Darlington Pair using BC 547

Thread Starter

pal114525

Joined Jul 3, 2015
46
Hi,

Would you be kind to tell me if I can use two BC547 transistor to design a darlington pair amplifier?

Thanks & Regards.
 

Thread Starter

pal114525

Joined Jul 3, 2015
46
Hi,
Thanks for your valuable feedback.
Would you be kind to tell me the following point?

I need 500mA current to pass through a rectangular coil to create an EM field.
My input is 3V sinusoidal wave with frequency 16KHz and the current is very low ( Generated from a Hartley oscillator). I want to amplify this current to ~500mA.
Shall I use a darlington pair amplifier or shall I use a push-pull amplifier along with a preamplifier? Which one would be the best suitable for this?

Thanks & Regards.
 

Lestraveled

Joined May 19, 2014
1,946
Please post more information, as in, inductance of the coil, voltages, a block diagram that shows signals, amplitudes and signal flow. Your description is vague, please clarify.
 

absf

Joined Dec 29, 2010
1,949
From the datasheet of BC547, the maximum Ic=100mA and Icm=200mA. So even you connect them in Darlington pair, the output can never exceed its max current though the combined gain is very high. Take a look at the BC547 pdf attached.
 

Attachments

Thread Starter

pal114525

Joined Jul 3, 2015
46
Hi,

Please see the attachment.
My input to the amplifier is 3V sinusoidal wave with frequency 16KHz and the current is very low ( Generated from a Hartley oscillator). I want to amplify this current to ~500mA.
Shall I use a darlington pair amplifier or shall I use a push-pull amplifier along with a preamplifier? Which one would be the best suitable for this?

Thanks & Regards.
 

Attachments

crutschow

Joined Mar 14, 2008
26,866
To drive that amount of current into a coil at 16kHz will likely require a push-pull amplifier.
What is the coil resistance and inductance? Without that info we can't help any further.
 

bertus

Joined Apr 5, 2008
21,263
Hello,

That would be about 2.5 Watts. (500 mA X 500 mA X 10 Ohms)
There are a lot of audio amplifier circuits that will do that for you.

Bertus
 

Thread Starter

pal114525

Joined Jul 3, 2015
46
Hello,

That would be about 2.5 Watts. (500 mA X 500 mA X 10 Ohms)
There are a lot of audio amplifier circuits that will do that for you.

Bertus
Hi,

Thanks for your valuable feedback.
Would you be kind to explain me the following point?
1. How to determine the value of resistors for a typical Class B push -pull amplifier?

Thanks & Regards.
 

Thread Starter

pal114525

Joined Jul 3, 2015
46
Hello,

You could have a look at a power-opamp like the LM675.

Bertus
Hi,

Thanks for your valuable feedback.
LM675 uses supply voltage range from 16V to 60V. In my design, the supply voltage is 12V.
Would you be kind to tell me if there is any other way of current amplification of the order ~500mA?

Thanks & Regards.
 

kubeek

Joined Sep 20, 2005
5,748
To get 0.5A peak current at 16kHz through a 458uH coil you need roughly 24V peak wave. I you would have to quadruple your 12v supply voltage to get that 48Vpp required.
 

crutschow

Joined Mar 14, 2008
26,866
If you add a 220nF in series with the coil it will be resonant at near 16kHz.
Driving that with a 0-12V, 16kHz square-wave showed a peak inductor current of about 350mA in simulation.
To get more current you could drive the resonant circuit with a push-pull audio bridge circuit such as the TDA2005, which would near double the supply voltage across the load (about 20Vpp with a 12V supply).
That should give a maximum peak current in the resonant circuit (220nF in series with the coil) of over 600mA.

Edit: If you can tolerate some frequency deviation then you could add a series capacitor to form a resonant circuit at about 16kHz and use feedback to form a high current resonant oscillator at this resonant frequency. You can do that with a fairly simple bridge driver circuit, such as below:
The LTspice simulation shows a peak inductor current of a little over 700mA.
Note: R4 needs to be rated for at least 2W.

Resonant Driver.gif
 

Attachments

Last edited:

Thread Starter

pal114525

Joined Jul 3, 2015
46
If you add a 220nF in series with the coil it will be resonant at near 16kHz.
Driving that with a 0-12V, 16kHz square-wave showed a peak inductor current of about 350mA in simulation.
To get more current you could drive the resonant circuit with a push-pull audio bridge circuit such as the TDA2005, which would near double the supply voltage across the load (about 20Vpp with a 12V supply).
That should give a maximum peak current in the resonant circuit (220nF in series with the coil) of over 600mA.

Edit: If you can tolerate some frequency deviation then you could add a series capacitor to form a resonant circuit at about 16kHz and use feedback to form a high current resonant oscillator at this resonant frequency. You can do that with a fairly simple bridge driver circuit, such as below:
The LTspice simulation shows a peak inductor current of a little over 700mA.
Note: R4 needs to be rated for at least 2W.

View attachment 88160
Hi,

Thanks for your valuable feedback.
Would you be kind to explain me the following point?

1. If the inductor value (inductance) is changed from 458uH to some other (say 1.1 mH) value, then what are the components would require a change? What are the equations involved in that?

Thanks & Regards.
 
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