High frequency switch-mode power amplifier
A switch-mode power amplifier circuit using high power, low distortion waveforms is connected to an electromagnetic load to provide a high degree of control over the load. The circuit comprising a plurality of half-bridge networks having outputs combined at a summation point. The half-bridge networks are switched to provide power outputs sequenced to generate an interlaced output at the summation point which is operably connected to the load so that for a given switching frequency of the networks the operational frequency of the circuit is increased. The sequencing of the half-bridge outputs to generate an interlaced output facilitates the reduction of the switching frequency of individual switching components within the half-bridges while at least maintaining the overall operational frequency of the circuit. For N half-bridges operating at ƒkHz, the overall operational frequency of the circuit is NƒkHz. Alternatively, the switching frequency of individual switching elements of a system operating at ƒokHz may be reduced by a factor of N. A feedback signal generated across the load is included at the summation point and is optionally augmented to decrease distortion.
1. A switch mode power amplifier circuit connectable to an electromagnetic load, the circuit comprising:
a plurality of half-bridge networks having outputs combined for summation at a summation point, the half-bridge networks being switched to provide power outputs sequenced to generate an interlaced output at the summation point which is operably connected to a load so that for a given switching frequency of the networks the operational frequency of the circuit is increased; and
a current sensor on the output of each half-bridge network so that a current error signal can be derived, in which the error signal is compared with a plurality of waveforms to give a timing signal to regulate the switching of the half-bridge switching elements.
2. A switch-mode power amplifier circuit as claimed in claim 1 , in which the sequencing of the half-bridge outputs to generate an interlaced output facilitates the reduction of the switching frequency of individual switching components within the half-bridge while at least maintaining the overall operational frequency of the circuit.
3. A switch-mode power amplifier circuit as claimed in claim 1 , in which, for N half-bridges operating at ƒkHz, the overall operational frequency of the circuit is NƒkHz.
4. A switch mode power amplifier circuit as claimed in claim 1 , in which, for N half-bridges, the switching frequency of the individual switching elements of a system operating atƒ 0 kHz.\ may be reduced by a factor of N.
5. A switch-mode power amplified circuit as claimed in claim 1 , in which a feedback path is provided so that a feed back signal is generated across a load.
6. A switch-mode power amplifier circuit as claimed in claim 5 , in which the summation of the half-bridge network outputs includes the feedback signal.
7. A switch-mode power amplifier circuit as claimed in claim 5 , in which, where the operating frequency of the circuit is increased, further feedback may be imposed on the circuit to reduce distortion.
8. A switch-mode power amplifier circuit as claimed in claim 1 , in which the half-bridge networks are arranged in a push-pull configuration about a load, the configuration defining a left and right channel for which a power drive signal may b derived to generate timing signals for controlling individual switching elements of the half-bridge networks.
9. A switch-mode power amplifier circuit as claimed in claim 1 , in which a timing strategy is used to ensure current sharing between the networks.
10. A switch-mode power amplifier circuit as claimed in claim 1 , in which each half-bridge network comprises two switching components in opposite switched states.
11. A switch-mode power amplifier circuit as claimed in claim 10 , in which the states are a high impedance state representing “OFF” and a low impedance state representing “ON”.
12. A switch-mode power amplifier circuit as claimed in claim 1 , in which an identical supply voltage is supplied to each half-bridge network.
13. A switch-mode power amplifier circuit as claimed in claim 1 , in which the switched power outputs of the half-bridge networks are provided with an in-line inductance.
14. A switch-mode power amplifier circuit as claimed in claim 13 , in which the inductance is identical for each output.
15. A switch-mode power amplifier circuit as claimed claim 1 , in which an out put filter stage is provided on the circuit at least part of which is shunt-connected across a load in use.
16. A switch-mode power amplifier circuit as claimed in claim 1 , in which the switching of the half-bridge switching components is controlled using Pulse Width modulation (PWM) techniques.
17. A switch-mode power amplifier circuit as claimed in claim 1 , in which the use of a plurality of power devices operating in an interlaced fashion in order to increase the apparent operating frequency of the system, allows more feedback to be imposed on the system.
18. A switch-mode power amplifier circuit as claimed in claim 1 , in which the system is used to drive a load, particularly an electromagnetic load, using high power, low distortion waveforms with a high degree of control.