Hi Everyone,
I'm working through Electronic Principles 7th ed by Albert Malvino. I have a quick question about material presented on page 973 regarding current boosters. To offer better context, I took a picture of the diagram.
The book states that as the load current increases, the current increases through the LM78xx, producing more voltage across the current-sensing resistor. In this way, the outboard transistor produces the bulk of any increase in load current above 1A, with only a small increase in the current through the 78xx.
Is this statement correct? I thought that once the base-emitter voltage reaches ~.7v, it remains constant. I thought what would happen is that as the load current increases and as the current through the LM78xx increases, more current is drawn from the base of the transistor. Consequently, due to current gain, the majority of the current is contributed by the transistor. Nevertheless, the current through the resistor and consequently the voltage across it remain the same.
Any thoughts?
I'm working through Electronic Principles 7th ed by Albert Malvino. I have a quick question about material presented on page 973 regarding current boosters. To offer better context, I took a picture of the diagram.
The book states that as the load current increases, the current increases through the LM78xx, producing more voltage across the current-sensing resistor. In this way, the outboard transistor produces the bulk of any increase in load current above 1A, with only a small increase in the current through the 78xx.
Is this statement correct? I thought that once the base-emitter voltage reaches ~.7v, it remains constant. I thought what would happen is that as the load current increases and as the current through the LM78xx increases, more current is drawn from the base of the transistor. Consequently, due to current gain, the majority of the current is contributed by the transistor. Nevertheless, the current through the resistor and consequently the voltage across it remain the same.
Any thoughts?