Nokia Siemens Networks Flexi WCDMA teardown: integrated Doherty amplifier (part 5)

Nokia Siemens Networks Flexi Multiradio BTS is a GSM/EDGE, WCDMA/(I-)HSPA, and LTE base station for use in mobile telecommunication antenna networks. A network that you use daily on your cellphone. Teardown of a NXP BLD6G22L-150 integrated Doherty amplifier from a …

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Transistor Base Resistor Calculator

To use the calculator for transistor base resistor values, Its IMPORTANT that you read the following.

Transistor datasheet values

  • First, calculate the current you need to pass through the transistor when its on, that is your collector current.
  • Secondly, find the current gain, beta, Hfe. These values is in the datasheet for the specific transistor. To calculate for the worst case, use the minimum Hfe value or the correct value, for the collector current you need.
  • Vce voltage is the voltage across collector and emitter.
  • Base voltage is the voltage that you use to drive the base of the transistor with.
  • Voltage drop is the Vbe(sat) value, you will get this from the datasheet looking at the graph for Vbe and Vce(sat) vs. collector current.

To get the best result, consider the following

  • To insure to turn the transistor fully on, you can double the value for collector current. As a result you get a base resistor value half of what this calculator gives you.
  • For example, it is here given for the highest collector current and worst case amplification factor, Hfe. Values for your circuit might vary, be sure to enter values for your own needs.
  • To calculate for a PNP transistor, enter negative numbers in collector current, base voltage and voltage drop.
Choose transistor
  Max rating Input Calculated
Collector current A A  
Beta (Hfe)    
Vce voltage V    
Base voltage V V  
Voltage drop   V  
Base resistor value     Ω

To help you remember the pinout of the NPN and PNP transitors:

npn transistor and pnp transistor with base resistor
NPN transistor and PNP transistor with base resistor

Examples are given for NPN transistors 2N2222, 2N3055, 2N3904, BC547, TIP31, TIP31A, TIP31C, TIP41, TIP41A, TIP41C and PNP transistors 2N3906.

Formulas and math used for the transistor base resistor calculator

Ohms law: Base resistor = (Supply voltage – Voltage drop) / (Collector current / Beta)

The electronic components needed are a regular color banded 5-band resistor, the bands represent the Ohm value, resistor tolerance and in some cases temperature coefficient.

Calculators

A collection of online electronics calculators written by Mads Barnkob.

  • Transistor base resistor calculator with examples given for NPN transistors 2N2222, 2N3055, 2N3904, BC547, TIP31, TIP31A, TIP31C, TIP41, TIP41A, TIP41C and PNP transistors 2N3906.
  • Tesla Coil MMC calculator for configuring multiply mini capacitor strings in parallel and series
  • Capacitor energy calculator for energy storage in Joule and charge in Coulombs
  • Helical coil calculator for Tesla Coil secondary or other single layer coil calculations
  • Spiral coil calculator for Tesla Coil primary or other pancake coil calculations
  • IGBT gate drive calculator with duty cycle, frequency and power consumption
  • Snubber capacitor calculator for eliminating transients and switching spikes from parasitic inductance

Transistor Base Resistor Calculator

To use the calculator for transistor base resistor values, Its IMPORTANT that you read the following. Transistor datasheet values First, calculate the current you need to pass through the transistor when its on, that is...

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MMC calculator

MMC calculator
MMC tank design calculator for SGTC, VTTC, DRSSTC and QCWDRSSTC Tesla coils. Results are guidelines to designing a MMC and should always be double checked in your final design! Most importantly is that voltage rating is the...

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Capacitor energy calculator

To calculate capacitor charge in Coulombs and capacitor energy in Joule, enter the rated capacitance of the capacitor and the voltage it is charged to. Switch between the input fields to automatically calculate the values. Capacitor...

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Helical coil calculator

Here you can calculate the inductance for a given size of helical coil wound in one layer. It is optional to add the capacitance for f.ex. a primary tank capacitor or topload capacitance to find...

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Spiral Coil Calculator

Spiral Coil Calculator
Here you can calculate the inductance for a given size of a spiral coil wound in one layer. Secondly you can to add the capacitance for f.ex. a primary tank capacitor or topload capacitance to...

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IGBT gate drive calculator

Published on: Feb 17, 2016. Updated: Dec 06, 2017. To insure that we switch our IGBT fast enough to lessen losses, slow enough to avoid ringing and the drive circuitry is stable we have to...

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Snubber capacitor calculator

Snubber capacitor calculator
Here you can calculate the snubber capacitance that is needed to keep transient voltages below the maximum allowed value. Stray inductance is the inductance in the primary circuit of the inverter. If the stray inductance...

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2n3055 flyback driver

Introduction

This driver is among the simplest, with just six components it will be able of delivering high voltage with a strong enough current for various experiments.

There is also a push-pull version of this driver, more on that can be found following this link: http://wiki.4hv.org/index.php/Flyback_transformer

Safety

WARNING!: Working with electricity is dangerous, all information found on my site is for educational purpose and I accept no responsibility for others actions using the information found on this site.

Read this document about safety! http://www.pupman.com/safety.htm

Considerations

The transistor used in this circuit should not have a voltage rating higher than 250V, due to the higher base current needed of higher voltage rated transistors, this might in some cases cause problems where the self-resonating circuit can no longer drive the transistor.

At voltages higher than 12 VDC input, the components will dissipate a lot of heat and the 2n3055 transistor is most likely to burn as it is not rated for more than 15 A and it has to be derated even further for case temperatures above 25 oC.

MOSFETs are not suitable in this driver.

The frequency of operation in this circuit is determined by the capacitor across the transistors emitter and collector, experiment with the value of this capacitor to find the best performance, this capacitor have to be a good film or foil type (MKP/MKT)

 

Specifications

The driver is supplied with 12 to 17 VDC from a computer ATX PSU.

 

Schematic

 

Construction

3rd may 2008

The driver is built on a piece of vero board with multiply resistors to obtain the needed wattage rating, this is far from optimal as the load sharing between them is horrible, to ensure better sharing.

The 2n3055 transistor is mounted on a 30 x 10 cm aluminium profile, this is just about enough to keep it alive doing long runs.

4th may 2008

I experimented with voltages between 12 to 17 VDC, there is no incredible performance with higher voltage compared to the amount of heating the higher voltage generates.

Different capacitors were tried, ranging from 10 nF to 300 nF, 220 nF was found to work the best for my flyback transformer.

8 primary windings and 4 feedback windings gave the best results.

 

Sparks

7th may 2008

18 to 20 mm sparks were achieved

Keeping the electrodes just far enough apart for no spark to jump, a beautiful corona breakout is visible.

With the output coupled through a home made salt water capacitor it was possible to have loud and very bright sparks.

 

Conclusion

This is a very simple and cheap circuit to achieve around 20 kV high voltage, but where it excels in simplicity it lacks a lot in stability and efficiency.

A rough estimate is that 25-50% of the input energy is wasted as heat in the transistor.

It is cheap and simple, but inefficient and unstable.

 

Demonstration