What Are the Best BJTs for a 17.5 MHz Pulse Input Application?

In summary, the conversation discusses the need for a pulse input ranging from +15v to -3v at 17.5 Mhz, with a load capacitor of 150pF and a required rise and fall time of 10nS. The person is building a circuit using BJT's and is seeking recommendations for NPN and PNP transistors that can handle this range. They also mention searching for RF transistors, but are unsure if they can handle the load and ask for input on their calculations and any other suggestions or references. Another person mentions using a 2N5770 npn for similar pulses, but with a lower voltage and impedance. The conversation ends with a question about the application, with possible
  • #1
VASANSNS
2
0
Hello everybody,
I have an application which needs a pulse input ranging from +15v to -3v operating at 17.5 Mhz. The load capacitor is 150pF and the required rise and fall time of the pulse is 10nS. I am building a circuit with BJT's (both NPN and PNP) . I need some idea about the criteria for selection of BJT's available in the market.

Can somebody suggest some available NPN and PNP transistors which work in this range.
Also i tried searching for some RF transistors, but i was not sure if they are capable of handling such huge loads. The max collector current for RF transistors was around 50mA. I was not whether its possible to get such a strict rise/fall time with the given load. Can somebody comment on this calculations.

Also any other suggestion or reference links are also welcomed.

Regards
SNS
 
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  • #2
I used to use a 2N5770 npn for 1-2 ns risetime pulses, but it was only about a 0.75 volt to 1.5 volt pulse into 50 ohms. Are you talking about a pulse that goes from 15 volts to -3 volts? Into what impedance? To get the fastest pulses, always keep the transisitor conducting, but never in saturation.
Bob S
 
  • #3
What is your application? Electro-optic modulator? Polarisation scrambler maybe?
 
  • #4
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What is a transistor and how does it work?

A transistor is a semiconductor device that is used to amplify or switch electronic signals. It works by controlling the flow of electrical current through a circuit by using a small current to control a larger current.

What are the different types of transistors?

There are two main types of transistors: bipolar junction transistors (BJTs) and field effect transistors (FETs). BJTs are further divided into NPN and PNP types, while FETs are divided into junction field-effect transistors (JFETs) and metal-oxide-semiconductor FETs (MOSFETs).

What are the common applications of transistors?

Transistors are used in a wide range of electronic devices, including computers, televisions, radios, and mobile phones. They are also used in power supplies, amplifiers, and switching circuits.

How do I choose the right transistor for my project?

When choosing a transistor, you should consider its voltage and current ratings, as well as its gain and frequency response. You should also make sure that the transistor can handle the power and heat dissipation requirements of your circuit.

What are some common problems with transistors and how can I troubleshoot them?

Some common problems with transistors include overheating, incorrect wiring, and incorrect biasing. To troubleshoot these issues, you should check the connections and ensure the correct biasing is applied. You may also need to replace the transistor if it is damaged or not functioning properly.

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