Conex Club Magazine - no.11 - 2000

Conex Club Magazine - no.11 - 2000 - LM4651 / 52 - 170W in class D - Subwoofer

Reading time: 4 minute

The main topics presented

1. LM4663 - Class D audio amplifier

Intended for use, in particular, on multimedia equipment, laptops or any portable equipment with low consumption.

Integrated circuit LM4663 offers 4W (or 2 x 2W Stereo) electric power, on a load of 4 Ohm at 5V supply voltage.

The output stages are configured in class D operation, the efficiency reaching, at maximum power, 83%.

Shows distortions, measured at 1W, of THD = 0.2%. To reduce them, the Delta-Sigma modulation technique is used, which compares the input signal with the output signal.

It has input for multiplexed signal and is provided with thermal protection. It is mounted in a capsule 24-pin TSSOP.

2. LM4651 / 52 - 170W in class D - Subwoofer

National Semiconductor proposes for the audio domain an assembly consisting of two integrated circuits: the LM4651 driver and the LM4652 power module.

First, it offers the necessary properties of an audio amplifier (short circuit protection on outputs, overvoltage, overtemperature and overmodulation) plus an oscillator block and comparator with PWM modulation that keep the distortion at a low level.

On the task of 4 Ohm electrical power is obtained from 120W, the efficiency being 85%. The entry into normal operation is slow ("soft-start").

Power module - LM4652 - contains four MOSFET transistors powered by a double voltage source. The output on the load is made with a filter for low frequencies.

3. Operational power amplifiers - OP547 / 8/9 series

This series, made by Burr-Brown, offers thermal protection and logical control by switching to standby if the thermal protection is not activated (or passes the amplifier output in a high impedance state).

Integrated circuits can be powered from a single or double source. The maximum supply voltage is 60V, and the maximum peak current through the load: 10A for OPA549, 5A for OPA548 and 0.75A for OPA547. Slew Rate is 9,10 and 6V / us, respectively.

The circuits are provided with pins for adjusting the limit current by means of potentiometers or D / A converters.

4. LM2907 / LM2917 - applications

The two integrated circuits LM2907 / LM2917, through their electrical qualities, are of particular interest to the manufacturers of measuring equipment and automation equipment.

For measuring low and medium frequency signals, determining the speed of internal combustion engines, measuring high electrical capacities in electrolytic capacitors, speed control or actuators with voice and sensory control - LM2907 or LM2917 are immediate practical solutions.

Frequency / voltage converter - under this name National Semiconductor describes in its application notes, where and how the two types of integrated circuits can be used.

These are made in an 8-pin capsule - DIP8 (LM2907M-8 / LM2907N-8 or LM2917M-8 / LM2917N-8) or 16-pin - DIP16 (LM2907N or LM.2917N / M).

The following applications are presented:

  • Tachometer with LM2907;
  • Frequency-voltage converter with LM2917;
  • Capacitometer with LM2907;
  • Maximum permitted frequency (speed) exceeding indicator;
  • Electronic lock with LM2917;
  • Tachometer / voltmeter adapter (car);

5. AF generator

The described generator covers the frequency band of 1 Hz - 1 MHz in 6 ranges being considered as an indispensable accessory in the practical activity of any electronician.

The rather high cost of professional laboratory instruments results in the impossibility of their acquisition by the vast majority of young amateurs of electronic constructions.

An article is dedicated to young builders, which presents the realization of a simple generator that, once built and adjusted, will help them in cthey more diverse practical situations such as:

  • regulation of low frequency amplifiers;
  • adjusting low and medium frequency filters;
  • tact generator for experiments with digital circuits of CMOS type (but also if necessary TTL if an interface with a Trigger-Schmitt SN74HC13 is added);
  • generator for inductors and capacitors.

6. Protection of acoustic enclosures

From a functional point of view, the protection is achieved through relay contacts that are actuated or not during transient electrical phenomena.

The proposed assembly provides two functions:

  • starting the relay (hence the connection of the speakers) with a delay of a few seconds, protecting them from the transient mode when starting the power amplifier; thus, it also gets rid of the annoying "click" that is heard in the speakers;
  • the immediate tripping of the relay at the direct current detected on any of the amplifier outputs to which the assembly is coupled, regardless of the polarity with respect to ground.

7. Digital voltmeter with LCD display

The integrated circuit has been designed to display the measured value on the LCD ICL7106 (relative to ICL7107 presented in the previous issue), which performs all the functions necessary for a digital voltmeter.

The measured value is displayed with 3 1/2 digits and decimal point. Unlike the other circuits with which it is related, ICL7106 has internal voltage reference.

The number of external components is low. Measured voltage, in the range 0… 200mV, is applied to the circuit through the integration group R3-C5 at the IN + and IN- terminals, respectively. The input current is 1 uA.

8. Transceiver 144Mhz - Local oscillator

The peculiarity of the presented transceiver, fruit of the experiments from Conex Club consists in the fact that the local heterodyne is an oscillator with variable frequency that covers the gap within the limits. 133.3… 135.3MHz.

This oscillator also allows work on retransmitters for amateur radio, that is, it achieves a 600kHz gap between the reception and transmission frequencies.

Figure 1 (from the article) shows the block diagram. Variable frequency oscillator within limits 8.5… 10.5MHz (frequency modulated in the transmission mode) is applied to the balanced mixer shown in figure 4 (from the article).

The signal from the crystal oscillator is also applied to this mixer. It outputs signals with a frequency of 124.8MHz - for reception and 124.2MHz - for transmission.

At the output of the balanced mixer, signals with a frequency of 133.3… 135.5MHz, both for reception and for transmission.

9. MC3356 integrated circuit

MC3356 is a broadband receiver. Includes oscillator, mixer, amplitude limiter, squelch, detector, audio preamplifier comparator and output for and meter.

It is mounted in plastic capsule with 20 terminals in the classic version and SMD.

The MC 3356 circuit is supplied with two voltages, namely for RF (pin4) with 3-12V, and for the other floors (pin 6-10) with 3-9V.

The recommendation is that at pin 4 to apply 12V, and at pin 6 and 10 to apply 5V. The circuit works correctly at ambient temperature between -40C and 85C.

The power dissipated by the capsule is 1.25W. The maximum operating frequency is approximately 200 MHz.


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