Sign in

Not a member? | Forgot your Password?

Search Sci.Electronics.Design

Search tips

Recent Blogs on Electronics-Related

Two Capacitors Are Better Than One
posted by Jason Sachs


Voltage Drops Are Falling on My Head: Operating Points, Linearization, Temperature Coefficients, and Thermal Runaway
posted by Jason Sachs


Optimizing Optoisolators, and Other Stories of Making Do With Less
posted by Jason Sachs


Someday We’ll Find It, The Kelvin Connection
posted by Jason Sachs


10 Items of Test Equipment You Should Know
posted by Jason Sachs


First-Order Systems: The Happy Family
posted by Jason Sachs


Lost Secrets of the H-Bridge, Part IV: DC Link Decoupling and Why Electrolytic Capacitors Are Not Enough
posted by Jason Sachs


April is Oscilloscope Month: In Which We Discover Agilent Offers Us a Happy Deal and a Sad Name
posted by Jason Sachs


Specifying the Maximum Amplifier Noise When Driving an ADC
posted by Rick Lyons


BGA and QFP at Home 1 - A Practical Guide.
posted by Victor Yurkovsky


3 LEDs powered by fingers - puzzle
posted by Henryk Gasperowicz


Series circuit - 3 LEDs
posted by Henryk Gasperowicz


Video: The PN Junction. How Diodes Work?
posted by Stephane Boucher


Two jobs
posted by Stephane Boucher


2N3055 | 8051 | Amplifier | AVR | Battery | Capacitors | Charger | CMOS | Converter | DAC | Decoder | Demodulator | Diode | Ethernet | Flash | FPGA | GPS | I2C | IDE | Laser | LCD | LED | LTSpice | MOSFET | Op-amp | Oscillator | Oscilloscope | PCB | PID | PLL | PSpice | PSU | PWM | RFID | RS232 | RS485 | SMPS | Solenoid | Spice | Switcher | TCP/IP | Transformer | Transistor | TTL | USB | VCO | Zener

See Also

DSPEmbedded SystemsFPGA

design | When and Why use resistors between base and emitter


There are 3 messages in this thread.

You are currently looking at messages 1 to 3.

When and Why use resistors between base and emitter - Précis d'electronique - 2010-06-02 22:50:00

Hi, I would like to know in your opinion  when and why use resistors
between the base an the emitter in a transistor.


I'm making a bridge h but not to control a motor, it is for having a
+/- signal at a frequency>100Hz, I just have a resistor as a charge,
my signal is 200Vpp Iam considering to use MOSFETs.

my circuit its very similar to this one

http://www.mcmanis.com/chuck/Robotics/tutorial/h-bridge/images/bjt-schematic.gif

 I simulate it but it seems (the signal) better without the resistors.

Thanks in advance.

Re: When and Why use resistors between base and emitter - Bill Sloman - 2010-06-03 05:22:00

On Jun 3, 4:50 am, Précis d'electronique <ee.jce...@gmail.com> wrote:
> Hi, I would like to know in your opinion  when and why use resistors
> between the base an the emitter in a transistor.
>
> I'm making a bridge h but not to control a motor, it is for having a
> +/- signal at a frequency>100Hz, I just have a resistor as a charge,
> my signal is 200Vpp Iam considering to use MOSFETs.
>
> my circuit its very similar to this one
>
> http://www.mcmanis.com/chuck/Robotics/tutorial/h-bridge/images/bjt-sc...
>
>  I simulate it but it seems (the signal) better without the resistors.

The base-emitter resistor carries the collector-base leakage current
when the transistor is off; without the resistor this current flows
into the base and is multiplied by the beta (current gain) of the
transistor.

It also speeds up turn-off. The collector-base (Miller) capacitance
will discharge much more slowly through the base-emitter junction than
through the 10k resistors shown.

--
Bill Sloman, Nijmegen


Re: When and Why use resistors between base and emitter - Jamie - 2010-06-03 18:21:00

Précis d'electronique wrote:
> Hi, I would like to know in your opinion  when and why use resistors
> between the base an the emitter in a transistor.
> 
> 
> I'm making a bridge h but not to control a motor, it is for having a
> +/- signal at a frequency>100Hz, I just have a resistor as a charge,
> my signal is 200Vpp Iam considering to use MOSFETs.
> 
> my circuit its very similar to this one
> 
> http://www.mcmanis.com/chuck/Robotics/tutorial/h-bridge/images/bjt-schematic.gif
> 
>  I simulate it but it seems (the signal) better without the resistors.
> 
> Thanks in advance.
So they can drain any charge on the base to force it to turn off sooner?

  Other wise, you can run into a problem of hanging transistors which 
could cause them to be slightly in conductive state. This can cause some
heating of the bridge.. Especially as the freq increase..

   This is just my guess and a good one I might add ;)