High-Frequency Buck Converter that Includes a Cascode MESFET-MOSFET Power Switch
A Buck converter that includes a cascode switch comprising a series connected MESFET and MOSFET power switch. The cascode power switch is typically connected in between a power source and a node Vx. The node Vx is connected to an output node via an inductor and to ground via a Schottky diode or a second MESFET or both. A control circuit drives the MESFET (and the second MESFET) so that the inductor is alternately connected to the battery and to ground. The MOSFET is switched off during sleep or standby modes to minimize leakage current through the MESFET. The MOSFET is therefore switched at a low frequency compared to the MESFET and does not contribute significantly to switching losses in the converter.
1 . A Buck converter that includes a cascode switch comprising a series connected MESFET and MOSFET.
2 . The Buck converter of claim 1 where the MOSFET is a P-channel.
3 . The Buck converter of claim 2 where the P-channel MOSFET has its source connected to the battery input.
4 . The Buck converter of claim 1 where the MESFET has its drain connected to the battery input.
5 . The Buck converter of claim 1 where a Zener diode is connected in parallel to the cascode switch.
6 . The Buck converter of claim 1 the gate of the MESFET is switched at a higher frequency than that of the MOSFET.
7 . The Buck converter of claim 1 where the MESFET is made of GaAs.
8 . The Buck converter of claim 1 including a Schottky rectifier.
9 . The Buck converter of claim 8 where the Schottky rectifier is made of silicon.
10 . The Buck converter of claim 8 where the Schottky rectifier is made of gallium arsenide.
11 . The Buck converter of claim 10 where the Schottky rectifier is integrated on the same piece of gallium arsenide as the MESFET switch.
12 . The Buck converter of claim 1 where the MOSFET is an N-channel.
13 . The Buck converter of claim 1 where the MOSFET has its drain connected to the battery input.
14 . The Buck converter of claim 1 where the MOSFET has its gate powered by a charge pump.
15 . A synchronous Buck converter that comprises:
a cascode MOSFET-MESFET switch comprising a first N-channel MESFET switch;
a series connected MOSFET;
and a synchronous rectifier comprising a second N-channel MESFET switch having its source connected to ground.
16 . The synchronous Buck converter of claim 15 where the first and second MESFET switch are driven out of phase so that only one of them conducts at any one time.
17 . The synchronous Buck converter of claim 15 where the on-times of the first and second MESFET switches are determined by a pulse-modulation-modulation (PWM) control circuit.
18 . The synchronous Buck converter of claim 15 where a Zener diode is in parallel with first MESFET.
19 . The synchronous Buck converter of claim 15 where a Schottky diode is in parallel with second MESFET.
20 . The synchronous Buck converter of claim 15 where a first gate buffer limits the maximum gate-to-source voltage of the first MESFET to a voltage below which substantial gate current flows into the first MESFET.
21 . The synchronous Buck converter of claim 15 where the second gate buffer limits the maximum gate-to-source voltage of the second MESFET to a voltage below which substantial gate current flows into the second MESFET.
22 . The synchronous Buck converter of claim 15 where a second gate buffer driving the gate of the first MESFET is powered from the battery input to the converter.
23 . The synchronous Buck converter of claim 15 where a first gate buffer is powered by a bootstrap circuit to drive the gate of the first MESFET to a voltage more positive than the converter's battery input voltage.
24 . The synchronous Buck converter of claim 15 where the first N-channel MESFET has its drain connected to the battery input.
25 . The synchronous Buck converter of claim 15 where the MOSFET is a P-channel device.
26 . The synchronous Buck converter of claim 25 where the P-channel MOSFET has its source connected to the battery input.
27 . The synchronous Buck converter of claim 15 where the MOSFET is switched at a lower frequency than the first MESFET.
28 . A synchronous buck converter that comprises: an N-channel MESFET to a node Vx; a MOSFET to the node Vx; and a control circuit, where the control circuit drives the MESFET and MOSFET out of phase so that the node Vx is alternately connected to ground and to a battery.