Transistor as an amplifier theory of a deadman

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Content:

• RF Power Semiconductor Generator Application in Heating and Energy Utilization
• The Curse of the Ramones
• PWM Circuit for MC-2100 Motor Controller Board
• An Introduction to Practical Electronics Microcontrollers and Software Design
• PHYSICS PROJECT TOPICS AND MATERIALS
• Amp/Preamp Asylum
• Mike Plotnikoff Has Worked with Rock/Metal’s Leading Talent

WATCH RELATED VIDEO: The transistor as an amplifier (Part 2)

RF Power Semiconductor Generator Application in Heating and Energy Utilization

T his transmitter is based, more or less, on equations presented in a Mark Mallory article detailing a single-ended class-E output stage for a 1-watt transmitter operating in the kHz Part LowFER band. The circuit should be adaptable to transmitting in the meter ham band with slight component value changes, or to any frequency within the medium or longwave bands MHz by following the design steps below. The 'as-built' transmitter can be tuned about kHz either side of kHz kHz without modification.

The transmitter has the same basic layout as any AM transmitter, though it may differ in specifics. A block diagram of the as-built unit appears below. Refer back to this diagram as the parts are explained in the article below.

Items marked "external" are not described except in a general way in the article. The transmitter's output amplifier circuit is shown in Figure The amplifier circuit consists of two of the Mallory circuits connected in a push-pull configuration with a coupling transformer acting as both the finals' tank inductance and output matching device. The push-pull configuration allows current sharing between two transistors while the transformer provides great flexibility in matching the amplifier to a load.

The push-pull configuration also greatly reduces the second harmonic content of the output signal, lowering the demands on the output filtering. The number of turns specified for the transformer primary winding was determined from the winding chart for the specified core.

The output power of Mallory's prototype was adjusted by selecting an appropriate tap on the final tank inductor. The 8-to turns ratio shown on the schematic was selected to take full advantage of the current available from the power supply. To state it another way, the ratio shown adapts the final-stage ohm output impedance to the unit's ohm output feedline load impedance.

The output filter consists of the output coupling capacitor C2 and series inductor L1. This type filter satisfies the basic requirement for class-E operation: The final 'sees' the output load at the fundamental frequency only. Higher order harmonics are blocked and the filter presents a high impedance back to the amplifier stage at those frequencies.

The output filter has a Q of 5. This type has a reduced gate drive power requirement compared to 'standard' types. Additionally, class-E operation substantially cancels the 'Miller effect', a dynamic interaction between the FETs' drains and gates caused by inter-electrode capacitances, further reducing the drive power requirement.

Adjustment of the pF variable capacitor C1 across the primary between the drains of the output transistors , along with SYM and BAL adjustments in the exciter, serve to fine tune the transformer primary to achieve optimal class-E operation. After adjustment, two watts of drive power easily drives the final stage to its full watt output. The output transistors are mounted on a 5.

A small fan circulates air across the heatsink. The driver transistors are mounted on a small board mounted directly on the output transistor leads. The push-pull drive signal for the power amplifier is developed by the exciter circuitry shown in Figure 2. This circuit's adjustability is the key to obtaining optimal efficiency of the class-E output stage:.

An input signal must be provided to this circuit from a signal generator, crystal oscillator, VFO or other source at TWICE the operating frequency, kHz in the case of the as-built transmitter. The carrier source for the as-built unit is a programmable synthesizer. A telegraph key could be connected at this point for CW code operation.

The drive signals are buffered and delivered to the driver transistors via short lengths of shielded wire. If you'd like to reproduce this transmitter, the components and values shown should work as advertised at kHz using a volt power supply.

Fixed capacitors should be mica dielectric or low ESR type where indicated; the values shown can be made up with smaller-value units in parallel. C2 should be a transmitting type air or vacuum variable. The output transformer primary windings should be made with AWG 16 or heavier wire.

The secondary should be of AWG 18 or heavier. Cores other than the one shown the biggest one I could find can be used with the number of primary turns recalculated see below. The core material should be type-2 powdered iron. The output transistors should be mounted to the heatsink with insulating hardware.

