Power-adjustable radio frequency output circuit

1. A power-adjustable RF (radio frequency) output circuit, comprising: a RF frequency source transformer, wherein:

one output end of the RF frequency source transformer is connected with a gate of a power amplifier module, another output end of the RF frequency source transformer is connected with a gate bias voltage control circuit; a source of the power amplifier module is connected with ground; the gate of the power amplifier module is connected with a resistor which is connected with ground, a drain of the power amplifier module is connected with a fixed voltage DC (direct current) power supply and also connected with a RF filtering network for outputting a RF power through the RF filtering network;

the gate bias voltage control circuit comprises an operational amplifying module, a positive input terminal of the operational amplifying module is connected with a bias voltage control network, an output terminal of the operational amplifying module is connected with a relay which is controlled by an interlocking circuit; a normally open contact of the relay is connected with the output terminal of the operational amplifying module, a normally closed contact of the relay is connected with a negative bias voltage circuit; a moving contact of the relay is connected with an AC (alternating current) isolation transformer, the AC isolation transformer is connected with the RF frequency source transformer.

2. The power-adjustable RF output circuit, as recited in claim 1 , wherein: the operational amplifying module comprises an OA (operational amplifier), a negative input terminal of the OA is connected with a 10V power supply through a 178 KΩ resistor, and also connected with ground through a 1 KΩ resistor; an output terminal of the OA is in feedback connection with the negative input terminal thereof through a 150 KΩ resistor; a positive input terminal of the OA is connected with the bias voltage control network; the output terminal of the OA is connected with the relay.

3. The power-adjustable RF output circuit, as recited in claim 1 , wherein: the relay is connected with a diode in parallel which is adapted for protecting the relay; the relay is connected with the interlocking circuit through a voltage stabilizing circuit; the interlocking circuit is adapted for providing a power and an internal interlocking signal for the relay; the voltage stabilizing circuit comprises a zener diode and a resistor.

4. The power-adjustable RF output circuit, as recited in claim 1 , wherein: the gate bias voltage control circuit comprises a filtering capacitor.

5. The power-adjustable RF output circuit, as recited in claim 4 , wherein: there are two filtering capacitors, one filtering capacitor is connected with the output terminal of the operational amplifying module and the other filtering capacitor is connected with the moving contact of the relay.

6. The power-adjustable RF output circuit, as recited in claim 1 , wherein: a filtering capacitor is located between the AC isolation transformer and the RF frequency source transformer.

7. The power-adjustable RF output circuit, as recited in claim 1 , wherein: a protector is located between the AC isolation transformer and the RF frequency source transformer, the protector comprises two zener protection diodes.

8. The power-adjustable RF output circuit, as recited in claim 1 , wherein: the AC isolation transformer, the RF frequency source transformer and the power amplifying module are all installed on a RF power amplifier circuit PCB (printed circuit board), and the AC isolation transformer is connected with the gate bias voltage control circuit through a 3-pin connector.

9. The power-adjustable RF output circuit, as recited in claim 1 , wherein: the fixed voltage DC power supply is provided by a switching power supply.