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# How to find the circuit output

#### KRK

Jun 20, 2017
27

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
27
Quote removed by moderator

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#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,761
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
7,682
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 ]

Last edited by a moderator:

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
The circuit also has a practical fault which will likely cause it to destroy transistors.

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