Charging circuit, an inductive load control circuit, an internal combustion engine, a vehicle and a method of charging a bootstrap storage element
View Patent ↗A charging circuit for a bootstrap capacitor comprises a P MOSFET having a body diode and an N channel power MOSFET also having a body diode. The drain of the P MOSFET is coupled to the source of the N channel power MOSFET, and the source of the P MOSFET receives current from a vehicle's battery. The gate of the P MOSFET receives a control signal for turning the P MOSFET either on or off and the drain of the N channel power MOSFET is connected to a bootstrap capacitor The P MOSFET's body diode prevents current flow from the battery to the bootstrap capacitor when the P MOSFET is turned off and the N MOSFET's body diode prevents current flow from the bootstrap capacitor to the battery when the N MOSFET is turned off. The use of a power MOSFET device with its low ON resistance ensures that the capacitor is charged to a sufficiently high voltage even under low battery conditions.
1. A charging circuit for a bootstrap charge storage element, the charging circuit comprising:
a switch arrangement, configured to connect between a voltage source and the bootstrap charge storage element, wherein
the switch arrangement comprises a first switch and a second switch connected in series, and
said switch arrangement is arranged to allow charging current to flow from the voltage source through the first and second switches to the bootstrap charge storage element to allow the bootstrap charge storage element to charge while both of the first and second switches are turned on;
the first switch comprising a first reverse bias element in parallel to current terminals of the first switch, wherein said first reverse bias element is arranged to prevent current flow from the power supply to the bootstrap charge storage element when the first switch is turned off;
the second switch comprising a second reverse bias element in parallel to current terminals of the second switch, wherein the second reverse bias element is arranged to prevent current flow from the bootstrap charge storage element to the voltage source when the second switch is turned off;
a charge pump coupled to a control terminal of the second switch; and
a control arrangement coupled to the second switch and arranged to prevent turning on of the second switch while the first switch is turned off.
2. The charging circuit of claim 1 , wherein the first switch is a P channel MOSFET device which comprises a body diode and the second switch is an N channel power MOSFET device which comprises a body diode and wherein a drain node of the P channel MOSFET device is coupled to a source node of the N channel power MOSFET device, a source node of the P channel MOSFET device is arranged to receive current from a voltage source, a gate of the P channel MOSFET device is arranged to receive a control signal for turning the P channel MOSFET device either on or off, and a drain node of the N channel power MOSFET device is arranged for connection to the bootstrap charge storage element.
3. The charging circuit of claim 2 , wherein the charge pump is coupled to the gate node of the N channel power MOSFET device.
4. The charging circuit of claim 2 , further comprising a control arrangement coupled to the N channel power MOSFET device and arranged to short the gate node of the N channel power MOSFET device to its source node thereby preventing turning on of the N channel power MOSFET device while the P channel MOSFET device is turned off.
5. The charging circuit of claim 4 wherein the control arrangement comprises an N channel MOSFET having a gate node arranged to receive a control signal, and a second P channel MOSFET having a gate node coupled with a drain node of the N channel MOSFET and a source node coupled with the gate node of the N channel power MOSFET device and a drain node coupled to the source node of the N channel power MOSFET device.
6. The charging circuit of claim 1 , wherein the charging circuit is implemented in an integrated circuit device.
7. An inductive load control circuit comprising the charging circuit of claim 1 .
8. The indicative load control circuit of claim 7 , wherein the inductive load is a fuel injector.
9. An internal combustion engine, comprising a fuel injector provided with an injector drive circuit, the injector drive circuit comprising a charging circuit as claimed in claim 1 .
10. A vehicle comprising an internal combustion engine as claimed in claim 9 .
11. A method of charging a bootstrap charge storage element within an inductive load driver circuit, wherein the bootstrap charge storage element is charged from a voltage supply via first and second serially-connected switches, the method having at least one cycle of a charging phase followed by a non-charging phase and comprising:
upon entering a charging phase, receiving a first control signal at the first switch, and, in response to receipt of the first control signal, turning on the first and second switches thereby allowing charging current to flow from the voltage supply through the first and second switches to the bootstrap charge storage element to allow the bootstrap charge storage element to charge while both of the first and second switches are turned on;
during the charging phase, driving the second switch to saturation by a charge pump applying a suitable voltage to a gate of the second switch;
at the end of a charging phase, removing the first control signal from the first switch thereby turning off the first and second switches;
upon entering a non-charging phase, receiving a second control signal at a control node of a control arrangement, and, in response to receipt of the second control signal, turning on a control device thereby inhibiting the second switch from turning on, and preventing current flow from the bootstrap charge storage element to the voltage source when the first switch is turned off; and
at the end of the non-charging phase, removing the second control signal from the second switch.