31 July 2024Editor's Choice
Power Electronics / Power Management
By Antoniu Miclaus and Doug Mercer, Analog Devices, www.analog.com.
A basic definition of a step-up and step-down transformer is that it is a device that takes AC at one voltage and transforms it into another voltage either higher (step-up) or lower (step-down) than the original voltage. A transformer can also be used to isolate a circuit from the ground, which is called an isolation transformer. But importantly, the usage of the transformer in the circuit used in this article is in its capability to match impedances of circuits to achieve maximum power transfer.
Figure 1. Transformer-coupled Class A power amplifier.
Consider the circuit presented in Figure 1. The circuit is a transformer-coupled Class A power amplifier. This is like a normal amplifier circuit, but has a transformer connected in the collector load.
In this setup, R1 and R2 establish potential divider biasing, while emitter resistor R3 is utilised for bias stabilisation. The emitter bypass capacitor C2 is employed to prevent negative feedback within the emitter circuit.
The power transferred from the power amplifier to the load will be maximum only if the amplifier output impedance equals the load impedance RL (R4). This is in accordance with the maximum power transfer theorem. The transfer of maximum power from the amplifier to the output device, matching the amplifier output impedance with the impedance of the output device, is necessary. This is accomplished by using a step-down transformer of suitable turns ratio.
Thus, the ratio of the transformer input and output resistances varies directly as the square of the transformer turns ratio:
giving equation 2 which calculates the reflected impedance:
where:
• n is the ratio of primary to secondary turns of the step-down transformer.
• RLP is the reflected impedance in the primary.
The efficiency of a Class A power amplifier is nearly 30%, which is improved to 50% by using a transformer-coupled Class A power amplifier. Increased efficiency is one of the advantages of this configuration, but aside from that there are other advantages to a transformer-coupled Class A power amplifier:
• No loss of signal power in the base or collector resistors.
• Excellent impedance matching is achieved.
• Gain is high.
• DC isolation is provided.
But this configuration is not perfect, and has the following disadvantages:
• Low-frequency signals are less amplified, comparatively.
Potential risks of plasma treatment on PCBs MyKay Tronics
Editor's Choice
Plasma treatment involves exposing PCBs to an ionised gas, known as plasma, but despite many advantages, several risks must be managed to ensure safe and effective plasma application in EMS.
Read more...X-band radar RF Design
Editor's Choice Telecoms, Datacoms, Wireless, IoT
X-band radar systems, particularly those leveraging beamforming ICs (BFICs), advanced gallium nitride (GaN) and gallium arsenide (GaAs) components, are leading the way in providing the high-performance radar capabilities required for modern defence and surveillance.
Read more...Reference board for cardio monitoring Altron Arrow
Telecoms, Datacoms, Wireless, IoT
The STDES-ESP01 reference board from STMicroelectronics demonstrates the capability of the ST1VAFE6AX and ST1VAFE3BX biosensors to detect ECG and SCG signals.
Read more...ST MCUs extend ultra-low power innovation Altron Arrow
DSP, Micros & Memory
STMicroelectronics has introduced new STM32U3 microcontrollers with cutting-edge power-saving innovations that ease deployment of smart connected tech, especially in remote locations.
Read more...Multicell battery monitoring Altron Arrow
Power Electronics / Power Management
The LTC6811 from Analog Devices is a multicell battery stack monitor that measures up to 12 series connected battery cells with a total measurement error of less than 1,2 mV.
Read more...Innovative satellite navigation receiver Altron Arrow
Telecoms, Datacoms, Wireless, IoT
STMicroelectronics has released an innovative satellite navigation receiver to democratise precise positioning for automotive and industrial applications.
Read more...LED driver for industrial power supply indication Altron Arrow
Editor's Choice Circuit & System Protection
A simple and small solution for driving an LED to provide visual feedback in the presence/absence of a system’s power using a chip not originally designed for this purpose.
Read more...Case Study: Siemens Valor automation solution ASIC Design Services
Editor's Choice Manufacturing / Production Technology, Hardware & Services
Electronics manufacturer BMK used Siemens Valor to enhance accuracy and speed up bill-of-materials quotations.
Read more...High-voltage step-down DC-DC converter Altron Arrow
Power Electronics / Power Management
The MAX17793 is a high-efficiency, high-voltage, synchronous step-down DC-DC converter with integrated MOSFETs operating over an input voltage range of 3 to 80 V.