Class E amplifier question

[amal banerjee]

Here is a question for all electronics gurus here.
Can a class E amplifier be termed efficient - given
the shunt capacitor from BJT collector to ground,
which is an AC short -- unless the capacior value
is very small, such that the capacitive reactance
is large. Any flaws in this argument ?

 

[Tauno Voipio]

On 8.11.19 08:13, amal banerjee wrote:

Here is a question for all electronics gurus here.
Can a class E amplifier be termed efficient - given
the shunt capacitor from BJT collector to ground,
which is an AC short -- unless the capacior value
is very small, such that the capacitive reactance
is large. Any flaws in this argument ?

The capacitor is a part of a tuned circuit, so
the simple short circuit idea is moot.

I have a kilowatt RF amplifier, where there is
a capacitor from the tube plates to ground and
another across the output (Google for a pi-filter).

--

-TV

 

On Thu, 7 Nov 2019 22:13:06 -0800 (PST), amal banerjee
<dakupoto@gmail.com> wrote:

Here is a question for all electronics gurus here.
Can a class E amplifier be termed efficient - given
the shunt capacitor from BJT collector to ground,
which is an AC short -- unless the capacior value
is very small, such that the capacitive reactance
is large. Any flaws in this argument ?

A transistor dissipates instantaneous power Vce*Ic, so discharging a
charged capacitor heats the device. The trick to get efficiency is to
only turn on the transistor when Vce is low, namely pump a lot of
current into a resonant load for part of the cycle, as the resonator
voltage swings close to ground. The resonant load gets pumped by the
full supply voltage times the current, a lot of power, but the
transistor dissipation is low, high Ic but low Vce while it's on.

Resonant power supplies aren't called class E, but work the same way.
Some are called "zero voltage switching" circuits.

http://www.classeradio.com/theory.htm



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[amdx]

On 11/8/2019 12:13 AM, amal banerjee wrote:

Here is a question for all electronics gurus here.
Can a class E amplifier be termed efficient - given
the shunt capacitor from BJT collector to ground,
which is an AC short -- unless the capacior value
is very small, such that the capacitive reactance
is large. Any flaws in this argument ?

Class E amps dramatically lower switching losses
in your FET/Transistor where most of you losses are.
Although, I've seen some hot inductors and transformers!

This article has some numbers I haven't seen spelled out regarding
efficiency and conduction angle and duty cycle.
Be aware it starts as wireless energy transfer, but quickly gets to
the class E numbers.
> https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=11&cad=rja&uact=8&ved=2ahUKEwjjsdqv_NrlAhVJQ6wKHTOIDOgQFjAKegQIAhAC&url=https%3A%2F%2Fwww.mdpi.com%2F1996-1073%2F10%2F9%2F1409%2Fpdf&usg=AOvVaw0bVgtR6ccI9arMQykU4JAN

Or use this.
> https://tinyurl.com/y66rlxcd

Mikek

 

[amal banerjee]

On Friday, November 8, 2019 at 10:50:33 AM UTC-5, jla...@highlandsniptechnology.com wrote:

On Thu, 7 Nov 2019 22:13:06 -0800 (PST), amal banerjee
dakupoto@gmail.com> wrote:

Here is a question for all electronics gurus here.
Can a class E amplifier be termed efficient - given
the shunt capacitor from BJT collector to ground,
which is an AC short -- unless the capacior value
is very small, such that the capacitive reactance
is large. Any flaws in this argument ?

A transistor dissipates instantaneous power Vce*Ic, so discharging a
charged capacitor heats the device. The trick to get efficiency is to
only turn on the transistor when Vce is low, namely pump a lot of
current into a resonant load for part of the cycle, as the resonator
voltage swings close to ground. The resonant load gets pumped by the
full supply voltage times the current, a lot of power, but the
transistor dissipation is low, high Ic but low Vce while it's on.

Resonant power supplies aren't called class E, but work the same way.
Some are called "zero voltage switching" circuits.

http://www.classeradio.com/theory.htm



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

Thanks for the explanation. Most treatments of the
class E amplifier(including SPICE simulations) use
an ideal switch, instead of a real BJT or FET.

 

[amal banerjee]

On Friday, November 8, 2019 at 7:36:18 AM UTC-5, Tauno Voipio wrote:

On 8.11.19 08:13, amal banerjee wrote:
Here is a question for all electronics gurus here.
Can a class E amplifier be termed efficient - given
the shunt capacitor from BJT collector to ground,
which is an AC short -- unless the capacior value
is very small, such that the capacitive reactance
is large. Any flaws in this argument ?


The capacitor is a part of a tuned circuit, so
the simple short circuit idea is moot.

I have a kilowatt RF amplifier, where there is
a capacitor from the tube plates to ground and
another across the output (Google for a pi-filter).

--

-TV

The PI filter is not essential, i.e., the capacitor to ground(in parallel with the load) is of the low pass L impedance matching sub-circuit, and and can be replaced with a high pass(inductor to ground) L impedance
matching sub-circuit, with marginal change in performance characteristics. Ub fact, the L impedance matching sub-circuit can be done away with. I have dirtied my
hands a fair bit with SPICE simulations(HSpice, Ngspice) to say this.