Current Regulation – Diodes, Transistors
1. What are Current Regulation Diodes?
Constant-Current Diode
Also known as current limiting diodes (CLD) or current regulating diodes (CRD), the internal structure realizes the current clamping function through semiconductor characteristics. Its core function is to limit the current to a preset maximum value, and it is often used in scenarios such as LED driving and sensor protection.
Typical characteristics include asymmetric conduction characteristics, which present an approximate constant current source characteristic when forward conduction, and have a high impedance state when reverse cutoff.
Zener Diode
Use the reverse breakdown characteristics to maintain a constant voltage. In current regulation, it is often used in conjunction with a current-limiting resistor to form a simple voltage stabilization circuit.
Varactor Diode
Control the change of PN junction capacitance through reverse bias voltage, and are used in circuits such as voltage-controlled oscillators that need to adjust the resonant frequency.
2. What are Current Regulation Transistors?
1) Bipolar Transistor
Control the collector-emitter current through the base current, and accurate current regulation can be achieved in the amplifier circuit. Typical applications include linear regulators, current mirror circuits, etc.
2) Field Effect Transistor (FET)
Metal Oxide Semiconductor Field Effect Transistor (MOSFET): The drain-source on-resistance is controlled by the gate voltage, which is suitable for high-efficiency current regulation scenarios such as switching power supplies.
Junction Field Effect Transistor (JFET): The depletion region formed by the reverse biased PN junction is used to adjust the conductive channel width, and is often used as a constant current source.
3) Darlington Transistor Combination
Ultra-high current gain is achieved through a multi-stage amplification structure, which is used for precise current control when driving high-power loads.
3. Application Characteristics Comparison
|
Device Type |
Adjustment Method |
Typical Application Scenario |
Efficiency Characteristics |
|
Constant Current Diode |
Passive Current Limiting |
Simple Current Source/Protection Circuit |
Low Power Consumption |
|
MOSEFT |
Voltage Control |
Switching Power Supply/PWM Speed Regulation |
High Efficiency (>90%) |
|
Bipolar Transistor |
Current Control |
Linear Voltage Regulation/Analog Amplifier Circuit |
High Efficiency (>90%) |
4. Selection Considerations for Current Regulation Diodes and Transistors
Maximum adjustment current range
Operating frequency response characteristics
Temperature stability (such as thermistor compensation design)
Package heat dissipation capability (TO-220/TO-263, etc.)
5. Current Regulation Diodes and Transistors FAQs
1) How does a constant current diode achieve current regulation?
The constant current diode (CLD/CRD) limits the current to a preset maximum value within a specific voltage range through the special design of the internal semiconductor structure. Its characteristics include temperature stability and unidirectional conductivity, and it is often used for LED driving and sensor protection.
The name has not yet been unified, and common nicknames include current limiting diode (CLD) and current regulating diode (CRD).
2) What is the relationship between the current source and the compliance voltage?
The compliance voltage is the maximum voltage range that the constant current source can output to maintain the set current, and its value is equal to the power supply voltage minus the internal impedance voltage drop.
If the load resistance is too large and the required voltage exceeds the compliance range, the current will not be able to remain constant.
3) What is the difference between the regulation of transistors and constant current diodes?
Constant Current Diode: simple structure, fixed current limiting can be achieved without external circuits; the disadvantage is that the current value cannot be adjusted.
Transistor Circuit: more precise current control is achieved through the PNP/NPN combination, and the output range is adjustable. For example, the accuracy of transistor circuit B is better than that of the discrete diode solution.
4) What are the common application scenarios of current regulation devices?
Diode Solution: LED array drive, battery charging protection;
Transistor Solution: laboratory power supply, precision instrument current source;
Hybrid Solution: high-precision regulation system combining an op amp and feedback network.
5) How to choose current regulation devices?
Fixed Current Requirement: a constant current diode is preferred;
Adjustable/Wide Range Requirement: a transistor or integrated circuit solution is adopted;
High Frequency/High Temperature Environment: frequency response and thermal characteristics of the device data sheet need to be paid attention to.