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How to find the circuit output

KRK

Jun 20, 2017
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Please help to resolve the circuit

Base Control switches from 0 to 5V

Transistor Data: Beta =100, Vce (Sat) = 0.3V, Vbe(Sat) = 1.2V (Max); IC(Max) = 1 A

Relay Data: coil 12V, impedance 300 ohm

Calculate:

1. R1?

2. Power dissipation when transistor ON

3. Find base voltage, base current, collector voltage, collector current

4. What is the purpose of D1?
 

KRK

Jun 20, 2017
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Quote removed by moderator
 

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Harald Kapp

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The required sequence of calculations is not meaningful.
  • Start with number 3. E.g. proceed as follows: the base current can be calculated from the collector current (which is the same as the current through the relay coil) and Beta. So you first need to find the collector current using the impedance of the relay coil, the supply voltage (12 V) and the collector-emitter saturation current.
  • Use the results from the above claculation to calculate R1. You need the base current into T1, the base-emitter voltage and the control voltage.
  • "Calculate power dissipation" is way too general. Power dissipation of which component?
  • Re the purpose of D1: consider when will it be active? What does it do when active?
 

BobK

Jan 5, 2010
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Think about what happens when the input voltage goes to -12V, with and without the diode.

Bob

[mod edited to remove comments about AG's post that has now been removed
Thanks Bob :) ]
 
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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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The circuit also has a practical fault which will likely cause it to destroy transistors.
 
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