable IC is? Is it just an op-amp?

What's the supply voltage?

You can get 60V op-amps which might be a good solution.
 
Thanks, Hero.
The frequency on posts #5, #14 "62 & 63" waveforms is the setting used to confirm calibrations by the service manual. The operation goes to 5nSec/division = 50nSec/sweep :
http://www.millivolt.se/bilder/2465/2465.jpg

The load impedance is unknown and cannot guess how to speculate on it or what capacitance to put in the simulator. It is an electrostatic deflection plate as said in post #5

Yes, I bellieve it has to be DC coupled.

Yes, I do have the service manual. The pertinent schematic portion is the second link on post #5 ; and shows the Tektronix unobtanium IC U800, part number 155-0241-02 and it is not an op-amp, but a complex/multiple functions circuit with no way to find what is in its design.

The supply voltage is +87V as said in posts #3, #8

I looked at op-amps to start with, and the only kind of applicable device was the Apex PA19, with a too high cost and the doubt of being suitable on top of it.
 
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Sorry there's not much more I can suggest to help because I don't have enough to go on.

I hope you get it working in the end.
 
Could you post details of this fix please.

I have a similar problem and would be very interested in seeing a schematic or some sort of diagram of your fix. It would help a lot!
 
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