How can this circuit work as a current booster?

[zhi_yi]

please tell me how could this circuit work as current booster? and how do this circuit can prevent overcurrent to flow? what is the function of the diode in the circuit?

thank you very much

 

[IanP]

Re: current booster 2

Again, as in Current Booster1, the vale of the resistor is wrong .. it should be somewhere between 3-10Ω ..
In this case current is limited by additional transistor, the 2N6049.
It happens when the voltage accross Rsc riches ≈0.65V and this tranistor starts to control Vbe of the power PNP transistor .. Iout≈0.65/Rsc
The function of the protection diode is exactly the same as in Current Booster1 --> protection against discharge of the output capacitor to the output of the IC if the input is shorted ..
Regards,
IanP

 

[zhi_yi]

Re: current booster 2

okay, thank you, is it the Rsc should be more smaller than the Rs? is it true? for example, if i set the Rs = 0.7ohm and Rsc = 0.07ohm, so, if the current through Rs > 1A, it would drive the 2955 on, and provide more current to the load, so it's called current booster, and if excessive current flow to the load because of it is shorted or the load reduced, the current through the Rsc would be rises, and if the current through Rsc rises about >= 10 A, the Rsc would drive the 6049 on, so it would protect the circuit from over current to flow, is it true? please correct me, thank you very much

 

[IanP]

Re: current booster 2

I am not sure what do you mean by Rs ..

You have to be aware that this is PNP transistor so to fors it to conduct current you acteally draw current from its base .. and this is done by the regulator IC ..

To set output current you need Rsc to be approximately 0.07Ω. If current riches 10A it will cause 0.7V voltage drop accross Rsc and this also causes the current limiting transistor to shorten the Ube of 2N2955 ..
The lower the Ube the less current is conducted by 2N2955 ..

Regards,
IanP

 

[zhi_yi]

Re: current booster 2

sorry, the Rs i mean is the R between the fuse and the collector of the 2N6049..

okay.. thank you