E7D06
PRACTICAL CIRCUITS · Power supplies and voltage regulators; solar array charge controllers
E7D06E7D →
What is the purpose of Q1 in the circuit shown in Figure E7-2?
- AIt provides negative feedback to improve regulation
- BIt provides a constant load for the voltage source
- CIt controls the current to keep the output voltage constant
- DIt provides regulation by switching or "chopping" the input DC voltage
Why Figure E7-2 is a classic linear series regulator: R1 feeds zener diode D1, which holds the transistor's base at a fixed reference voltage, and Q1 sits in series between the raw input and the load. Q1 acts as a variable resistance, passing whatever current the load demands while dropping the excess voltage, so the emitter (output) stays about one base-emitter drop below the zener voltage. That is why Q1 is called the series pass transistor: it regulates by adjusting current flow to hold the output voltage steady.
Watch out The 'chopping' description belongs to a switching regulator, where the pass device is driven fully on and off at high frequency and the output is filtered; in this circuit Q1 operates continuously in its linear region, not as a switch.
Q1 = series pass transistor: zener sets the reference, Q1 passes the current. Chopping means switcher, not this circuit.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
The rest of E7D
- E7D01 How does a linear electronic voltage regulator work?
- E7D02 How does a switchmode voltage regulator work?
- E7D03 What device is used as a stable voltage reference?
- E7D04 Which of the following describes a three-terminal voltage regulator?
- E7D05 Which of the following types of linear voltage regulator operates by loading the unregulated voltage source?
- E7D06 What is the purpose of Q1 in the circuit shown in Figure E7-2?
- E7D07 What is the purpose of C2 in the circuit shown in Figure E7-2?
- E7D08 What type of circuit is shown in Figure E7-2?
- E7D09 How is battery operating time calculated?
- E7D10 Why is a switching type power supply less expensive and lighter than an equivalent linear power supply?
- E7D11 What is the purpose of an inverter connected to a solar panel output?
- E7D12 What is the dropout voltage of a linear voltage regulator?
- E7D13 Which of the following calculates power dissipated by a series linear voltage regulator?
- E7D14 What is the purpose of connecting equal-value resistors across power supply filter capacitors connected in se…
- E7D15 What is the purpose of a step-start circuit in a high-voltage power supply?