Showing posts with label or. Show all posts
Showing posts with label or. Show all posts
Tuesday, October 1, 2013
11 W Stereo or 22 W Mono Power Amp
Integrated AF power amps have seen great improvements in recent years offering improved power and easier use. The TDA1519C from Philips contains two power amplifiers providing 11 W per channel stereo or 22 W mono when the two channels are connected in a bridge configuration. The special in-line SIL9P package outline allows the chip to be conveniently bolted to a suitable heatsink. The TDA1519CSP is the SMD version, in this case the heat sink is mounted over, and in contact with, the top surface of the chip.
The operating voltage of this device is from +6V to +17.5V. The two channels of the amplifier are different in that one channel, between pins 1 and 4, is a non-inverting amplifier, while the other between pins 9 and 6 is an inverting amplifier. It is therefore necessary in stereo operation, to wire the speakers so that one of them has its polarity reversed. Each amplifier has an input impedance of 60kΩ and a voltage gain of 40dB, i.e. 100 times. When both amplifier are used in a bridge configuration, the inputs are in parallel so that the input impedance will be 30kΩ.
A combined mute/standby function is provided on pin 8. In its simplest form this can be connected to the positive rail via a switch. When the switch is open the amplifier will be in standby mode and current consumption is less than 100µA. When the switch is closed, the amplifier will be operational. A circuit is also shown that uses the mute input to prevent the annoying switch-on plop heard when power amps are first switched on This is caused by the rush of current to charge capacitors C1 and C2.
The circuit shown generates a ramp voltage, which is applied to pin 8. At switch on, as the voltage rises from 3.3 V to 6.4 V, the amplifier will switch out of standby mode and into mute mode allowing C1 and C2 to charge. Only when the ramp voltage on pin 8 reaches 8.5V will the amplifier switch into active mode. Protection built into the TDA1519C would seem to make it almost foolproof. The two outputs can be shorted to either of the supply rails and to each other. A thermal shutdown will prevent overloading and the power supply input is protected against accidental reversal of the supply leads up to 6V.
Author : G. Kleine - Copyright : Elektor Electronics
Wednesday, March 13, 2013
Connecting Two or More Transistors in Parallel
How to Connect two or more transistors in parallel
While making power electronic circuits, configuring the power output stage correctly becomes very crucial.
These stages primarily may consist of power devices like the power transistors or MOSFETs.
Using power transistors are more common due to the greater ease of configuring them. However when higher outputs are desired, it becomes necessary to add more number of these devices together.
And as per the rules, it becomes necessary to connect them in parallel. Though using transistors in electronic circuits is pretty easy, connecting them in parallel needs some attention due to the one significant drawback with transistor characteristics.
As per transistor specs, the devices needs to be operated under reasonably cooler conditions and thats why we install heatsinks on them to maintain the above criterion. Moreover, transistors have the "bad habit" of conducting proportionately rising currents through them as they get heated up.
Therefore if its case temperature tends to increase, the current through it also increases, which in turn heats it up further. The process may get aggravated until the devices become too hot to sustain and gets permanently damaged. This situation is called thermal runaway, in transistors.
When connected in parallel, due to non-consistent characteristics, the transistors in the group may dissipate varying amounts of current through them. Consequently, the transistor which passes more current through it starts getting heated up faster and pretty soon we find the device entering into the above thermal runaway situation damaging itself and promoting the phenomenon to the remaining devices in due course of time.
The situation can be effectively tackled by adding a small value resistor at the emitter of each transistor connected in parallel. The resistor inhibits and controls the amount of current passing through the transistors and never allows it to go to dangerous levels.
The value should be appropriately calculated, as per the magnitude of the current passing through them.
How its connected? See the figure below.
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