The heatsink should be grounded. A m version of the watt transmitter can be built by following the schematic in all respects except for the following change: substitute. If you'd like to try the circuit at other frequencies or power levels, first carefully read the Mallory article , then decide at what frequency you'd like the transmitter to operate usually in the range from 10 kHz to 2 MHz; see frequency below , at what power level taking into account the available power supply voltage and current , and the required output load impedance typically 50 ohms , then:.

Their application to this or any real-world transmitter circuit is a function of the switching characteristics of the transistors used in the circuit. Generally, as frequency is increased, gate charge times become an increasingly larger fraction of the on portion of the duty cycle. The result is a shortening of on-time as frequency is increased.

See also the frequency paragraph below. The adjustable exciter Fig 2 provides for duty-cycle adjustment during tune-up, compensating for this effect. The adjustable exciter also allows the designer to take some liberties with calculated component values.

Whether or not a particular transformer core you may have on hand will work in the circuit depends on the desired operating parameters frequency, power, power supply voltage. You can check this out experimentally by first running your numbers through Mallory's equations or using the calculator to find the value of the resonating capacitor s.

Wind a few turns on the candidate core, parallel the winding with a capacitor of the calculated value and check the resonant frequency with a signal generator and oscilloscope. Add or remove turns as necessary until you obtain resonance at your desired operating frequency. The number of turns you end up with will be the number of turns you will use in winding the transformer primary the number determined in step 2.

If you are not able to obtain resonance with the calculated capacitor value, the core likely will not work in the application. The adjustable exciter compensates somewhat for variations in component values L and C but won't compensate for a large discrepancy.

The transmitter's final current ammeter and voltmeter should be used to check for proper loading on the output stage. Thus, for the unit's volt power supply, the correct DC current is about 5. The transmitter is tolerant of reactive high VSWR loads. Mismatches can be tuned out by adjusting the output coupling capacitor C2.

However, depending on the nature of the mismatch, the transmitter may not deliver the calculated output power in that situation. Remember that the transmitter's output power is limited only by the capability of the power supply. If the non-reactive resistive component of the load impedance is less than the amplifier's design load impedance, the amplifier will dutifully try to deliver the extra current, possibly overheating the power supply.

If the load's non-reactive component is greater than the design impedance, the output power will be less than calculated. As mentioned, the amplifier can be designed to operate into almost any load impedance - refer back to construction step 3 above - but employing an external tuner, like the one shown in Figure 7 below, is usually a more practical approach to unusual or unknown impedance situations.

Power : Input power of the presently built unit is limited by its power supply 42 volts 5. The amp continuous current, amp pulsed current and watt dissipation ratings of the IRFPLC FETs used in the as-built unit suggest the design is capable of CW operation in the to watt range when used with a suitably hefty power supply, heatsink and cooling fan.

For AM service, watts is about the limit. Remember that a watt AM transmitter must deliver watts, four times its rated power, on modulation peaks. Limit the power supply voltage to about 50 volts for AM service using an external modulation amplifier, or volts for CW or AM using a series-type modulator.

Other transistors capable of higher voltages probably can be substituted in the circuit but I can't vouch for any in particular. The T core shown should be capable of power levels up to a couple of kilowatts, but if your design calls for more power, stack multiple cores for higher current capability.

Stacking of cores will require recalculating primary turns per the cores' winding chart. Add the A L values when stacking cores. For example, stacking 2 cores, each with an A L value of , will result in a total A L value of The output transformer should be wound with wire heavy enough to carry the expected current with minimal heating loss, as should inductor L1.

Output coupling capacitor C2 likewise should be sized to handle the expected current and voltage. Consider using a vacuum variable for C2. Multiple-Strand Litz Wire for Transformers and Coils Transformers in switching power supplies are often wound with multiple small-diameter strands of insulated wire rather than with single, large-diameter strands.

This is done to minimize the "skin effect", the increase in resistance seen in conductors carrying alternating current. Because the core of the transformer used in the transmitter shown on this page is physically large and the number of turns small due to the core's relatively large A L value , ordinary single-strand Romex was quite adequate for winding; little heating was noticed in the conductors. Winding the output transformer and L1 with multiple twisted strands instead might have resulted in a percentage point or two greater efficiency.

It could be argued that the largest number of conductors possible should be stuffed onto the core, whatever its size, but there's probably some point where the effort will begin to produce diminishing returns. Capacitors in transmitter service are subject to much higher voltages than those encountered in typical consumer electronic equipment. To generate watts in a 50 ohm load, for example, requires about peak-to-peak volts. This is not the whole story however.

The output filter of the watt version of the class-e transmitter L1 and C2 has a Q factor of 5. This means that the actual voltage across C2 is x 5, or V p-p. During modulation peaks, this voltage doubles to V p-p.

Prudence suggests a minimal rating of volts for C2. Frequency : Class-E operation requires that final transistor switching take place during the part of the RF cycle when drain voltage is zero see article. As frequency is increased, gate charge and discharge times become an increasingly larger fraction of the voltage-zero time.

At that point the circuit will no longer be operating in class-E mode and efficiency will begin to drop. Unfortunately for transmitter builders considering this transmitter for meter operation, watts in class-E mode at 3. The as-built transmitter is amplitude modulated by an external 8-ohm transformer-coupled audio power amplifier, salvaged from a public-address system, connected through the modulation input terminals shown in Figure 1.

Audio amplifiers, tube or solid-state, meant for public-address service are ideal in this application since they are almost always of transformer-coupled output design. Before connecting the modulator to the transmitter, a check should be made with an ohmmeter to make sure the output winding of the modulation amplifier is floating i. If there is a ground connection, it should be removed.

Connect the terminal from which the ground connection was removed to the positive terminal of the power supply Fig 3, Opt 1.

The Curse of the Ramones

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PWM Circuit for MC-2100 Motor Controller Board

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An Introduction to Practical Electronics Microcontrollers and Software Design

This interdisciplinary conference explored the relationships between sound instruments and sonic cultures. Modernity has witnessed an accelerating proliferation of sound instruments—devices that allow humans to purposefully produce, capture, observe, manipulate, broadcast or otherwise interact with sound. Sound recording, playback, and listening devices are sound instruments—record, CD, and MP3 players, tape recorders, loudspeakers, headphones, etc. Radio and television sets are sound instruments, as are terrestrial and mobile telephones, as are hearing aids. The list goes on.

PHYSICS PROJECT TOPICS AND MATERIALS

This saying holds true for so many products today. It bothers me that almost everything we buy today has limited serviceability and is built to be, at some point, disposable. Replacement parts are often priced such that the most economical decision is to not repair but to replace. The life cycle of a product is carefully engineered to ensure that, as reliability decreases, you fall right into line with the plan and buy a new one. Thanks for coming, see you in four years, a year after your warranty expires. Along with limited serviceability, we also see clever engineering and marketing; have you ever believed you are buying something superior, when this was simply not true?

Amp/Preamp Asylum

Looking for a new Amp or Preamp? If you're after tubes, post over here. Anyone experience getting over the power hump? I have. Let me explain. My Thiel CS2. The 'hump' seems to be around wpc.

Mike Plotnikoff Has Worked with Rock/Metal’s Leading Talent

Both Volt and Volt lines. Will measure current consumption amperes while the applionce under test is in operation. Will test all TV tubes including Incorporates a sensitive direct - picture tubes for open filaments reading resistance range which and will burned measure out tubes.

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A transisorized communications receiver! Works fine for SSB also. How high will they go with transistors? Looks awful works great! Really works out!

Korn was originally formed by three of the members of the band L. Korn made a demo tape , Neidermayer's Mind , in , which was distributed free to record companies and on request to members of the public. The band experienced mainstream success with Follow the Leader and Issues , both of which debuted at number one on the Billboard